Effect of hot extrusion on microstructural evolution and tensile properties of Al-15%Mg2Si-xGd in-situ composites

This study investigates the effect of hot extrusion on microstructure and tensile properties of Al-15 wt % Mg2Si in-situ composite in unmodified and modified with (0.5-5.0 wt %) Gd addition. Furthermore, the morphology evolution of primary and eutectic Mg2Si particles in both unmodified and modified with 1.0 wt % Gd prepared by hot extrusion were examined in detail. The results showed that hot-extrusion process was efficient in transforming truncated octahedral primary and rod-like eutectic Mg2Si particles into near spherical and dot-like morphology, respectively in the modified alloy in which the particle fragmentation and thermal disintegration are the main mechanisms responsible for refinement/modification of primary and eutectic Mg2Si particles. It was suggested that the alteration of Mg2Si particles as well as fragmentation of Gd intermetallic compounds (IMCs) by hot extrusion played a significant role in strengthening the composite, i.e., the ultimate tensile strength (UTS) and elongation (%) values increased from similar to 224.62 MPa to 3.75% in the 1.0 wt % modified composite to similar to 245.83 MPa and 7.65% in the extruded modified one, respectively. In fact, a higher fracture stress can be established by fine near spherical primary Mg2Si particles through impeding dislocation motions and freeing stress concentrations. Furthermore, fragmentation of eutectic Mg2Si and Gd (IMCs) after extrusion lead to enhancement in ductility. This study demonstrated that combination of Gd addition and hot extrusion is a promising approach in modifying the microstructure and enhancing the tensile properties of in-situ Al-15%Mg2Si composite for industrial applications. (C) 2018 Elsevier B.V. All rights reserved.