US2568179A - Aluminum base alloys - Google Patents

Description

Patented Sept. 18, 1951 ALUMINUM BASE ALLOYS Charles B. Willmore, Aurora, 111., assignor to William F. Jobbins, Incorporated, Aurora, 111.,

a corporation of Illinois No Drawing. Application April 12, 1949,

. Serial No. 87,109

5 Claims. 1

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 described have been used in the manufacture of castings.

They have not achieved wide commercial acceptance 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 suf fered by these alloys resides in the inability of securing an acceptable product by sand casting or by casting in permanent molds. planation, 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,

characteristicof surface shrinkage, accompanied by undesirable crystal structure. Collapse to form surface shrinkage usually occurs in regions In the event cult to handle when casting about a core in permanent molds. Their inferior casting characteristics cause undesirable sticking of the core. This oftenleads to the destruction of the casting and excessive damage to the mold.

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 By way of eX-' 2 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 ageing; said alloy also beingcharacterized by improved castability not secured by the corresponding alloy without the additions of chromium, manganese and titanium.

I have found that by the addition of a small amount of chromium to an aluminum base alloy, castability of the alloy in sand or permanent molds is markedly improved. It is believed that the chromium, either by itself or in combination with the other elements of the alloy provides for sufficient liquid medium to fiow through available open channels to fill the voids and microscopic spaces left within the matrix of crystals formed by the freezing metal and produce substantially complete soundness in the solidified structure. Thus, by the almost immediate filling of the voids by a molten metallic component, the low pressure areas developed are eliminated and the danger of collapse of the casting surface or the development of porosity is greatly minimized, or entirely avoided. It is undesirable to have too much of the liquid metallic component at this stage, because the molten metal might then occupy the greater proportion of the alloy and its characteristics will predominate in the casting. When this condition prevails, the alloy is said to be hotshort because the liquid has insufficient strength to maintain the integrity of the freezing mass.

The desired relationship for'effectively reducing shrinkage and porosity of the casting, whether fabricated by sand casting or by permanent mold or chill casting, is achieved when chromium is present in the alloy in concentrations ranging from 0.05 to 1.0 by weight, while best use is made of 0.10 to 0.45 percent by weight of chromium.

While it is conceivable that chromium may have this desirable effect on any aluminum base alloy, it is especially applicable to aluminum base alloys containing silicon, zinc, and copper as alloying elements and particularly when the alloying elements are present in amounts ranging from 2 to 4 percent copper, 2 to 8 percent zinc and 2 to 8 percent silicon, and the total of iron and nickel impurities are maintained below 0.75 percent.

castability can best be determined by comparative tests made with a pattern that is difli- ,cult to cast without shrinkage. By such test, improvement in shrinkage secured in both sand and permanent mold casting by the addition of chromium to an aluminum base alloy containing zinc, and copper alloy as major alloying elements, and iron, nickel and up to 0.15 manganese as impurities, is shown in Table I.

TABLE III Effect of manganese on physical properties of aluminum base alloy TABLE I In addition to the improvement in castability Chemical Composition of Alloying Elements, Amount of Shrinkage in Per Cent Zinc Copper Silicon Chromium Sand Casting fi g gg A 5. 4-5. 5 2. 9-3. 19 5. 4-5 5 B 5. 4-5. 2. 9-3. 1 5. 4-5 5 0.10 C 5. 4-5. 5 2. 9-3. 1 5. 4-5 5 O. D 5. 4-5. 5 2. 9-3. 1 5. 4-5 5 0.45

Impurities 0.46 iron, 0.04 nickel, 0.15 manganese.

Ordinarily it has been considered that grain refinement occasioned by the addition of grain refining substances has the tendency to give improved castability. While this concept may be correct in some instances, it will be significant that this relationship does not exist with respect to the improvement of castability of an aluminum-silicon-copper and zinc alloy. In fact, the addition of chromium in the amounts by which castability is notably improved causes an increase in grain size, while the addition of titanium, a grain refining element, to the aluminum base alloy without chromium will further increase the degree of shrinkage and porosity, as will be apparent from Table IV.

Castability and physical properties may be improved when additional manganese, over and above that existing as impurity is substituted in whole or in part for chromium. To get comparable effects however it is desirable to use greater amounts of manganese. For example, it is necessary to use as much as 0.6 percent manganese to achieve the improvement in castability secured by the addition of 0.1 to 0.25 percent chromium. However, more manganese, up to at least 1.5 perby alloying with chromium, I have discovered that improvements in physical properties are also secured, especially when titanium is incorporated with the chromium and/or manganese. Titanium in amounts greater than 0.20 percent is seldom used and best results are secured when titanium is present with the elements for improving castability in amounts from 0.05 to 0.15 percent. The improved characteristics may constitute a cooperative relationship wherein castability of a desired character is influenced by the presence of chromium and manganese in the prescribed amounts, and any harmful effects resulting from the use of these metals are more than fully compensated by the addition of titanium. In fact, the product secured by the addition of both chromium and titanium has physical properties which are better in most instances than those which characterize the corresponding compositions with only one of the elements or in complete absence of either of the elements, as shown by the following Tables IV and V.

cent can be tolerated in the alloy with increas- TABLE IV in enefi s.

g b t TABLE, II Sand cast Eflect of manganese on castability of aluminum A C F F 7 base alloys containing about 5.5 percent zinc, 6O 3.0 percent copper and 5.5 percent szlzcon as Zinc m 5M5 Mrs-5 My mayor alloying elements C0pper 2. 0-3.1 2.9-3.1 2.0-3.1 2. 0-3.1 Silicon 5.4-5.5 5.4-5.5 5.4-5.5 545.5 ghromium. 0. 2(5) 0.25 Chemical Com osition itanium 0.10 0.10 in Percen l; Amount of shrinkage Grain Size, mm. diam 1.43 1.06 0. 77 1. 25

Impurities Man- Sand Permanent Shrinkage gig Heavy Slight ganesc Casting Mold Iron Nickel AS Gist: t 1 25 500 20 00 200 5 u timates rengt1 ,5 25 2 ,300 15 Heavy fg? yield strength 131000 13,000 1 11500 14, 000 0 40 004 030 Veryslight Slight mam-Gated: 46 61 N Db ultimate strength 32, 000 33, 700 31, 400 34,500 Medium-1 yield strength 10,000 10, 300 17,800 17,700 70 04 Sn ht Heat Treated and Aged, ulti- 0170 mate strength 10, 200 46,900 40,400 51,000

TABLE V Permanent mold cast Grain Size, mm. diam 0. 45 0. 52 0.42 0. 37

Shrinkage Medium Very Slight Slight to Very Slight Medium As Cast:

ltimate 30, 000 30, 900 29, 300 30, 100

yield 13, 450 12, 400 14, 300 Heat Treated:

ultimate 36, B 38, 400 40, 300 39, 800

yield 16, 400 16, 900 17, 600 19, 400 Heat Treated and Aged,

ultimate 50, 100 49, 200 53, 700 55, 600

Impurities 0.46 iron, 0.04 nickel, 0.15 manganese. I Ultimate strength and yield strength are given in lbs. per sq. inch.

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.

Artificial ageing in the tested compositions was carried out by exposure of the heat treated casting to 305 to 315 F. for about three hours.

It will be observed that chromium and in most instances manganese has the effect of increasing grain size without appreciable loss in the excellent casting characteristics secured by the addition of chromium alone.

In practically every instance the ultimate strength of the casting is increased by the addition of chromium, while the yield strength remain substantially unchanged. The combination of chromium and titanium gives ultimate strengths and yield strengths which exceed, by a large amount, any of the values secured by the addition of either of the elements alone. Exceptional results in this respect are secured in the heat treated and aged alloys. In practically every instance the yield strength, ultimate strength and castability are improved by the addition of manganese.

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 1 minutes in the mold, while a corresponding composition without chromium or chromium and titanium requires a setting time of 1 to 2 minutes. This enables the shortening of the time cycle by about percent. Furthermore, the reduced shrinkage occasioned by the improved casting characteristics of the alloy permits casting in permanent molds without the difficulties 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 solution heat treatment and may be further 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 approximately from 2 to 4 percent copper, 2 to 8 percent zinc, 2 to 8 percent silicon and from 0.05 to 1.00 percent chromium the remainder being aluminum with less than 0.75 percent impurities in the form of iron and nickel.

2. An aluminum base casting alloy consisting essentially of from 2 to 4 percent copper, 2 to 8 percent zinc, 2 to 8 percent silicon, 0.05 to 1.00 percent chromium and from 0.05 to 0.20 percent titanium the remainder being aluminum with less than 0.75 percent impurities in the form of iron and nickel.

3. An aluminum base casting alloy consisting essentially of from 2 to 4 percent copper, 4 to 8 percent zinc, 2 to 8 percent silicon and 0.10 to 0.45 percent chromium, 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, and 0.05 to 0.15 percent titanium, the balance being aluminum with less than 0.75 percent impurities made up of iron and nickel.

5. An aluminum base casting alloy consisting essentially of from 2 to 4 percent copper, 2 to 8 percent zinc, 2 to 8 percent silicon, and an element selected from the group consisting of 0.05 to 1.00 percent chromium, 0.15 to 1.5 percent manganese and mixtures thereof, the rest being aluminum with less than 0.75 percent impurities made up of iron and nickel.

CHARLES B. WILLMORE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,572,489 Johnston et a1 Feb. 9, 1926 2,098,081 Bates Nov. 2, 1937 2,280,170 Stroup Apr. 21, 1942 2,290,016 Bonsack July 14, 1942 2,511,551 Smith et al June 13, 1950 FOREIGN PATENTS Number Country Date 723,417 France Apr. 8, 1932 OTHER REFERENCES Manual of Aluminum Casting Alloys, published by the Aluminum Research Institute, Chicago, 1947, page 26.

Metals Handbook published by the American Society for Metals, 1948 ad, page 840.

Claims (1)

1. AN ALUMINUM BASE ALLOY CONSISTING ESSENTIALLY OF APPROXIMATELY FROM 2 TO 4 PERCENT COPPER, 2 TO 8 PERCENT ZINC, 2 TO 8 PERCENT SILICON AND FROM 0.05 TO 1.00 PERCENT CHROMIUM THE REMAINDER BEING ALUMINUM WITH LESS THAN 0.75 PERCENT IMPURITIES IN THE FORM OF IRON AND NICKEL