Microstructure and mechanical properties of in-situ TiB2/AlSi7Mg composite via powder metallurgy and hot extrusion

In this work, in-situ TiB2/AlSi7Mg composites were successfully fabricated using TiB2 decorated AlSi7Mg alloy powder synthesized via salt-metal reaction and gas atomization, followed by powder metallurgy and hot extrusion. Microstructure and mechanical properties were investigated by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and tensile tests. The results show that the formation of fine grains and homogeneous subspherical silicon particles in as-extruded composites with high ductility (elongation of 21.7%) is achieved by perfect metallurgical bonding during severe plastic deformation. The covering effect of TiB2 aggregates around silicon particles as particle shells has hindered the dissolution of silicon in the composite. After T6 treatment, the ultimate strength, yield strength and elongation at fracture of the 2 wt% TiB2/AlSi7Mg composite reach up to 344 MPa, 298 MPa and 8.6%, respectively. The excellent mechanical properties are mainly attributed to grain refinement, silicon optimization and precipitation strengthening. This study provides a good solution for improving the strength and toughness of Al–Si alloy.