INDUSTRIAL A N D ENGINEERING CHEMISTRY
Qctober, 1927
Conclusion
The results point to the existence of wide differences in the adhesive strength of glues of the same grade obtained from different manufacturers. For instance, sample A-1 is higher and A-2 is lower in grade, as measured by viscosity, than samples C-I, C-2, or C-3. Yet the briquet strengths of samples A-1 and A-2 are approximately equal while thoseTof samples C-1, C-2, and C-3 are nearly 15 per cent
1193
higher. This. as well as the results of over two hundred other tests (not given here), shows the futility of relying on viscosity or jelly strength measurements alone for testing the suitability of glues for joints of the specific type. Whether these variations in the adhesive strength of glues actually depend on differences in the raw hide stock, or whether they are due to differences in the manufacturing methods of the respectire makers, is as yet undetermined.
Magnesium and Its Alloys' By John A. Gann and Arthur W. Winston THEDow CHEXICAI, COMPANY, MIDLAND, MICH.
Recent advances have changed magnesium from a laboratory product to an important engineering metal. Production and cost figures have shown steady improvement during the last five years. The relationship between compositions, microstructures, and properties of magnesium-base alloys are discussed. This information has been used to develop various Dowmetal alloys with particular combinations of properties. The foundry practice, as here disclosed, is a radical departure from that used elsewhere. It is based on the use of a flux,which protects the molten metal from deteri-
oration, gives a satisfactory refining method, and a simple casting procedure. Its economic value has been proved by years of commercial use. Many magnesium alloys are being fabricated by forging, rolling, and extrusion processes whereby the structures and properties are greatly improved. Adequate protection can be given magnesium alloys by paints, varnishes, and lacquers. Proper preparation of the surface insures good adhesion of the protecting coat. Magnesium alloys have a wide field of use in industries generally. Their ultra-lightness makes them of particular value in automobile and aircraft production.
....
M
AGNESIUM is rapidly winning recognition as a useful engineering material. Practically unknown before the war, except in the college laboratory, it is now assuming real commercial importance. Because it is the lightest metal known to science possessing properties of permanence and stability, magnesium has long been a material of interesting possibilities to engineers, but any commercial application on a large scale was forced to wait upon lower manufacturing costs and the development of highstrength alloys. Both of these preliminary steps have now been so far accomplished that the cost of magnesium today compares favorably with that of the older metals, and alloys are available possessing strength and other properties amply sufficient for their intended uses. Eventually, magnesium will find extended uses in industries generally, as well as those particularly concerned with automobile and aircraft manufacture. Production
Magnesium may be commercially produced by electrolysis of a fused chloride or of a fused fluoride-oxide bath. -411 European magnesium and the greater portion of that now being produced in this country is made by the chloride process. The development of a low-cost raw material together with modifications of European practice has made the chloride process an economic success. Dehydrated magnesium chloride is now commercially available. This has substituted continuous operation of the electrolytic cells for the batch process required when using mixtures of MgClz with NaCl or KCl. Still further advance was made when it became possible t o use a partially dehydrated magnesium chloride. The metal thus produced is very pure, as shown by the analysis in Table I. Received August 30, 1927
Table I-Analysis Copper Manganese Silicon Chlorine Iron and aluminum Magnesium
of Commercial Magnesium Per cent 0.015 10.005
0 005~0.002
0.020 * 0 . 0 0 5 0.015 t0.005 0.025 * 0 . 0 0 5
99.92 1 0 . 0 2
The increasing use of magnesium is indicated in the domestic production statistics of the Department of Commerce, which include castings and other fabricated forms as well as ingot metal. As production increases, there is no inherent reason why magnesium cannot compete with aluminum on a weight-for-weight basis. Table 11-Yearly
Magnesium Production AVERAGEINGOT P R I C E PER
YEAR
POUNDS
1921 1922 1923 1924 1925 1926
48,000 60,000 125,000 128,000 245,000 322,660
Table 111-Magnesium
VALUE $ 86,000 89,000 155,000 150,000 274,400 390,400
POUND $1.30 1.60 1.25 1.07 0.86 0.80
Production-1926
CLASS
Castings Tubing, wire, powder, etc. Ineots Total
POUNDS 36,940 50,710 23 5.000 322,650
Magnesium Alloys
Magnesium forms alloys with most of the common metals except those of the iron and chromium groups. An exception occurs with nickel, which alloys with magnesium in all proportions. Magnesium shows a very strong tendency to form intermetallic compounds, even with metals in the same group of the periodic system. I n general, these compounds are hard and brittle, but they do exhibit marked differences in their resistance to corrosion, melting points, solubility in
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1194 s0.000
z
K
ZB.000 ~ 8 , ~ o }
C
E
3 1
TEH3(LE LE ,STRCffiTH ND MC M T BINARY ALLOY5
$ 2c.000
L
E
7s
365-
,g.'
D
I
8 zo,ooo R E
h4.000
-
YI '
IG,OOO
I
0
PERCENTAGE
' 1
' 4
' C
OF ADDED I
8
Figure 1
' 10
METAL I
I2
' I4
''
IC
-
so
-
45
-
T;
LL 0
2
12,000
55
2
+ 4
18,000
?
I=-
..
F
I
40 PERCENTABE OF ADDED METAL
0
BRINELL HARDNEJS S A N D CAST B I N A R Y ALLOYS
0
C'
22,000
t
ACT TOUGHNESS
4'
24,WO
Vol. 19, No. 10
0
I
I
I
I
I
I
I
I
1
4
C
8
10
I1
14
IC
Figure 2
magnesium, and nature of the eutectics formed-all of which are factors affecting the properties of the resulting alloys. Since some of these characteristics can be deduced from the constitutional diagrams, it is to be regretted that many of the published diagrams are incorrect or incomplete. This is illustrated in the magnesium-aluminum, magnesium-copper, and magnesium-zinc series, where the existence of solid solutions, not. shown in earlier w ~ r k s , ~isJ indicated by more recent investigations. 4 - 7 It is believed that additional work will reveal similar changes in still other diagrams. Considerable evidence indicating the existence of a limited solid solution of tin, silver, and lead in magnesium has already been obtained by this company. Table IV includes a rbum6 of the more important facts shown by the magnesium-rich portions of these diagrams. BINARY ALLOYS-Several binary systems have been studied individually, but no serious attempt has been made to correlate this information. When the various magnesium alloys are classified according to their constitutional diagram characteristics and their microstructures, we find that they are likewise grouped according to their mechanical properties. (Table V) Pure magnesium is tough, soft, and moderately strong. The intermetallic compounds and eutectics are hard, but weak and brittle. Intermediate compositions have properties which are largely governed by the amount, shape, and distribution of these compounds. The addition of increasing amounts of alloying metals causes the hardness to increase, the toughness to decrease, and the tension to increase to a maximum and then decrease. Note-All impact toughness values have been obtained on the Dow impact testing machine, designed for work with light alloys. Toughness is here expressed in foot-pounds energy absorbed by a specimen 0.5 by 0.5 inch, with a round notch 0.125 inch wide by 0.125 inch deep.8 Earlier impact' numbers reported by this company were obtained with a light hammer and a different scale reading. They may be converted t o foot-pounds energy by multiplying by 0.055.
All properties, however, are not equally affected by a given structure. The globular eutectic, for example, is decidedly superior to that of the network eutectic from the standpoint of toughness and strength, while but little difference is observed in hardness. Furthermore, there is no sharp boundary between the different groups, but rather a gradual merging of one into the other. This is well illustrated by the magnesium-tin alloys which have a combined globular plus Grube, Z.anorg. Chem., 46,225 (1905); 49,72 (1906). Sahmen, Ibid., 6'7, 1 (1908). 4 Hansen and Gayler, J . Inst. Metals, 24, 201 (1920). 5 Hansen, Ibid., 8'7, 93 (1927). EStoughton and Miyake, Trans. Am. Inst. Mining Met. Eng., 73, 641 (1926). 7 Jones, J. R o y . Aevonautical SOL.,30, 743 (1926) I Proc. A m . SOC.Testing Materials, 22, 78 (1922). 2
3
Figure 3
network eutectic structure coupled with some solid solution, and whose properties (particularly toughness) lie between groups 2 and 3. These facts are graphically shown in Figures 1 to 3. These curves show average values obtained on a number of sand castings made a t different times. Chill castings give somewhat higher results. Percentage elongation curves are not included. They run more or less parallel to the impact toughness curves. The magnesium-aluminum alloys are an exception, as they show a maximum elongation a t 2 per cent aluminum. Ta
e IV-Constitutional
Diagram Data
MG-RICH COMPOUNDEUTECTIC SYSTEM C O M P O U N
M.P. Mg
O C .
%
Mg-Ag
MgaAg
492= 4 0 . 3
469
52
Mg-AI
hfgaAlz
454
435
68
Mg-Cd
Mg Cd
427
17.8
..
..
Mg-Cu
MgzCu
570
43.3
485
68
Mg-Ni
MgzNi
768" 45.2
512
66
Mg-Pb
MgzPb
551
19.1
459
33
Mg-Si Mg-Sn
Mg& hfgzSn
102 6 3 . 2 783 2 9 . 1
646 565
96 61
hlg-Zn
hIgZnz
595
344
48
OC.
" Transition
% 57.4
15.7
M.p.
Mg
REMARKS
Limited solid solution of silver in magnesium 10-l170 aluminum soluble i n magnesium a t 435' C., decreasing to 6 % or less aluminum in solution a t room temperature Complete series of solid solutions About 0,57" copper soluble in magnesium a t 485' C., decreasing t o O.ly0 a t room temperature No indication of solid solution of nickel in magnesium Limited solid solution of lead in magnesium Eutectiferous series of alloys Limited solid solution of t m in magnesium Approximately 10% zinc soluble in magnesium a t 344O C.: solubility decreases with lowering temperatures
temperature.
POLYNARY A ~ ~ o ~ s - - W h i lcertain e binary alloys (chiefly those of the magnesium-aluminum series) have proved satisfactory for commercial use, many desirable combinations of properties are found only in the ternary and more complex alloys. The effects produced by adding two or more metals are often additire, but it is also possible so to modify the structure and properties of the alloys with network eutectics that they substantially correspond to those having a globular eutectic. Aluminum is the best addition metal for this purpose, although beneficial effects are obtained with zinc and cadmium. While manganese is introduced primarily as a corrosion inhibitor, it likewise improves the mechanical properties.O The changes in the properties of the 4 per cent copper alloy as occasioned by the addition of increasing amounts of aluminum are shown in Figure 4. Aluminum not only improves the mechanical properties, but likewise imparts a metallic ring to the alloy and enhances the casting qualities. @
Moore, Proc. A m . SOC.Testing M a t c r i d s , 24, 547 (1924).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
October, 1927
1195
With relatively small amounts of aluminum, the general brittling action of the copper and still further increase the characteristics are those of a magnesium-copper alloy. When stiffness. the proportions of the two ingredients are reversed, the strucT a b l e VI-Thermal C o n d u c t i v i t y of S a n d - c a s t Alloys ture and properties resemble those of a magnesium-aluminum (C. G. S. units, 100’ to 300” C . ) alloy. The most important differentiation between these MAGNESIUMMAGNESIUMBINARY curves and those given in Figures 1 to 3 for the binary alloys ALUMINUM COPPER ALLOYS is in the impact toughness curve, which exhibits a pronounced Conduc. Cu Alloy ‘Onductivity tivity maximum a t about 2 per cent aluminum. Similar results are obtained with other ternary and more complex alloys, 0 12% Cd 0.30 2 12% A1 0.16 where the embrittling action of copper, nickel, or tin is coun4 12% Zn 0.27 .. teracted by aluminum, zinc, or cadmium. The maximum 12% Sn 0.18 8 0:32 127, Cu 0.31 in the toughness curve becomes less pronounced as the per12 12% Ni 0.33 centage of copper, nickel, 01 tin increases, but is still evident cent of these metals. in allovs containing 0’31 - 12 per . Dowmetal “T” is a good illustration of T a b l e VII-Develooment of D o w m e t a l “T” 30,000 MECHANICAL PROPERTIES the application of the IMPACT FATIGUE. ELONTHERabove alloying princi~ I N 2~ %:E?L ~ CMAL ~N - $ 2b 26,000CI -70 -7 I ples. A magnesium- ALLOY lWpACT P o w ) Inch-pound blows s O INCHES NESSDUCTIVITYb 4 2.5 1 base piston alloy was required which had t h e r m a l properties 1.0 40 0.32 1 . 5 200 1400 10,000 16,000 s u p e r i o r to those 4%Cu 3.0 43 0.30 oCu-20/oAI 2 . 3 300 2000 16,000 20,000 3.0 46 0.30 3 . 2 I 400 3000 24.000 I 21,000 found in the magnesium-alu m i n u m a 1a Eden-Foster machine. b C. G. S. units, 100-300° C. loys. A study of the melting point data of T a b l e VIII-Development of D o w m e t a l “D” Table I V and the PERCENTAGE O f ALUMINUM IMPACT FATIGUEa ELONTHBR12,000 ’ C 8 1’0 12 1‘4 IC’ t h e r m a l conductivi0 2 A TENSILE GA’CION nRINELL MAL ALLOY Inch-pound blows sTRENoTH ties given in Table VI IN 2 H A R D cONFigure 4 INCHES NESS D U C T I V I T Y b shows that the mag4 2.5 1 nesium-cadmium, magnesium-copper, and magnesium-nickel Lbs. per sq. i n . Per cent alloys-have the most satisfactory thermal properties. The 4.0 26,000 55 0.18 160 1300 10,000 877“41 3.2 magnesium-cadmium alloys are eliminated, as they are too 23,000 2.0 59 0.17 700 15,000 40 1 0 9 A l 2.3 21,000 1.0 62 0.16 10 200 18,000 1 2 g A I 1.5 ductile and lack rigidity. Both the magnesium-copper and “D” 2.3 22,000 2 . 0 58 0.18 190 2300 35.000 I magnesium-nickel binary alloys have network eutectics and a Eden-Foster machine. unsatisfactory mechanical properties. These objections are b C. G. S. units, 100-300° C. overcome by the addition of small amounts of aluminum and cadmium, as shown in Table VI1 for the 4 per cent copper I n addition to pure magnesium, four Dowmetal alloys are alloy. It should be noted that while the addition of 2 per being commercially produced and used. They possess a cent aluminum, or 2 per cent aluminum plus 2 per cent cad- range of properties sufficient for a large variety of applicamium, has caused marked changes in the mechanical prop- tions. Detailed information regarding their compositions erties, the thermal conductivity has remained almost con- and properties, both cast and forged, together with an outstant. The amount of aluminum that can be added without line of fields of utility, are given in Tables I X and X. lowering the conductivity increases with the percentage of Although only a limited amount of fatigue endurance data copper present. After the critical aluminum concentration on magnesium alloys has been obtained, the values available has been passed, the conductivity drops off quite rapidly. are very favorable. Table XI tabulates some of Moore’s Increasing the cadmium content does not have this same results.SJ0 This phase of the work has not progressed far effect owing to the high cmductivity of the binary magnesium-cadmium alloys. T a b l e IX-Dowmetal Alloys: C o m p o s i t i o n and Use
j
c2:;y-
I
I
I
I
?F,,
I
I
‘5,;;
I
I
T a b l e V-Structural MlcRosTRucTaRE
Classification: C a s t Alloys TYPICAL GENERAL MECHANICAL SYSTEMS PROPERTIES Mg-Cd Moderate strength: high toughness; softness
1
Solid solution
2
Limited solid solution plus globular eutectic
Mg-AI; Mg-Zn
High strength; moderate t o high toughness; maximum hardness
3
Setwork eutectic with little to no solid solution
Mg-Cu; Mg-Ni
Low t o moderate strength: low toughness; moderate hardnehs
Dowmetal “D” is another example of satisfactorily modifying the properties of a binary alloy. I n certain respects it is comparable to the 10 per cent aluminum alloy (Table VIII), but is superior to the magnesium-aluminum alloys in impact fatigue endurance and rigidity. The effects of copper and aluminum are roughly additive from the standpoint of strength, hardness, and stiffness. The small amounts of cadmium and zinc in solid solution counteract the em-
ALLOY
AI Mn
7% .. R ..
Cu Cd Zn %. 70. 70.
Magnesium
.. . . . .
Dowmetal “F”
4.0 0.3
.. .
Dowmetal
6.0 0.25
,
E”
,
Mg
70
... ...
99.9
. . ., .
Balance
. . , .. ..,
Balance
,
,
,
Doymetal D”
8 . 5 0 . 1 5 2 . 0 1 . 0 0 . 6 Balance
Dowmetal “T”
2.0 0 . 2 0 4 . 0 2 . 0
10
.. .
Balance
USE
Mechanically worked parts t h a t require excessive plastic deformation: radio rectifier electrodes Casting and forging alloy where ductility and corrosion resistance are paramount Casting and forging alloy where maximum strength is important General casting alloy, especially for thin-walled and difficult castings: possesses greater hardness and rigidity than the other casting alloys Casting and forging alloy characterized by its high thermal conductivity, well adapted for pistons in internal-combustion engines; more subject to corrosion than the other alloys listed above
Proc. A m . Soc. Testing Materials, 23, 106 (1923); 26, 66 (1925).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1196
T a b l e X-Dowmetal CAST P R oP E R T Y Specific gravity Tensile strength, lbs. per sq. in. Elastic limit,o Ibs. per sq. in. Elongation in 2 inches, per cent Compression strength, Ibs. per sq. in. Brinell hardness Scleroscope hardness Impact (Dow), footpounds Impact fatigue b 4 in.-lb. blow 2 . 5 in.-lb. blow 1 in.-lb. blow Melting point, O,C. Thermal expansion per 0
0 L.
Thermal conductivity, C. G. S. units, 100300° C. a b
Magnesium
“F”
Alloys: Physical a n d M e c h a n i c a l Properties FORGED ALLOYS
&LOYS
“E”
Vol. 19, No. 10
“T”
“D”
Mag-
iesium
“F”
EXTRUDED ALLOYS “T”
“E”
MagneSlum
“F” “ E ”
“D”
“T”
1.74
1.76
1.78
1.84
1.82
. . . . . .
...
...
. . . . . . . . . . . . . . .
14,000
26,000
28,000
22,000
21,000
30,000 38,000
42,000
39,000
33,000 39,000 43,000 47,000 38,000
4,000
9,000
11,000
14,000
13,000
19,000 22,000
27,000
23,000
20,000 22,000 25,000
5
8
25,000 35 18
40,000 44 22
7 42,000 00 24
2 45,000 58 28
3
40,000 45 22
8.0
6.1
4.1
2.3
3.2
610 1,600 4,400 651
600 3,000 16,000 625
580 2,400 11,000 610
190 2,500 35,000 590
400 3,000 24,000 640
3.000029 0.000029 0.000029 0.000029 0.38
0.23
0.20
7
16
43,000 48,000 40 54 17 23 10.4
12.5
11
7
52,000 58 27
55,000 52 22
11.4
11.2
1 , 0 0 0 ’ 1,300 2,400 850 2,600 5,000 10,000 36,000 22,000 38,000 130,000 105,000
...
...
10 ,
..
42 19
16 ,
.. 53 24
...
11 ,
.. 55
22
24,QOO
7
10
62 25
‘56
,
21
. . . . . . . . . . . . . . 1,000 goo 1,200 1,000 e50 2,800 2,800 .5,000 6,700 2,300 14,000 34,000 90,000 14,000 25,000
0.00002s
0.18
. . . . . . . . . . . . . . .
0.30
Elastic limit here reported as the load a t 0 . 5 per cent elongation. Eden-Foster machine.
enough to establish a definite relationship between fatigue and chemical composition or microstructure. It is worth emphasizing that the true value of magnesium alloys is best shown by a comparison of properties on an equal-weight basis. This is a fundamental consideration in modern transport problems. Table XI1 clearly shows these superior characteristics of magnesium alloys when compared with other common engineering materials in both the cast and wrought conditions. Metallography
POLISHING-AUOYS containing appreciable amounts of added metals are much easier to polish than pure magnesium owing to their increased hardness and rigidity, which decrease the amount of plastic flow and embedded polishing compounds. The specimens are roughly polished on No. 1 to No. 000 emery papers. Fine polishing is done on velvet well wetted with a suspension of alumina in 0.001 N sodium hydroxide. A satisfactory finish is produced by repeatedly alternating a light polish with a light etch in aqueous nitric acid. ETcHmG-The chemical activity of magnesium permits the use of a large variety of etching reagents, but a t the same time necessitates careful control of etching technic. Satisfactory results for general work are obtained by gently shaking the specimen in an aqueous 2 per cent nitric acid solution at about 20’ C. for 5 to 10 seconds. After washing in water, the samples are rinsed in alcohol or acetone and quickly dried in a blast of warm air. Increasing the strength of the acid or the etching time increases the contrast between ground mass and eutectic, but a t the sacrifice of detail in the latter. Holding the specimen still in the etching medium gives little contrast, while rubbing with a cotton swab is equivalent to the use of stronger acid. Increasing the temperature limits the control and yields a coarse and indistinct detail. An alcoholic nitric acid solution is often valuable to help remove oxide films, but its slight etching action limits its application. BINARYALLOYS-The development of the three structural types (Table V) in cast magnesium binary systems is illustrated in alloys containing 4 and 12 per cent added metal. Figures 5 and 6 show the cored crystals of the magnesiumcadmium solid-solution type of alloy. The globular eutectic structure in the magnesium-aluminum and magnesium-zinc alloys is shown in Figures 7 and 11. The addition of increasing amounts of aluminum or zinc develops a branched chain (Figures 8 and 9), and finally an enveloping structure (Figures 10 and 12). All photos of these last two series likewise show cored crystals, indicating a limited solid solubility.
The network eutectic of the magnesium-copper and magnesium-nickel alloys is shown in Figures 13 to 16. Copper and nickel, even in quantities less than 1 per cent, are sufficient to give a more or less continuous network structure. The magnesium-tin alloys (Figures 17 and 18) reveal cored solid-’ solution crystals and a eutectic which exhibits some of the characteristics of both the globular and the network structure. The 4 per cent alloys show a greater variation in structure than do the 12 per cent alloys and they likewise show greater variations in properties, hardness excepted. The globules of eutectics stiffen and harden the alloy but decrease the impact toughness only in so far as they break up the continuity of the magnesium crystals. The network eutectic also stiffens and hardens the alloy, but a t the expense of toughness and ductility. As the amount of globular eutectic is increased, the structure approximates the network type, and with 12 to 15 per cent added metal, all but the magnesiumcadmium alloy are approaching the same general structure and properties. T a b l e XI-Fatigue
E n d u r a n c e : M a g n e s i u m Alloys
ALLOY Magnesium Mg-4.2 %AI Mg-4.4 %A1-0.26 Mn Mg-6.7YAI Mg-6. 8%Al-O.26%Mn Mg-8.68YoAI Mg-S.6870Al Mg-8.68%AI Mg-4.38%Zn-O. 4 1 % C ~ 0.257$Fe-O, 2 4 % B
CONDITION Extruded
ENDURANCE LIMIT
Lbs. der sa. in.
Cast Forged (cross-grain) Forged (longitudinal)
-7,800 12,000 15,000 13,000 15,000 12,500 13,000 15,000
Rolled
17,000
T a b l e XII-Comparative Properties Dow- ALUMI- G R A Y DURA- LOW-CARDow. NUX CAST LUBON STEEL, METAL M~TAL E” ALLOY IRON M I N -0.20 70 E” PROPERTY (CAST) (FORGED) No. 12 C Specificgravity 1.78 1.78 2.9 7.8 2.8 7 8 Tensile strength, Ibs. per sq. in. 28,000 42,000 20,000 30,000 65,000 62,000 I m aci toughness (%ow), foot-lbs. 4.1 11.4 2.0 2.4 8,000 Specific tenacityn 15,700 23,600 6,900 3,800 23:200 Soecific touehnessb 2 . 3 6.4 0.7 0.3 ... ... a Specific tenacity is the tensile strength in pounds per square inch divided by the spectfic gravity. b Specific toughness in the impact toughness (Dow) in foot-pounds divided by the specific gravity.
POLYNARY ALLOYS-The
microstructural changes in the
4 per cent copper alloy due to the additions of increasing amounts of aluminum are shown in Figures 13 and 19 t o 22.
Small amounts of aluminum break up the network structure and a t the same time produce a marked improvement in strength and toughness (Figure 4). As the aluminum content is still further increased, so that it exceeds the copper
present,l the uiebal likewise assiiiiies the structurnl and property characteristics of ilie siingnesiiirn-alurriinurn alloys. (Compare Figure 22 with Figure 10) The microstructures of I ~ o n ~ u e t a l“T” u and “1)” are in good ngrcoment with their mechanical properties. Ilowmetal “T”Ii&sbeen derived from the 4 per cent copper alloy by introducing 2 per cent each of aluininuni arid cadmium. Tlie addibion of aluininitrn results in considerable grain refincrnent and breaking up of the magneuiurn-copper ent,ectic. Both of these changes have been carried s t i l l fiirtlici by t,be additiun of cadmium. (Compare Figures 13, 19, and 23) Downietiil “I)” (Figure 24) has been derived from the 8 per cent alooiinum ;illoy (Figure 0). Tlic addition of copper has increased the amount of cuteciic. so that tlie structure
roughly corresponds to t h e 10 per cent alunriniim alloy. Cadirriuur and zinc, however, liavc cniised very l i t t l e additional clmugc in structure, but have irriprovcd rigidity. The smnll a s i ~ ~ u i iof W 11miganese preseiit in tlie Dowrnetal d l o y s listed in Tebles IX and X have no appreeiable effect oii the eutect,ic distribution. Stmct.uriiily speaking, therefore, Donmetals “F” and “E” are suhstaritially the sanie as the 4 and 6 per cent aluminurn alloys, respectively. TJie rernnining Donmetal alloys in both the sand-cast and forged conditions are show11 in Figures 23 to 29. The forged alloys received a solution heat treatnient prior t o working so no magnesium-aluminum eutectic iu visible. The magnesiumcopper eutectic in “T” alloy s t i l l remains, but is much more tlioroughly broken up than in t,he cast state. All forged
INDUSTZIAL A N D 8N@IDEERIINGCHEMISTZY
1198
alloys have been subjected to considerable grain refinement, which 1s reflected in improved mechanical properties.
Yol. 19, No. 10
It is not neecssary to empty and clean a pot after each melt or a t the end of each dav's work. but onlv when the flus has become so dirty that it'no longer propeily functions. The Foundry Practice sludge, however, should be removed Deriodicallv. usuallv FLux---Magnesium and its alloys are best melted with a 8. day. CkaNng consists in simply dipping out the hillgreached by E~~~~~~~ molten contents and scraping the sides of the pot substanflux. his conc~uaion~~ is investigators, although their technic is different from that tialb free from adhering sludge. No harm 3.i done by allowhere described. Other melting including the ing both metal and flux to solidify in a pot. When heat is use of a vacuum or inert atmosphere, or simply a tightly amlied again, the flux d l melt first and protect the metal i l s l d . In case the pot shonld stand unused several da-js, that are eliminated closed veaql have serious the surface film of flus will be eonvorted to magnesium oxide by the present procedure. The more important functions of the flus are (1) to pre- and oxychloride, and this is easily scraped off before remelting, vent oxidation and nitridation hy prot,ecting the molten PmFlCAnoN-The elimination of non-metallic impurities metal from the air, from the molten metal constitutes one of the chief functions ( 2 )to purify themetal of the flux. This is accomplished by a mechanical vashing by the removal o f rather than by a solvent action exerted on the impurities. non-metallic imp"& Dry masses of magnesium oxide are light and float on the surfac,eof the metal, bat when wetted by flux they form comties, and (3) to of a simple and eon- Pact bodies that sink to the bottom of the pot as sludge. tinuous melting and Sand, adhering to foundry scrap, liewise goes into the sludge T~ before it can reaet with the magnesium. Films of oxide on end, the surface of ingots and scrap, however, remain suspended in the metal unless removed by the cleansing action of the flus. Thorough puddling of the metal and flux is therefore carefu]]y and surface essential, preferably a t a temperature above that used for casting, in order to secure greater fluidity and ease of mixing. t metal Maximum purification is obtained by use of clean flux conand a t the same time completely envelop the same with & taining a minimum Of suspended impurities. It is often advantageous to melt in comparatively old flux and then thin protecting film. This combination of propertiesis factorily obtained in a flux containing &bout60 per centan- transfer to, and cast from, another pot containing fresh flux. The Purification process as thus developed is applicable hydrous magnesium chloride and 40 per cent potassium sodium chloride. The M&lrNaC1 flux is used with alloys not only to ingot metal but to all forms of foundry and macontaining appreciable amounts of added metals, the ohine-shop scrap, including sprues, shavings, and sawdust. MgClrKCl flus, because of its lower density, is recommended In fact, the finer the scrap with its corresponding greater accumulation of surface oxide and dirt, the more beneficial is for use vith pure magnesium. the refining. The process is so successfulthat the magnesium MELTINC---The melting and casting practice developedby this company is unique and radically different from that used industry is not confronted with the problem of virgin versus with other non-ferrous metals and heretofore advocated for secondary metal. Repeated tests have been made wherein magnesium.?.'* The metal is melted in oi[&ed caskstee] the metal has been remelted and recast ten to twenty times pots (23 inches in diameter by 24 inches deep), mounted & Without causing the least deterioration, either in microstrnca brick setting. From 125 to 150 pounds of flux are placed LoYING-The preparationLaof a given alloy is readily in the bottom of the pot and 300 pounds of metal added. keet additions of the individual metals or The flux is the first to melt and serves as a bath into which ers. The added ingredients are best alloyed with a the metal sinks and melts. Oxidation or incipient burning that may start on semi-molten metal is readily stopped by small m o u n t of magnesium in puddling or by sprinkling on powdered flus in case too much the ladle, and this magnesi solid metal is present to allow easy puddling. When corn- rich alloy is subsequent1 pletely molten, the metai floats as a ball in t,hc flus, as illus- withthemassofmetalin Low-melting metals, 1 trated in Figure 30. Overheating a pot of metal is not detrimental; in fact, it and cadmium, alloy v i may be advantageous, as explained under I'urification. Since nesium instantly, while the coefficient of expansion of the molten flux is greater than like copper, mangaoose, an that of molten metal, the higher the temperature the more nickel, with m e l t i n g p o i n t s the flux will rise to form an increasingly thicker protect.ive 400' to 800' C. above that of film on the surface of the met,al. At sufficiently high tem- magnesium, alloy more s1owly =lamre 31-~aafine. Ladle perature the ratio of densities is even reversed, so that the owing to the slower rate of solution and, in the ease of manganese, limit,ed sohihility. metal floats the flux. CAsTrr;o-Castings are made with ladles, such as illusThe protecting actio11 of the flux likewise allows a pot of metal to be held molten for an indefinite time. This permits trated in Figure 31, while the technic is described in U. S. continuous casting throughout the entire day. The pot can Patent 1,476,192. The thin film of flus on the surface of be rcplenished from time to time by the addition of more the molten metal in the pot is broken and brushed back by. metal, which should he pre-warmcd to insure complete dry- the paddle welded to the oukide of the ladle. This momenness and thus prevent explosions dne to the sudden reaction tarily exposes clean metal, which is then readily removed before the flux film is reformed. The retaining lip and the botbetween moisture and hot metal. i g J ~ it.~ Aeraaaulicnl ~ ~ Research ~ . c~,,,,~. R ~ M ~ ~ ~~ No. ~. ~10x7 . . tom draw-off Prevent the oxide skin formed on the metal in (1926): de Fleury, Rm. m&L. as, 649 ( 1 9 2 6 ) ; Kciiiixer, z. ZLS. ~ i e r i e r e i , the ladle from,eutering the mold. Large castings are made 17, 129, 133 (1926). by two or more operators, each having his own ladle and pour-
.
Ip
American Magnesium Corp., Handbook, 1 9 B
11,79611925).
l>m>ic,l%, M e i h .
Ens.,
1% U.
S. Patent 1,558,066 (19251.
October, 1927
ing into different sprues. After a number of casts, the ladle becomes fouled by oxide films. It is cleaned by washing in the flux a t the bottom of the pot. The adhering flux film is then removed by rinsing several times with clean metal dipped out as if for a cast. Oxidation of the metal during the pouring operation is prevented by burning a little sulfur or a mixture of sulfur and gasoline around the sprue. I n many instances it is likewise advisable to replace the air in the mold by carbon dioxide or sulfur dioxide. U. S. Patent 1,463,609 advocates dusting the mold with sulfur prior to casting. Castings are made in metal molds, likewise in both dry and green sand. Except in the case of very small castings, which cool quickly, an addition agent is necessary with green sand to prevent surface burning. Various chemicals may be so used, boric acid and sulfur being covered, respectively, by U. S. Patents 1,584,072 and 1,614,820. The pouring temperature depends on the alloy composition and on the nature of the casting, varying from 620' to 700" C., with 90 per cent of the work done at 660" * 15" C. MoLDmG-The few special precautions that are essential for successful molding are occasioned by two properties of the metal-namely, extreme lightness and ease of oxidation. These call for the use of an open sand that is lightly rammed and well vented, and a good pressure head to insure complete expulsion of air and filling of the mold. Several small gates are usually preferable to a single large gate as an aid in reducing burning. Mechanically entrapped air is kept from entering the mold by the use of wedge gates backed by a pocket trap. Inserting a screen skimmer in the sprue or runner helps to maintain a full sprue and thus reduces mechanically entrapped air. Chills are used on heavy sections to prevent shrinking and at sudden changes in cross section of the casting to prevent cracking. Fabrication
HEATTREATMENT-The properties of certain cast magnesium alloys are improved by heat-treating at a temperature somewhat below the melting point of the eutectic, resulting in solution of the compound in the primary magnesium crystals. With both binary and p o r e complex alloys, the heat treatment can be regulated to secure partial or complete solution of the soluble alloying constituents. The process is of small benefit t o alloys having little or no solid solution of the added metals a t high temperatures, such as those of magnesium with copper and nickel. The course of the treatment can be followed microscopically and by property determinations. I n the case of the magnesium-aluminum alloys,l* the maximum improvement in properties is reached in from 2 to 4 hours a t 420' C., while 12 to 24 hours are required for complete solution. Improvement is noticeable with the 2 per cent aluminum alloy, for, though recent work indicates a solid solution of approximately 6 per cent aluminum a t room temperature, the cast 2 per cent alloy usually shows the presence of some eutectic. The effect on the properties increases with the aluminum content. reaching a maximum between 8 and 12 per cent, and is evident in improved strength and ductility and decreased hardness. On quenching a solution heat-treated alloy containing more than 8 per cent aluminum, some of the aluminum is retained in a supersaturated solid solution. Subsequent aging of the quenched alloy a t a low temperature (150" C.) for se\reral hours precipitates the excess dissolved compound as very fine particles along cleavage planes. Archer15 states that the keying effect of these particles results in increased hardness. The strength is also increased, but the toughness 1' 15
1199
I,VDUSTRIdL A S D EAVGINEERINGCHEMISTRY
Gann. Trans. A m SOL Steel Treating, 2,607 (1922). I b i d , 10, 718 (1928).
and ductility are lowered, as shown in Table XIII. Metallographic samples of precipitated alloys etch much more rapidly than cast or solution heat-treated alloys, indicating somewhat greater corrodibility. This process of heat treatment may be applied where strength, rigidity, and hardness are desired, and toughness is not essential. Age-hardening has been observed with magnesium-zinc alloys6 and may occur with others. Table XIII-Properties
of a Heat-Treated 13 Per Cent Aluminum Alloy SOLUTION PLUS CHILL-CAST SOLUTIONPRBCIPI-
Hours a t 420' C. Hours at 150° C. Tensile strength, Ibs. per sq.in. Elongation in 2 in., per cent Brinell hardness Impact (Dow), foot-pounds
TATION
...
16
22',660
16 15 32,000
27,000 2.0 50 3.1
1.5 60
1.3
0.7 80 1.4
Several methods have been suggested for preventing the surface oxidation which sometimes accompanies heat treatment a t high temperatures. They include the use of inert atmospheres, vacuum chambers, liquid and dry mediums, and surface coatings. Of these, the granular or powdered dry medium is most convenient of application and gives good results. Some dry powders, such as lime and magnesium oxide, act as oxidation accelerators. Of the many materials tried, powdered fluorspar is most effective. FORGING-Many magnesium-base alloys lend themselves readily to pltstic deformation above 250" C. Cold-working is not successful owing to the rapid embrittling of the alloys. Forging and other methods of mechanical working should be preceded by a solution heat treatment to secure maximum ductility. Most of the forging work has been done on alloys of the solid solution type, such as those of magnesium with aluminum and zinc. The addition of manganese to the magnesium-aluminum alloys makes them stiffer and harder to work a t high temperature, but also decreases the tendency to crack or crumble. Alloys containing more than 8 per cent aluminum cannot be forged readily because of the increasing stiffness and the narrowing of forging temperature. The forging temperature range for the magnesium-aluminum alloys is approximately: Aluminum, per cent Highest initial temperature, O C. Lowest finishing temperature, C.
0 550
250
4 480
8
420 300
275
Forging above these limits results in surface oxidation and "hot shortness," while cracking is caused by working too cold. Maximum strengths are obtained by forging a t as low a temperature as is possible without cracking. To get the greatest forging effect a reduction of 50 per cent in cross-section area is necessary, and the working should be done in a t least two directions. Annealing reduces the strength and ductility of forgings. (Table XIV) of Annealing on a Forged Magnesium-Aluminum Alloy Composition, 4 . 7 % A1-0.3% Mn. Forging temperature, 375O C.
Table XIV-Effect
TENSILE ELONGATION IN
As forged
Annealed 2 hours a t 260° C. Annealed 2 hours a t 450' C.
STRENGTH Lbs. per sq. rn. 41,500 39,600
37,500
2 INCHES
Per cent 13.0 12.0
9.5
At the present time consistent results are being obtained on the various Dowmetal alloys by heat-treating for 16 hours at 420" C., and then forging with heated tools at the same temperature. The work is reheated often enough to maintain the temperature above the lower forging limit. After finishing to size and shape, it is allowed to cool in the air without annealing. ExTRusroN-Many of the considerations affecting forging apply to extrusion. While the power consumption is high,
INDUS1‘ItIAL A N D ENGINEERING CHEMISTflY
1200
better properties are secured at relatively low temperatures. The following resuIt.8 vere obtained on extruded pure ms,gnesium rods of 0.5 inch diameter: TENBUS
FXBSSURB
TIIYPBXATUKB STBBNTTIZ E ~ o ~ c n r ~ oKns Q u w D “ c. u s . per sp. in. Per cent Toni 480 82,NO 2.9 35 310 32,800 10.2 8n
The niicrostructure of the metal extruded at 310” C consisted of small equi-axed grains, indicating that t.he w o r k was done above therecryst.allizing temperature. All the Dowmetal alloys have been successfully extruded, with the result.sgiven uiTableX. b RoLLIxG--1\1agnes i u m a l l o y s can be hobrolled to any desired gage d o w n t o 0.005 i n c h Maxim u m strengths are obtained by finishing a t lower t e m p e r a tnres. On annealing at 250” C., the ductility of rolled sheet is increased, though Figure 32-Crankcase of Mellnosium a t the expense of the Alloy tensile strength. The tramverse strength averages 20 per cent greater than that in the longitudinal direction. Annealing makes the sheet of approximately equal strength in all directions. Table XV gives the average results obtained on several rolled alloys. Table XV-Ropertiea CONOiWJ*
As roiled
of Rolled Magnesium-Aluminum Alloys
PRO*EYIY
Teosiie strength, ibs. per sq. in. Eiongafion in 2 inches, per cent
Annealed 2 hours. Tendle strength. lbr. per 59. in 250” C . Elongation in 2 inches. per cenf
AGuumvu 6 43,600 46,750 1.8 3.2
PER C B N T
0 35,200 4.1
3
. .
Heated tools and metal are necessary for forming rolled magnesium alloys by such methods as pressing and drawing. lf~cmNINo-lfagnesium and its alloys can be machined very rapidly with none of the dragging and tearing which are characteristic of the aluminum-base alloys. Cutting speeds vary from 600 feet per minute for heavy roughing cuts to 1400 feet per minube for light finishing cuts. As there is little heating carbnnsteel tools are satisfactory and they may be used without lubrication. The work is easily taken to a very smooth finish and exact dimensions. All the commercial magnesium alloys have equally good machining qualities, which are not excelled by those of any other metal. Surface Finishing
trouble was due to impure metal and spongy sputs in the castings. Improved technic has practically eliminated these faults and the alloys obtainable today are much improved in their corrosion resistance. On exposure to ordinary atmospheric conditions, magnesium alloys slowly become covered with a thin grayish film of oxide, which effectively prevents further corrosion. While some alloying agents accelerate the corrosion of magnesium, manganese acts as an inhibitor. BoyerlE concludes that impurities and alloying constituents accelerate corrosion through lowering the hydrogen overvoltage of magnesium, rather than through their occupying lower positions in the electromoti~.eseries. Hemeasures the effect of manganese and concludes that it raises the overvoltage of the aluminum alloys back to practically that of pure magnesium. CHEMICAI, FhrsHz+-Various colored finishes may be given magnesium alloys by immersion in heavy-metal salt solutions. While distinctive in appearance, they offer little protection from corrosion. Heating in steam at high pressures (U. S. Patent 1,451,755) gives a dense oxide coating which exhibits good atmospheric resistance. The iiature of the film varies with the alloying metals, copper being particularly beneficial. A fairly good coating is also produced by making the alloy the anode ill a bath containing soluble fluorides (U. S. Patent 1,574,289). The most recent development is to immerse the article in a bot acid phosphate solution, with the formation of a very adherent non-metallic covering, composed of insoluble magnesium phosphates. Pione of these chemical finishes give absolute protection from the action of salt water, though their resistance to atmospheric corrosion is very good. , \I.~I~XISHES, A N D Lncaum-Where conditions are not very severe, a paint or varnish film may be applied to the bare metal. It is, however, much better togive aprcliminary phosphate treatment, which leaves a surface to which paints and varnishes adhere very tenscioiwly. Spar varnishes give much better protection than oil paints under very moist or wet conditions. The clear varnish is further improved by the addition of aluminum-bronzing powder. Pyroxylin lacquers offer a high degree of protection because of their imperviousness, but the films are hard and brittle and sometimes chip or crack. When i t is not practical t.o apply the phosphate coating, good protection can be obtained by the use of a newly developed rubber paint. Neither the paint nor its adhesion is affected by moisture or eveii by immersion in water. It is, however, rather soft and is more easily abraded than the spar varnish or lacquer films.
FiOure 33-Various
Conaosiow-The corrosion of magnesium and magnesium alloys during their early development was a large factor in retarding the rapid extension of their uses. Much of the
Vol. 19, No. 1@
Applications of Magnesium Alloys
Magnesium alloys, therefore, can be satisfactorily protected by the application of any good paint, varnish. or lacquer to the prepared surface. Which finish should be applied d l be determined by the service required in any particular case. Null. I d o i 8 0 r y Cornm. .Aeronaxiiis, RaDL. 248 (1026).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
October, 1927 Uses
Because of the brilliance of its flame when burned in powder or ribbon, magnesium is used in flashlight powder, fireworks, and military flares. Its chemical affinity for oxygen and nitrogen a t high temperatures makes it useful in degasifying radio tubes. Radio trickle chargers use magnesium rectifying electrodes. The Grignard synthesis is now commercially practical because of the low cost of the pure metal. Magnesium finds application as a deoxidizer and degasifier in the metallurgical industries. A large tonnage is used in the refining of nickel and nickel alloys, and its use is extending rapidly to other non-ferrous metals. Zinc-base die castings have recently been found to be improved by the addition of small amounts of magnesium. A considerable amount of magnesium is used as a mjnor constituent of modern high-strength aluminum alloys. The Duralumin type alloys contain about 0.5 per cent, while the “Y” casting alloy contains 1.5 per cent magnesium. It is estimated that one-fifth of the more important aluminum alloys have magnesium as an alloying ingredient. While not present in large amounts, it is necessary in order that maximum strength will be developed. These magnesiumcontaining alloys are more extensively used in Europe than in this country. The greatest development in the uses for magnesium will be in the extension of the engineering and structural uses of its ultra-light alloys. A saving of three-quarters of the weight is possible where they replace steel and one-third where they are substituted for the light aluminum alloys. The strength properties are good, even on a volume basis, and are quite superior on a weight basis. Castings made from magnesium alloys are dense and nonporous. They are therefore well adapted for supercharger housings, manifolds, and other parts required to hold gas pressure. Crankcases are successfully cast, even when of large size and intricate design as illustrated in Figure 32. Applications still in the experimental stage are cast cylinders,
1201
cylinders heads, and other large motor parts. One of the first uses proposed for magnesium alloys was for pistons in internal-combustion engines. The high thermal conductivity and light weight peimit much higher engine speeds with increased power and lessened vibration. Forged pistons and connecting rods have recently developed which are harder and stronger than the original castings. Airplane propellers, forged from a solid billet, offer maximum strength combined with lightness. Forged tail skids and landing gear are in successful operation. Extruded shapes are useful for aircraft structural members while rolled sheet finds application as wing covering. An interesting use is the press-forged resonator disks for automobile horns. No other metal produces such clear and resonant tones as do certain magnesium alloys. Many hundreds of thousands of these horns have been made and they are standard equipment on several of the better grades of motor cars. There are possibilities in utilizing this property in other sound producing or amplifying apparatus. Owing to the absence of distortion or warping on aging, magnesium alloys are used for jigs in machine-shop practice. Instrument parts, portable machines and tools, artificial limbs, and metallic furniture are all lightened and strengthened through the use of magnesium. Golf clubs with magnesium alloy heads are in use. Metal patterns can be made in large sizes because of their light weight. Many typical applications of magnesium alloys are shown in Figure 33. I n Europe, where the economic saving through the use of light alloys is more widely recognized than in this country, even such commonplace articles as buttons, combs, and pencil sharpeners are made from magnesium alloys. As designers and engineers become familiar with the metal, numerous other uses will suggest themselves. With goodstrength alloys, well-developed technic for casting and working the metals, and adequate means for surface protection magnesium will undoubtedly become an increasingly important engineering metal.
Determination of Carbon Disulfide in Its Emulsions’ By H a r r y J. Fisher CONNECTICUT AGRICULTURAL EXPERIMENT STATION, NEWH A V E N , CONN.
ARBON disulfide emulsions have lately come into use shaken, then 45 CC. of hot water were added and the mixture agitated until the rosin was dissolved. Five cubic centimeters of for the treatment of lawns infested with the J~~~~~~~U. S. P. oleic acid were added t o this mixture, which was shaken beetle.’ It is thel’efore frequently necessary to de- agaln. Thirty cubic centimeters of this soap solution were
C
termine the carbon disulfide content of such emulsions as marketed commercially. Most of the work heretofore done on the analysis of carbon disulfide mixtures has dealt with the determination of carbon disulfide in crude benzene, where the percentages are small. Xone of the methods is suitable without modification for emulsions of a high - carbon disulfide content. For experimental purposes two emulsions of known carbon disulfide content were prepared, of types actually recommended for use in the contiol of the Japanese beet,le. Emulsion No. 1. One part by volume of a commercial potassium rosin-fish oil soap was mixed with three parts of water. Twenty-eight cubic centimeters of this soap solution were added t o a tared, glass-stoppered, 100-cc. volumetric flask, and weighed. Seventy cubic centimeters of carbon disulfide were then added, the flask stoppered and weighed, and the contents shaken until completely emulsified. Emulsion A70. 2. Five grams of powdered rosin were added to 13.5 cc. of warm 7 per cent sodium hydroxide solution and 1 2
Received M a y 26, 1927. Pennsylvania Dcpt. Agr. General Bull. 410, A u g u s t 15, 1925.
weighed in a 100-cc. flask, 70 cc. of carbon disulfide were added, and the flask was weighed again as in preparing emulsion No. 1. The mixture was shaken until completely emulsified. The carbon disulfide used was the C. P. product, further purified by allowing i t to stand for several days over solid potassium hydroxide, then distilling, discarding the first and last portions of the distillate. It had a boiling range of 0.02’ C.
After attempting to adapt both the methods of Harding and Doran3 and we is^,^ it was found that the best results were obtained by a modification of the method of Weiss, oxidizing the carbon disulfide in an alkaline peroxide solution and precipitating the resulting sulfate and weighing as barium sulfate. Method
Add about 2 grams of emulsion t o a tared, glass-stoppered, 100-cc., volumetric flask containing 40 re. of 8 per cent a J . A m . Chem. SOC.29, 1476 (1907). THISJOURXAI,, 1, 604 (1909); see also Warren, A m . J. Pharm., 96, 864 (1923) ; Annual Reports Chemical Laboratory American Medical
Assocn., 16. 42.
