Study On Composition Optimization And Heat Treatment Of High Strength And Toughness Die Cast Aluminum Alloy

With the development of automobile lightweight,aluminum alloy is widely used and applied in a wide range of scenarios.Among them,pressure cast aluminum alloy parts have attracted much attention because of its unique advantages,and the development of high strength and toughness die cast aluminum alloy is an important way to achieve automotive lightweight.However,the research on high strength and toughness die cast aluminum alloy is relatively scarce in China,and it is difficult to heat treatment because of the defects such as porosity in ordinary die cast aluminum alloy.In view of the above problems,based on die casting ADC12 alloy and Al-6Mg-2Si alloy,this paper adopts OM,XRD,SEM,EDS,DTA and other characterization methods,combined with Vickers hardness test,tensile property test and electrical conductivity test,through composition optimization to improve the mechanical properties of the alloy.The effects of Pore-free die casting and heat treatment on the properties of the alloy were also studied.The main research contents of this paper are as follows:（1）Effect of alloying elements on microstructure and properties of ADC12 alloy:The effect of alloying elements such as Cu,Mg and Zr on microstructure and properties of ADC12 alloy was studied.The results show thatα-Al,eutectic Si,Al₂Cu,β-Al₅Fe Si andα-Al₁₅（Fe,Mn）₃Si₂phases mainly exist in the microstructure of the alloys.Coarse Al₃Zr phase exists in the microstructure of Zr-added alloy.The strength and plasticity of the alloy can be improved by adding different alloying elements.ADC12 alloy with 0.2%Zr has the best tensile strength,yield strength and elongation of 261 MPa,165 MPa and 5.12%respectively.（2）Effect of microalloying on microstructure and properties of Al-Mg-Si alloy:The effect of Mn,Zr and their compound addition on microstructure and properties of Al-6Mg-2Si alloy was studied,and the effect of Different Zr content on microstructure and properties of Al-6Mg-2Si alloy was analyzed under the condition of maintaining Mn content.The results show thatα-Al and Mg₂Si phases mainly exist in the alloy,andα-Al₁₅Mn₃Si₂and Al₃Zr phases are formed by adding Mn and Zr.The addition of Mn can effectively prevent the sticking mold and improve the performance.The addition of Zr effectively refines the grain size,but the addition of Zr alone leads to the deterioration of the properties of the alloy.The addition of0.5%Mn and Zr content did not improve the properties of the alloy.Among them,Al-6Mg-2Si-0.5Mn-0.1Zr alloy has the best comprehensive mechanical properties,with tensile strength of 265 MPa,yield strength of 155 MPa and elongation of 9.86%.（3）Effect of Pore-free die casting and heat treatment on microstructure and properties of Al-Mg-Si alloy:The effect of Pore-free die casting on microstructure and properties of Al-6Mg-2Si-0.5Mn-0.1Zr alloy was studied,and the optimal heat treatment process was explored and determined on this basis.The results show that the Pore-free die casting alloy has denser microstructure,higher strength than ordinary diecasting alloy,and does not bubble under solution treatment at higher temperature,but does not have solution strengthening effect.However,mechanical properties of the alloy are improved after artificial aging treatment.The tensile strength,yield strength and elongation of the alloy are 276 MPa,222 MPa and 5.44%respectively after aging at 200℃for 4 h.