Investigation On Microtsructure And Properties Of Non-heat-treat Strengthening Hpdc Al-Ce-Mg Alloys

Die-casting aluminum alloy has been widely used in automobile industry,and the demand for integrated lightweight die-casting aluminum alloy in automobile lightweight technology has driven the research of non-heat-treat strengthening die-casting aluminum alloy,non-heat-treat strengthening aluminum alloy can be directly used without any heat treatment at as-cast state.In this paper,the microstructure and properties of Al-Ce alloys were firstly investigated,and then the Al-8Ce alloy was selected as the base alloy.The solid solution strengthening contributed by the Mg alloys was expected to further improve the strength of Al-8Ce alloys,aiming to explore the microstructure and properties of non-heat-treat strengthening Al-Ce-Mg alloy.In the high pressure die casting(HPDC)Al-x Ce(x=2,4,6,8 wt.%)alloys,the main phases were primary?-Al matrix and lamellar Al-Al₁₁Ce₃ eutectic phase,whereas the block primary Al₁₁Ce₃ phase begin to appear in HPDC Al-x Ce(x=10,12 wt.%)alloys.The addition of Ce can notably refine the primary?-Al grain and thus to improve the strength of the alloys.While the increase of the eutectic phase and the appearance of block primary Al₁₁Ce₃ phase deteriorate the thermal conductivity of the alloys.With the Ce content increasing from 2 wt.%to 12 wt.%,the yield strength and ultimate strength were improved from 59MPa and 116MPa to116MPa and 210MPa,while the elongation and thermal conductivity separately decrease from 36.8%and 205 W/(m·K)to 8.9%and 149 W/(m·K).Conclusively,the HPDC Al-8Ce alloy shows the best comprehensive properties and is a suitable candidate for the study of ternary HPDC Al-Ce alloys.In the HPDC Al-8Ce-y Mg(y=0,0.10,0.25,0.50,0.75 wt.%)alloys,the Mg atoms exist in the matrix as the solid solution state and the lattice distortion caused by the solid solution of Mg atoms enlarge the lattice constant of the primary?-Al and decrease the thermal conductivity of the alloys.The solid solution strengthening achieved by the Mg atoms constantly improve the strength of the alloys and the hardness of the primary?-Al matrix.With the Mg content increasing from 0 wt.%to 0.75 wt.%,the yield strength and ultimate strength were improved from 92MPa and 177MPa to 115MPa and231MPa,while the elongation and thermal conductivity separately decrease from 28.3%and 165 W/(m·K)to 7.9%and 148 W/(m·K),the hardness of the primary?-Al matrix increase from 0.50GPa to 0.58GPa.In addition,the solid solution of Mg atoms apparently promote the work hardening behavior of the alloys.With the inhibition of the Mg atoms,the dislocation continuously multiply and the cross slip of the dislocation is activated more frequently which finally lead to the formation of forest dislocation and dislocation networks.In the HPDC Al-8Ce-y Mg(y=1.50,3.00 wt.%)alloys,Mg atoms not only exist in form of solid solution,but also in the form of ternary Al-Ce-Mg intermetallics.The solid solution of the Mg atoms causes the left shift of the eutectic composition point,that's why the block primary Al₁₁Ce₃ phase is observed.The strength of the alloys increase with the Mg content,but the ductility and thermal conductivity exhibit reverse trend.With the Mg content increasing from 0 wt.%to 0.75wt.%,the yield strength and ultimate strength were improved from 122MPa and261MPa to 133MPa and 273MPa,while the elongation and thermal conductivity separately decrease from 3.5%and 134 W/(m·K)to 2.7%and 112 W/(m·K).Among all the Al-8Ce-y Mg alloys,HPDC Al-8Ce-0.50Mg shows the best comprehensive properties,the yield strength,ultimate tensile strength,elongation and thermal conductivity are 113MPa,225MPa,10.3%and 154W/(m·K)individually.