Microstructure And Properties Of Al-12%Sn-x%MgH₂ Bearing Alloy Prepared By Mechanical Alloying

Aluminum tin alloy is one of the most widely used bearing alloys owing to its excellent seizure resistance, corrosion resistance, wear resistance, antifriction combined with environmental performance. With the direction of modern engine towards high power, high load and high-speed development, there are demands for higher fatigue strength and carrying capacity of bearing alloys, therefore, the research and development of high performance aluminum tin alloy becomes the hotspot of sliding bearing workers. Al-12%Sn bearing alloy produced by mechanical alloying(MA) not only exhibited higher hardness, but also showed better tribological performance. However, ball milling could bring serious oxidation problems to Al particles, which led to low relative density and bonding strength of Al-12%Sn alloy after sintering. Research showed that Mg addition could effectively disrupt oxide film covered on Al particles surface, however, Mg mixed to MA Al-12%Sn can not uniformly dispersed in the nanocrystals, and if directly ball milling Al-Sn-Mg powder, Mg and Sn would complete reaction and losing disrupt the oxide film effect. In this study, we used Mg H2 instead of Mg as a deoxidizer, Mg H2 would not react with Al and Sn in the ball milling process, and could homogeneous dispersed in the Al-Sn alloy around, in the following sintering process dehydrogenated to highly activated Mg and promoted aluminum tin alloy’ sintering. By using X ray diffraction(XRD), scanning electron microscopy(SEM), micro-hardness, tensile test and wear test method to investigate addition Mg H2 on the microstructure and performance of MAAl-12%Sn.Firstly, The mechanical alloying was used to prepare Al-12%Sn-x%Mg H2 alloys powder with Sn phase and Mg H2 phase homogeneously dispersed in Al matrix. In the subsequent sintering process, Mg H2 dehydrogenated to highly activated Mg to disrupt the oxide film of Al particles, which greatly improved the relative density and the tensile strength of the alloy, when Mg H2 amount increased from 0 to 0.8%, the relative density increased from 92% to 98%, tensile strength increased from 32 MPa to 230 MPa.Secondly, researched the tribological properties of sintered Al-12%Sn-x%Mg H2 alloys, and selected industrial bearing alloy Al Sn12Si2.5Pb1.5Cu for comparison. It was demonstrated that Mg H2 improved MA Al-12%Sn alloys’ wear resistance and antifriction, especially when Mg H2 amount was 0.8%, the friction coefficient decreased by 22% and the wear mass decreased nearly by 50% compared with industrial bearings alloy. Added Mg H2 significantly increased the bonding strength of MA Al-12%Sn alloy, which helped to the formation of a more complete wear oxide layer covered on wear surface and simultaneously the oxide layer was not easy peeled off under high load, significantly improved the wear resistance of the alloy.Finally, in order to achieve the application of MA Al-12%Sn-x%Mg H2 alloys in sliding bearings, powder rolling sintering method was used to obtain CG30 Al-12%Sn-0.8%Mg H2 bearing strip. After researching the effect of rolling deformation rate and sintering process,we successfully obtained a bearing strip with smooth surface. The interface of CG30 Al-12%Sn-0.8%Mg H2 alloy layer / interlayer / steel back of the bearing strip showed a good bonding.and the alloy layer was dense with clear dual-scale microstructure. In addition, the hardness and wear test results demonstrated that the hardness of the self-made bearing strips was much higher than industrial bearing strip(Al Sn12Si2.5Pb1.5Cu), and the wear resistance and antifriction of the former was better than the latter, meeting the requirements for the development of high strength aluminum tin bearing alloy.