Investigation Of Preparing Process And Property For Aluminum Base Sintered Oil Bearing

Compared with antifriction bearing, sintered metal oil bearing has many advantages, such as lower noise, less libration, saving material and energy, no special lubricant oil supply system, suitable for mass production, and lower cost. Specially, aluminum base sintered oil bearing has a lower density, lower cost, better anticorrosion, and so on. Therefore, more and more people have interesting in this type of material.In this paper, using powder metallurgy process, the aluminum base oil bearing are prepared under different pressing pressure, sintering temperature, and other process parameters. The aluminum powder atomized by nitrogen has been used as the base material. The sintered aluminum base oil bearing, with addition of Cu, Mg, and Si, has the higher crushing strength and better shape. The influences of preparing parameters and element addition on the sample microstructure and properties, such as crush strength, relative density, porosity, and so on, have been investigated. And the mechanism has been analyzed.Result shows that the relative density of green billet is 80% pressed at the pressure of 132MPa. Pressed at this pressure, the green billet has a better shape and higher strength. According to the Walker theory, the dependence of relative density on the prepared pressure can be calculated by the fit formula:ρ=24. 52+27.98lgP.Cu content has important influence on sintered temperature. Different Cu content samples have different critical sintered temperature. The higher Cu content is, the lower critical sintered temperature is. When samples are sintered at critical sintered temperature, relative density decrease first, and then increase as the Cu content increases. The differential of relative density is less than 1.5%, and samples have good shape.When Cu content is low, Cu diffuses and solids solution into Al powder. Alloy interior generates lattice distortion and lattice constant increases. So sintered samples volumes expand. Porosity generated by in-situ Cu melts, makes effective porosity increase. Samples volumes expansion and effective porosity variation result in the oil content increases as Cu content increases. There are excessive liquid in the sintered samples when Cu content is more than 10%.This will decrease the amount of interconnected pores, and reduce effective porosity. At the moment the oil content of sintered samples begins to decline drop down as Cu content increases.The crushing strength of sintered samples without Cu is very low. The crushing strength increases first, and then decreases as the Cu content increases. Addition of 10% Cu has the biggest strengthening effect, and the value of crushing strength is 97MPa. Pore amount, microstructure and structure composition decide the changing trend of crushing strength. Addition of has significant effect on relative density and oil content. The relative density rises and oil content declines as the Si content increases. When Si content is low, Si particles precipitate from Al matrix and disperse in it. Lattice distortion and stress field, existed in Al matrix and Si particles interface, hinders the movement of the dislocation. This makes the alloy strengthen. When Si content is more than 1%, rending influence of Si particles become remarkable. This will make alloy crushing strength decrease. Result shows the sintered samples have the biggest crushing strength at 1% Si content, the value is 177.11MPa.Research shows that Mg element causes the expansion in sintered process. Addition of Mg in alloy will make relative density decrease and oil content increase. MgO generated by charging reaction of Mg and Al₂O₃ film and reaction of Mg and O2,cause the sintered samples expansion. Mg reacts with the oxide film on the surface of Al powder,and abolishes the oxide film. This will accelerate atoms diffusion and alloying process in particles. S phase (Al₂CuMg) formed by reaction of Al and Mg, disperses in the Al matrix. Existence of S phase in Al matrix hinders the movement of the dislocation and strengthens the alloy. Result shows addition of 1% Mg has the biggest strengthen effect, and the crushing strength is up to 190MPa.Through the test, the optimum composition is Al-10%Cu-1%Mg-1%Si.The pressure is 132MPa and the relative density of billet is 80%. And samples are sintered at 540℃in vacuum environment for 4 hours. The oil content of sintered samples is at 22% and crushing strength is 190MPa. Oil content and crushing strength of oil bearing meet to relevant technical standard requirements. The oil bearing initially has the practical value.