Effects of cyclic closed-die forging on the microstructural evolution and mechanical properties of SiC/AZ91D nanocomposites

A two-step cyclic closed-die forging (CCDF), with the first step to enhance the formability and the second step to refine the matrix grain, was implemented on a solution-treated SiC/AZ91D nanocomposites. Results show that the initial coarse grain is refined from ∼105 μm to ∼27 μm after the implementation of CCDF at 400^∘C, and further refined to ∼6.8 μm after another 6-pass of CCDF at 300^∘C. Mg₁₇Al₁₂ precipitates are gradually crushed with the progress of CCDF and eventually evolve into small particles uniformly distributed within the matrix. SiC clusters are effectively dispersed into smaller clusters or single particle. Yield stress (YS) and ultimate tensile strength (UTS) of the SiC/AZ91D nanocomposites increase after 1 pass of CCDF at 300^∘C, while the elongation to fracture decreases. With the progress of CCDF, YS, UTS and elongation to fracture exhibit a continual increase, reaching their maximum values of 196 MPa, 371 MPa and 9.2% after 6 passes of CCDF.