Influence of Al and Si additions on the microstructure and mechanical properties of Mg-4Li alloys

The microstructure and mechanical properties of four hot-rolled alloys,Mg-4Li, Mg-4Li-3Al, Mg-4Li-3Al-0.38Si and Mg-4Li-6A1-0.76Si, (weight percent) were investigated. The results showed that the addition of Al and Al-Si eutectic results in the precipitation of Al3Li(Mg) within the hot-rolled alloys. The Al3Li(Mg) is present as a solid solution of Mg in Al3Li with an L1(2) superlattice structure, which precipitates as small spherical particles. Another minor constituent present as a precipitate in the Si-containing alloys, Mg-4Li-3(Al-Si) and Mg-4Li-6(Al-Si), is a Mg2Si phase which is broken into polygonal particles in the hot-rolled alloys. Ultimate tensile strength (UTS) up to 295 MPa was measured for the Mg-4Li-6(Al-Si) alloy, compared with 143 MPa for the Mg-4Li alloy. This improvement is attributed to precipitation strengthening imparted by the Al3Li(Mg) and Mg2Si phases, as well as solid-solution strengthening due to Al atoms dissolved in the alpha-Mg matrix of the alloys.