Improving mechanical properties of a cast Al–Mg alloy with high Mg content by rapid solidification

Abstract

Cast Al–Mg alloys with high Mg contents (>10 wt%) have received particular attention due to much lower density than those of other cast Al alloys. However, high amounts of coarse dendritic Al–Mg intermetallic phases substantially deteriorate both strength and ductility. This work aims to reduce amount and size of Al–Mg intermetallic phases by rapid solidification (RS) and to improve both strength and ductility in a cast Al-15 wt%Mg alloy. This paper reports a study on Al-15 wt%Mg alloy processed by a RS technique, namely twin-roll casting (TRC). The results of optical microscopy, electron backscatter diffraction and scanning electron microscopy analysis show refined Al grains and refined granular Al3Mg2 particles, and the results of X-ray diffraction analysis reveal the increased Mg solid solubility and correspondingly the decreased amount of Al3Mg2 phase, in the TRC Al-15 wt% alloy, as compared to the conventionally mold cast (CMC) counterpart. Consequently, the tensile testing results show 0.2% offset yield strength of 243 MPa and ultimate tensile strength of 355 MPa, accompanied by uniform elongation of 3.6%, in the TRC Al-15 wt% alloy, relative to premature fracture in the CMC counterpart. The microstructural features and the mechanisms underlying improved strength and ductility in the TRC Al-15 wt%Mg are analyzed and discussed.