On the role of Laves phases on the mechanical properties of Mg-Al-Ca alloys

As-cast Mg-Al-Ca alloys are among the most promising alloys for elevated temperature applications (<= 200 degrees C) due to their superior creep properties when compared to conventional AZ or AM series Mg alloys. The microstructures of Mg-Al-Ca alloys consist of a soft a-Mg phase reinforced with hard interconnected Laves phases. These interconnected Laves phases are the main reason for the good creep resistance of these alloys as they impede creep deformation. The volume fraction, type and morphology of Laves phases can be controlled through the Ca/Al ratio. Consequently, the Ca/Al ratio can be used to manipulate the mechanical properties of this alloy system in order to achieve optimum creep resistance. We show here that a higher Ca/Al ratio results in i) higher volume fraction of intermetallic Laves phases in the microstructure, ii) improvement in the yield strength (YS), and iii) enhancement in creep resistance at a stress level of 50-70 MPa and a temperature of 170 degrees C of the as-cast alloys. Moreover, the local strain distribution and partitioning at the microstructural level occurring during high temperature tensile deformation (at 170 degrees C) was measured using quasi in-situ DIC in SEM revealing stress localisation at the alpha-Mg Laves phase interfaces.