Influence of extruding temperature and heat treatment process on microstructure and mechanical properties of three structures containing Mg-Li alloy bars

The Mg-Li alloy bars with density of 1.38 g/cm3 as well as ultimate tensile strength of 329.2 MPa were fabricated. Simultaneously, an industrial process with convenience and low cost was developed. In the cast alloys, hcp-Mg was transformed gradually into bcc-Li with increasing Li content. During extruding at different temperatures, the dynamic recrystallization (DRX) in Mg-8Li-5Al-2Zn-0.5Y was weaker than Mg-5Li-5Al-2Zn-0.5Y and Mg-11.4Li-5Al-2Zn-0.5Y due to the mutual limitation between hcp-Mg (α) and bcc-Li (β). In the annealing process, abnormal grain growth in Mg-11.4Li-5Al-2Zn-0.5Y was found at 573 K, and a kind of regular dendritic structure was discovered in the coarse grains at 593 K. Additionally, a sort of solid solution strengthening behavior in bcc-Li was observed and enhanced remarkably the alloy strength (increased by ～160 MPa in maximum). Through controlling cooling velocity, a precipitation behavior could be achieved in the alloys. Through mathematical modeling with high accuracy, the relationships among microstructural evolution and alloy properties in the solid solution and precipitation processes were quantitatively analyzed and determined.