Enhanced microstructure homogeneity and mechanical properties of AZ31–Si composite by cyclic closed-die forging

For the as-cast in situ AZ31–xSi composites, the yield strength increases with increasing Si contents at room temperature at the cost of both elongation and ultimate tensile strength reduction. Cyclic closed-die forging (CCDF) was applied to severely deform the as-cast composites at 350, 400, and 450 °C for 1, 3, and 5 passes for the improvement of both strength and elongation. During processing both dendritic and Chinese script type Mg2Si are broken up into smaller particles due to the shear stress imposed by the matrix. With the increasing number of CCDF passes, a finer grain size and more uniform distribution of Mg2Si particles are obtained along with significant improvement in both strength and ductility. AZ31–2Si composite exhibits a tensile strength of 250 MPa and elongation of 10.5% after 5 CCDF passes at 400 °C as compared to initial 128 MPa and 5.4%. Further investigation indicates that the strength and ductility of the composite first increase and then decrease with the increase of processing temperature, which can be attributed to that most uniform distribution of grains and Mg2Si particles are achieved at 400 °C.

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► In situ AZ31–Si composite was refined by cyclic closed-die forging at 350–450 °C.
► Coarse dendritic and Chinese script type Mg2Si were broken into fine particles.
► Uniform distribution of Mg2Si particles was achieved after 5 passes at 400 °C.
► Simultaneous increase in both strength and ductility is observed after CCDF.
► AZ31 2Si composite exhibits a strength of 250 MPa and elongation of 10.5%.