Preparation of Mg2Si/Al-Cu composite under a novel continuous squeeze casting-extrusion process assisted with ultrasonic treatment

In this study, in-situ 3 wt% Mg2Si/Al-Cu composites have been prepared by a novel continuous squeeze casting -extrusion (CSCE) process assisted with ultrasonic treatment (UT) for the first time. Different from the traditional semi-continuous hot extrusion process, the new method eliminates billet homogenization annealing and pre-heating. After UT + CSCE, the fine Al2Cu and eutectic Mg2Si phases in the UT + SC (squeeze casting) billet are further crushed to form a fibrous microstructure distributed along the extrusion direction (ED). Moreover, the alpha-Al grains are elongated along the extrusion direction, and the proportions of LAGBs (low-angle grain bound-aries) and HAGBs (high-angle grain boundaries) are 72.3% and 27.7%, respectively. Meanwhile, fiber textures with orientations < 111 >//ED and < 100 >//ED are formed, and the ratios of the two textures are 60.9% and 30.5%, respectively. After UT + CSCE, the ultimate tensile strength (UTS), yield strength (YS) and elongation of the in-situ 3 wt% Mg2Si/Al-Cu composite are 330 MPa, 250 MPa and 11%, and its YS and elongation are 23.2% and 69.2% higher than those of the UT + SC billet, respectively. Compared with the Al-Cu alloy prepared by UT + CSCE, its UTS and YS are increased by 11.9% and 38.9%, respectively.