The Influence Of Si Addition On The Microstructure And Properties Of MA Al-sn Bearing Alloy

Al-Sn based alloys are applied widely in the modern industry as sliding bearing materials.With the increase of speed, load and power in modern automobile, the carrying capacity,anti-fatigue strength and compliance of Al-Sn alloy can’t satisfy the current requirement forbearing materials. The addition of appropriate amount of Si has been proven to be an effectiveroute to significantly enhance above mentioned properties. In addition, the high energymilling increases the surface energy of MA Al-Sn powders and leads to a thicker surfaceoxide film and higher hardness of Al powders, which are the main obstacles for compactingand sintering. It was reported that Si powder was used as sintering activator to facilitatesintering and assist in consolidating MA Al-based powders. In this thesis, the microstructureand properties of MA Al-Sn bearing alloy with addition of Si were investigated.Firstly, MA Al-12%Sn-3%Si alloy powder was prepared by ball milling a mixturecomposing of Al, Sn and Si powder in the weight percent of Al:Sn:Si=85:12:3. Secondly, Sipowder was ball milled prior to mix with initial Al and Sn powder to prepare MAAl-12%Sn-X%Si (X=0,0.5,2.5,5) alloy powders via mechanical alloying. Microstructure andproperties of those alloys were systematically investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM), microhardness test, tensile strength test and friction andwear test.MA Al-12%Sn-X%Si (X=0,0.5,2.5,3,5) alloy powders with nano-composite structurecan be obtained by high energy ball milling. It was found that the relative density of samplecontaining Si is higher than Si-free alloy after sintering. Morever, the higher temperature, thehigher relative density. Microhardness decreased with the increasing of sintering temperature,but addition of Si can improve the microhardness of Si-free Al-Sn alloys under allcircumstances. Sn phase appears as net-like distribution along powder particle boundarieswhen sintering temperature exceeds eutectic reaction temperature for Si-free MA Al-Sn;while the addition of small amount of Si can eliminate it effectively. Moreover, it is alsofound that the addition of Si can improve tensile strength of MA Al-Sn alloys remarkably atdifferent temperature. The results of friction and wear confirmed that MA Al-Sn samplescontaining Si lead to increase in friction coefficient, but improve the wear resistance.The addition of pre-milled Si in the MA Al-Sn-Si alloy can obtain a homogeneousmicrostructure containing fine Si distributes as dispersed particles inside bulk sample, whichleads to the enhancement of both mechanical and tribological properties in a certain extent.The influence of different Si content on the microstructure and properties were studied by adding different amount of pre-milled Si, and the results showed that green density decreaseswith the increasing of Si, which implied there is no need of excessive Si additive. Moreover,microhardness increases with the increasing of Si content after sintering, while the sinteringdensity showed a trend from ascent to descent. And the best tensile and tribological propertiesare achieved at the amount of2.5wt%Si element.