Impact Of Mg On Structure And Performance Of Al-12%Sn Bearing Alloy With Multi-scale Structure

Aluminum alloy with mid-tin has the advantages of light weight, good corrosionresistance, high mechanical properties and wear resistance, while no toxic Pb contaminationto environment. It is one of the most widely used bearing materials in the modern industry.Mid-tin-aluminum Al-12%Sn alloy prepared by mechanical alloying (MA) has uniform andfine structure, whose hardness is about2to4times as compared to those fabricated by thetraditional casting method, and both the carrying capacity and tribological properties of MAalloys are much better than that of the powder metallurgy alloys with the same composition.But MA Al-12%Sn alloy also accompanies with the low density and low strength aftersintering process. In the present experimental conditions, a certain proportion of coarsepowder with the same composition and Mg addition were added into MA Al-12%Sn alloypowder to mix uniformly, and finally, a mixed multi-scale structured Al-12%Sn-(Mg) alloywas obtained after cold pressing and sintering. The effect of the incorporation of the coarsepowder and Mg element to the microstructure and properties of Al-12%Sn alloy weresystematically investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM),microhardness test, tensile fracture, and friction and wear test. Then the rolling and sinteringprocesses of the multi-scale mixed Al-12%Sn-(Mg) powders with steel back were explored.The experiment results showed that the dispersed coarse Al particles with about30μmsize were scattered in the MA matrix, which contained uniform nano-sized Sn grains, aftersintering at600℃for1h. Moreover, appropriate Mg addition could dirupt with the oxidefilm covered on the surface of Al particles and generate MgO and MgAl2O4phases, andfinally improve the sintering. Surprisingly, it also could reduce the network structure of Snphase in the multi-scale structured Al-12%Sn alloy, and obtain a much more uniformstructure.There was an optimized Mg concentration in multi-scale structure Al-12%Sn-(Mg) alloywith different coarse powder content, when the Mg addition exceeded the optimized value, alot of hard and brittle phase Mg2Sn appeared in the alloy, which caused stress concentrationand poor distribution of Sn phase, and some surface bubbling and internal cracking were also observed in the sintered alloy. The maximum Mg content were slightly less than2.0%,1.4%,1.0%for multi-scale alloy contained10%,30%,70%coarse powders, and showed adecreasing tendency. The sintering density and tensile strength of the multi-scale structuredAl-12%Sn-(Mg) alloys increased with Mg concentration and reached maximum values at theoptimized Mg addition, and then decreased with further increase of Mg content. Moreover,the optimized Mg addition decreased as the coarse powder content increased, which wereapproximately1.2%,1.0%,0.5%with the coarse powder ratios of10%,30%,70%,respectively. The sintering density of Al-Sn alloy with10%coarse powder and1.2%Mgadditions was99.8%, nearly fully dense material; its corresponding tensile strength was about198MPa, which was about6times as compared with the sample without Mg addition. Thehardness of multi-scale structured Al-12%Sn-(Mg) alloys increased with the decreasing ofcoarse powder content. When with a constant content of coarse powder, the hardness of alloyfirst reduced and then increased with the Mg content. Friction and wear experiments indicatedthat, the appropriate Mg addition could reduce the wear volume and friction coefficient of themulti-scale structured Al-12%Sn alloy, and the wear volume first decreased and reached alowest value at Mg concentration of1.2~1.4%, and then increased with further adding of Mgelement.Through exploring process, we successfully rolled the Al-Sn alloy powder containing30%p/m and0.5%Mg with steel back, and then a initial bearing strip after sintering was obtained.The analysis results indicated that the interfaces between the Al-Sn alloy layer and transitionlayer and steel back layer bonded well in the bearing strip, the structure was very uniform anddense, the hardness and wear resistance were also better than industrial bearing(AlSn12Si2.5Pb1.7Cu) prepared by traditional methods.