Research On The Microstructure And Mechanical Properties Of Vacuum Die Casting Al-Si-Mg-Mn Alloy

In order to expand the application of die castings in industrial production,the vacuum-assisted high-pressure die cast process?VA-HPDC?was developed to reduce the internal defects of die castings,so that the castings can meet the requirements of subsequent heat treatment and welding processing.It is of great significance to systematically study the effects of alloy composition,die casting process parameters and heat treatment process on the microstructure and mechanical properties of the vacuum-assisted high-pressure die casting aluminum alloy.In this paper,three alloy compositions were designed:Al-10%Si-0.3%Mg-Mn?A1?,Al-11%Si-0.3%Mg-Mn?A2?and Al-11%Si-0.6%Mg-Mn?A3?.On this basis,the effects of alloy composition and heat treatment process on the microstructure and mechanical properties of vacuum-assisted die-casting AlSiMgMn alloy were investigated.The results showed that increasing the Si content on the basis of the A1alloy was beneficial to the strength of the as-cast alloy.The A2 alloy had the best as-cast comprehensive mechanical properties,and its tensile strength,yield strength and elongation were 315.2 MPa,160.3 MPa and 7.9%.Increasing the content of Si and Mg could further increase the yield strength of the alloy,but the plasticity of the alloy was obviously reduced at this time.After the optimal T6 heat treatment conditions?530?×3h+165?×6h?,the A3 alloy had better mechanical properties,of which tensile strength,yield strength and elongation were of 377.3 MPa,307.8 MPa and 8.9%respectively.The improvement of mechanical properties can be attribute to the high density of needle-like???Mg₅Si₆?precipitation after aging treatment and the fine and spherical eutectic Si particles uniformly distributed in the?-Al matrix.Based on the research of alloy composition,Al-10%Si-0.3%Mg-Mn composition was selected to investigate the effect of process parameters adjustment on the microstructure and mechanical properties of aluminum alloy die castings.The results showed that with increase with the increase of pouring temperature,switch position of fast velocity and fast shot velocity,the mechanical properties of the castings increased first and then decreased.The larger the injection pressure,the smaller the internal hole defects of the casting.The optimal process parameter combination was investigated,and when the pouring temperature was 695?,the fast shot velocity was 4.5 m·s^-1,the switch position of fast velocity was 790mm,the tensile strength,yield strength and elongation of aluminum alloy die castings were increased to 282.8 MPa,142.2MPa and 11.5%.Finally,combined with the actual industrial application requirements,the optimal heat treatment process for die castings was explored.After the optimal heat treatment of 180?×3h,the tensile strength,yield strength and elongation of aluminum alloy die castings were 313.6MPa,216.4 MPa and 6.2%.