Microstructure and hardness of Mg-9Li-6A1-xLa (x=0, 2, 5) alloys during solid solution treatment

The microstructure evolution of Mg-9Li-6A1-xLa (x=0, 2, 5) alloy under different solid solution parameters was investigated. The results show that, during solution treatment at 350 degrees C, the lamellar AlLi is precipitated from alpha-Mg in Mg-9Li-6A1, while the MgLi(2)A1 is dissolved into the matrix. However, during solution treatment at 450 degrees C, the AlLi phase is wholly dissolved into matrix, while the MgLi(2)A1 is precipitated from beta-Li. The addition of La can reduce the size of a-Mg, restrain the formation of AlLi, and make the precipitated MgLi(2)A1 from beta-Li at 450 degrees C be finer than that in Mg-9Li-6A1. With the addition of La, the decrease of the amount of AlLi and MgLi(2)A1 leads to a descent of hardness, while the refinement, Al-La phase precipitation, and the solution of Al atoms can improve the hardness of the alloys. (C) 2014 Elsevier B.V. All rights reserved.