Study On The Preparation And Properties Of High Performance Al-Sn Based Bearing Alloy

With the development of modern machinery towards high speed,high load and environmentally friendly(Pb-free),there are continuous demands for developing new Al-Sn based bearing alloys.For this objective,the key point is how to make Sn phase small and scattering in the Al matrix.Nano-phase composite Al-Sn alloy can be produced by mechanical alloying(MA)process.However,the MA Al-Sn alloy powder not only exhibited a higher hardness,but also introduced a stable aluminium oxide film on the surface of particles,inhibiting the spread of atoms.Thus,the common pressed-and-sintered(PS)consolidation method can hardly make it densification,weakening the alloy's performance.Study found that Si could effectively promote the metallurgical bonding by improving the sintering character of MA Al-Sn alloy powder.So,this paper first would investigate the microstructure and properties of MA Al-Sn alloy with addition of Si.And then,to further improve the comprehensive performance of MA Al-Sn alloy,the PS Al-Sn-Si alloy would be severely deformed by using room-temperature rolling(RT-rolling)combined with subsequent thermal treatment,creating a dual-scale microstructure.By investigating the microstructure,mechanical properties and wearing properties,an optimal consolidation method was got.At last,to further control the shape and size of Sn phase,a reaction ball milling process was used,providing a new strategy to preparing nano-phase composite Al-Sn alloy.Firstly,the plasma ball milling Si(P-Si),Al powder and Sn powder were mixed and milled to obtain the MA Al-12%Sn-2.5%Si alloy powder,and then the MA powder was consolidated by “pressed + 600? sintered”.The results show that the P-Si had better improvement effect on the Al-Sn alloy's properties compared with the common ball milling Si(C-Si).After the “pressed + 600? sintered”,the Al-12%Sn-2.5%Si(with P-Si)alloy reached to a relatively high sintered density(about 97%)and tensile strength(about 167MPa),and the plasticity was improved obviously.Secondly,the PS Al-12%Sn-2.5%Si alloy was severely deformed.The results show that the density,hardness and tensile strength were improved significantly with the increase of the deformation.When the reduction was 40%,the alloy was nearly full density(about 99.5%),and the hardness and tensile strength reached the highest about 87 HV and 247 MPa respectively.However,when the reduction was higher than 50%,the PS alloy was broken.Furthermore,the RT-rolling sample(40% in reduction)was annealed under different temperatures,a dual-scale structure consisting of ultra-fine grain(UFG)and coarse grains(CG)was obtained.When the annealing temperature was below Al-Si eutectic point(measured value was 550?),the CG was individual and in a low ratio;When the annealing temperature was higher than this point,the CG became coalescence;When the annealing temperature was between 500?~550?,the CG and UFG reached a proper proportion,and the Sn was fine dispersed in the UFG zone.Mechanics experiments show that when the annealing temperature was 500?~550?,the alloys reached an optimized combination of strength and ductility about 194MPa~205MPa and 4.9%~6.7% respectively.And meanwhile,the alloys showed the best tribological properties about the friction coefficient and abrasion loss was 0.4 and 2.0mg respectively.Compared with the PS sample,the abrasion loss reduced by nearly 70%.This was due to the synergistic effect of strength and plasticity,leading to the formation of a stable friction oxidation layer on the surface,exhibiting excellent tribological properties,and the worn mechanism was oxidation wear.Finally,with Al powder,SnO2 powder and MgH2 as raw material,reaction ball milling process was used to prepare nano-phase composite Al-Sn alloy.The results show that the SnO2 in the MA Al-SnO2-MgH2 alloy powder,which was produced by a two steps method and MgH2 addition,was almost deoxidized into monolithic Sn after “pressed + 600? sintered”,and the Sn was fine dispersed in the Al matrix.The sintered density and hardness was 98.3% and 120 HV respectively,obviously higher than the MA Al-12%Sn alloy(about 94.5% and 60HV).And meanwhile,compared with the MA Al-12%Sn alloy,the Al-Sn alloy produced by two steps method exhibited better tribological properties,and the friction coefficient and abrasion loss reduced 20% and 70% respectively.