US2026591A - Alloy - Google Patents

Description

' Patented Jan.- 7, 1936 Roy E. Paine,- Cleveland, Ohio, assignmto Magnesium Developmentcorporation, a corporation of, Delaware No Drawing. Application 0ctober4, 1933,

I Serial No. 692,135

zblaima. (ci ia-n The invention relates .to magnesium-base alloys and is directed to the development of alloys of this class which have good corrosion resistance,

particularly in the cast and in the cast and heat treated condition.

The art of casting magnesium presents many practical difliculties which must be surmounted before the true commercial possibilities of magnesium castings can be fully realized. An alloy which is suitable for one application may be entirely unsuited to another and, as. a consequence, it is frequently necessary to sacrifice desirable characteristics of the alloy in order to more fully realize the advantages of some one or more important characteristics. Thus a compromise must quite frequently be made in order to approach in one alloy the optimum properties for a given application. For example, it may be found that corrosion resistancecan be sacrificed to a certain extent to obtain higher tensile strength, yield point, hardness, or similar mechanical properties. Again, tensile strength may be sacrificed in order to obtain proper casting or working characteristics. It is an object of the present invention to develop magnesium alloys which will conbine to a maximum degree the characteristics of corrosion resistance, favorable mechanical properties, workability, susceptibility to improvement by heat treatment and adaptability to sand outing.

.A further object is the provision of magnesium alloys characterized by their susceptibility to be improved in mechanical properties by suitable thermal treatments. A further object is the provision of magnesium-base alloys characterized by good corrosion resistance in either the cast or in the cast and heat treated condition. A further object is the provision of magnesium alloys possessing excellent casting characteristics. A further object is the provision of magnesium-base alloys susceptible, within certain ranges, to me-,

chanical deformation.

I have discovered that magnesium-base alloyscontaining from 0.5 per cent to 22 per cent of lead possess to an appreciable degree the col-.

\ lective characteristics of alloys which are resistdeformation. A

.In accordance with my invention lead may be present in amounts as low as 0.5 per The preferred casting alloys are those containing above about 5 per cent of lead since it is in these alloys that the most pronounced combination of these diiferent properties is obtained. The alloy may be worked by extrusion over a range of from 5 about 0.5 per cent to about 22.0 per cent of lead.- As an all around casting alloy I have found a magnesium alloy containing 5 to 10 per centof lead to be particularly adapted to general foundry purposes. Alloys falling withinthis preferred 10 range of composition as well as other alloys comprised within the broader limits previously defined, have been subjected to severe tests designed to produce accelerated corrosion. Sand cast test bars poured in accordance with the best casting i5 practice in the art were subjected to corrosion tests in the as cast'and in the heat treated" condition. In the example referred to the heat treatment was carried out at about v4=59 centi-' grade for about 20 hours followed by quenching 10 in water, and both heat treated and-unheat treated test bars were subjected to that corrosion test which comprises alternately immersing the metal in, and removing it from, a 3 percent sodium chloride solution for about 80 hours, a treatment 26 referred to hereinafter as the alternate immersion treatment. There. are certain elements which may be added to the binary magnesium-lead alloys to particular advantage. Such, for instance, are 80' themetals calcium, cadmium and zinc. These may be added singly or in combination with each other, the zinc in amounts between about 1.0 per cent and 10.0 per cent, the calcium between about 0.1 per cent and 2.0 per cent, and the cadmium as between about 1.0 per cent and 10.0 per cent. These alloying elements are substantial equivalents as indicated by their susceptibility to thermal treatment in magnesium-lead alloys. The

calcium favorably aflects the casting properties of. the alloy without markedly decreasing its corrosion resistance. For instance, a magnesium alloy containing 21.4 per cent of lead and 0.25 per cent of calcium shows, ,in-tbe' as test condition, a;

strength loss of only 17 per cent after alternate 45 immersion in a 3 per cent sodium chloride v solution for about 80 hours, while a heat treated magnesium alloy containing about 5 per cent of lead'to which about 0.25 per centof calcium had been:-

- added did not undergo any ,appreciable'loss. iii-50 lead and 10.0 per cent of cadmium had in the suit was obtained with a magnesium-base alloy containing about 5.3 per cent of lead and about 5.0 per cent of cadmium. An alloy of magnesium with about 5.0 per cent of lead and 5.0 per cent of zinc had in the sand cast condition a tensile strength of about 23,370 pounds per square inch. After a thermal treatment of about 20 hours at 540 centigrade followed by an aging=treatment of about 20 hoursat 150 centigrade its strength had increased to about 25,710 pounds per square inch. After an alternate immersion corrosion test of 80 hours the lossin strength was only 12 per cent. Another alloy of magnesium with about 5.2 per cent of lead and 3.2.per cent of zinc under similar conditions lost only about 10 per cent after 80 hours alternate immersion in the corrosive solution. As a'preferred composition for alloys of this nature I advise (1) 5.0 per cent lead, l.0per cent calcium, balance magnesium; (2) 5.0 per cent lead, 5.0 per cent cadiiun, balance magnesium; (3) 5.0 per cent lead, 5.0 per cent zinc, balance magnesium. If more than one of the elements calcium, cadmium, or-zinc be present simultaneously, I prefer not to exceed a total of 10.0 per cent for these elements.

One of the disadvantages of the alloys described herein which may affect theiruse in certain applications, particularly where high strength is a leading or very material consideration, is the fact that the grain structure of these alloys (with or without calcium) tends to be coarse. I have found that the metals aluminum and silicon form a class of alloying elements which may be added to magnesium lead alloys and are substantially equivalent in this respect that they materially refine the grain structure of the alloy. Aluminum, for instance, can be added over a wide range, such as between 1.0 and 15.0

per cent; silicon may be effectively present for this purpose in amounts of about 0.1 to 2.0 per cent. When used in combination it is advisable that the total content of aluminum and silicon does not exceed 15.0 per cent. In the preferred practice of my invention I have found that the best results are usually obtained when the aluminum is present in amounts between 5 and 10 per cent.

As a. preferred magnesium-lead-silicon composition I use a magnesium-base alloy containing 7.0 per cent of lead and 0.5 per cent of silicon. As a preferred magnesium-lead-aluminum alloy I use a magnesium-base alloy containing 7.0 per cent of lead and 5.0 per cent of aluminum. When the aluminum and silicon are used in conjunction I prefer to use a total of about 5.0 per cent of aluminum and silicon com bined, for instance about 4.0 per cent aluminum and 1.0 per cent silicon.

Manganese alone may be added to magnesiumlead alloys in amounts between 0.1 per cent and 1.0 per centand has a stabilizing efiect upon the alloy properties in that it raises the hardness slightly, does not materially decrease, the corrosion resistance, and adds to the matrix of the alloy a hardening element which expresses itself not only in an increase in tensile strength but also in surface hardness. An alloy of this nature containing about 8.0 per cent of lead and 0.85 .per cent of manganese lost only 6 per cent of its original strength after 80 hours alternate immersion in a 3 per cent aqueous solution of sodium chloride and in the solution heat treated condition lost only 7 per centof its strength in the alternatev immersiontreatment. A magnesium alloy containing about 10.37 per cent of lead had lost only about 10 per cent of its strength at the expiration of this period as compared with certain other commercial alloys, such as, for instance, the well known magnesium alloy containing about 7 per cent of aluminum and 0.4 per cent of manganese which, at the end of 40 hours of alternate immersion, had lost about per minum from about 1.0 per cent to about 15.0 per cent, the tin from about 1.0 per cent to about 15.0

per cent, the manganese from about 0.1 per cent to about 1.0 per cent, and the zinc from about 1.0 per cent to about 10.0 per cent. A sand cast alloy within this range had, in the as cast condition, a tensile strength of 27,500 pounds-per square inch and an elongation of 5.7 per cent in 2 inches. After a thermal treatment of 16 hours at 315 centigrade, the alloy had a tensile strength of 29,640

pounds per square inch and an elongation of 6.0 per cent in 2 inches. Some of the heat treated specimens were then given an alternate immersion treatment for 40 hours and after the treatment the specimens had a tensile strength of 28,413 pounds per square inch and an elongation of 5.8 per cent in 2 inches, this alloy containing 5.0 per cent of aluminum, 5.0 per cent of lead, 0.4 per cent of manganese and 2.0 per cent of zinc. The loss in strength on the corrosion treatment is observed to be less than 5 per cent as compared to about 60 per cent with the commercial magnesium-aluminum-manganese alloy disclosed here-.

inbefore which contains about 7 per cent of aluminum and 0.4 per cent of manganese. As preferred compositions for alloys of this nature I advise (1) 7.0 per cent of lead, 7.0 per cent of aluminum, 2.0 per cent tin, balance magnesium; (2) 7.0 per cent lead, 7.0 per cent aluminum, 2.0

per cent tin, 0.5 per cent manganese, balance mag-' nesium; (3) 7.0 per cent lead, 7.0 per cent aluminum, 2.0 per cent tin, 2.0 per cent zinc, balance magnesium.

Two alloy compositions within this range which I have used to advantage are as follows: A magnesium-base alloy containing 8.0 per cent of aluminimum, 3.0 per cent of lead, 0.4 per cent of manganese, 1.0 per cent of zinc, and 3.0 per cent of tin; a magnesium-base alloy containing 8.0 per cent of aluminum, 1.0 per cent of lead, 0.4 per cent of manganese, 1.0 per cent of zinc, and 1.0 per cent of tin.

Theaddition of lead to the magnesium-aluminum-manganese alloys increases very considerably the corrosion resistance of these alloys, since with the addition of about 7 per cent of lead to an alloy containing 7 per cent of aluminum and l per cent of manganese, the loss of strength after the alternate immersion test was only about 30 per cent, as compared with about 60 per cent of the same alloy without lead.

Alloys of magnesium with lead, aluminum, and manganese have. been disclosed hereinabove. I have discovered that-if to a base alloy of magnesium-lead-aluminum-manganese I add one or more of the class of metals calcium or cadmium, the resulting alloys become .-considerably more susceptible to variation of properties by thermal treatments and their hardness can be markedly increased by artificial aging after thermal solution treatments;- In these alloys the lead content should range from about 0.5 per cent tolabout 22.0 per cent, the aluminum from about 1.0 per cent to about 15.0 per cent, and the manganese from about 0.1 per cent to about 1.0 per cent. --To these elements as a common base I add the elements calcium, or cadmium, singly or in combination, the calcium in amounts from about 0.1 per cent to about 2.0 per cent, the cadmium from about 1.0

per cent to about 10.0 per cent. As an example of an alloy of this nature, a sand cast specimen of a magnesium-base alloy containing about 10.0

per cent of lead, about 7.0 per cent of aluminum, about 0.4 per cent of manganese, andabout 5.0"

per cent of cadmium had inthe cast condition a of the alloy had increased to about 36,000 pounds per square inch, a gain in strength of about 55 per cent. The same alloy after the solution treatment had a Brinell hardness of about 61 and this hardness was raised to about 84 by an additional aging treatment of 20 hours at about 175 centi- I grade, the tensile strength increasing slightly to about 37,000 pounds per square inch.

Similarly a magnesium-base alloy containing about 5.0 per cent of lead, 7.0 per cent-of aluminum, 10.0 per cent of cadmium, and 0.4 per cent of manganese had in the sand cast condition a; tensilestren'gth of about 24,000 pounds per square inch. After a thermal treatmentof 21 hours at about 430 centigrade the alloy had a tensile strength of about 35,000 pounds per square inch. An additional aging treatment raised the Brinell hardness of the alloy from about 61 to about 79. Similarly, a magnesium-base alloy containing about 5.0 per cent of lead, 10.0 per cent ofcadmium, 7.0 per cent of aluminum, 1.0 per cent of manganese, and 0.25 per cent oi calcium had in the sand cast condition a tensile strength of about 24,290 pounds per square inch. After a thermal treatment 20 hours at about 430 centigrade this alloy had a tensile strength of about 33,200 pounds per square inch. After an additional thermal treatment of about 20 hours at about 150 centigradethe strength increased to about 35,600-

pounds per square inch and the Brineli hardness from about 47 to about 66.

Another magnesium-base alloy' containing about 10.0 per cent of lead, 7.0 per cent of aluminum, 5.0 per cent of cadmium, 0.4 per cent of manganese, and 0.1 per cent of calcium, had in the sand cast condition a tensile strength'of about 23,210 pounds per square inch. After a thermal solutiontreatment of 21 hours at about 430 centigrade the alloy had a tensile strength of about the lead should range from 0.5 per cent to 22.0

stituting about 1.0 per cent silicon tor part or all of the aluminum. 1

. ments calcium or cadmium are present simulta- 5 neously, the total should not exceed about-10.0 per cent for preferred purposes.

The addition of zinc'in amounts .irorn about 1.0 per cent to about 10.0 per cent to magnesium-lead alloys containing aluminum and silicon in combination decreases the linear shrinkage, thus favorably affecting the casting properties, and also increases the corrosion resistance and raises the yield point of these alloys. In alloys of this-type per cent, the aluminum from 1.0 per cent to 15.0 per cent, and thesilicon from 0.1 per cent to 2.0 per cent, but the total amount of aluminum and silicon should preferably not exceed 15.0 per cent.

A useful alloy of this nature. is a magnesiumbase alloy containing about 10.0 per cent lead,

'8.0 per cent aluminum and 3.25 per cent zinc.-

Another useful composition is attained by sub- An alloy similarly improved in casting properties. although not to such a decided extent, is one containing from about 0.5 per cent to 22.0 per cent of lead, from about 1.0 per cent to about 10.0 per cent of zinc, and from about 0.1 per cent to about 2.0 per cent oi silicon. A favorable alloy within this range is a magnesium-base alloy. consisting of about 10.0 per cent of'lead, about 3.25 per cent claim, and about 1.0 per cent of silicon, the balance being substantially magnesium.

In making up alloys of the compositions disclosed hereinabove the alloys may be compound- -ed by any oi'the methods blown in the 811.. In

casting the alloys recourse may be had to the protective measures disclosed in existing pat- 4o ents and the published literature relating to easily oxidizable metals. The alloys, especially the magnesium-lead binary alloys, may be extruded over the entire disclosedcomposition range, but other types of mechanical deformation such as rolling or forging should be carried on with due regard for the fact that as the percentage of total added alloying elements increases, the necessity for precaution in working the alloy also increases.

It is my object. to retain, as far as possible, so the advantages of the use of magnesium base, such as low specific gravity, while securing in addition the hereinabove disclosed benefits accruing from the additions of the other alloying elements herein-outlined. Accordingly, where in the ap- 55. pended claims the term magnesium-base alloy is used, it refers to an alloy containing more than approximately per centiof magnesium.

'This application is a continuation in part of my copendlng application Serial No. 643,052, filed to November 17, 1932. p

What I claim is:

l. A magnesium-base alloy containing from 0.5 to 22.0 per cent of lead, from 1.0 to 15.0 per cent of aluminum, and from 1.0 to 15.0 per cent of tin, the balance being magnesium.

2. A magnesium-base alloy containing about 7.0 per cent of lead, about 7.0v per cent of aluminum, and about 2.0 per cent of tin, the balance being magnesium.

ROY 3. PAIRS.

CERTIFICATE OF CORRECTION.

Patent No. 2,026,591. I I January 7, 1936.

ROY E. PAINE.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: *Page 2, first column, line 17, for "540" read 450; and that the said Letters Patent shouldbe read with this correction therein that the same may. conform to the record of the case in the Patent Office.

Signed and sealed this 25th day of February, A. D. 1936.

Leslie Frazer (Seal) Acting Commissioner of Patents.