Microstructure, mechanical and creep properties of high Ca/Al ratio Mg-Al-Ca alloy

Abstract

In the present study, the microstructure, mechanical and creep properties of Mg-3.7Al-3.8Ca (AC4a), Mg-4.4Al-4.5Ca (AC4b) and Mg-4.9Al-5Ca (AC5) alloys were investigated. Direct water-cooling semi-continuous ingots were subject to hot extrusion at 673K with the extrusion ratio of 16:1. After being extruding, these Mg-Al-Ca alloys turned into situ composites consisting of ɑ-Mg (solid solution)+Al2Ca. Such alloys showed high strength at high temperatures. The ultimate tensile strength of as-extruded AC4b at 448K and 523K are 200MPa and 112MPa, respectively. The strain rate sensitivity exponent, m, estimated from the slope of the stress-strain curve, exhibits from 0.11 to 0.14, implying that climb-controlled dislocation creep could be a dominant deformation process of AC4a, AC4b and AC5. During the creep test, the creep properties of as-extruded AC5 is better than that of as-extruded AC4a and AC4b, the total elongation of as-extruded AC5 is 0.97% under 60MPa at 448K after 100h and the total elongation increased to 1.3% under 70MPa at 448K after 100h. The stress exponent (n) value of as-extruded AC5 is 6.67, which implies that the dislocation climb is the dominant creep mechanism in the creep test at 448K.