Study On Microstructure And Mechanical Properties Of Mg-9Al-2Sn-Mn/Sr(wt.%) Alloy

The effects of Mn and Sr addition on microstructure and mechanicalproperties of cast Mg-9Al-2Sn (hereinafter referred as AT92) alloys areinvestigated, and the improved AT92-0.1Mn alloy are applied in the15inches wheels, meanwhile, the microstructure and mechanical properties areanalyzed.The microstructure and mechanical properties of cast AT92-xMn (x=0,0.1,0.3) alloys in as-cast, solution treated and aged conditions are studied.The results reveal that Mn addition into AT92alloy leads to the formation ofAl8(Mn,Fe)5phases, the grain refinement and the increase of discontinuousMg17Al12precipitates along the grain boundaries.0.1%Mn addition has anobvious effect on accelerating the aging behavior of AT92alloy at the earlyaging period up to8h, while0.3%Mn addition alloy has an comparableaging behavior with the Mn-free alloy. Mn addition has less influence on thefracture behavior of AT92alloy, while the fracture pattern is mainlydetermined by the thermal conditions. AT92-0.1Mn alloy has the bestcombination of strength and elongation when aged at200°C for8h and theyield strength, ultimate tensile strength and elongation are154MPa-292MPa-5%, respectively. Meantime, the corrosion resistance ofas-cast AT92-0.1Mn alloy is improved to0.175mg/(cm2·day).In AT92-0.1Sr alloy, Sr prefers to enrich with Sn, and it is helpful tochange the morphlogy of Al-Mn phases, but the effect of grain refinement is not obvious. Compared to the tensile strength of AT92-0.1Mn, that ofAT92-0.1Sr-0.1Mn decreases at ambient temperature. However, the ductivityis improved after aging treatmen. The yield strength, ultimate tensile strengthand elongation of AT92-0.1Sr-0.1Mn at200°C for8h are119MPa-249MPa-5.26%.The microstructure and mechanical properties of AT92-0.1Mn in wheelswith low pressure die casting are studied. The results shows that the rim andspoke consist of multiple shrinkages, porosities and cracks et al., especially inthe junction between rim and spoke, where the cavity comes out. Thesamples for the mechanical properties indicate that the mechanical propertyofAT92-0.1Mn decreases, the ultimate tensile property is less than125MPa andhence is difficult to meet the demand of the wheels. It should be solved howto apply the AT92-0.1Mn alloys without any shrinkages and cracks in thewheels.