Effect of rolling reduction on the microstructure and mechanical properties of hot-rolled Mg-Li-Al-Ca alloys

Abstract

To improve the strength of magnesium (Mg)-lithium (Li) alloy without sacrificing plasticity, Mg-7.3Li-4Al-3Ca alloy is designed and subsequently rolled at 350 °C. The microstructure evolution and mechanical properties of the alloy under different rolling reductions are studied. The results show that the as-cast and hot rolled alloy is composed of α-Mg, β-Li matrix phases as well as Al2Ca and (Mg, Al)2Ca precipitated phases. After hot rolling, the agglomerated Al2Ca precipitates are broken and dispersed in the matrix. A large amount of continuous filamentous (Mg, Al)2Ca phase becomes discontinuous and the phase content decreases monotonously with increasing rolling reduction due to the decomposition of (Mg, Al)2Ca phase and the corresponding constituent elements dissolve in the matrix. During the hot-rolling process, some fine equiaxed grains appear in the alloy matrix due to dynamic recrystallization. Both the strength and elongation of Mg-7.3Li-4Al-3Ca alloy increases monotonously with increasing rolling reduction. For the alloy with rolling reduction of 60%, the ultimate tensile strength and elongation are 218Mpa and 24.8%, respectively, which are 52.4% and 153% higher than those for the as-cast alloy. The strengthening mechanism is attributed to fine grain strengthening, precipitation strengthening and solid solution strengthening. Grain refinement and the appropriate distribution of Al2Ca and (Mg, Al)2Ca phases causes the obvious increase of the plasticity.