US2026576A - Free cutting alloys - Google Patents

Description

Patented Jan. 7, 1936 PATENT OFFICE FREE CUTTING ALLOYS Louis W. Kempf and Walter A. Dean, Cleveland, Ohio, assignors to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Original application September 18,

1933, Serial No. 689,886. Divided and this application May 3, 1935, Serial No. 19,627

3 Claims.

The invention relates to aluminum base alloys and is particularly concerned with alloys of this nature containing substantial amounts of copper. This application is a division of our copending application Serial No. 689,886, filed September.

18, 1933. Alloys disclosed but not claimedherein are claimed in our copending application Serial No. 19,626, filed May 3, 1935.

Despite the manifold advantages connected with the use of aluminum and its alloys in commercial fields, there is an inherent drawback which somewhat curtails their use in certain potential adaptations. Aluminum alloys, for instance, containing from about 4 per cent to about 12 per cent of copper have a wide range of usefulness because of their favorable mechanical properties and their susceptibility to improvement by suitable thermal treatments. Mechanical cutting operations, however, such as boring, drilling, planing, -or lathe-cutting are successfully carried out only by using certain precautions which increase the expense of the operation and which occasionally necessitate the substitution of another alloy which may be machined more readily but which is otherwise not so desirable from the standpoint of physical properties. When alloys are diflicult to machine this disadvantage becomes evident in many cases through rapid wear of the cutting tool edge which necessitates frequent resharpening. In such cases where machining is diflicult, continual lubrication is required. The machined surface is rough and irregular, and the chip has a tendency to form continuous curls or spirals that may foul the tool or the operating parts of the machine. These drawbacks retard production and increase the cost of operation. Many articles require a variety of machining operations before being applied to their final purpose and it is particularly desirable that these articles be finished economically and satisfactorily.

An object of this invention, therefore, is the production of alloys containing substantial amounts of copper which may be readily machined.

A further object is the production of such alloys whose mechanical properties in the preferred composition range are perfectly adequate to suit most commercial purposes.

These objects we have effected by the addition to aluminum-copper-tin alloys of at least one of the elements lead, bismuth or thallium. For the purposes of our invention these elements are substantially equivalent, their behavior in alloys of the class herein described being similar in their effect on machining characteristics.

We have discovered that tin, when used in amount between about 0.01 per cent and 2 per cent in aluminum base alloys containing from about 4 per cent to about 12 per cent of copper, forms a particularly desirable base alloy to which can be added one or more of the alloying elements lead, bismuth or thallium. The lead may be present in amount between about 0.1 per cent and 10 per cent, the bismuth between about 0.05 per cent and 1.5 per cent, and the thallium between about 0.05 per cent and 3 per cent. These elements, in combination with tin in aluminumcopper alloys, have a very favorable effect on the machining properties of the alloys. In this sense the elements tin, lead, bismuth and thallium may be termed free machining constituents, just as the alloys they form are now called free machining alloys, to indicate the fact that they may be machined more rapidly, with better quality of chip, and cleaner machined surface than similar alloys not containing the tin, bismuth, lead or thallium.

Tin within the disclosed range effects an increase in the tensile strength, shear strength, and Brinell hardness of the aluminum-copper alloys, while the elongation is caused to drop off correspondingly. The remaining constituents, namely lead, bismuth, or thallium, appear not to materially afiect, in many cases, the mechanical properties of the aluminum-copper alloys except insofar as they are beneficial to the machining properties. We have found that when the tin is used in combination with one or more of the other free machining elements lead, bismuth or thallium, the advantageous efiect of the tin on the tensile strength, shear strength and hardness of the aluminum-copper alloys is not diminished materially, whereas the machining properties of the resulting alloys are very materially accentuated.

The simultaneous presence of more than one of the free machining elements is more advantageous than that of thesame total amount of either of the elements used separately. If, for instance, we are working with an aluminum base alloy containing about 6.0 per cent of copper and 1.0 per cent of tin, and in a particular application we desire to add about 1.5 per cent of free machining constituents in combination with the tin, it is more advantageous to make up this 1.5 per cent by using more, than one of the elements lead, bismuth or thallium, than to add 1.5 per cent of one element alone. In conformity with the same principle the addition of one or more of the elements lead, bismuth or thallium to the aluminum-copper alloys in which tin is present is more helpful to the machining properties than the use of an equivalent total amount of the tin alone. One of the advantages of our invention lies in the retention of the improvement in tensile properties due to tin, and the accentuation of the beneficial effect in cutting characteristics of the alloys.

If only one of the elements lead, bismuth or thallium is to be added to aluminum-copper-tin alloys, we prefer to use about 1.0 per cent of the element. As a preferred alloy base we use an aluminum alloy containing about 6 per cent of copper and 0.1 per cent of tin. If more than one of the elements lead, bismuth or thallium is to be added to an aluminum-copper-tin alloy, the preferred amount of free machining elements, inclusive of the tin, should also be about 1.0 per cent, although amounts in excess of this composition, and up to the total amount of each disclosed hereinbefore, continue to exert a beneficial effect on the cutting properties of the alloy. The preferred amount of 1.0 per cent of total free machining constituents represents a point at which the mechanical properties and the machining properties of the alloy reach a most favorable balance, although, of course, there may be many commercial applications wherein improved machining characteristics may more than compensate for the lowering of mechanical properties,

The tin, lead, bismuth and thallium may be added by introducing these constituents in solid form into a molten heat of the aluminum-copper alloy, since they melt at a temperature considerably below that customarily encountered in the commercial handling of molten aluminum or its alloys in the foundry. Since the specific gravity of the disclosed free machining elements is considerably higher than that of aluminum and their liquid solubility is limited, the melt should be heated somewhat above the ordinary temperature and stirred vigorously to assure a thorough mixture of the alloying constituents. The method of adding heavy low melting point metals to alumi- 5 num here referred to is more fully described in copending application, Serial No. 689,885 now issued as U. S. Patent No. 1,959,029.

The alloys herein disclosed may be subjected to the usual thermal treatments familiar to those 10 skilled in the art of treating aluminum-copper alloys for the purpose of altering their physical characteristics.

The term aluminum as used herein and in the appended claims embraces the usual impuri- 15 ties found in aluminum ingot of commercial grade or picked up in the course of the usual handling operations incident to ordinary melting practice.

We claim: 20

1. An aluminum base alloy containing from about 4 to about 12 per cent of copper, from about 0.01 to about 2 per cent of tin, from about 0.1 to 10 per cent of lead, and from about 0.05 to 1.5 per cent of bismuth, the balance being aluminum. 5

2. An aliuninum base alloy containing from about 4 to 12 per cent of copper, from about 0.01 to 2 per cent of tin, and from about 0.15 to 1.5 per cent of lead and bismuth, there being not less than 0.1 per cent lead nor less than 0.05 per cent 30 bismuth present, the balance being aluminum.

3. An aluminum base alloy containing from about 4 to 12 per cent of copper, at least about 0.01 per cent of tin, at least about 0.1 per cent or lead; and at least about 0.05 per cent of bismuth, 35 the total amount of the tin, lead and bismuth not exceeding about 1 per cent, the balance being aluminum.

LOUIS W. KEMPF. WALTER A. DEAN. 40