Microstructure And Mechanical Properties Of Al-Cu-Si-Mg Cast Aluminum Alloy

Cast Al-Cu alloy is a kind of high-strength and tough cast aluminum alloy,mainly used in rail transit,aerospace and other fields,but due to the wide solidification crystallization temperature range,it is easy to produce casting defects.The results show that Mg can enhance the mechanical properties of alloys,and Si can improve the properties of alloy casting processes.In this paper,the effects of Mg and Si elements on the mechanical properties and microstructure of Al-Cu alloy casting were studied by dip casting method,and the influence of Mg and Si elements on the mechanical properties and microstructure of Al-Cu alloy casting was studied by DSC,EDS,SEM,TEM,tensile test,hardness test and other analytical test methods,and the evolution of residual crystalline phase in solution treatment was discussed,and the effect of aging process on the mechanical properties and precipitated phase of cast Al-Cu-Si-Mg alloy was studied.The main results are as follows:（1）The cast structure of Al-Cu-Si-Mg alloy mainly includes Al₂Cu phase,Q phase and Si phase.Si mainly exists in the grain boundary as a networked elemental phase,and with the increase of Si content,the massive Q phase and Al₂Cu phase increase.Mg is mainly present in the Q phase,when the Mg content is greater than0.6wt%,the massive Q phase and the Al₂Cu phase transform into a complex eutectic structure,but Mg will exacerbate the stomatal defect.Al-5Cu-1.5Si-0.6Mg alloy has excellent comprehensive mechanical properties,tensile strength and elongation can reach 195MPa and 7.5%,respectively.（2）Single-stage solid solution can effectively reduce the residual crystalline phase,when the solid solution temperature reaches 510°C,the ultrafine quaternary eutectic structure melts,resulting in pre-melting holes.Two-stage solid solution can not only avoid pre-molten pores,but also reduce the residual crystalline phase;The increase of Mg content will lead to an increase in the residual crystal Q phase;The increase of Si content reduced the spheroidization process of Si phase.The best two-stage solution process is 500°C×2h+515°C×6h.（3）The non-isothermal aging treatment of HX20°C/h,40°C/h and 60°C/h showed that with the increase of heating rate,the peak hardness of the alloy decreased,and the peak hardness of HX20°C/h was the highest（176.5HV）.The effects of Mg and Si on the properties of alloys after non-isothermal aging showed a trend of first increasing and then decreasing.The alloy composition with the best comprehensive mechanical properties is Al-5Cu-1.5Si-0.6Mg,and the tensile and elongation can reach 382.3MPa and 8.1%,respectively.（4）The peak aging temperature point of Al-5Cu-1.5Si-0.6Mg alloy is CX140°C,and the main strengthening phase is granular Q’phase and slat-likeθ’phase;after aging,the number of precipitated phases increases but coarsening occurs.Q’phase andθ’are interdependent to limit the growth of the two and increase in number.（5）TEM and fracture analysis showed that Al-5Cu-1.5Si-0.6Mg alloy mainly improved the strength of the alloy through precipitation strengthening,and a large number of tenaments were distributed on the fracture surface,mainly ductile fracture.The few residual crystalline phases,spheroidization of Si phases,fine dispersion distribution of precipitated phases,and reduced porosity defects are the main reasons for the improvement of the comprehensive tensile properties of Al-5Cu-1.5Si-0.6Mg alloy.