Co-Deformation of the Metallic Matrix and Intermetallic Phases in an Mg-3.68Al-3.8Ca Alloy

Abstract

Mg-Al-Ca alloys are well-known for their excellent creep resistance at elevated temperatures (≤ 200 °C). In the present study, the deformation behaviour of an Mg-3.68Al-3.8Ca alloy containing a network composed of an α-Mg phase matrix and an intragranular eutectic Laves phase network was studied within the temperature range of 20-170 °C using (instrumented) indentation at constant and variable strain rate including creep (relaxation) tests in combination with SEM, TEM and AFM. The geometry of the deformation zone around and below microindents was found to be orientation-dependent and influenced by the presence of Laves phases. The Laves phase was found to exhibit slip lines at intersections with slip lines and twins in the α-Mg phase. In addition to basal slip, non-basal slip was also observed in the α-Mg matrix (especially at α-Mg/Laves phase interfaces) along with basal slip in the Laves phase as confirmed by post-mortem TEM. The strain rate sensitivity, m, of the softer α-Mg phase and the interfaces was observed to increase with temperature. The nanoindentation creep tests showed that the creep properties of the Mg2Ca Laves phase are much better than those of the α-Mg phase. However, creep tests on interfaces indicated deformation by interfacial sliding and revealed creep properties similar to those of the α-Mg phase.