Investigation Of Preparation Process For Al-based Sintered Oil Bearing In Nitrogen Environment

The oil sintered bearing has the advantages of low mechanical shock,low noise,low costand no need of external lubricating oil.In the present,Fe-based and Cu-based sintered oil bearings have been widely applied.Compare with Fe-based and Cu-based sintered oil bearings,Al based oil bearing has excellent properties of lower density,lower cost,higher thermal conductivity,better anticorrosion,and so on.Therefore,Al-based oil bearing was concerned by more and more people.Al-based sintered oil bearing was prepared by powder metallurgy.The property and microstructure was tested by SEM,XRD,microhardness tester,SWX digital universal tester.The influence and mechanism of attention content of alloys,sintering time,sintering temperature and sintering atmosphere was discussed.The results show that the temperature range of liquid phase formation of sintered samples could be effectively measured by resistivity method,and the sintering temperature range is 530?-590 ?.Under the atmosphere of nitrogen,the properties and microstructure of sintered samples were significantly affected by sintering temperature and sintering time.At the same sintering time,the liquid phase of sintered samples was increased,the metallurgical bonding was better and the crushing strength was higher with the increase of sintering temperature.Simultaneously,the connected pores became closed-pores,the tiny pores almost disappear,the oil content of sintered samples was reduced.In the same sintering temperature,the crush strength of sintered samples was increased,while the oil content was decreased with the increase of sintering time.When the sintering temperature is 560?and the sintering time is120 minutes,the sintered samples have the best comprehensive property.Under the atmosphere of nitrogen,proper addition of alloying elements has a positive effect on Al-based sintered oil bearing.The strengthening phase?Cu Al₂?was generated and the amount of liquid phase was increased by the addition of copper.Therefore,the crushing strength of the sintered sample was significant increased.With the increase of the additive amount of copper,there is an excess of Cu Al₂ was generated and the Cu Al₂ was gathered to grown up and it could cuts apart the base of sintered sample,the crushing strength gradually decrease.When the Cu content of sintered is 7.5%,the samples have the best comprehensive property.Adding alloy element Mg on the basis of Al-7.5%Cu,The strengthening phase?Al₂CuMg?was generated and the amount of liquid phase was increased by the addition of Mg,the crushing strength was increased.Meanwhile,the addition of Mg caused theexpansion of sintered sample,the oil content of the sintered sample would increase.The excessive magnesium content makes the matrix loose,the crushing strength was decreased.When the magnesium content is 1.5%,the sintered sample has the best comprehensive performance.The addition of alloying element Si can significantly improve the crush strength of sintered samples,but reduce the oil content of sintered samples.With the increase of Si content,the shrinkage rate and crushing strength of sintered samples gradually icrese but the oil content sharply decrease.During the sintering process,the excessive Si particles were gathered to grown up and it could splits the base of sintered sample,reduced the crushing strength.Result shows that 1.5% Si content of sintered sample has the comprehensive property.Different sintering atmospheres also affect the microstructure and mechanical properties of the samples.The larger pore diameter in the sintered samples under the protection of nitrogen.Meanwhile,the samples sintered in atmosphere of nitrogen with higher surface hardness than the samples sintered in atmosphere of vacuum.The optimized composition of Al-based sintered oil bearing is Al-7.5%Cu-1.5%Mg-1%Si%,sintering temperature is 560?and the sintering time is 120 minutes.The oil content and crushing strength of Al-based sintered oil bearing is 19.6% and 187.3MPa,the surface hardness is 101.7HV.