Co-deformation Between the Metallic Matrix and Intermetallic Phases in a Creep-Resistant Mg-3.68Al-3.8Ca Alloy

TL;DR

This study investigates the deformation behavior of a Mg-Al-Ca alloy, revealing slip transfer mechanisms between phases and providing insights for designing creep-resistant magnesium alloys.

Contribution

It introduces a detailed analysis of co-deformation between the Mg matrix and intermetallic phases using nano- and microindentation, highlighting slip transfer pathways and temperature effects.

Findings

Hardness of Mg2Ca phase is higher than Mg matrix.

Slip transfer occurs via basal planes from Mg to Laves phase.

Deformation zones depend on matrix orientation and phase presence.

Abstract

The microstructure of Mg-Al-Ca alloys consists of a hard intra- and intergranular eutectic Laves phase network embedded in a soft $\alpha$-Mg matrix. For such heterogeneous microstructures, the mechanical response and co-deformation of both phases under external load are not yet fully understood. We therefore used nano- and microindentation in combination with electron microscopy to study the deformation behaviour of an Mg-3.68Al-3.8Ca alloy. We found that the hardness of the Mg$_2$Ca phase was significantly larger than the $\alpha$-Mg phase and stays constant within the measured temperature range. The strain rate sensitivity of the softer $\alpha$-Mg phase and of the interfaces increased while activation volume decreased with temperature. The creep deformation of the Mg$_2$Ca Laves phase was significantly lower than the $\alpha$-Mg phase at 170 $^{\circ}$C. Moreover, the deformation zone around and below microindents depends on the matrix orientation and is influenced by the presence of Laves phases. Most importantly, slip transfer from the $\alpha$-Mg phase to the (Mg,Al)$_2$Ca Laves phase occurred, carried by the basal planes. Based on the observed orientation relationship and active slip systems, a slip transfer mechanism from the soft $\alpha$-Mg phase to the hard Laves phase is proposed. Further, we present implications for future alloy design strategies.