US2131520A - Aluminum alloy - Google Patents

Description

Patented Sept. 27, 1938 Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing.

Application September 16, 1936,v

Serial No. 101,132 7 Claims. (Cl. 148-32) This invention relates to aluminum base alloys, especially those containing from 2 to 12 per cent copper, 0.1 to 2 per cent silicon, and 0.005 to 0.1 per cent tin. These alloys develop exceptionally -5 desirable physical properties when subjected to the well known solution and precipitation hardening thermal treatments. In order to obtain the best combination of high physical properties and resistance to corrosion, it has been found that the alloys must be practically free from any magnesium impurity. In commercial practice not more than 0.01 per cent is generally permitted, and less than 0.005 per cent is preferred. Such requirements have necessitated the use of virgin aluminum, or carefully selected scrap metal containing a minimum of magnesium impurity, and the exercise of particular care in preventing contamination from the melting furnace hearth and other containers of the molten metal. Such 20 precautions obviously add to the cost of producing the alloys, as well as restricting the supply of metal which can be drawn upon for this purpose. It is therefore highly desirable both to utilize metal having a larger magnesium impurity 5 content and yet to overcome the deleterious effects of this impurity, particularly if it happens to exceed the specified limits. My invention is directed to achieving the foregoing improvements, and it is primarily concerned with providing a 30 means of improving the resistance to corrosion of these alloys.

A means of suppressing the. harmful effect of magnesium impurity in aluminum-copper-tin alloys of the type referred to hereinabove, is

35 described in formerly co-pending application, Serial No. 750,016, now issued as Patent No.

2,063,942. It is pointed out in that application that the addition of from 0.05 to 0.15 per cent cadmium to the alloys containing between 0.005 40 and 0.03 per cent magnesium, in'the ratio of 5 to 1, improves the resistance to corrosion as well as increasing the strength of such alloys. I have now found that the resistance to corrosion can be even further improved by the addition of 0.1

45 to 3 per cent zinc along with the cadmium in the aforesaid amounts and ratio. The zinc addition is of particular benefit where the alloys are subjected to severe corrosive conditions while under stress. To distinguish this form of corrosion 50 from other types, and for the sake of convenience of reference, it is herein designated as stress corrosion. Resistance to this type of corrosive attack is especially important in cases where ness to the usual thermal treatments. The principal effect of the zinc is to increase the resistance to stress corrosion. However, in order to obtain this effect, the zinc must be used in combination withcadmium, since zinc alone does not produce the improvement.

The amount of 'zinc which is needed to effect this improvement varies between 0.1 and 3 per cent, with 1 to 2 per cent being preferred. If especially severe conditions areto be encountered, it is generally desirable toadd zinc within the upper portion of the foregoing ranges rather than to use smaller amounts.

Although the beneficial effect of' zinc and cadmium in inhibiting stress corrosion is evident in alloys containing 2 to 12 per cent copper, 0.1 to 2 per cent silicon, and 0.005 to 0.1 per cent tin, I

have found that these alloy additions are especially effective in cases where these elements are present within theranges of 2 to 6 per cent cop'- per, 0.2 to l per cent silicon, and 0.03 to 0.07 perv cent tin.

In order to adapt the base alloy of aluminum, copper, silicon and tin to special conditions it is frequently desirable tomodify or amplify certain properties without substantially altering the fundamental characteristics. I have found it to be advantageous for this purpose to add a total of from 0.01 to 1.5 per cent of one or more of the hardening elements manganese, chromium, titanium, molybdenum, boron, tungsten, vanadium, zirconium, beryllium, nickel, and cobalt. The addition of these elements permits a closer control of such properties as grain size, recrystallization temperature, workability, machinability, and others. The amounts of the individual elements that maybe used fall within the following I r ranges: manganese, 0.1 to 1.5 per cent; chromium dium, 0.05 to 1 per cent; zirconium, 0.05-t 0.5

per cent; beryllium, 0.01 to 0.5 per cent; nickel, 0.05 to 1 per cent; and cobalt, 0.05 to 1 per cent.

An illustration of the effectiveness of cadmium and zinc in improving the resistance to stress corrosion is to be found in the following test results. Five alloys in the form of sheet specimens 0.064 inch in thickness were tested. The composition of the alloys was as follows:

Per cent composition Alloy Copper g Silicon Tin E? Zinc A 4.4 0.8 0.8 0.05 0.005 B 4.4 0.8 0.8 0.05 0.02 C 4.4 0.8 0.8 0.0 0.02 0.1 D 4. 4 0. 8 o. 8 0. 05 0. 02 1 E 4.4 0.8 0.8 0.05 0.02 0.1 1

These alloys in the form of sheet were heated at 515 C. for 15 ,minutes, quenched in water, and aged at 160 C. for 12 hours. .specimens were cut from these sheets formechanical property determinations, and tested. Other specimens of a shape corresponding to that of a wedge, were also cut from the sheets for the stress -corrosion tests. These specimens were mounted in futures with the base of the wedge rigidly held in position,-and a load applied to the apex of the wedge normal to the plane of the specimen. The specimens thus carried a load as a cantilever beam.

' The load applied to each specimen was equivalent to 75 per cent of the yield strength of each alloy as determined by the aforesaid mechanical property tests. The stressed specimens were then immersed in an aqueous 6 per cent sodium chloride solution, connected as anodes to an external source of current, and an electrical potential of 0.9 volt impressed upon them. This form of test,

while much more severe than conditions encountered in actual service, has been found to give in a short time a satisfactory indication of the relative resistance to stress corrosion of various aluminum base alloys. The time required for each specimen to bend, or fail to support the pplied load, was noted. The average mechanical properties of each alloy, and the lengths of time the various specimens supported the loads,

are given in the table below.

Tensile Yield Elonga- Time of my strength strength tion failure sq in sq. a Per coat Hours A.-- 52M i0 10 B 42, 100 12. 5 4. 6 0 52. 200 11.8 4 44,400 11.2 a 650 9. 5 13 cent tin,

- ant condition equal to that of the original alloy M A containing magnesium within the permissible impurity range, and in some cases, there is an improvement over 'alloy A. The alloys herein described are susceptible to fabrication in the manner generally practiced in the art of making and shaping of aluminum base alloys. They may, furthermore, be subjected to the usual thermal treatment employed to improve the strength of aluminum base alloys. This'treatment generally consists in heating the alloys at an elevated temperature, above about 475 C., and rapidly cooling to ordinary or slightly elevated temperatures. This may befollowed by an aging or precipitation hardening at room temperature, or at any temperature up to about 200 C. The aging above room temperature is generally referred to as artificial aging and is usually applied to those alloys which do not age order to take full advantage of the high strength which can be developed in the alloys.

The term aluminum as used hereinabove and in the appended claims denotes the metal of the purity-exclusive of the magnesium impurity as herein deflnedthat is commercially available.

Having thus described my invention and a preierred embodiment thereof, I claim:

1. A heattreated and artificially aged aluminum base alloy containing from 2 to 12 per cent copper, 0.1 to 2 per cent silicon, 0.005 to 0.1 per centtin, 0.005 to 0.03 per cent magnesium, 0.01 to 0.15 per cent cadmium and 0.1 to 3 per cent zinc, the balance being aluminum.

2. A heat treated and artificially aged aluminum base alloy containing from 2 to 12 per cent copper, 0.1 to 2 per cent silicon, 0.005 to 0.1 per cent tin, 0.005 to 0.03 per cent magnesium, 0.01 to 0.15 per cent. cadmium, 0.1 to 3 per cent zinc and 0.1 to 1.5 percent of hardening metal of the group composed of manganese 0.1 to 1.5 per cent, chromium 0.1 to 1 percent, titanium 0.03 to 0.5 per cent, molybdenum 0.05 to 1 per cent, tungsten 0.05 to 1 per cent, vanadium 0.05 to 1 per cent, zirconium 0.05 to 0.5 per cent, beryllium 0.01 to 0.5 per cent, nickel 0.05 to 1 per cent, boron 0.01 to 0.5 per cent, the balance of the alloybeing aluminum.

3. A heat treated and artificially aged aluminum base alloy containing from 2 to 6 per cent copper, 0.2 to l per cent silicon, 0.03 to 0.07 per 0.005 to 0.03 per cent magnesium, 0.01 to 0.15 per cent cadmium, and 1 to 2 per cent zinc, the balance of the alloy being aluminum.

4. A heat treated and artificially aged aluminum base alloy containing from 2 to 6 per cent copper, 0.2 to 1 per cent silicon, 0.03 to 0.07 per cent tin, 0.005 to 0.03 per cent magnesium, 0.01 to 0.15 per cent cadmium, 1 to 2 per cent zinc, and 0.1 to 1.5 per cent of hardening metal of the group composed of manganese, 0.1 to 1.5 per cent, chromium 0.1 to 1 percent, titanium'0.03 to 0.5 per cent. molybdenum 0.05 to 1 per cent, tungsten 0.05 to 1 per cent, vanadium 0.05 to 1 per cent, zirconium 0.05 to 0.5 per cent, beryllium 0.01 to 0.5 per cent,-nickel 0.05 to 1 per cent, boron 0.01 to 0.5 per cent, the balance of the alloy being aluminum.

5. A heat treated and artificially aged aluminum base alloy containing from 2 to 12 percent copper, 0.1 to 2 percent silicon, 0.005 to 0.1'per cent tin, 0.005 to 0.03 per cent magnesium, 0.01 to 0.15 per cent cadmium and 0.1 to 3 per cent zinc. said alloy being characterized by the fact 7 4 ably improved over that of en aluminum base alloy containing the me amount of copper, tin, magnesium, and cadmium but without zinc.

6. A heat treated and artificially aged aluminum base alloy containing from 2 to 6 per cent copper, 0.2 to 1.5 per cent siliccm. 0.1 to 1.5 per cent meng ainese, 0.03 to 0.07 per cent tin, 0.005 to 0.03 per cent magnesium, 0.01 e 0.15 per cent cadmium, end oJ to 3 per eent zihc, end the teal-j ance of the alloy being aluminum.

7. A heat treated and artificially aged aluminum base alloy containing 4.4 per cent eepper,

0.8 per cent silicon, 0.8 percent manganese, 0.02 percent magnesium, 0.05 per cent tin, 0.1 per cent cadmium, 1 per cent mm, and the balance aluminum.

JGfiWH A. NOCK. JR.