Microstructure And Mechanical Property Of Mg-Li-Gd-Y Alloys

The Mg-Li alloys are the lightest metallic structural materials at present. Theypossess many special properties such as low density, high strength-to-density tatio andspecific stiffness, nicer electromagnetic shielding, strong antiknock and cushioningcapacity, high-energy particle penetration resistance, easy-to-machine tooled figuration,and so on. Based on these advantages, Mg-Li alloys have comprehensive and hugepotential application in aviation, spaceflight, military regions, and electronic product.Nevertheless, the relatively low strength of Mg-Li alloys limits its further application.In order to improve the strength of Mg-Li alloys, new kinds of Mg-Li alloys aremade with the addition of Li into the Mg-Gd-Y alloys. The alloys of Mg-12Li-3Gd-3Y-0.6Zr and Mg-8Li-3Gd-3Y-0.6Al were prepared in vacuum conditions with theprotection of argon atmosphere. To strengthen the alloys further, the samples wereforging and hot rolling. And then different heat treatment was carried out in order toinvestigate the changes of the microstructures and mechanical properties. They werestudied by optical microscopy, SEM, XRD and tensile test.The results show that, the phase structure of the Mg-12Li-3Gd-3Y-0.6Zr alloy isβ-Li, Mg2Gd and Mg24Y5. After annealing treatment, the second phase of rod-like andneedle-like dissolves in the matrix, while the size of the cubic phase is only reduced.The optimal homogenization process is500℃×8hThe tensile strength and elongation of the investigated alloy are improvedremarkably after forging and rolling. The tensile strength of the rolled alloy increasesto152MPa from114MPa of the as-cast, and the elongation reaches to33%comparedwith21%of the as-cast. This is mainly due to the deformation strengthening, secondphase strengthening and refined crystalline strengthening in the process of forging androlling.The hot compression experiment of the Mg-12Li-3Gd-3Y-0.6Zr alloy indicatesthat the stress-strain curves of the alloy belong to the characteristics of dynamic recrystallization. The flow stress of the investigated alloy decreases with theincreasing of deformation temperature and the decreasing of strain rate. Hotdeformation behavior of the alloy can use the hyperbolic sine constitutive equation andZ parameters accurately describe, average activation energy of Q=121.9915kJ/mol.The phase structure of the Mg-8Li-3Gd-3Y-0.6Al alloy consists of α-Mg, β-Li,Mg17Al12, Mg2Gd, Mg2Y, Mg3Gd. The optimal homogenization process is500℃×8h.The highest tensile strength of the as-cast alloy reaches228MPa after solid solutionand ageing treatment at500℃×8h+100℃×48h. This phenomenon can be explained bythe solution strengthening and ageing strengthening.