864
Vol. 14, No. 9
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
Recent Progress in Magnesium Alloys By John A. Gann Dow CREMICAL Co., MIDLAND,MICHIQAN
AGNESIUM alloys are now being widely advertised under trade names such as Dowmetal, Magna Metal, M. W. Metal, and Elektronmetal, the last named being a product of the Chemische Fabrik Griesheim-Elektron. All of these alloys are characterized by their high magnesium content, which exceeds 80 per cent and may run as high as 100 per cent. The term “Dowmetal” is a generic one covering an entire series of magnesium alloys, as made by The Dow Chemical Company. Their chemical composition and physical properties vary according to the use for which the alloy i s intended. “Elektronmetal” is likewise a generic term. Magna Metal has the same composition as the German Elektron casting alloy. The writer knows very little concerning W.W. Metal beyond the fact that the literature distributed by the M. W. Metal Company is a direct translation of parts of the German Elektron catalog. The commercial production of Elektronmetal dates back to 1912, Dowmetal to 1918, while Magna Metal and M. W. Metal have not yet reached the commercial stage. The Magnesium Corporation of America at Niagara Falls, however, is producing extruded magnesium alloy parts on a quantity production basis. The published literature relative to magnesium and its alloys is somewhat meager on account of the comparative newness of the subject and the necessity for secrecy on the part of the investigator and manufacturer during the development period and until after they are fully protected. The most recent work on the constitutional diagrams of magnesium alloys is that of Hanson and Gaylerl which deals with the magnesium-aluminium series. These investigations are quite complete, and confirm in general the earlier finding of Grube. The main difference likely to be of any practical importance is that magnesium is capable of holding about 10 per cent of aluminium in solid solution as contrasted with 6 per cent previously given. The magnesium-rich part of this series has been discussed more in detail by Gann.2 The relationship between chemical composition, physical properties, microstructure, and equilibrium diagram of these alloys is here shown and some of their industrial applications briefly indicated. Elektronmeta13 has been described at various times, some of its physical properties given and commercial uses discussed. The most complete report, however, is given in the Elektron catalog, which includes methods of melting, casting, and coloring four of the alloys they are now producing. The physical properties of magnesium alloys necessarily vary with the chemical composition and method of treatment. Pure cast magnesium, for example, has a tensile strength of only 14,000 to 15,000 lbs. per sq. in. The addition of 6 per cent aluminium practically doubles this value, that is, it increases the tensile strength to 28,000 lbs. per sq. in., while it increases the specific gravity only 2 to 3 per cent. Heat treatment of these alloys results in up to 25 per cent increase in tensile strength, while mechanical working may increase the strength 50 to 100 per cent. The general characteristics of standard products of the different manufacturers are given in Table I, the figures being taken from published scientific literature or, where neces-
M
J . Inst. Metals, a8 (1920), 201. Am. SOC.Steel Treating. April 1922. Adolph Bergman, M e f a l l n d . ,aq(l922), 1: Felix Thomas, StahE u. Eiscn, 40 (1920). 290; Selvc Z. Metallkunde. 18 (1921), 474; Ibid., 816 (1921). 1
1 Trans.
sary, from advertising material. Corresponding values of No. 12 aluminium casting alloy and gray cast iron are given for comparison. TABLEI-COMPARATIVEPHYSICAL PROPERTIES
DowDowPROPERmetal metal Elektron TIES No. 1630 No. 217 21 Tensile strength lb./sq. in. 22,000 28,000 19,000 Yield point Ib./sq. in. 14,000 11,000 13,000 Specific 16,000 10,400 tenacity 12,000 Per cent elongation (2 in.) 2.0 6.0 2.0 Brinell hardness 68 50 48 Scleroocope hardness 28 24 13 TABLE11-PHYSICAL PROPERTIES Dowmetal Dowmetal No. 220 No. 1045 Tensile strength lb./sq. in. 22,000 22,000 Yield point Ib./sq. in. 14,000 14,000 Per cent elongation (2 in.) 2.0 2.0 Brinell hardness 58 58 Scleroscope hardness 28 28 Single blow impact2 26 32 Impact fatigue blows* 1,300 2,800 Maximum fiber stress, lb./sq. in.4 200,000 reversals 6,000 8,900 40,000,000 reversals 8,050 1 Sand cast in our own foundry. 2 Dow machine, a Eden-Foster machine. 4 Farmer alternating stress machine.
Magna Metal
CAST ALLOYS Aluminium AIGray loy Cast No. 12 Iron
19,300
20,000
6,500
13,000
30,000 Indeterminate
7,000
4,200
OF
11,000
8.5
2 . 0 Negligible
.. ..
70
125
15
30
DOWMETAL ALLOYS Dowmetal Aluminium1 NO. 1630 Alloy No. 12
OF
22,000
20,000
14,000
13,000
2.0
2.0
58
75
28
15
40
26
3,200
200
11,000 9,800
Probably the most recent advance in magnesium alloys is the production of new Dowmetal piston alloys, in which the toughness and fatigue endurance have been very materially increased without any sacrifice whatsoever in other desirable properties. An exhaustive study of this subject is now in progress, and although this program is still in the elementary stages the results are of interest (see Table 11). Our results on No. 12 aluminium alloy are again given for comparison. Within the last two months a new alloy especially designed for use in high-speed motors and in racing cars has been developed. This alloy has a thermal conductivity nearly 70 per cent higher than the usual magnesium-rich alloy, thereby insuring a cooler running motor, while the toughness and impact fatigue endurance are fully as high as that of the alloys listed in Table 11. The excellent results obtained in actual service from these various Dowmetal pistons indicate great possibilities in the future development and use of magnesium alloys. The Second Annual Report of the Scientific and Industrial Research Council of Alberta, covering work done during the year 1921, has just been printed. The greater part of the work was done in relation to various types of fuels, although considerable attention was given to road materials, forest products, and a geological reconnaissance in Alberta.
