The effect of Zr on the microstructure and tensile properties of hot-extruded Al-Mg2Si composite

This work was carried out to investigate the effect of different amounts of Zr on the microstructure and tensile properties of homogenized and hot extruded Al-15% Mg2Si composite using optical microscopy and scanning electron microscopy (SEM). The results showed that Zr addition has no significant effect on the morphology of both primary and eutectic Mg2Si phase in as-cast condition. But, applying homogenizing and extrusion processes changed the morphology of Mg2Si phases from irregular to a more spherical shape. Further results demonstrated that the average size of primary Mg2Si decreases with the addition of Zr up to 0.1% from 56 mu m to 24 mu m in hot-extruded condition. As the mount of Zr increased up to 0.1 wt.%, ultimate tensile strength (UTS) and elongation values were also increased from 160 MPa and 3.2% to 292 MPa and 9.5%, respectively. Fracture surface examinations revealed a transition from brittle fracture mode in as-cast composite to ductile fracture in hot-extruded Zr-modified specimens. This can be attributed to the changes in size and morphology of Mg2Si intermetallic and porosity content. (C) 2011 Elsevier Ltd. All rights reserved.