US2076578A - Free cutting alloys - Google Patents

Description

oFF f 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. Application December 28, 1935,

Serial No. 56,552

4 Claims. (01. 75147) The invention relates to aluminum base alloys Despite continual lubrication the machined surand is particularly concerned with aluminum base face is rough and irregular, and the chip has a alloys containing magnesium and silicon. tendency to form a continuous curl or spiral Aluminum base alloys containing from about which often fouls the tool or the moving parts.

5 0.1 per cent to 1.0 per cent of magnesium, and of the machine. It is immediately apparent that from about 0.5 per cent to about 2.5 per cent of there is need for .an alloy of good working charsilicon have heretofore been used. They are acteristics and satisfactory physical properties, usually in the wrought condition since they are yet possessing such favorable machining properradily susceptible to mechanical deformation ties that the complete machining operations may such as rolling, forging, or extrusion. It is posbe performed economically and successfully, and slble, by appropriate thermal treatments to very y be du ti e f apl s n su f appearsubstantially' improve their physical properties. ance. After ahigh temperature s l ti treatment; they Accordingly an object of our invention is the do not age-harden to any great extent at room Provis on of n um m base al y Containing 16 temperature but may be artificially aged by temfrom about 0.1 to about 1.5 per cent of magperatures somewhat in excess of room temperanesium and from about 0.5 to 2.5 per cent of ture as is well known in the art. For this reasilicon, which may be readily and economically son these alloys may be wrought to substantialmachined- 1y fi al form, th subjected t high tempera,- Our invention resides in the discovery that 20 ture solution treatment, and while in a relativehe foregoing Obj s e f cted by adding at ly soft condition they may be given certain final least One O t e elements lead and tin to the Working, steps at low temperature. Since th y aluminum-magnesium-silicon alloy. When these finishing steps may be performed t any fied below, the alloys are known as free cutting venient time. They may ultimately be artificialfree ac i alloys because y a be ly aged if the maximum tensile strength, yield machined 'e p yo a Similar alloys Withstrength, and hardness are d d, out the lead or tin, and yet have as good or a Since all commercial l mi ba alloys better finished surface. After an extended seit is to be understoodthat the amount of silicon alloying elements which h a favorable eflec discussed herein, and hereinafter claimed, repupon the machining P p s 0 aluminumresents the total quantity of silicon present and magnesium-Silicon yS- n O fi O t s that the silicon content of the aluminum used effect We term lead a t free ma n n should be known in order to provide a basis for elements- We have further discovered a the determining th e tu composition of t simultaneous presence of both of these elements aluminum-magnesium-silicon ,11 is productive of an improvement in free machin- There are, however, some applicatjons whereing characteristics which is considerably greater in alum num-magnesium-silicon alloys a h r than that caused by the presence of the same 40 inabove disclosed might be conveniently and total amount of either one alone. For example, profitably used except for an inherent disadthe addition p cent of d a d D vantage which militates against their use in cent of t to an aluminum base alloy containing the production of certain articles requiring exactabout D cent of magnesium d De ing machining operations, Mechanical cutting cent of silicon eifects a greater improvement in r tions such asdrilling, shaping, or 1 ,1; tmachining quality than does the addition of 1.0

ting are successfully carried out only by using P cent f either l tin s ycertain precautions which increase the cost of Since these two elements have Such a production and perhaps favor th choice of vorable effect on the machining characteristics of other metal or alloy which can be machined 'elll inum nagnesium-silicon alloys, it is formore readily but which is not s d i b i tunate that they are also of relatively low meltother respects, as for example, in physical propg po nt, a a Which makes p b e e r ad- .erties. When alloys are difiicult to machine this ditien in molten aluminum in the p a disadvantagev becomes evident, in many cases, without the intervention of so-called rich althrough rapid wear of the cutting tool edge, loys. It is also a fact that the elements lead so that frequent tool re-sharpening is required. and tin form with aluminum a series of alloys 2 of limited liquid solubility. Within the range disclosed and claimed howeverthese free machining elements may be added without unusual difificulty. We suspect that this characteristic 5 feature of the elements lead and tin may be one of the significant factors which contribute to their free machining efiect. We believe that this effect is further-strengthened by distributing the free machining constituent relatively homogeneously throughout the solid matrix, since lead and tin are also practically insoluble in the solid aluminum-magnesium-silicon base alloy.

The lead or tin, if used alone, may be added in amounts between about 0.05 per cent and 6.0 per cent. If used together the total amount of free machining constituent should not be less than 0.05 per cent, and need not exceed 6.0 per cent. We have determined that the maximum limit of, 6.0 per cent of free machining metalis suflicient for satisfactory commercial results,

since although the free machining effect persists beyond this amount, certain of the other physical properties may be unfavorably affected.

Aluminum-magnesium-silicon alloys containing one or both of the free machining elements lead or tin may be machined more rapidly, with less tool wear, less tool sharpening, better quality of chip and better machined surface than the same base alloys without the free machining additions and as previously indicated the simultaneous presence of tin and lead is considerably more helpful to the machining quality of the alloy than an equivalent total amount of either lead or tin alone. 7,

As a preferred alloy within the range of the respective elements disclosed hereinabove we su gest an alloy containing about 0.6 per cent of magnesium, 1.0 per cent of silicon and a total of 3 per cent of lead and tin, the balance being 40 aluminum. For some applications which do not require a high degree of free machining quality a lesser amount of the free machining metal may be added to the alloy base, for instance 0.5

per cent of lead or 0.5 per cent of tin, 45 per cent total of lead and tin.

For certain purposes, notably the "improvement of tensile strength, hardness and grain structure, the alloys as hereinabove disclosed may be improved by the addition of one or more 50 of the group of elements composed of molybdenum, vanadium, titanium, tungsten, zirconium and chromium. From 0.05 to 1 per cent of any one of these elements may be used alone, but it more than one is employed the total amount 55 should not exceed about 2 per cent.

' March 15, 1934.

-a critical period of time.

. to 2.5 per cent silicon,

The free machining alloys which have been described hereinabove maybe subjected to the thermal treatments well known in the art to improve their strength and hardness. We have found that a solution heat treatment and subsequent aging does not impair the free machining quality of the alloys and in many instances the treatment even tends to improve this property. For many purposes a relatively high strength and hardness are necessary to the successful performance of the machined article and hence the alloy must be heat treated. This treatment is generally applied prior to the machining operation.

As hereinabove indicated the free machining elements, by reason of their'low melting point, may be added to the molten aluminum in pure metallic form. However, since some difliculty may be encountered in introducing them in the higher percentages of scribed in No. 1.959.029, issued Briefly it involves heating the melt to a somewhat higher temperature than is customary, and vigorously stirring it in excess of The term aluminum as used herein and in the appended claims embraces the usual impurities found in aluminum ingot of commercial grade-or picked up in the course of the ordinary handling operations incident to melting practice.

We claim:

our disclosed range we prefer to use the method which is more fully de- 1. A free cutting aluminum base alloy containing from 0.1 to 1.5 per cent magnesium, from 0.5 and a total of from 0.05 to 6 per cent of one of the group of free machining elements composed of lead and tin, the balance being substantially aluminum.

2. An aluminum base alloy containing from 0.1 to 1.5 per cent magnesium, from 0.5 to 2.5 per cent silicon, and from 0.05 to 6 per cent of lead, the balance being aluminum. v

3. An aluminum base alloy containing from 0.1 to 1.5 per cent magnesium, from 0.5 to 2.5 percent silicon, and from 0.5 to 6 per cent of tin, the balance being aluminum.

4. An aluminum base alloy containing from 0.1 to 1.5 per centmagnesium, from 0.5 to 2.5 per cent silicon, from 0.05 to 6 per cent of one of the group of free machining elements composed of lead and tin, and from: 0.05 to 2 per cent of hardening metal from the group composed of molybdenum, vanadium, titanium, tungsten, zirconium and chromium, the balance being aluminum.

- LOUIS W. KEMPF.

WALTER A. DEAN. v