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

The microstructure evolution of Mg–9Li–6Al–xLa (x=0, 2, 5) alloy under different solid solution parameters was investigated. The results show that, during solution treatment at 350 °C, the lamellar AlLi is precipitated from α-Mg in Mg–9Li–6Al, while the MgLi2Al is dissolved into the matrix. However, during solution treatment at 450 °C, the AlLi phase is wholly dissolved into matrix, while the MgLi2Al is precipitated from β-Li. The addition of La can reduce the size of α-Mg, restrain the formation of AlLi, and make the precipitated MgLi2Al from β-Li at 450 °C be finer than that in Mg–9Li–6Al. With the addition of La, the decrease of the amount of AlLi and MgLi2Al 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.