Microstructure and mechanical properties of Mg–Si alloys processed by cyclic closed-die forging

Mg–xSi (x=0, 1.5, 3.3) alloys were fabricated and subjected to cyclic closed-die forging (CCDF), a new severe plastic deformation process, at 450 °C for 1, 3, and 5 passes. With applying CCDF, tensile strength, elongation and hardness increase, while coarse Mg2Si particles break into smaller pieces and exhibit more uniform distribution. Mg–1.5%Si alloy exhibits a combination of improved strength and elongation after 5 passes of CCDF processing. The tensile strength is about 142 MPa and elongation is about 8%. The improvement in mechanical properties was further characterized by dry sliding wear testing. The results show that wear resistance improves with silicon content and CCDF process passes, particularly the first pass. The wear resistance increases by about 38% for Mg–3.3%Si after 5 passes of CCDF compared with pure Mg. The improvement of wear is related to microstructure refinement and homogenization based on the Archard equation and friction effect.