Study On Technology And Properties Of Aluminium Based Oiled Bearing By Powder Metallurgy Method

Compared with copper and iron oil-retaining bearings by powder metallurgy, aluminium bearings have good thermal conductivity, light weight, low temperature rise, good wear resistance, low noise and the advantages of corrosion resistance, and at the same time, aluminium is cheaper than copper and iron. In recent years, the change of copper alloy and iron alloy is small in oil-retaining bearing by powder metallurgy, but the development of aluminium alloy is quite fast. More and more types of aluminium alloy are researched and its applications are more and more wide, which shows that the aluminium alloy is the most promising material of oil-retaining bearings and it is an important development direction for researchers in the field of international oil-retaining bearing materials now.In this paper, qualified aluminium bearings are manufactured by controlling important parameters like pressing pressure, sintering temperature and holding time with powder metallurgy. Because of low hardness, weak loading capacity and high wear extent, aluminium bearings can’t be used until other elements are added into aluminium alloy. So Cu, Mg, Si and other elements are needed in this study to improve parameters like hardness, crushing strength, oil content and anti-friction and wear resistance properties.In this study, sizes of the powder should be confirmed first because both big and small sizes will create bad influence on bearings. If powder sizes are too small, inner structure will become tight and pores have no communication, and the result is that oil content is low. If powder sizes are too big, metallurgical bonding force is not enough after sintering and hardness as well as strength is not in a good situation. Through experiments, the fact can be found that if keeping powder size from 75pm to 150μm, testing results of experiments are optimum.Cu is the mainly added element in this study and it has an important effect on aluminium oiled bearings. When the content of Cu in alloy is not more than 10%, oil content and crushing strength will be improved with the increasement of Cu content. And wear extent will be reduced with the increasement of Cu content. When the content of Cu in alloy is more than 10%, oil content and crushing strength will be reduced with the increasement of Cu content. And wear extent will be increased with the increasement of Cu content. Hardness will be always increased with the increasement of Cu content.Si can notably increase hardness and wear resistance property of alloy. But Si will also shrink samples and largely decrease oil content of bearings. When the content of Si is not more than 1.0%, crushing strength of bearing will be improved with the increasement of Si content. When the content of Si is more than 1.0%, crushing strength of bearing will be decreased with the increasement of Si content.MgO can be created with the addition of Mg in aluminium bearing alloy. MgO is fluffy and it can expand samples. So it can offset the effect of Si and increase the oil content of bearing. But expansion of the samples will weaken hardness and anti-friction and wear resistance. With the increasement of Mg content, hardness continuously decreases and wear extent continuously increases. When Mg content is not more than 2.0%, crushing strength of bearing will be improved with the increasement of Mg content. When Mg content is more than 2.0%, crushing strength of bearing will be decreased with the increasement of Mg content.Element Cr has no obvious influence on oil content of bearing. But it has significant influence on other properties of bearing. With the increasement of Cr content, hardness of the bearings will be continuously improved. When Cr content is not more than 2.0%, crushing strength and anti-friction and wear resistance of bearings will be improved with the increasement of Cr content. When Cr is more than 2.0%, crushing strength and anti-friction and wear resistance of bearings will be decreased with the increasement of Cr content.Element Sn will improve oil content and decrease hardness of the bearings. When Sn content is not more than 2.0%, crushing strength will be improved with the increasement of Sn content. When Sn content is more than 2.0%, crushing strength will be decreased with the increasement of Sn content.In the end, the optimum ingredient of bearings is Al-7.5%Cu-l%Si-2%Mg-2%Cr-2%Sn. And the pressing pressure is 32MPa. The sintering temperature is 600 ℃. Gas Argon is used as shielding gas and holding time is 6 hours in this atmosphere. At last, final bearing samples can be gotten and their oil content, crushing strength and hardness are 18.3%,155.2MPa and 63.4HB.