US2568180A - Aluminum base alloys - Google Patents

Description

Patented Sept. 18, 1951 ALUMINUM BASE ALLOYS Charles B. Willmore, North Aurora, 111., assignor to William F. Jobbins, Incorporated, Aurora,v 111., a corporation of Illinois No Drawing. Application April 12, 1949, Serial No. 87,110

This invention relates to aluminum base alloys, and it has particular reference to the improvement in castability of aluminum base alloys, as measured by reduced surface shrinkage and less porosity in the casting. It also relates to the improvement in other physical properties of an aluminum base alloy containing zinc, copper and silicon as major alloying elements.

Aluminum base alloys of the type prescribed have been used in the manufacture of castings. They have not achieved wide commercialacceptance because they do not have desirable casting characteristics and their physical properties are not sufficiently superior to other commercial alloys having more desirable casting properties. One of the principal difficulties suffered by these alloys resides in the inability of securing an acceptable product by sand casting or by casting in permanent molds. By way of explanation, when the cast molten alloy cools down through the liquids range, the change from a liquid state to a solid state does not occur immediately. Instead, crystals or nuclei are formed which grow into a matrix having microscopic voids caused by the decrease in volume of the liquid as it assumes crystalline form. The voids that are formed are called pores when of small dimension and widely distributed, or pin holes, if the voids collect in certain areas.

These voids constitute low pressure areas and unless they are quickly filled, the casting surfaces may actually collapse to form depressed areas, characteristic of surface shrinkage, accompanied by undesirable crystal structure. Collapse to form surface shrinkage usually occurs in regions of relatively thick cross section. In the event that the matrix is sufliciently set to resist the effect of shrinkage forces, or in the event that gases originally dissolved in the metal fill the voids, the porosity defect remains as a permanent part of the casting. When either of these conditions prevail, a defective casting is produced which may be inadequate for the use for which it was intended.

Alloys of the type described are especially diflicult to handle when casting about a core in permanent molds. Their inferior casting characteristics causes undesirable sticking of the core. This often leads tothe destruction of the casting and excessive damage to the mold.

5 Claims. (Cl. 75-141) It is an object of this invention to provide an aluminum base alloy having improved castability when cast in sand or permanent molds.

Another object is to formulate for improvements in castability and other physical properties in an alloy composed chiefly of aluminum and containing silicon, copper and zinc as major alloying elements.

A further object is to provide an aluminum base alloy characterized by improved physical properties and improved castability when compared to alloys of corresponding composition heretofore produced.

Still another object is to provide a heat treatable aluminum base alloy containing silicon, zinc and copper as major alloying elements and characterized by improved castability and strength when fabricated by sand or permanent mold casting methods.

A still further object is to produce an aluminum base alloy having physical properties which may be improved by solution heat-treatment and which may be further improved by artificial agemg.

This is a continuation-in-part of my 00- pending application, Serial No. 87,109, filed on this same date and entitled Aluminum Base Alloys wherein description is made to the im-- provement in castability and physical properties in an aluminum base alloy by the addition of chromium and/or manganese with or without titanium to an aluminum base alloy for casting in green sand or permanent molds. The additions of the minor alloying elements have particular merit when the aluminum base alloy is constituted with copper, silicon and zinc as the major alloying elements present in amounts ranging from 2 to lpercent copper, 2 to 8 percent zinc, 2 to 8 percent silicon and the sum of iron and nickel impurity is less than 0.75 percent.

I have discovered that physical properties of the desired character and improved castability may be secured by the addition with the elements employed in the parent application of a small amount of zirconium as an additional alloying element. By the further addition of zirconium, improvements are secured which cannot be achieved by a corresponding composition, devoid of zirconium or by increasing the ratio of elemerits chromium, manganese or titanium. Zir.

conium in amounts ranging from 0.05 to 0.30 percent is suflicient and best results are secured when zirconium in combination with chromium is added in an amount ranging from 0.10 to 0.25 percent.

Unlike chromium, zirconium offers some grain refining characteristics in either sand or chill casting whether chromium or titanium are present or not. Unlike titanium, however, zirconium is not detrimental to casting properties when chromium or manganese also is present. In chill or permanent mold casting, zirconium further improves castability with or without chromium, manganese and titanium.

These improved characteristics are shown by the following charts made from tests of aluminum base alloys containing impurities to the extent of 0.46 percent iron, 0.04 percent nickel and 0.15 percent manganese. Table I gives the physical properties developed by sand casting and Table II gives the physical properties developed by the particular alloy in permanent molds.

TABLE I Physical properties developed m sand castmg 5. 4 5 4 5. 4 5. 4 3. 3.0 3.0 3.0 5.4 4 5.4 5.4 0. 25 0. 25 0. 25 0 19 0.19 0.19 Titanium 0.10

Grain Size, diam. in mm. 1.43 1.66 1.11 1.11 0.3 Shrinkage Very Slight Me- Slight Meheavy dium dium As Cast:

ultimate strength 25,500 26, 500 20,300 26,900 26,200 yield strength i- 13, 000 13,000 14,800 15,600 14, 900 Heat Treated:

ultimate strength 32,900 33,700 32,400 31,500 30,800 yield strength 16, 900 10,300 16, 300 16,700 17,200 Heat Treated, Aged, ultimate 46, 200 46,900 44, 700 47, 900 44,900

TABLE II Physical properties developed by permanent mold casting Zinc 5.4 5.4 5.4 5.4 5.4 Copper 3 0 3.0 3.0 3.0 3.0 Silicon 5 4 5.4 5.4 5.4 5.4 Chromium 0. 25 0. 25 0. 25 Zirconium..- 0.19 0.19 0.19

Titanium.... 0.10

Grain Size, diam. in mm... 0.45 V 0.52 0.40 0. 47 0. 30

cry ihrnkage ..Medium Slight Slight None None s ast:

Ultimate strength 30,000 30, 900 29,800 30,100 31,800 yield strength 13,450 12,400 15,300 15,700 16,000 Heat Treated:

ultimate strength 36,500 38,400 40,900 41,200 39,600 yield strength 16,400 16,900 17,000 16,300 16,700 Heat Treated, aged, ultimate 50,100 49, 200 5'1, 900 52,800 49, 700

It will be apparent that the addition of zirconium alone to the base alloy gives certain reduction in grain size in both sand and permanent mold casting, a reduction which is far greater than that secured by the addition of chromium alone and less than a combination of chromium and zirconium but not less than that secured by the further addition of titanium. The addition of zirconium alone also gives improvement in castability, but the improvement is not as marked as that secured by the addition of zirconium in the present of chromium. Further, the addition of zirconium is more effective in most instances than an addition of chromium but the combination of zirconium and chromium with or without titanium gives best results in almost every case. While the physical data presented is for the system zirconium, chromium and titanium, it should be understood that corresponding results will be secured when manganese is used in whole or in part for chromium, though ordinarily res ent in correspondingly larger proportion by weight.

As used in the tables, the term heat treated refers to solution heat treatment of the casting for 6 hours at 935 to 945 F. followed by quenching in hot water. Heat treatment time may be extended or shortened depending upon the weight of the casting, and heat treatment may be carried out at lower temperatures with a corresponding increase in time. The term aged" refers to artificial ageing of the heat treated casting to precipitate out elements or compounds put into solid solution during heat treatment. Arti ficial ageing in the tested compositions was carried out by exposure of the heat treated casting to 305 to 315 F. for about three hours.

A very decided advantage is observed in the use of my new alloy in permanent mold casting. The alloy sets more rapidly in the mold with the consequent desirable advantage in that the molding cycle can be greatly shortened. For example, in one operation, a casting formed with my alloy composition can be removed after 1 to l /2 minutes in the mold, while a corresponding composition without zirconium and chromium or chromium and titanium requires a setting time of 1 to 2 minutes. This enables the shortening of the time cycle by about 30 percent. Furthermore, the reduced shrinkage occasioned by the improved casting characteristics of the alloy permits casting in permanent molds without the dimculties heretofore occasioned upon casting about a core.

It will be apparent from the description that I have produced a new and improved aluminum base alloy containing zinc, copper and silicon, which alloy has greatly improved castability as measured by shrinkage and porosity and also has considerably better physical properties. The alloy corresponding to my invention is an alloy having desirable physical properties which may be improved by artificial ageing at relatively low temperatures.

It will be understood that changes may be made in the ratio of materials and compositions within the limitations prescribed and their method of treatment without departing from the spirit of the invention, especially as defined in the following claims.

What is claimed is:

1. An aluminum base alloy consisting essentially of 2 to 4 percent copper, 2 to 8 percent zinc, 2 to 8 percent silicon, 0.05 to 1.00 percent chromium, 0.05 to 0.30 percent zirconium, the balance being aluminum with less than 0.75 percent impurities made up of iron and nickel.

2. An aluminum base alloy consisting essentially of 2 to 4 percent copper, 2 to 8 percent zinc, 2 to 8 percent silicon, 0.05 to 1.0 percent chromium, 0.05 to 0.3 percent zirconium, 0.05 to 0.20 percent titanium, the balance being aluminum with less than 0.75 percent impurities made up of iron and nickel.

3. An aluminum base casting alloy consisting of from 2 to 4 percent copper, 4 to 8 percent zinc, 2 to 8 percent silicon, 0.10'to 0.45 percent chromium and 0.10 to 0.25 percent zirconium, the balance being aluminum with less than 0.75 percent impurities in the form of iron and nickel.

4. An aluminum base casting alloy consisting of from 2 to 4 percent copper, 4 to 8 percent zinc, 2 to 8 percent silicon, 0.10 to 0.45 percent chromium, 0.10 to 0.25 percent zirconium, and 0.05 to 0.15 percent titanium, the balance being alumiwith less than 0.75 percent impurities in UNITED STATES PATENTS the form of iron and nickel. Number Name 7 Date 5. An aluminum base casting alloy consisting 1,572,439 Johnston 9, 1926 essentially of from 2 to 4 percent copper, 2 to 8 2,043,355 Kener June 9, 1936 percent zinc, 2 to 8 percent silicon, an element 5 2,093,031 Bates 2 1937 selected from the group consisting of 0.05 to 1.00 2,280,170 stroup Apt 21 1942 percent chromium, 0.15 to 1.5 percent manganese 2,290,016 Bonsack July 14 1942 and mixtures thereof, and 0.05 to 0.30 percent zirconium, the rest being aluminum with less FOREIGN PATENTS than 0.75 percent impurities made up of iron 10' Number Country Date and nickel, 576,230 Great Britain Mar. 25, 1946 A L WILLMORE, 64,251 France Apr. 23, 1941 OTHER REFERENCES REFERENCES CITED 15 Manual of Aluminum Castmg Alloys, pub- The following references are of record in the lished by the Aluminum Research Institute, Chifile of this patent. cago, 1947, page

Claims (1)

1. AN ALUMINUM BASE ALLOY CONSISTING ESSENTIALLY OF 2 TO 4 PERCENT COPPER, 2 TO 8 PERCENT ZINC, 2 TO 8 PERCENT SILICON, 0.05 TO 1.00 PERCENT CHROMIUM, 0.05 TO 0.30 PERCENT ZIRCONIUM, THE BALANCE BEING ALUMINUM WITH LESS THAN 0.75 PERCENT IMPURITIES MADE UP OF IRON AND NICKEL.