A Study On Microstructure And Property Of Al-Si-Li-Mg-Cu Alloy

The aim of this project is to optimize the microstructure of Al-Si-Li alloys by adding Mg and Cu alloy elements to the Al-Si-Li alloy.The effects of Cu and Mg content on the microstructure and properties of cast Al-Si-Li-Mg-Cu alloy were investigated by means of OM,XRD,DSC and SEM?EDS?.The alloy was homogenized and the artificial aging treatment process parameters were studied.The results show that the main phase in the as-cast microstructure of the alloy is?matrix and AlSiLi phase,With the increase of Cu content,grain size,dendrite arm spacing and the number of precipitated S?CuMgAl₂?phase increase.At the same time,the grain boundary becomes clearer and grain distribution is more uniform.In addition,the adding of Cu element promotes the precipitation of primary Si phase in the solidified structure,decreases melting temperature of the low melting point eutectic phase,?-Al matrix,and reduces the initial solidification temperature of the alloy and the precipitation temperature of the eutectic phase structure.The optimum homogenization temperature of 0 and 1%Cu content alloy is between530°C and 550°C,while Cu content up to 2%³%,the overheating temperature of the alloy will decrease.It can be found that the two alloys with 1%and 2%Cu content show a higher tensile strength.The increase of Mg content inhibits the precipitation of the primary Si phase,AlSiLi phase and Cu-containing phase in the solidified structure,promotes the precipitation of the non-equilibrium eutectic phase and densifies microstructure.When the Mg content increase to2%,a large number of acicular eutectic phases composed of Al-Li and AlSiLi phases precipitate in the solidification structure,and obvious dark intermetallic phase gather on the grain boundaries,and the melting points of the low-melting eutectic and the matrix phases decrease.In the homogenized treatment microstructure of 2%Mg alloy,the content of Mg element in the eutectic phase is higher than that in the matrix,while the distribution of Cu content both in the matrix and eutectic phases is uniform.The higher the Mg content is,the lower tensile strength and elongation is.Therefore,the Mg content of the alloy should be controlled between 0.5%¹%.