US2102869A - Zinc alloys - Google Patents

Description

Patented Dec. 21, 1937 UNITED STATES .ZINC ALLOYS Herbert Winter, Buchschlag in Hessia, Germany, assignor to The New Jersey Zinc Company, New York, N. Y., a corporation of New Jersey No Drawing. Application August 18, 1937, Serial No. 159,711. 'In Germany August 26, 1936 1 Claim. (Cl. 75178) This invention relates to improvements in extruded zinc alloys and to methods of forming such alloys. The invention contemplates extruded zinc alloys having high tensile and impact strengths, improved machinability and high resistance to corrosion. The alloys of the invention are of such character that they can be substituted for brass in many applications.

Zinc alloys have been used heretofore 'princi pally for the manufacture of castings and die castings. The heretofore known zinc alloys are diflicult to extrude at a high velocity into rods or profiles. For example, in the case of an alloy containing 1% copper and 4% aluminum, the

' balance being zinc, the extrusion velocity possible in extruding a sharp edged strip with a cross section measuring about 5 x 24 mm, was only 5 to 5.1 meters per minute. Under exactly comparable circumstances, it was possible to obtain an extrusion velocity of 35 to 40 meters per minute with brass containing 58% copper.

It has been proposed heretofore in United States Patent No. 1,540,006 to subject to hot forging zinc alloys containing about 10 to 20% aluminum and 2.01 to 8.5% copper together with small amounts of manganese and titanium. However, such an alloy in extruded form possesses inferior mechanical properties in that its impact "and tensile strengths are relatively low. For example, such an extruded alloy has a tensile strength of only 35 to 38 kilograms per square mm., which is to say, something less than 55,000 lbs. per square inch. Moreover, its susceptibility to corrosion is relatively high. Y

v As a result of my investigations I have discovered that extrudedz inc alloys possess superior tensile strength, impact strength, machinability and resistance to corrosion if they contain from 10 to 15% aluminumJrom 1.5 to 4% copper and from .01 to .04% magnesium, the .balance being zinc having a purity of at least 99.98%. Moreover, an alloy of this composition may be extruded into rods and profiles at greater speeds than heretofore employed in the case of zinc alloys. My invention therefore contemplates an extruded zinc alloy consisting of 10 to 15% aluminum, 1.5 to 4% copper, 0.01 to 0.04% magnesium, the balance being zinc at least 99.98%"pure, and also contemplates the improvement in the manufacture of alloy objects which comprises extruding an alloy containing about 10 to 15% aluminum, 1.5 to 4% copper, and 0.01 to 0.04% magnesium, the balance being zinc having a purity of at least 99.98%. 1

It will be noted that my alloy contains substantially no other elements than aluminum,

copper, magnesium and zinc within the limits stated above. The presence of other elements, particularly the presence of impurities such as lead, cadmium or tin in proportions exceeding For example, alloy .01% is objectionable, because it brings about greatly lessened resistance to corrosion.

Moreover, it is essential that the alloy of my invention contain from .01 to .04% (preferably .02%) of magnesium which greatly increases the tensile strength of the extruded alloy. For example, an extruded alloy of my-invention containing 10% aluminum, 2% copper and .02% magnesium has a tensile strength of 49 kilograms per square millimeter with a hardness of 116 kilograms per square millimeter. The presence of magnesium within the limits stated is also responsible in part for the corrosion resistance of the extruded alloy of my invention.

The following test results show the effect of magnesium in the extruded alloy of my invention. Strips having a cross section of 6 x 24 mm. were extruded to produce test rods having cross sections of 6 x 16 mm. in the test section of the rods. The alloys themselves consisted of zinc of a purity of 99.99%, 10% aluminum and 2% copper, in one case without magnesium, in another case with the preferred proportion of magnesium (.02%), and in still another case with a magnesium content of .05%, that is to say, in excess of the desirable limit. The symbols in the following table indicate the treatment to which the various test rods were subjected prior to test:

G=Annealing for 5 hours at 300 C.

A=Annealing for 10 days at C. K=Corrosion in steam 10 days at 95 C.

' *Throughout this specification, hardness is specified on the basis of tests conducted as follows:

A sphere of hardened steel having a dis. eter of 10 mm. was pressed against a fiat surface of the e tal undergoing test for 30 seconds under a wei ht of 500 kilograms. .The area of the depression thus pr weight in kilograms divided by the measured area m square millimeters ives the figures reported for hardness. '0. 1 had a hardness of 84 kilograms per square millimeter. The similarity between this test method and that of the standard Brinell will be apparen need was measured. The j The foregoing test results indicate clearly that the absence of magnesium results in a decrease in the tensile strength and hardness of the extruded alloy. When the desirable magnesium limit is exceeded, as in the case of alloy No. 3, the tensile strength is still good but the malleability of the alloy is decreased so much, particularly after the corrosion test, that the alloy is no longer practically useful. This will be apparent from the figures for elongation and reduction of area prior to rupture inthe foregoing table.

I have discovered that the extruded alloy of my invention is admirably suited for treatment in automatic lathes, since it forms brittle chips during machining. The superiority with respect to machinability of the alloy of the invention as compared with similar alloys is shown by the following test results for extruded zinc base rods:

velocity 800 R. P. M., pointed tool, clearance angle about 11", front rake 15.

Fine Rough turning turning Feed, mm 0. 2 0. 2 Depth of chip, mm 0. 3 2. 0

Machinability Al M percent perc nt percgnt g g 8% gg I claim:

10 0.3 D31 An extruded zinc alloy consistingof 10 to 15% i 38- aluminum, 1.5 to 4% copper and 0.01 to 0.04% magnesium, the balance being zinc having a The rods were 20 mm. in diameter and were tested under the following conditions: Rotational purity of at least 99.98%.

HERBERT WINTER.