December, -
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1924
1243
Cast Alloys of Aluminium Containing Small Amounts of Magnesium’ By Samuel Daniels2 WAR DEPARTMENT, AIR SERVICE, MCCOOK FIELD,DAYTON, OHIO
added elements as copper, nickel, zinc, iron, silicon, and manganese. Among these more or less complex alloys are the 10 copper-1.25 i r o n 4 2 5 magnesium (Lynite 122, Air Service Specification 11,024) alloy, used for pistons, manifolds, and other parts operating a t elevated temperatures; the 4 copper-2 nickel-1.5 magnesium (“Y”)alloy, employed, in the heat-treated condition, for much the same purposes as the previously mentioned alloy; the 3 copper-8 zinc-1 iron-0.25 magnesium (Lynite 145) alloy, cast for parts requiring high strength, ductility, and shock resistance; the 4.5 copper-0.15 magnesium (Duralumin type) alloy, used for heat-treated parts postulating high strength and greater ductility (Air Service Specification 11,300) than is afforded by Lynite 145; and the 2.5 copper-1.25 iron-0.5 magnesium alloy, utilized as a casting alloy for general purposes for parts not to be heat-treated but to have considerably greater strength and ductility than is possessed by the well-known 8 per cent copper (Lynite 12) alloy. It will be seen from this resume that magnesium is usually added to aluminium in amounts less than about 2 per cent and in company with one or more other added elements. I t s effect in these alloys is in general to intensifv their hardness, a t the sacrifice of ductility. The simple alloys of aluminium and magnesium have not been prominent as foundry materials, because they are more expensive and difficult to handle than the alloys described above, and because their mechanical properties are not outstanding. The original “magnalium” alloys contained between 5 and 30 per cent of magnesium, but the term is now loosely applied t o cover a number of alloys with other additions besides magnesium. Alloys of aluminium containing more than about 30 per cent of magnesium take a high polish and are used for reflecting purposes. Hanson and Gayler3 report that 40 to 70 per cent additions of magv
1 Received July 26, 1924. Published by permission of the Chief of Air Service, W a r Department. 2 Chief, Metals Branch, Material Section., Enaineerine Division. Air Service, U. S. A. a J . rest. .&feta/s,24, 213 (1920).
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Magnesium-Per
and- arrived a t thk representation shown in Fig. 1. The liquidus curve has four branches-the compound AlaMg, (beta) being formed a t the maximum at C; and the compound AlzMga (gamma) a t the point E , below an apparent maximum at X , at about 54 per cent of magnesium, where a compound, A13Mg4, is possibly indicated. The alloy of this particular composition, however, melted over a range of temperature of 5” C . Three eutectics were observed: one of alpha (the aluminium-rich solid solution containing dissolved beta) and beta, a t about 35 per cent of magnesium; one of beta and gamma, at about 56.6 per cent of magnesium; and one of gamma and delta (the magnesium-rich solid solution holding dissolved gamma) a t 68 per cent of magnesium. Under equilibrium conditions the maximum solubility of magnesium (as beta) is about 13 per cent, at 448” C. (point H ) ;whereas a t room temperatures but 10 per cent is soluble. Under normal conditions of cooling in sand, however, the eutectic of beta and alpha is precipitated when the magnesium content exceeds about 6 per cent.6 Magnesium also unites avidly with silicon to form the deep blue compound Mg2Si. When the silicon content of the aluminium-magnesium alloy is about 0.25, as little as about 0.5 per cent of 600 magnesium causes the separation of this compound in the sand-cast metal. According to the work of Hanson and Gayler,6 the effect of magnesium joo in excess of that quantity necessary to combine with silicon to form MgZSi is to reduce the solubility a t high temperatures of that constituent in aluminium from a maximum of 1.6 too per cent (Mg 0.94, Si 0.66; ratio 1.7: 1) to 1.1per cent with an excess of only 0.7 per cent of magnesium and to practically nil when 5 per cent of magnesium is present. Besides the alpha solid solution and the compound MgZSi, the latter arising from the presence of silicon as an impurity in the alu3 0 minium ingot, there is to be found one and possibly two constituents bearing iron, also 4 Z. m o w . Chem.. . 46.. 225 (1905).
cent by Weight
FIG.~-EQUILIBRIUM DIAGRAM FOR ALUMINIUM-MAGNGSIVM ALLOYS (HANSON AND GAYLER)
6 Jeffries, J . SOC.Automotive Eng., 1, 296 (1920).
e
J . I n s t . Metals, 26,343 (1921).
ai1 inrpurity. The very ~rriallarnounts of copper in the ingot take the form of Cu.41~in solution in the aluminium. The present. paper describes a portion of the reeearch into the properiies of the alumirrium-riiagnesi~iin-silicotiseries of alloys, undcrtaken by t,he hkiterinl Section, Engineering Division, Air Service, V. S. A . In tliis article are covered the alloys of aluminium containing less t,liiln 5 per cent of magnesium, lyiiig therefore entirely xithin thc alpha field shown to the left in Fig. 1.
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~ s Sri W X M E K s
The maxiimim furnace and the pouring temperatures iveri, measured with a hare chromel-alumcl bliermocouple and :I potent,iometcv. The metal 1 well skimmed hefire casting. The sand-cast tension test specimens w w c temperature of 1300' 1 1 0 " F. A mold of th is sliown in Fig. 2. The biws ivere cast to sis diameter), t h e e t,o the mold, with individual riscrs rind rome, iii green Satidusky sand. spwimerrs were ciist fro1 into a, permanent,, split i e bar lying in a plime a horizontal, :is depii,t,ed in Fig. 3. The mold tenipcwnturr was wlimiitPd to lmve rniigcd brtrreen 20O0 :id300" V.
CEIEI~:~:AI. A x ~ ~ , ~ s i s - - Atlic! l l molts uwe :tiiulyae
