Enhanced strength and ductility of high pressure die casting AZ91D Mg alloy by using cold source assistant friction stir processing

This study demonstrated that cold source assistant friction stir processing could remarkably improve the mechanical properties of high pressure die casting AZ91D Mg alloy, particularly in ductility. The obtained results showed that the friction stir processing associated with additional liquid nitrogen cooling caused the significant dissolution of the coarse β-Mg17Al12 phase into the α-Mg matrix and the remarkable grain refinement in the stir zone. The stir zone exhibited bimodal grain structure with relatively high dislocation density. Abundant (101¯2) twin boundaries were successfully introduced into the stir zone, resulting in superior strength-ductility synergy with an ultimate tensile strength of 323 MPa and a uniform elongation of 10.3%.