Effect of Heat Treatment on Microstructure and Mechanical Properties of Mg-10Li-3Al-3Zn-0.22Si Alloy

The microstructure evolution and mechanical properties of as-extruded Mg-10Li-3Al-3Zn-0.22Si during heat treatment from 473 to 673 K were investigated in this paper, and then the strengthening mechanism and fracture behavior of the studied alloy was also analyzed. Experimental results show that the matrix of as-extruded Mg-10Li-3Al-3Zn-0.22Si alloy mainly consists of alpha-Mg and beta-Li, and dispersive granular phases are AlLi and Li2MgAl. Mg2Si phase shows banded distribution along extrusion direction. The morphology of alpha-Mg is from long strip to nearly spherical block at 573 K. The alpha-Mg reprecipitates from beta-Li matrix in the orientation relationship: (0001) alpha-Mg // (110) beta-Li, [11 2- 0] alpha-Mg // [1 1- 0] beta-Li at 623 K. While the Al-rich granular phase is decomposed and dissolve into the gradually, and then AlLi increase again at 673 K, which may be caused by the dissolution at high temperature and precipitation during air cooling in heat treatment. Besides, the solid solution and dispersion strengthening enhances the strength of alloy after heat treatment. After heat-treated at 573 K for 1 h and then air cooling, alloy presents excellent mechanical properties with the ultimate tensile strength of 253 +/- 3 MPa and elongation of 27 +/- 3%, respectively. Compared with the extruded state, ultimate tensile strength of alloy can be increased by about 49%.

Automated summary

This paper investigates the microstructure evolution and mechanical properties of Mg-10Li-3Al-3Zn-0.22Si alloy during heat treatment and analyzes the strengthening mechanism and fracture behavior. Results show that heat treatment can enhance the strength of the alloy, and the alloy exhibits excellent mechanical properties after being heat-treated at 573K and air cooled.