US2749239A - Aluminum base alloy - Google Patents

Description

.-:erties at elevated temperatures. :provide analloy casting which undergoes substantially no United States Patent ALUMINUMBASE ALLOY Walter E. Sicha, Shaker Heights-and Harold Y. Hunsicker and Robert C. .Lemon, Cleveland, Ohio, .assignors t Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application March 14, 1955, SerialNo. 494,264

6 Claims. 5(Cl. 75-142) 7 This invention relates to the composition of improved aluminum .base alloys which in cast form are especially .suited forservice at higher temperatures than have been considered heretofore to be feasible for aluminum "base alloy-s.

Aluminum base alloys have been employed in the manufacture of 'many articles which 'have been exposed to a wide variety of service conditions. For the most tions which would better meet the new requirements.

Special attention has been given to alloys which can be ireadily cast and do-not require thepresence of high cost alloying elements.

It is accordingly an object of this-invention to provide an aluminum base alloy'casting which possesses superior :strength and :hardness at temperatures on the :order of 600 to 700 F. Another objecttis'to providean'aluminum b'ase alloy =castin'g which does not require'thermal treat- :ment to develop its maximum :strength at elevated temperatures. 'Still another objectis to provide an'aluminum base alloy casting which possesses superior fatigue prop- A further object 'is to permanent change in dimensions as a result of exposure to elevatedstemperatures.

Theserand-other objects and advantages are realized in castings of an aluminum'base alloy which contains copper,

magnesium, manganese and nickel as the primary added :alloying components. We have discovered 'thatunique and unusual properties are obtained in an alloy which,

:in addition "to aluminum and impurities, -contains from previously used for such articles as pistons,'cylinder head-s and the like. Castings of our alloy have a tensile strength .at 600 F. ofnot less than 15,000 p. s. i. in the as-cast :condition. In addition, the cast alloy has a fatigue strengthrat 600 F., on the order of 8,000 p. s.i. at 10'' cycles, which is much higher than that of prior'well known aluminum base alloys.

The copper content of the alloys, 6 to 18%, which is :higherfthanthat found in most alloys of the aluminum- ;copper type, should not be less than the magnesium :content. :For best results, the copper should be within 'nal stresses.

2,749,239 *Patented June 5, 1956 "ice temperatures. Hitherto, magnesium "has been employed in relatively small amounts in aluminum-copper type alloys, especially those which are subjected to solution heat treatment and precipitation hardening to develop maximum strength and hardness. In the present case, from 4 to 8% should be employed, but 'optimumresults are obtained if the range .is confined to between 5 and 7%. Particularly advantageous properties are developed where the proportion of magnesium to copper is *such that the magnesium content is atleast one-half the copper content .andthe copper does notexceed 16%. When the preferred proportions of'the two'elements are employed the tensile strength tit-600 F. is not less than 17,000 p. s. i.

The manganese and nickel components are necessary to produce the required properties .of the alloy at high temperatures, ;although the quantities used are relatively small. As mentioned above, the amount of each .element should be between 0.1 and 2% but in our preferred practice from 0.4 to =1'%:should be employed. :Moreover, for optimum .results the two elements should be used in substantially equal amounts.

As is Wellrecognized in the aluminum base alloy art, it is often desirable to add minor Quantities of certain elements to improve "certain characteristics such as grain 'size or resistance'to oxidation. 'For example, the presence -of 05001 to 0. 1% boron or 0.01 to 0.2% titanium, or both, -will'serve to reduce the grain size while the addition of 00001 to 0.1% "beryllium imparts resistance to oxidation.

Another group of elements, which may be called supplementary hardening agents, which we have found can be used to-advantage consists of chromium, cobalt, molybdenum, tungsten, zirconium and vanadium.

'Th'ese elements may beused individually in amounts of 031 to 0.6%, 'but where two ormore are employed, the 'totalquantity should not exceed 1 .0%.

The aluminumemployed -in'making the alloy maybe of -the purity normally used in making castings. Generally, the iron impurity contents of the alloy should not exceed 1% and the silicon impurity should not'be over 0.75%. It is to *be'understood that traces of other elements may al'so'be present'but they'can'be disregarded for present purposes.

Our alloy may be melted and cast in accordance with conventional procedures and hence it is welladapted to use with existing equipment. Furthermore it can be n'ea'dily cast in sand or permanent molds.

The alloys herein described do not require any solution :heat treatment to develop the desired properties at elevated temperatures. This is "an important advantage both from the standpoint of cost and stability at high temperatures. .In respect to the latter-feature, it may be mentioned that the beneficial effects of solution heat treatment of other alloys can be dissipated upon long exposure to elevated temperatures "butthis eifect would 'not be encountered'withour alloy since it does not require suchpreliminary treatment. For'some purposes it has been found to'be desirable to subject the cast alloy 'to a stabilizing thermal treatment to relieve any inter- This involves heating the castings for "a period of 2 to 5 hours at a temperature between 550 :and '70'0'F.

'One o'f the important-features of the castings made "from our alloyis that they do not exhibit any significant permanent dimensional changes upon long exposure to elevated temperatures. The castings are therefore free from the objectionable growth which has characterized many previous casting alloys when used at temperatures on the order of 400 F and higher.

The advantages and benefits of our invention can be better appreciated by referring to the elevated tempera ture properties of castings of some representative alloys in comparison with the properties of the same type of casting made from Y alloy, a composition long regarded as being particularly adapted for elevated temperature service. Melts of the various alloys were prepared in accordance with conventional practice and poured in sand tensile test bar molds, and the castings cooled to room temperature. A portion of the bars were heated to 600 F., held at that temperature for 48 hours and tested while at temperature. The alloy compositions and average tensile properties of the cast bars are given in Table I below.

TABLE I Tensile properties of various alloy castings at 600 F.

Composition, Percent Tensile Yield Elonga- Strength, Strength, t s. i. p. s. i. Pelee-n Cu Mg Mn N1 p in 2 m.

10 4 0. 5 0. 5 19, 500 12, 000 5 G O. 5 O. 5 20, 500 13, 000 1O 8 O. 5 U. 5 18, 000 13, 000 20 G 6 O. 5 O. 5 18, 000 12, 500 S 5 O. 5 0. 5 19, 500 14. 500 25 14 6 0. 5 O. 5 23, 500 14, 500 1. 0

S G O. 5 1. O 18, 500 11, 700 14 8 6 1. 0 1. 5 19, 100 11, 200 5 8 6 1. 5 1. 5 20, 500 11, 000 5 S 6 1. 5 2. O 19, 500 11, 300 4 4 1. 5 2 (Y alloy) 12, 500 8, 000 5 It is to be noted that the tensile strength increases with the copper content and that higher tensile strength values were obained in those alloys in which the copper exceeded the magnesium content. It is also apparent that the elongation diminishes sharply where the magnesium content is less than half that of copper and 0.5% each of maganese and nickel are present.

In respect to the effect of varying the proportions of manganese and nickel it is to be seen that although the highest tensile strength is obtained when both elements are present in equal amounts, the difference between such alloys and those containing other proportions is not great.

The effect of exposure of sand cast test bars to a higher temperature, 700 F., is illustrated in the examples given below in Table II. In this case the bars were heated to 700 F., held at that temperautre for 48 hours and then tested while at temperature.

TABLE II Tensile properties of alloy castings at 700 F.

Composition, Percent Tensile Yield t lilonga- Strength, Strength, 1 fg s. i. p. s. 1. Cu Mg Mn M P in.

ing test where sand cast test bars of an aluminum, 8% copper, 6% magnesium, 0.5% manganese and 0.5% nickel alloy were held at 600 F. for different periods of time and the bars tested at the elevated temperature. The Brinell hardness values were determined by use of a 10 mm. diameter ball under a 500 kg. load for a period of 30 seconds. The results of the tests are given below is also important.

in Table III.

TABLE III Effect of time on tensile properties at 600 F.

Tensile Yield Percent Time, Hrs. Strength, Strength, Elonga- BHN p. 5.1. p. s. 1. tion From the foregoing it will be seen that there was no substantial change in properties between /5 and 1000 hours at temperature. This is further evidence of the superiority of our alloy over prior alloys.

The fatigue strength of the foregoing alloy at 600 F. The fatigue strength values of this alloy at 600 F. as compared with those of Y alloy under the same conditions are given below in Table IV.

TABLE IV Fatigue strengths at 600 F.

Number of Cycles gg 18, 000 14, 500 14, HX] 11, 000 11, 000 8, 500 S, 000 6, 000 G, 000 4, 000

Having thus described our invention and certain embodiments thereof, we claim:

1. An aluminum base alloy casting composed essentially of aluminum, 6 to 18% copper, 4 to 8% magnesium, 0.1 to 2% manganese and 0.1 to 2% nickel, the amount of copper not being less than the amount of magnesium, said alloy being characterized in the as-cast condition by a tensile strength at 600 F. of not less than 15,000 p. s. i.

2. An aluminum base alloy casting composed essentially of aluminum, 7 to 11% copper, 5 to 7% magnesium, 0.4 to 1% manganese and 0.4 to 1% nickel, said alloy being characterized in the as-cast condition by a tensile strength at 600 F. of not less than 17,000 p. s. i.

3. An aluminum base alloy casting composed essentially of aluminum, 6 to 16% copper, 4 to 8% magne' sium, 0.1 to 2% manganese, 0.1 to 2% nickel, the proportion of magnesium to copper being such that the amount of magnesium is at least one-half the copper content but does not exceed the copper content, said alloy being characterized in the as-cast condition by a tensile strength at 600 F. of not less than 17,000 p. s. i.

4. An aluminum base alloy casting composed essentially of aluminum, 6 to 18% copper, 4 to 8% magnesium, 0.1 to 2% manganese and 0.1 to 2% nickel, the amount of copper not being less than the amount of magnesium, said alloy also containing at least one element selected from the group of vrain refining elements consisting of 0.001 to 0.1% boron and 0.01 to 0.2% titanium, said alloy being characterized in the as-cast condition by a tensile strength at 600 F. of not less than 15,000 p. s. i.

5. An aluminum base alloy casting composed essentially of aluminum, 6 to 18% copper, 4 to 8% magnesium, 0.1 to 2% manganese and 0.1 to 2% nickel, the amount of copper not being less than the amount of magnesium, said alloy also containing 0.0001 to 0.1%

and a total not exceeding 1.0%, said alloy being characterized in the as-cast condition by a tensile strength at 600 F. of not less than 15,000 p. s. i.

References Cited in the file of this patent UNITED STATES PATENTS 1,831,584 Weiss Nov. 10, 1931 1,932,861 Wood Oct. 31, 1933 1,940,133 Kempf Dec. 19, 1933

Claims (1)

1. AN ALUMINUM BASE ALLOY CASTING COMPOSED ESSENTIALLY OF ALUMINUM, 6 TO 18% COPPER, 4 TO 8% MAGNESIUM, 0.1 TO 2% MANGANESE AND 0.1 TO 2% NICKEL, THE AMOUNT OF COPPER NOT BEING LESS THAN THE AMOUNT OF MAGNESIUM, SAID ALLOY BEING CHARACTERIZED IN THE AS-CAST CONDITION BY A TENSILE STRENGTH AT 600* F. OF NOT LESS THAN 15,000 P.S.I.