The effects of Bi modification and ultrasonic treatment (UST) on the microstructure and mechanical properties of AlMg5Si2Mn alloy were investigated. The results show that the eutectic Mg 2 Si phase is modified effectively through its morphology change from coarse plate-Chinese characters or mazelike thick lamellar for the base alloy to thin coralline fiber for the Bi-containing alloy. Meanwhile, the primary α-Al phase in the AlMg5Si2Mn alloy can be remarkably refined by UST and its morphology is changed from coarse dendrite to small near-spherical equiaxed crystals. Compared to unmodified alloy, the yield strength, ultimate tensile strength and elongation of the alloy modified by 0.3% Bi addition and UST at 660 °C are obviously enhanced by 17.26%, 24.38% and 89.66%, respectively, and the fracture modes are changed from brittleness to toughness. Furthermore, the mechanism and effects of Bi addition and UTS on the refinement and modification of the alloy were discussed.
