Study On Al-Li Alloy In Ultra Low Density Casting

Based on Al-5Li-5Mg alloy,three groups of experiments were designed to explore its structure and properties.Firstly,three groups of Al-5Li-5Mg alloys with different Cu contents were melted and poured in atmospheric environment by argon protection law.The microstructure changes were analyzed by OM,SEM,EDS,XRD,and the mechanical properties were analyzed by tensile and hardness tests.Subsequently,the effect of different cooling rates on the microstructure of the alloy was investigated.finally,the effect of trace Sc and Zr on the microstructure and properties of the alloy was investigated.The results show that with the increase of Cu content,the as-cast grains of the alloy are refined obviously,and the grain growth mode tends to be cellular,but there are coarse intermetallic compounds at the grain boundary.The coarse structure may be Al2CuMg and Al2MgLi eutectic structure,which is difficult to eliminate by heat treatment.Cu the content is high,the alloy will precipitate more phases in the aging process,improve the mechanical properties of the alloy,and the tensile strength and plasticity of the alloy are poor,which is characterized by brittle fracture.Increasing the cooling rate can significantly refine the grain size of the alloy and improve the size of intermetallic compounds in the alloy.The phase composition in the alloy at lower cooling rate may be Al8.9Li1.1,Al2CuMg,Al2MgLi and Al5Cu6Mg2 phases,while the phase composition of the alloy becomes Al8.9Li1.1,Al2CuMg and Al2MgLi phases under sub-fast solidification.The rapid cooling mode of water quenching makes the alloy form a metastable Al2CuMg phase.The addition of Sc and Zr can significantly refine the grain and eutectic structure of the alloy and increase the solid solution temperature of the alloy.The tensile strength of the alloy has also been greatly improved,but still shows brittle fracture.