Preparation Of Al-Ti-Sc Master Alloy And Its Refining Effects For Al-Mg-Si Based Alloy

Aluminum alloy has excellent mechanical properties,corrosion resistance and electrical conductivity,widely used in industry and national defense and other fields,as automotive 6016 aluminum alloy,under the premise of good shape,the strength needs to be further improved,and the addition of binary master alloy grain refiner strengthening effect is limited,and most of the master alloys are synthesized by metal elemental addition.The cost is higher.In this work,the preparation process of Al-Ti-Sc ternary master alloy was studied by thermite reduction of Ti O₂and Sc₂O₃,and the 6016 alloy was refined directly by adding,which has the technical advantages of simplifying the experimental process and reducing the cost,and has important research value for the development of new master alloy and new Al-Mg-Si-based aluminum alloy.Thermodynamic analysis by HSC 6.0 software and XRD results show that intermediate product Ti can be formed during the preparation of Al-Ti-Sc master alloy,which can further react with reduced Al₃Sc to form Al₃（Sc,Ti）,promoting the formation of Al₃Sc phase.The concentration of Sc and Ti in the master alloy can be increased effectively,and the maximum concentration of Sc and Ti can reach 2.48%and 1.4%,respectively,under appropriate process conditions.The main phase of the master alloy isα-Al and Al₃（Sc,Ti）phase,and Al₃（Sc,Ti）is the solid solution of the cubic crystal system Al₃Ti and Al₃Sc.After solid solution,it is more matched with the lattice ofα-Al.When the raw material ratio is 1,the reaction temperature is 820℃,and the reaction time is60 min,The concentration of Sc and Ti in the master alloy is 2.28%and 0.92%,respectively.In this case,Al₃（Sc,Ti）phase is the largest,the particle size is the smallest,and the distribution is the most uniform.The results of OM,SEM and EDS showed that with the concentration ratio of Ti and Sc,especially the total concentration of Ti and Sc increased,the number of Al₃（Sc,Ti）particles in the alloy increased,which could provide more heterogeneous nucleation,effectively inhibit the growth of recrystallized grains of aluminum alloy,and improve the microstructure refinement effect.It can play the role of fine grain strengthening and second phase strengthening at the same time.The alloy fracture dimple density is large,which is a typical ductile fracture mechanism,and has obvious improvement on the strength and plasticity of the alloy.The average grain size of aluminum alloy can reach the minimum of 27μm,and the tensile strength and elongation after fracture of the alloy reach the maximum of 280 MPa and 35%,respectively,which is significantly higher than 6016 aluminum alloy.The experimental results of heat treatment show that solution hardening and artificial aging can produce solid solution strengthening and second phase strengthening,and improve the distribution of equiaaxial crystals,so as to further improve the strength and plasticity of refined aluminum alloy.The increase amplitude is related to the concentration of alloy elements.When the Ti and Sc contents are higher than that of Si and Mg in the alloy matrix,Al₃（Sc,Ti）precipitated more strengthened phases thanβ"-Mg₅Al₂Si₄,etc.Due to the high thermal stability of Al₃（Sc,Ti）phase,the effect of thermal treatment is not obvious,so the strength and plasticity of Al₃（Sc,Ti）phase.The chemical corrosion and eddy current conductivity tests of the heat-treated aluminum alloy show that with the increase of the concentration of Ti and Sc in the alloy,the content of Si in the grain boundary decreases,and the intergranular corrosion tendency of the alloy samples decreases,but the conductivity decreases relatively due to the higher degree of alloying.