Study On The Effects Of Zr And Rare Earth On The Microstructure And Mechanical Property Of Al-Mg-Si Alloy

With the increasing emphasis on energy and environmental issues,the lightweight of transport is imperative.Aluminum alloy with its high specific strength,specific modulus and other advantages,has gradually become a new type of the important structural materials for car,high-speed trains and other lightweight transport.Al-Mg-Si alloys are the main aluminum alloys used for automobiles at present owing to their high strength,good formability,good corrosion resistance and machinability.However,the development and application of Al-Mg-Si alloys used for automobiles in China are relatively late,and it is low in strength,plasticity and fatigue performance compared with similar products in foreign countries,which can not meet the rapid development of the manufacturing industry.Therefore,it is urgent to further improve the mechanical properties of Al-Mg-Si alloy.In this paper,Zr + Er and Zr + Y elements were introduced into Al-Mg-Si alloy.The effects of Zr and rare earth on the microstructure and mechanical property of Al-Mg-Si alloy were studied through heat treatment and plastic deformation.Finally,the strengthening and toughening mechanism of Zr and rare earth on this alloy system was analyzed.The results of solidification microstructure analysis showed that the addition of Zr + Er and Zr + Y produced the rare earth-rich crystalline phases in the alloy.The addition of Zr + Er produced AlEr Zr phase in the grain boundary of the alloy.The addition of Zr + Y produced a large amount of needle-like AlCuYSi and a small amount of bulk Al3 Zr phases in the center of grain and near the grain boundary of the alloy.In addition,the introduction of two Zr and rare earth elements refined the as cast microstructure,and the refinement effect of Zr + Y is more significant.The analysis of the solidification process showed that the main refinement mechanism of Zr + Er is solute segregation,and the main refinement mechanism of Zr + Y is heterogeneous nucleation.The analysis of the structural evolution during the heat treatment and rolling process showed that during the heat treatment,the circular Q-AlMgCuSi and the bulk Mg2 Si crystalline phases disappeared and the grain boundary phases were reduced.In addition,the needle-like AlFeMn(Cr)Si and AlCuYSi phases melted down along its length,tended to granular.At the same time,Mn,Cr elements precipitated from the ?-Al matrix,and segregated to the dendritic boundary,and the smaller grain is,the more serious the segregation is.So the addition of Zr and rare earth not only refine the grains of alloy,but also exacerbate the segregation of Mn,Cr elements.Furthermore,the addition of Zr and rare earth also increase the rolling deformation resistance of the alloy grain,and the smaller the grain size is,the greater the deformation resistance of the alloy grain has.The study on mechanical properties showed that the addition of Zr + Er and Zr + Y resulted in an increase of 11.3% and 18.1% in the tensile strength respectively,an increase of 7.4% and 9.5% in the yield strength respectively and an increase of 22.4% and 4.8% in elongation respectively.After rolling and T6 heat treatment,the addition of Zr + Er resulted that the tensile strength of the rolled-T6 status alloy was increased by 2.7%,the yield strength was increased by 1.9% and the elongation was increased by 24.2%.While Zr + Y reduced the tensile strength of the rolled-T6 status alloy by 2.7%,reduced the yield strength by 4.0% and increased the elongation by 10.1%,which is closely related to the effects of Zr and rare earth on the evolution of the structure of the alloys during solidification,heat treatment and rolling process.