Effect of holding time on microstructure and mechanical properties of Al-40 wt.%Si alloys fabricated by combination of gas atomization and spark plasma sintering

Hypereutectic Al-40 wt.% Si alloys were fabricated by the combination of gas atomization and spark plasma sintering (SPS) technology. The effects of holding time (15–60 min) on phase composition, microstructure, density, mechanical properties of Al-Si alloys were investigated by XRD, SEM, a hydrostatic balance, an automatic micro hardness tester and a universal tensile testing machine. The results showed that homogenous distribution of ultrafine primary Si and high density of alloys can be obtained at holding time of 30 min. Compared with primary Si (3.7 µm) fabricated by gas atomization, the average size increased from 5.17 to 7.72 µm with the increase of holding time during SPS process. Overall, the relative density, maximum tensile strength and Vickers hardness of 94.9%, 205 MPa and HV0.2 196.86 were achieved at holding time of 30 min, respectively. In addition, all the diffraction peaks were corresponded to α-Al or β-Si and no other phase can be detected. Finally, the densification process of SPS was also discussed.