US2900288A - Process for heat-treating a bearing alloy - Google Patents

Description

PROCESS FOR HEAT-TREATING A BEARING ALLOY Erich Pelzel, Stolberg, Germany, assignor to Vereinigte Osterreichische Eiseuund Stahlwerke Aktiengesellscbaft, Linz (Danube), Austria, :1 firm No Drawing. Application July 5, 1956 Serial No. 595,835

Claims priority, application Austria February 9, 1952 2 Claims. (Cl. 148-13) The invention relates to an aluminum-zinc-copper alloy, which is particularly suitable for replacing the expensive bronzes containing copper and Zinc which have previously been used in most cases as a bearing alloy. The invention relates also to a process for heat-treating the bearing members made of that alloy.

The present application is a continuation-in-part of the copending US. patent application Ser. No. 334,973 filed.February 3, 1953, now abandoned. 7

Many alloys are known which consist of aluminum and copper, balance zinc. Previously, however, such alloys have been used only in single cases in bearings. For this purpose not only the generally desired higher characteristics as regards tensile strength, elongation and Brinell hardness are to be taken into consideration but also the internal structure and the adherence of oil films on the bearing surface. In that respect too bronzes are preferable to alloys of zinc, aluminum and copper.

In the co-pending application mentioned hereinbefore, an alloy was proposed for bearing purposes which contains 30-66% of aluminum, copper to the amount of at least one sixth and at most one fourth of the actual aluminum content, and the balance of zinc.

The general technological properties of such alloys are satisfactory but it has been found in experiments that in certain marginal regions of the aluminum content disadvantages occur which cannot be tolerated where the alloy is used for bearing bushings.

It has been found that the disintegration of the structure and resultant changes in volume increase as the content of aluminum is reduced. For instance, in an alloy consisting of 30% aluminum, copper, balance zinc, a dimensional change of 01-02% will result after a storage time of one month. Such a change is not tolerable for bearing bushings because such a shrinkage will obstruct the running of the shaft. Tests with alloys having a higher content of aluminum have shown that these detrimental shrinkage properties do no longer occur in alloys with 35% aluminum, 6.5% copper and 58.5% zinc. As a result, it is apparent that the aluminum content should not be less than 35%.

In further tests it has been shown that the upper limit of the aluminum content is also significant for bearing alloys because this upper limit is of special influence on the structure of the bearing metal. In that respect the interrelations are of a somewhat complex nature, as will become apparent from the following discussion.

When the alloys are being processed with the usual melting and pouring equipment a certain contamination of the alloy by iron cannot be avoided. That contamination has proved to be tolerable when the iron content of low-aluminum alloys does not exceed 0.3%. photographs of such alloys reveal precipitates consisting of crystals of iron and zinc in the form of small needle which are not disturbing.

With higher contents of aluminum, particularly up to the limit of 66% stated in the co-pending application Micro 0 Elongation: 3-6% mentioned hereinbefore, it was found that the precipitation of iron and zinc crystals increases disproportionately, i.e., by a multiple amount, compared to alloys having a low aluminum content. for this phenomenon resides in that with a high aluminum content a ternary field is entered wherein complex aluminum and iron silicon compounds are formed.

These diflferences depending on the aluminum content appear to be due to the following facts. Where the aluminum content and consequently also the silicon content is small, the afiinity of iron and zinc prevails so that the said fine needlelike iron and zinc crystals are formed, wherein one part of iron combines with about 9 parts of zinc. having a high silicon content, the afiinity relations are changed. One part of iron combines with about twice that amount of silicon and seven times that amount of aluminum to form a ternary crystal, which is voluminous owing to the high share of the lightweight aluminum. That process is promoted by the fact that the' rate of crystallisation of that ternary phase is so high that a relatively small number of coarse crystals areforrned instead of the aforementioned numerous fine needles.

The commercially pure aluminum, which is to be used for foundry purposes for economic reasons, contains always impurities up to 0.5% silicon. For this reason the detrimental content of silicon in the alloy can be kept down only by preventing the content of aluminum for exceeding a tolerable amount.

The tests made have shown that the undesired coarse ternary crystals begin to occur with an aluminum content of 50%, i.e. with a silicon content of about 0.25% if the contamination of the aluminum by silicon amounts to 0.5 In order to avoid the disadvantages set forth hereinbefore, residing in undesired dimensional changes and the formation of coarse ternary crystals, therefore, the teaching given in the co-pending application mentioned hereinbefore must be modified so that the aluminum content of the bearing alloy amounts to 35-60%, the copper content amounts at least to one sixth and at most to one fourth of the actual aluminum content, and the balance consists of zinc.

The range of alloys possible is limited by the series of alloys having the lowest copper content (copper content=% aluminum) and by the series of alloys having the highest copper content (copper content= A aluminum content).

The series of alloys having the lowest copper content Al Cu(=}6 Al) Zn cum The series of alloys having the highest tent is:

copper COD- Al Cu(= )6 Al) Zn Specific gravity: 4.5 to 4.0

Tensile strength: 30-35 kg./sq. mm.

-140 kg./sq. mm.

The shaped bearing members may be subjected to an Brinell hardness number:

1C6 Patented Aug. 18, 1959- The explanation found In high-aluminum alloys,-

3 after treatmentto improve the properties of the bearing alloy. That aftertreatment is performed, e .g byheat: ing the shaped parts to a temperature of 100-280 deg. C. The duration of the heat treatment is at least three hours, preferably 24-48. hours. The. efiectachieved by thev aftertreatment is surprising.

"Whereas Without heat. treatment the elongation is. The

3..6%, itincreases after the treatment to 10%. strength and. hardness remain substantially unchanged.

1 The impr'ovemeri'Lofthe'properties by the aftertreatment is'expla'ined. by a change in internal structure. In the range'ofconcentrationsstated the zinc-aluminumcopper alloys consist ofja ternary phase andaluminumzinc mjxedwcrystal. The treatment according to the invention leads to. a partly euteetoid disintegration of the,

Fr oni an alloy containing 35% aluminum, 7.5% cop- P9 11. a ance. mmercia p re i a bearing sleeve is magleby casting andheat-treated at 250 deg. C. for

24 h9urs. Thestrengthis 32 kg./sq. mm, the elongation 19%.. h Brins b rdness n mbe 120 a q- When the hearing was loaded with 50 kg./sq. cm. a

ternperature rise of 60 deg, C. was observed.

4 Example 2 From an alloy containing aluminum, 8% copper, and the balance of commercially pure zinc, a bearing sleeve is made by casting and is heat-treated at 250 deg. C. for 24- hours. elongation. 5%, the Brinell hardness number.l0 8 kg./sq. mm. When'the bearing .Was loaded witli kg.'/sq. cm.,

a maximum temperatufe'rise of deg'. C. was observed.

1. A method of producing an aluminumrzincfiopper alloy for bearing purposes comprising thejsteps of: 'producing a compositionalloy of. 35 to 50% Al 5.8.to 8.3% Cu, 0 to 0;3'%"1=e,"oto;0.2s j% s1, and 59.2"to 41.15% of Zn; of shaping said' alfoy; and of heat-treating said alloy at temperatufes from 10.0. to 280?. C.- fora time fro'm 24 to 48 hours.

2. A method of producing an aluminum-zinc-copper alloy comprisingthe steps of ,producingan alloy compo sitionloff35fto'50% iii/83116 1f2'i5'% Cu; 0 in 0.3%- FejO'to 0.25% Si, and 56.2 to 36.95% of'Zn, andheattreating said alloy attemperatures from for a perio'd'from 24 to. 48 hours. I

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES 1948 Meta1s I-Iandbook, page 1244.

The strehgthis 32.5 kg./sq. mm. the

' to 280 C;

Claims (1)

1. A METHOD OF PRODUCING AN ALUMINIUM-ZINC-COPPER ALLOY FOR BEARING PURPOSES COMPRISING THE STEPS OF: PRODUCING A COMPOSITION ALLOY OF 35 TO 50% AL, 5.8 TO 8.3% CU, 0 TO 0.3% FE, 0 TO 0.25% SI, AND 59.2 TO 41.15% OF ZN; OF SHAPING SAID ALOY, AND OF HEAT-TREATING SAID ALLOY AT TEMPERATURE FROM 100 TO 280*C. FOR A TIME FROM 24 TO 48 HOURS.