Study On Composition Optimization And Friction Stir Welding Process Of 6005A Aluminum Alloy For Battery Tray

The battery tray of aluminum alloy welded by friction stir welding process is the bearing part of the battery of new energy vehicles,with large overall mass and great lightweight space.With the improvement of materials and performance requirements for the lightweight of new energy vehicles,the materials and friction stir welding process used for battery trays can’t meet the performance requirements for the lightweight of trays.In this paper,on the basis of 6005A aluminum alloy used in battery tray,JMat Pro thermodynamic simulation and first-principles calculation were combined to optimize the composition of 6005A aluminum alloy,and different contents of La（0.1 wt.%,0.3 wt.%,0.5 wt.%,0.7 wt.%,1.0 wt.%）on the microstructure and mechanical properties of 6005A experimental aluminum alloy after homogenizing treatment（560℃/6 h,homogenized state）,66.7%deformation（rolled state）,after rolling solution and artificial aging treatment（535℃/50 min+175℃/8 h,T6 state）.And the influence of friction stir welding process on the microstructure and mechanical properties of 6005A experimental aluminum alloy plate with 8 mm thickness with 0.1 wt.%La was investigated.It provides theoretical and technological reference for developing a new 6005A experimental aluminum alloy for battery tray.JMat Pro thermodynamic simulation and first-principles calculation results show that:6005A aluminum alloy composition range（0.4 wt.%～0.7 wt.%Mg,0.5 wt.%～0.8 wt.%Si,0.1 wt.%～0.4 wt.%Mn,0 wt.%～0.3 wt.%Cr,0 wt.%～0.3 wt.%Cu,Fe fixed at 0.18 wt.%,Al:Bal.）There were seven precipitated phases:Mg₂Si,Al₅Cu₂Mg₈Si₆,Al₁₃Cr₄Si₄,Al₂Cu,Al₆Mn,β（Al Fe Si）,E-Al Cr Mg Mn in alloy.Mg₂Si,Al₅Cu₂Mg₈Si₆,Al₁₃Cr₄Si₄ and Al₂Cu are the main precipitated phases.The formation capacity,stability,shear modulus,young’s modulus and poisson’s ratio of the four precipitated phases are calculated and their influence on mechanical properties is integrated.The optimized 6005A aluminum alloy composition is Al-0.7 wt.%Mg-0.7 wt.%Si-0.3 wt.%Cr-0.2 wt.%Mn-0.18wt.%Fe,it’s as-cast tensile strength is 135.55 MPa,yield strength is 71.52MPa,and hardness is 43.64 HV.Adding 0.1 wt.%La is beneficial to the transformation of needle-like eutectic Si andβ（Al Fe Si）into point shape,while increasing the content of La can’t help to the transformation of needle-like eutectic Si andβ（Al Fe Si）into point shape,which is easy to form coarse Al Fe Si La.The addition of La did not significantly improve the tensile strength of 6005A experimental aluminum alloy in homogenized,rolled and T6 states,but had a great influence on its elongation,which increased firstly and then decreased to a gradual flat.The optimal mechanical properties of homogenized,rolled and T6 6005A experimental aluminum alloys are obtained at 0.1 wt.%La.Tensile strength is 119.2 MPa and elongation is 26.2%in homogenized state;Tensile strength is 220.7 MPa and elongation is 5.2%in rolled state;Tensile strength is 284 MPa and elongation is 17%in T6 state.The process parameters of friction stir welding（stirring head speed,welding speed）have significant influence on the grain size of welding zone.The grain size of welding zone increases with the increase of stirring head speed,but also decreases with the increase of welding speed.When the stirring head speed is 600 rpm and the welding speed is 200 mm/min,the minimum grain size of the welding zone is 6.56μm,and the mechanical properties of the joint are the best,the tensile strength is 204.7 MPa,the welding efficiency is 72%,and the elongation is 17%,which is almost the same as base metal in T6 state.