Effects of Li content on microstructure and mechanical properties ofas-cast Mg-xLi-3Al-2Zn-0.5Y alloys
(National Engineering Research Center of Light Alloy Net Forming and State Key Laboratory of Metal Matrix Composite, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China)
Abstract: The effects of Li content on the microstructure and mechanical properties of the as-cast Mg-xLi-3Al-2Zn-0.5Y (LAZx32-0.5Y) alloys were investigated by XRD, SEM, TEM, hardness tester and universal testing machine. The results show that the matrix of the alloy transforms from α-Mg to α-Mg+β-Li and then to β-Li when the Li content increases from 4% to 14% (mass fraction). All LAZx32-0.5Y alloys contain AlLi and Al2Y, while MgLi2Al appears only in the alloy containing the β-Li matrix. As the Li content increases, the content of AlLi and MgLi2Al gradually increases, while the content of Al2Y does not change much. As the Li content increases from 4% to 10%, the ultimate tensile strength and hardness of the as-cast LAZx32-0.5Y alloys gradually decrease while the elongation gradually increases. The corresponding fracture mechanism changes from cleavage fracture to quasi-cleavage fracture and then to microporous aggregation fracture. This is mainly attributed to the decrease of α-Mg and the increase of β-Li in the alloy. When the Li content continues to increase to 10% and 14%, the yield strength, ultimate tensile strength and hardness of the as-cast LAZx32-0.5Y alloys gradually increase, while the elongation decreases sharply, which is mainly attributed to the nano-scale MgLi2Al uniformly distributed in the β-Li matrix.
Key words: Mg-Li alloy; li content; alloying; microstructure; mechanical properties