Study On Microstructure And Mechanical Properties Of Al-Li Cast Alloy

Al-Li alloy is a aluminum alloy which has low-density,high elastic modulus,high specific strength and high specific stiffness.Except for the same advantages as deformed Al-Li alloys,as-cast Al-Li alloy can improve the amount of lithium,and is conducive to reducing the anisotropy of Al-Li alloy,has a broad application prospects in the field of aerospace.In this paper,six kinds of Al-Li(-Mg)-Cu-Zr-based Al-Li alloys were designed,using high purity argon gas protection smelting casting ladder type aluminum lithium alloy castings in the atmospheric environment.Scanning electron microscopy,XRD,tensile testing were used to study the effect of different alloy composition and heat preatment process on microstructure and mechanical properties of alloy.The results show:As-cast Al-Li-Cu-Zr alloy grains are fine equiaxed grains,and after ad ding Mg element,the grains are converted into coarse dendrites,with the increase of Mg content,the grain size becomes larger and the content of the second phase is also increased.There is ?'(Al3Li),T2(Al6Cu Li3),T(Al2Mg Li)and Al8.9Li1.1 phase in as-cast alloy which has 2.5wt.% Li,?(Al Li)is discovered in as-cast alloy which has 5wt.% Li.After heat treatment,the disperse distribution of irregular fine ?' phase is found in alloy which has 2.5wt.% Li,the second phase on the grain boundary is also smaller than as-cast alloy,and the aggregation growth of ?' phase is found in some of aging alloy.The effect of heat treatment on alloy which has 5wt.% Li is not very obvious.After the heat treatment,the second phase of the alloy is fragmented and the phase composition is not different from the as-cast.After adding Mg element,the microhardness of as-cast Al-Li-Cu-Zr alloy increases,and rise with the increase of Mg content,but the tensile st rength decreases first and then increases.The elongation is low in all alloys.There is a obvious effect of solid solution aging effect of alloy which has 2.5wt.% Li.The best aging treatment process of Al-2.5Li-1Cu-0.15Zr?Al-2.5Li-2Mg-1Cu-0.15Zr?Al-2.5Li-5Mg-1Cu-0.15 Zr is 140?×10h+190?×4h ? 140?×10h+190?×8h ?140?×14h+190?×4h.The tensile properties of the alloy after aging are almost the same as that of the as-cast,and the mechanical properties are poor.The tensile fracture mode of the as-cast alloy which has 2.5wt.% Li is a brittle fracture along the grain,after aging treatment,some small and shallow dimples and tearing edges are seen on the fracture.The tensile fracture modes of as-cast and aging alloy which has 5wt.% Li is brittle fracture,and there are a lot of tearing edges and river patterns in the fracture,and some casting defects can be observed.