AIME Technical Publications and Contributions - 1926 - A …library.aimehq.org/library/books/AIME Technical Publications... · The magnesium-aluminum system was first studied by Boudouard,!

TRANSACTlONS O F THE AMERICAN INSTITUTE OF M I N I N G A N D METALLUR- GICAL ENGINEERS [SUBJECT TO REVISION]

NO. 1638-E. I B ~ U E D WITH MINING A N D METALLURGY. FEBRUARY.' 1926. . . . .

DISCUSSION OF THIS PAPER IS INVITED. It should oreferablv be oresentedin Derson a t - - - - . . - - . . . - - - - - - - -. - - - - - . - - the New York Meeting! February, 1926, when an ,abstrhct of the 'paper will be iead: If this'is ifnljG- able, dlscusslon In w r ~ t ~ n g may be sent t o the Edltor, American Institute of Mining and Metallurgical Engineers, 29 West 39th Street. New York. N. Y.. fo r presentation by t h e Secretary or other representa- tive of its au thor . Unless special arrangement is made, the discussion of th i s paper will close April 1, 1926 A n y discussion offered thereafter should preferably be in the form of a new paper.

A Preliminary Study of Magnesium-base Alloys BY BRADLEY STOUGHTON* AND M. MIYAKE,~ BETHLEHEM, P'A.

(New York Meeting, February, 1926)

THE importance of magnesium alloys as engineering materials has increased rapidly in the past few years. The most important properties of magnesium alloys are their lightness and strength, which result in their extensive use in aircraft and automobile construction. Recent progress in the metallurgy of magnesium seems to offer hope of the production of the pure metal a t a reasonable cost. The use of magnesium would doubtless increase greatly if it could be produced a t a cost comparable with that of aluminum.

A preliminary survey of the magnesium-base alloys shows that the most promising from a practical standpoint are magnesium-aluminum and magnesium-zinc as binary alloys, and magnesium-zinc-aluminum as ternary alloys. The research reported in this paper is a preliminary study of binary magnesium-aluminum and magnesium-zinc alloys, as an introduction to a series of further investigations.

The magnesium-aluminum system was first studied by Boudouard,! who merely determined the liquidus. An accepted constitutional diagram was given by Grube12 who found a compound A13Mg4 (melting point = 462.7" C.) and two eutectics a t 35 per cent. magnesium (451.6" C.) and a t 68 per cent. magnesium (440" C.) * Between the first eutectic and' . .

the compound a solid solution exists. This diagram was checked: or

* Professor of Metallurgy, Lehigh University. t Graduate Student, Department of Metallurgy, Lehigh University. ' 0 . Boudouard: Sur les alliages d'aluminium et de magn6slum. Comp. Rend.

(1901) 132, 1325; 133, 1003; Bull. Soc. Chim. (1902) 27, 5, 45. G. Grube: 'ifber Magnesium-aluminiumlegierungen. Zeit. anorg. Chem. (1905)

46, 225.

copyright, 1926, by the American Institute of Mining and Metallurgical ~ n g i n e e i s , I ~ L c <

2 A PRELIMISARY STUDY OF MAGSESIUM-BASE ALLOYS

supplemented by PCcheux,3 Br~niewski,~ EgerI5 Schir~neister,~ Voge17 and Merica, Waltenberg, and Freeman.8

Recently this system was thoroughly studied and an excellent constitutional diagram was given by Hanson and G a y l ~ r . ~ The diagram,

Mognes~um, per cent by weight

FIG. l . -E~vr~renrvhf DIAGRAM O F HASSOX AXD GAYLEH.'

I modified considerably from those of earlier investigators, is shown in Fig. 1. There occur two compounds, A13Mg2 and A12Mg3, and three -

H. PCrheux: Contribution B, I'Ctude des alliages de l'aluminium. Rev. Girt. Sri. (1907) 18, 109.

W. Broniewski: Sur les propriEtEs Blertriques des alliages aluminium-magnesium. Comp. Rend. (1911) 162, 85.

G. Eger: Studie iiber die Konstitution der ternaren Magnesium-Aluminium- Zink Legierungen. Inl. Zeit. Metallog. (1913) 4 , 42.

H. Gchirmeister: Erganzung des Aluminium-Jlagnesium-Gustanddiagrames. Metall u. Ere. (1914) 11, 522.

R. Vagel: i'ber terngre Legierungen des Aluminiums mit hlag~esiurn und Kupfer. Zeit. anorg. Chem. (1919) 107, 265.

* P. D. Merica, R. G. UTaltenberg, and J. R. Freeman, Jr.: Con~titution and Metallography of Aluminun~ and I ts Light Alloys with Copper and with hlagnesium. Sci. Papers, B. S. (1919) 337; Trans. A. I. hl. E. (1920) 64, 3.

W. Ilanson and 31. L. V. Gayler: Constitution of the .klloys of Aluminium and Magnesium. J r 1 1 . Inst. ?rletals (1920) 24, 201; Engineering (1920) 110, 788, 819.

BRADLEY STOUGHTON .AND M. MIYAKE 3

eutectics. Both the pure metals and the compounds form solid solutions. The solid solubility of magnesium in aluminum is indicated as approximately 12 per cent. a t 448" C. and 10 per cent. a t room temperature. According to Merica and his associatesl8 aluminum dissolves about 12.5 per cent. of magnesium as Mg4A13 (really A13Mg,) a t 450" C. and the solubility of the compound decreases with decreasing temperature. At 300" C. the solubility is about 5.9 per cent. The later investigation of Ohtanilo shows the solid solubility is approximately 9.7 per cent. a t 400" C. and 7.3 per cent. a t 320" C. MehlH studied electrically thc beta + gamma field, and set the limit of the gamma field a t 49.8 per cent. magnesium. According to Hanson and Gayler's diagram, the solid solubility of aluminum in magnesium is about 10 per cent. a t 435" C., decreasing somewhat as the temperature falls. The experiments by the Aluminum Company of America,12 however, show that the solubility a t 435" C. is somewhat greater than 10 per cent., and that it decreases more rapidly with falling temperature. The diagram of Hanson and Gayler shows no indications of transfortnations below the temperkture of the solidus.

MECHANICAL PROPERTIES OF MAGNESIUM-ALUMINUM ALLOYS Aluminum seems to be the most favorable alloying metal for magne-

sium, because it not only has a low density, but is near to magnesium in the electrochemical series. The mechanical properties of the magnesium- aluminum alloys were fully investigated by the Dow Chemical Co., and jointly by the Aluminum Company of America and the American Mag- nesium Corp. Dowmetal,13 to l8 sold by the Dow Chemical Co., is ba~ically a series of alloys of magnesium and aluminum. The American Magnesium Corpn. sells various magnesium-aluminum alloys under the trade name of Greyhound brand.I3

The more important mechanical properties of magnesium-aluminum alloys, as reported by Gann17 of the Dow Chemical Co., are shown in

- -

lo B. Ohtani: Alloys of Aluminium-magnesium. Jn1. Cher~a. Znd. [Japan] (1922) 26, 36.

l1 R. F. Mehl: Preparation of Pnre Alloys. Trans. Am. Electrochem. Soc (1924) 46, 149.

l2 L'Magnesium.'' A Handbook by the American Magnesiunl Corpn., Niagara Falls, N. Y., 1923.

l3 Anon: New Light Plston Alloy. Autoinot. Z t~d. (1919) 41, 161. l4 E. J. Jenkins: The New Alloy of Magnesium. Iron Age (1920) 106, 193. l5 G. Gaulois: A New Magnesium Alloy for Motor Pistons. Sci:..ttt~. (1920) 123,

519. l6 Anon: New Light Piston Alloy, Dowmetal. Automot. Znd. (1920) 42, 967. l7 J. A. Gann: Dowmetal and Its Applications. Trans. Am. Soc. Steel Treat.

(1922) 2, 607. l8 J. A. Gann: Recent Progress in Magnesium Alloys. Jill. Znd. & Eng. Chern.

(1922) 14, 864, Raw Material (1922) 6, 394. l9 S. I<. Colhy: Marketing Rlagnesium. Eng. ck &fin. Jn1.-Pr. (1924) 118, 51.

4 A PRELIMISARY STUDY O F MAGSESIUXI-BASE ALLOYS

Fig. 2. The curves A refer to cast metal and B to metal heat treated for two hours a t 800" F. (427" C.). The curves showing per cent. elongation and. per cent. reduction in area have been omitted. They both begin a t about 5 per cent. for pure magnesium, rise rapidljr to 8 to 10 per cent. a t an aluminum content of 4 per cent., and gradually decrease to 1 per cent. at 12 per cent. aluminum. The Brine11 hardness is roughly proportional to the aluminum content, varying from 35 to 40 for pure magnesium up to 140 to 150 for a 30 per cent. aluminum alloy.

O d I A Q b ib L I 1 lb P b Alum~num, pQr cent

2.-STRESOTH O F SOME ALLOYS O F MAGSESIUM WITH ALUSfISUM, CAST METAL, (B) HEATED FOR 2 HR. AT 427' C .

UASS.' ( A )

I n Fig. 3, the data given by the joint research of the Aluminum Com- pany of America and the American Magnesium C ~ r p n . l ~ * ~ ~ are shown. The curves A refer to sand-cast metal and B to extruded metal. The results are approximately in agreement with those of Gann, and show the superiority of the 4 per cent. to 12 per cent. aluminum alloys. The alloys can be materially improved in mechanical properties by mechanical working. Almost the same figures are obtained by rolling as by extrusion. AitchisonZ1 gave the figures of Table 1 for the 6 per cent. aluminurrl allov.

20 Anon: ?1Zagnesium. Chenc. c!2 Met . Eng. (1924) 31, 383. L. ,litchison: l lerhanical Properties of Magnesium Alloys. Jnl. Inst. Metals

(1923) 29, 17; Engineering (1923) 116, 312; ,%fetal Ind. (S. Y . ) (1923) 21, 279; Metal Znd. (Imnd.) (1023) 22, 222; Min & M e t . (1923) 4, 288.

BRADLEY STOUGHTON AND bl. MIYAKE 5

TABLE 1.-Alloy of Magnesium with 6 Per Cent. Aluminum ELASTIC LIMIT, YIELD POINT. ULTIMATE STR., ELONGATION, 1.8. PER SO. IN. I.B. PER SO. IN. LB. PER SQ. IN. PER CENT.

Cast bar . . . . . . . . . . . . . . . 4,000 12,200 24,000 5.0 Rolled strip. . . . . . . . . . . . 12,500 37,200 41,500 7 .5 Extruded rod.. . . . . . . . . . 42,000

The strength of these alloys can be further increased by chill-casting. MaybreyzZ gave the results shown in Table 2.

The magnesium-aluminum alloys not only possess excellent mechanical properties, but have a remarkably low density even in the 12 per cent. aluminum alloy. The density of the alloys is given in Table 3.12f20923

TABLE 3.-Density of Magnesium-aluminum Alloys Aluminum, per cent.. . . . . . . . . . . . . . 0 2 4 6 8 10 12 Density . . . . . . . . . . . . . . . . . . . . . . . . . 1.74 1.75 1.77 1178 1.79 1.81 1.82

The Dow Chemical Co. recommends the 8 per cent. aluminum alloy for casting purpose, and calls it Dowmetal "A." The physical and mechanical properties of Dowmetal "A" are given in Table 4.

TABLE 4.-Dowmetal " A " Tensile strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25,000 lb. per sq. in. Elongation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 per cent. Specific tenacity.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 14,000 lb. per sq. in. Compressive strength.. . . . . . . . . . . . . . . . . . . . . . . . 44,000 lb. per sq. in. Brine11 hardness.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Thermal conductivity (20'-350" C.) . . . . . . . . . . . . 0.200 Thermal expansion (20'-400" C.) . . . . . . . . . . . . . . . 0.29 X lo-' Melting point. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615" C. Specific gravity.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 .8

The magnesium alloys containing 4 per cent. or more aluminum can be improved in mechanical properties by a suitable heat treatment.

2 2 H. J. hlaybrey: Magnesium in t,he Foundry. Foi~ndry Trade Jnl. (1923) 28, 227; Meial Ind. (N. Y. ) (1923) 21, 398; Metal Znd. (Lond.) (1923) 23, 315; F o ~ ~ n d r y (1924) 62, 96; Mcch. World (1924) 26, 12.

2 3 L. Aitchison: Materials in Aircraft Construction. Jril. Royal Aeronaut. POC. (1924) 28, 238; Proc. Inst. of Auto. Eng. (1924) 18, 557; Aufom3!iue Ind. (1924) 60, 924, 970.

(3 A PRELIMINARY STUDY O F MAGNESIUM-BASE ALLOYS

I t is reported by Gann," and by the Aluminum Company of America and American Magnesium Corpn.12 that the strength and elongation of cast alloys are improved by heating the alloys for some hours a t a temperature in the vicinity of 425" C. According to Gann, complete solid solution is produced in the 8 per cent. aluminum alloy in 4 hr. a t 820" F. (438" C.) while 24 hr. are required a t 750" F. (400" C.). However, the maximum increase in strength occurs long before complete solid solution is

O b i k B 1 , L l A A l u r n ~ n u m , ~ e r cent

F I G . 3.-SOME MECHANICAL PROP- FIG. SOME MECHANICAL PROP- ERTIES OF, MAGNESIUM-ALUMINUM ERTIES OF SOME ALLOYS OF MAG- ALLOYS AFTER ARTIFICIAL AD- NESIUM WITH A L U M I U M . ~ ~ . ~ ~ ( A ) I N D . ~ ' - ~ O (A) CAST METAL; ( B ) SAND-CAST METAL; ( B ) EXTRUDED EXTRUDED METAL. METAL.

reached, although some eutectic is left undissolved. As shown in Figs. 2,3, and 4, not only do heat treatment and mechanical treatment increase the strength of the alloy; they shift the position of the maximum tensile strength towards higher aluminum alloys. The per cent. elongation curve is the same as for the original castings up to 2 per cent. aluminum, and then follows the same tendency to shift the maximum as the other heat-treated curves, while the Brinell hardness is slightly lowered by the

BRADLEY STOUGHTON AND M. MIYAKE - i

heat treatment. The Aluminum Company of Amcrica and American I\,lagnesium Corpn. esplain that the improvement in strength and elongation by this heat treatmcnt is due to the solution of free magnesium- aluminum compound.

According to thc Aluminum Company of America and American Magnesium Corpn., if the alloy, either cast or worked, is cooled rapidly after this heat treatment and is reheated to a temperature of from 150" to 250° C. for a number of hours, the magnesium-aluminum compound precipitates out of solid solution in very small particles and causes hardening. This fact is quite analogous to the hardening and increasing in strength of aluminum-copper alloys by the quenching followed by

FIG. 5.-AL 4 PER CENT., SbND-CAST. FIG. 6.-AL 4 PER CICNT., CHILGCAST. X 100. ETCHED WITH 2 PER CENT. X 100. ETCHED WITH 2 PER CENT. HNOZ. HNOI.

so-called "artificial aging," advanced by Archer and Jef f~ies .?~ An example of the mechanical properties of magnesium-aluminum alloys subjected to this artificial-aging treatment after quenching is shown in Fig. 4.'hZ0 In those curves, A refers to cast alloys and B to extruded alloys. It will be noted that the maximum strength in these alloys is 55,000 lb. per sq. in. obtained from 10 per cent. aluminum alloy extruded, qucnched, and artificially aged. The corresponding elongation is only 2 pcr cent. The highest value for elongation is 20 per cent. with 4 per cent. aluminum alloy as extruded, orextruded, quenched, and artificially aged, and the corresponding strength is 36,000 1b. pcr sq. in.

The microstructures of sand-cast and chill-cast alloys are shown in Figs. 5 to 10. The grains of delta solid solution are partly or entirely

24 R. S. Archer and Z. Jeffries: New Developments in High-strength Aluminum A l l o y s . Trans. A. I. M. E. (1925) 71, 828.

8 -4 PRELIMINARY STUDY O F MAGNESIUM-BASE ALLOYS

surrounded by the eutectic. The size of grain and t.he amount of eutectic depend on the content of aluminum and the rate of cooling. I n

FIG. 7.-AL 8 I~rcrL CENT., S.4ND-C.4S1'. FIG. 8.-AL 8 PER CEYT. CHILkCAST. X 100. ETCHED WITH 2 ,PI~:R CENT. X 100. RTCHED WITH 2 PER CENT. HKOt. HKOa.

the alloys having higher content of aluminum and more rapidly cooled, the amount of eutectic is greater and the size of grain is smaller. It will be seen in Fig. 1 that magnesium can hold nearly 10 per cent. aluminum

FIG. 9.-AL 12 PER CEXT., SAND-CAST. FIG. 10.-AT, 12 PER CENT., CHILL-CAST. X 100. ETCHED WITH 2 PER CENT. X 100. ETCHED WITH 2 PER CENT. HNOa. HNO1.

in solid solution. The castings have cooled so rapidly, however, tha t there was not sufficient time for complete equilibrium to be established, and even the lower per cent. aluminum alloys retain some eutectic.

BRADLEY STOUGHTON A K D M. MIYAKE 9

A hardness test (Brinell, 500 kg., 10 mm., 30 sec.) shows that the hardness of the alloys is directly proportional to the amount of eutectic and inversely proportional t o the size of grain. The Rrinell hardness of the cast alloys is shown in Table 5.

TABLE 5.-Brine11 Hardness of Mnq~zesium-alum,inzcm Alloys

FIG. 12. F I G . 1 3 .

FIG. 11.-AL 4 PER CENT., SAND-CAST, HEAT-TREATED. X 1 0 0 . ETCHED WITH 2 IWR CENT. H N 0 3 .

FIG. 12.-AL 8 PER CENT., SAND-CAST, HEAT-TREATED. X 100. ETCHED WITH 2 I'ER CENT. H N O s .

FIG. 13.-AL 12 PER CENT., SAND-CAST, HEAT-TREATED. X 100. ETCHED WITH 2 PER CENT. HN03.

BRADLEY STOUGHTON AND M. MIYAKE n I

heat treatment. The Aluminum Company of America and American Magnesium Corpn. explain that the improvement in strength and elongation by this heat treatment is due to the solution of free magnesium-

. aluminum compound. According to the Aluminum Company of America and American

Magnesium Corpn., if the alloy, either cast or worked, is cooled rapidly after this heat treatment and is reheated to a temperature of from 150" to 250" C. for a number of hours, the magnesium-aluminum compound precipitates out of solid solution in very small particles and causes hardening. This fact is quite analogous to the hardening and increasing in strength of aluminum-copper alloys by the quenching followed by

so-called "artificial aging," advanced by Archer and J e f f r i e ~ . ~ ~ An example of the mechanical properties of magnesium-aluminum alloys subjected to this artificial-aging treatment after quenching is shown in Fig. 4.12rm In those curves, A refers to cast alloys and B to extruded alloys. It will be noted that the maximum strength in these alloys is 55,000 lb. per sq. in. obtained from 10 per cent. aluminum alloy extruded, quenched, and artificially aged. The corresponding elongation is only 2 per cent. The highest value for elongation is 20 per cent. with 4 per cent. aluminum alloy as extruded, orextruded, quenched, and artificially aged, and the corresponding strength is 36,000 lb. per sq. in.

The microstructures of sand-cast and chill-cast alloys are shown in Figs. 5 to 10. The grains of delta solid solution are partly or entirely

- - - -

24 R. S. Archer and Z. Jeffries: New Developments in High-strength Aluminum Alloys. Trans. A. I. AII. E. (1925) 71, 828.

8 A PRELIMINARY STUDY O F MAGNESIUM-BASE ALLOYS

surrounded by the eutectic. The size of grain and the amount of eutectic depend on the content of aluminum and the rate of cooling. In

the alloys having higher content of aluminum and more rapidly cooled, the amount of eutectic is greater and the size of grain is smaller. It will be seen in Fig. 1 that magnesium can hold nearly 10 per cent. aluminum

FIG. 9.-AL 12 PER CENT., SAND-CAST. FIG. 10.-AL 12 PER CENT., CHILGCAST. X 1 0 0 . ETCHED WITH 2 PER CENT. X 1 0 0 . ETCHED WITH 2 PER CENT. HNOI. HN02.

in solid solution. The castings have cooled so rapidly, however, that there was not sufficient time for complete equilibrium to be established-,

l and even the lower per cent. aluminum alloys retain some eutectic:

10 A PRELIJ I ISARY STUDY OF MA(:XESICM-BASE ALLOTS

As previously stated, the alloys can be improvecl in mechanical properties by sirnple heating a t a temperature sorliewhat below the solidus. In Figs. 1 1 to 13, the microstructures of sand-cast alloys heat treated a t 430" C. for 2 hr. are shown. I t will be noted that the size of grain grows and the amount of eutectic decreases. As already stated, the higher aluminu~n alloys can be hardened by quenching from a temperature below the solidus followed by an artificial aging a t a temperature between 150" and 250" C. In order to obtain the best rtiechanical properties an extended period of tirne of heating and reheating may be required, but it was not feasible to test this question during the present investigation. Ztesults were obtained of the change of hardness of the alloys due to heating for 2 hr. a t 430" C., quenching in water, and reheating for 4 hr. a t 170" C. The results of Brine11 hardness test, as shown in Table 6, exhibit a material increase of hardness in the 12 per cent. aluminum alloy, especially in the chill-cast alloy.

.\luminum, - Per Cent.

Oriain,~l C ~ s t i n g s ' ? f e d Original Castinzs Quenrhed Reheated and

The alloys, when aged a t the room temperature for seven days after quenching, did not show any change in hardness. The microstructures of the sand- and chill-cast alloys with 12 per cent. aluniinum, before and after the artificial aging, are shown in Figs. 14 to 17.

Some difficulty was experiencecl a t first in developing the structure of these alloys. The rnost satisfactory method seems to be to rub the polished surface of the specimens a few times with a swab of cotton wetted with a 2 per cent. alcoholic solution of nitric acid. All the photographs shown were etched by this method.

The magnesium-zinc system was first studied by R o u d ~ u a r d , ~ ~ who merely determined the liquidus. An accepted constitutional diagram

2 5 0. Boudounrd: Les alliages de zinc et de magn8sium. Comp. Rend. (1904) 139, 424.

BRADLEY STOUGIITON AND M. MIYAKE 11

w a s g i v e n by Grubc,?%hich was checked by Rruni, Sandonnini, and Quercigh," F~gcr;~ ' and I'icrce. 29

~ ' ' I G . 14.-AL 12 PER CEVT., SAND-CASr, FIG. 15.-AL 12 PER CENT. CHILL-C4ST, QUENCHED. X 1 0 0 . ETCHED WITH 2 QUENCHED. X 100. ETCHED WITH 2

1 PER CENT HNOj . PER CENT. K K O I .

F I G . 16.-AL 12 I'ER Cb:Nrr., S.4ND-C.4ST, FIG. 1 7 . - A ~ 12 PER CENT., CHILL-CAST, REHEATED. X 1 0 0 . ETCHED WITH 2 REHE.4TED. X 100. ETCHED WITH 2 PER CENT. HNOS. PER CENT. 11x0~.

The Grube-Eger d i a g r a m is s h o w n in Fig. 18. It s h o w s a compound, MgZnz (590°C.) and t w o eu tec t i c s , one at 51.1 per cent. z inc (355°C.)

26 G. Grube: u b e r die Legierungen des Magnesium mit Kadminium, Zink, Wismut und Antimon. Zeit. anorg. Chem. (1906) 49, 7 7 .

27 G. Bruni, C. Sandonnini and E . Quercigh: Uber die terniiren Legierungen von Magnesium, Zink und Kadmium. Zeil. anorg. Chem. (1910) 68, 7 8 .

28 G. Eger: Studie iiber die Ihnstitution der ternaren Magnesium-Aluminium- Zink Legierungen. Int. Zeit. Metallog. (1913) 4, 4 6 .

20 W. M. Peirce: Studies on the Constitution of Binary Zinc-base Alloys. Trans. A. I. M. E. (1923) 68, 7 8 1 .

12 A PRELIMINARY STUDY OF' MAGNESIUM-BASE ALLOYS

and the-other a t 96 per cent. zinc (369°C.). This diagram has been . confirmed by Pierce; namely, that there is no solubility on the zinc side, but it misses a solid solution on the magnesium side, which one of us has noted, as follows: At 'the eutectic temperature, magnesium holds more than 10 per cent. of zinc in solid solution. This solubility decreases as

Zinc, per con+ by welght

FIG. ~ ~ . - - G R w E - E G E R EQUILIBRIUM DIAGRAM O F MAGNESIUM-ZINC ALLOYS.

the temperature drops. This observation is important in connection with the heat treatment of the magnesium-zinc alloys.

MECHANICAL PROPERTIES OF MAGNESIUM-ZINC ALLOYS The mechanical properties of magnesium-zinc alloys seem to resemble

those of the magnesium-aluminum alloys. The tensile strength and specific gravity, as given by Aitchison," are shown in Table 7.

TABLE 7.-Tensile Strength and Specific Gravity of Magnesiumzinc Alloys ZINC, MAX STRENQTE,

PER CENT. LB. PER So. IN. SP. GR.

BRADLEY STOUGHTON AND M. MIYAKE 13

According to the Dow Chemical CO.,~O the 5 per cent. zinc sand-cast alloy '

has the following mechanical properties: . . . . .

Tensile Strength, Elongation, 1.b. per Sq. In. I Per Cent. Brinell Hardness

--

MaybreyzZ reports that the 8 per cent. zinc alloy has the mechanical properties shown in Table 8.

"Elektron," 18,21,31 to 4 6 made by the Chemische Fablik ~ f i e s h ~ i m - Elektron, Frankfurt a. M., Germany, is practically a series of magnesium- zinc alloys. Their analyses are summarized as follows:

30 Physical Properties of Materials. Circ. 101, Bur. of Stds. (1924) 124. 31 F. Thomas: 'ijber des Vergiessen von Elektronmetall. Stahl u . Ezsen (1920) 46,

90; Elekt. u. ilfasch. (1920) 38, 306; Brass Wld. (1920) 16, 342; Metal Ind. [Lond.] .

(1920) 17, 107. 32 Anon.: New High Magnesium Alloys. Automotive Ind. (1920) 42, 1343. 33 Anon.: Electron. Tech. Rev. (1921) 8, 162. 34 beckins ins ale: The Magnesium Alloy: Electron. Jnl. Inst. Metals (1921) 26,

375; Metal Ind. [N. Y.] (1921) 19,433; Metal Ind. [Lond.] (1921) 19, 305; Engineering (1921) 112, 641; Foz~ndrg (1921) 49, 821; L'Electrician (1922) 63, 297. 35E. Weinwurm: Das Elektronmetall. Chem. Zeit. (1921) 46, 579; Elekt. u .

Masch. (1921) 39, 516; Gdnie Czvil (1921) 79, 593. 36 C. Grard: Les alliages l6gers et leur emploi en a6ronautique. Bz~11. Soc. d'Enc.

(1921) 133, 863; Rev. Mdt. (1921) 18, 567; Rev. Gdn. Elec. (1921) 10, 27; C'hem. & Met. Eng. (1922) 26, 798.

A. Bregman: Electron Metal. Met. Ind. [ N . Y.] (1922) 20, 1 38 Anon : Magnesium illloys in Engineering. Prac. Eng. (1922) 66, 404. 39L. Guillet: Les alliages 16gers: Leurs recents progr6s. Rev. Mdl. (1922) 19,

688. C. Irresberger: Magnesiumguss. Giesserei Zeit. (1922) 19, 599; Mech. Eng.

(1923) 46, 48. A. Porterin: Le Magnesium et les alliages ultra-16gers. Bull. Soc. Ing. Civils

(1923) 76, 486; Rev. Met. (1923) 20, 428; Gdnie Civil (1923) 82, 452. 42 H. Icalpers: Le M6tal electron. Fond. Mod. (1923) 17, 74. 4 3 F. Thomas: Fortschritte und Aussichten in der Vermendung der Lichtmetalle.

Maschinenbau (1923) 2, 85. 44 It. R. Moore: Resistance of Manganese Bronze, Duralumin, and Elektron Metal

to Alternating Stresses. Proc. Am. Soc. Test Mat. (1923) 23, 106; Metal Ind. [Lond.j (1923) 23, 50.

45 E. H. Schulz: Die Nichteisenmetalle unter besonderer Berucksichtigung der Luftfahrzeuge. Zeit. Ver. deut. Zng. (1924) 68, 545.

46 G. Schreiher and R. Neumahl: Elektronmetall. Maschinenbaz~ (1925) 4, 7.

14 A PRELIJ~ISARY STUDY OF MAC:SESIUM-BASE ALLOYS

The more important physical and mechanical properties of a few kinds of " Elektron " are given in Table 9.

TABLE 9.-Physical and ,lIechanical P r o p ~ r t i e s of Elektron

z I I Wrought Alloy Sperially Iiard. Strong ;\11c,y

A z cast-Alloy

Extruded Hard-roiled Extruded k'xtruded and Harumpred

" E:lektronl' can be extruded, rolled or drawn a t 400" C . , and forget1 at 220" to 250" C. Cold working causes brittleness, but the ductility is recovered on annealing.

- - ~

Elastic limit, lb. per sq. i n . . .................

Proportional limit. lb. per sq. in. . ..........

Tensile strength. lb. per sq. i n . . . . . . . . . . . . . . .

Elongation, per cent. ... Compressive strength,

lb. per sq. i n . . . . . . . . . Brine11 hardness.. . . . . . . Electric conductivity. . . Tbernral c~)nductivity.. . Specific heat . . . . . . . . . . . Thermal expansioil. . . . . . M. P., degrees Centi-

grade

The mechanical properties of magnesium-zinc alloys xnay be irn- proved by a suitable heat treatment just as in the magnesium-aluminui~l alloys. The most important fact discovered by one of the authors is that the magnesium-zinc alloys can be hardened materially by quenching from a temperature somewhat below the solidus, followed by reheatng to a temperature higher than room temperatures (so-called artificial aging). No hardening effect occurs when the alloys are aged a t room temperatures for several days after quenching. An enormous increase in hardness is obtained by heating some of the magnesium-zinc alloys for 2 hr. at 340" C., quenching in water, and then reheating for 4 hr. a t 150" C. This is shown in Table 10.

I t will be seen that the effect is especially great in high-zinc and chill- cast alloys. By the proper selection of temperature and time, excellent results may be expected. The effect of quenching and reheating the magnesium-zinc alloys, together with the solubility of MgZnz in magne-

4.300- 7,000

8.500-1 3,000

17.000-2l.000 2- 4

3H.00&40.000 44-46 l ; ~ l ( i 0.32 0.24

ti30 Sperifir ernvity. . . . . . . . . i 1.80

BRADLEY STOUGHTOX AXII M. MIYAKF: 15

TABLE 10.-Brine11 Iiardness of Quenched and Art$cially Aged Alloys of Magnesium and Zinc

sium, offers an important subject for research, which we hope to be able to prosecute at some future time.

Sand-cant

Zinc Per ~ & l 1 Original Castings I Quenched and

I Reheated

FIG. 2 1 . - Z ~ 12 PER CENT., SAND-CAST. FIG. 22.-ZN 12 PER CEXT., CHILL-CAST. X 100. ETCHED WITH 2 PER CENT. HNO3. X 100. ETCHED WITH 2 PER CENT. H S 0 3 .

Chill-cant,

Oridnd Castings / Quenched and Rchcated

16 A PRELIMINARY STUDY O F MAGNESIUM-RASE ALLOYS

MICROSTRUCTURES O F MAGNESIUM-ZIXC ALLOYS

The microstructure of sand- and chill-cast alloys containing 8 and 12 per cent. zinc are shown in Figs. 19 to 22. The structures resemble those of magnesium-aluminum alloys, the grains of magnesium-rich solid solution being partly or entirely surrounded by the eutectic.

F I G . 23.-ZN 12 PER CENT., SAKD CAST, FIG. 24.-ZN 12 PER CEXT., CHILL-CAST, QUENCHED. X 100. ETCHED WITH 2 PEIt QUENCHED. X 1 0 0 . ETCHED WITH 2 PER CENT. H S O I . CENT. HNOa.

As previously stated, the magnesium-zinc alloys can be hardened by quenching followed by reheating. The microstructures of 12 per cent. zinc alloys, heated a t 340" C. for 2 hr. and quenched in water, are shown in Figs. 23 and 24; and reheated to 150" C. for 4 hr. in Figs. 25 and 26.

BRADLEY STOUGHTON AND XI. MIYAKE 17

That there exists a solid solution on the magnesium side is mentioned previously. The structuresof 8 per cent. zinc sand-cast alloys, heated for seven hours a t 340" C., and cooled in the air, and of 12 per cent. zinc sand-cast alloy, heated for 50 hr. a t 340' C. and quenched in water, are shown in Figs. 27 and 28. I n the alloys containing less than 10 per cent. zinc, heated for 50 hr. a t 340" C., the eutectic can no longer be found.

The alloys were etched with 2 per cent. alcoholic solution of nitric acid in the same manner as the magnesium-aluminum alloys.

FIG. HEATED WITH 2

27.-ZN 8 PER FOR 7 HR. X

PER CENT. HNOa.

CEKT., SAND, FIG. 2 8 . - Z x 12 PER CENT., SAND,. 100. ETCHED HEATED FOR 50 HR. X 1 0 0 . ETCHED

I WITH 2 PER CENT. HNO3.I

The constitutional diagram and mechanical properties of magnesium- aluminum alloys are reviewed.

A metallographical study of magnesium-aluminum alloys is offered. The constitutional diagram of magnesium-zinc alloys is reviewed,

suggesting the existence of a solid solution on the magnesium side. The mechanical properties of magnesium-zinc alloys, including

"Elektron," are reviewed. I t was found that the magnesium-zinc alloys can be hardened by

quenching in water from a temperature somewhat below the solidus, followed by reheating to a temperature higher than room temperature.

A metallographical study of magnesium-zinc alloys is offered.

Documents

AIME Technical Publications and Contributions - 1926 - A …library.aimehq.org/library/books/AIME Technical Publications... · The magnesium-aluminum system was first studied by Boudouard,!