Effect Of Mg And Cu And Heat Treatment On Microstructure And Mechanical Properties Of Al-Si-Cu-Mg Cast Aluminum Alloy

Al-Si-Cu-Mg alloy has low density,high specific strength,good corrosion resistance and excellent casting performance.It is often used in casting complex structural castings and is widely used in automotive and other industrial fields.Cu and Mg elements form Mg₂Si,Al₂Cu,Q-Al Cu Mg Si and other intermetallic compounds in Al-Si alloy,andθ’-Al₂Cu and Q’-Al Cu Mg Si precipitated phases after heat treatment can significantly improve the strength of the alloy.The strengthening effect of Cu and Mg elements will be weakened if the crystalline phase formed during alloy solidification cannot be completely dissolved during solution treatment.In order to improve the strengthening effect of alloy elements,it is necessary to optimize the alloy composition and heat treatment process.The effects of Cu and Mg content on microstructure and mechanical properties of Al-Si-Cu-Mg cast aluminum alloy were studied by OM,SEM,EDS,XRD,DSC,tensile test and hardness test.Modification ofα-Al and eutectic Si phases by addition of Al-10Sr and Al-5Ti-B intermediate alloys;Evolution law of crystallized phase in solution treatment;Effect of heat treatment on mechanical properties of Al-Si-Cu-Mg cast aluminum alloy.The results are as follows:（1）There are mainly Si phases,Al₂Cu phases and Q-Al Si Cu Mg phases in the as-cast microstructure of Al-Si-Cu-Mg cast aluminum alloy.Si is mainly distributed in the form of coral-like eutectic Si at theα-Al grain boundary.When Cu content is relatively fixed,increasing Mg content and decreasing Cu/Mg ratio can helpθ-Al₂Cu to transition to Q phase.When Mg element is fixed,the eutectic structure of Al₂Cu phase decreases with increasing Cu content and exists in bulk form.The volume fraction of Al₂Cu phase reached the highest when Mg content was 0.4%.When the content of Mg element exceeds 0.5%,the Al₂Cu phase decreases obviously,while the Q phase increases.（2）The addition of Al-Sr,Al-Ti-B and other intermediate alloys has a significant metamorphic effect on the alloy.With the increase of Ti content,the size ofα-Al dendrites decreases and the refining effect is obvious.Sr has remarkable effect on eutectic silicon modification of Al-Si alloy,and 0.03%Sr has the most complete modification.The composite effect of 0.1%Ti and 0.01%Sr can meet the modification requirements of Al-9Si alloy.（3）Under the as-cast condition,with the increase of Mg content,the tensile strength and elongation first decrease and then increase.The hardness of alloy has a process of first rising and then falling.Al-9Si-2.0Cu-0.2Mg alloy has good as-cast performance,with tensile strength of 264 MPa and elongation of 3.8%.（4）After solution treatment at 495℃for 6h+530℃for 2h,most of the Al₂Cu phase was dissolved,and a small amount of Al₂Cu phase,massive Al₂Cu phase,Q phase,Al_mFe Si,π-Al₉Fe Mg₃Si₅ and so on remained.（5）The peak hardness of Al-9Si-Cu-Mg alloy was obtained at the aging temperature of 155℃.After solution at 495℃for 6h+530℃for 2h+155℃for 10h,Al-9Si-2.0Cu-0.3Mg alloy has the best tensile strength and elongation of 407.6MPa and 6.6%,respectively.