Microstructure and mechanical properties of AZ31-Mg2Si in situ composite fabricated by repetitive upsetting

AZ31-4.6% Mg2Si (mass fraction) composite was prepared by conventional casting method. Repetitive upsetting (RU) was applied to severely deforming the as-cast composite at 400 °C for 1, 3, and 5 passes. Finite element analysis of the material flow indicates that deformation concentrates in the bottom region of the sample after 1 pass, and much more uniform deformation is obtained after 5 passes. During multi-pass RU process, both dendritic and Chinese script type Mg2Si phases are broken up into smaller particles owing to the shear stress forced by the matrix. With the increasing number of RU passes, finer grain size and more homogeneous distribution of Mg2Si particles are obtained along with significant enhancement in both strength and ductility. AZ31-4.6% Mg2Si composite exhibits tensile strength of 284 MPa and elongation of 9.8% after 5 RU passes at 400 °C compared with the initial 128 MPa and 5.4% of original AZ31-4.6%Mg2Si composite.