Effects of volume ratio on the microstructure and mechanical properties of particle reinforced magnesium matrix composite

•PDRs can be formed around M-SiCp.•Submicron SiCp is more conductive to grain refinement than micron SiCp.•Fraction of ΔσCTE, Δσload, ΔσHall–Petch, ΔσOrowan in Δσ0.2 depends on volume ratio.•The fracture characterization is affected by volume ratio.

In the present study, the AZ91 alloy reinforced by (submicron + micron) SiCp with four kind volume ratio was fabricated by the semisolid stirring casting technology. The influence of volume ratio between submicron and micron SiCp on the microstructure and mechanical properties of Mg matrix was investigated. Results show that the submicron SiCp is more conducive to grain refinement as compared with micron SiCp. With the increase of volume ratio, the submicron particle dense regions increase and the average grain size decreases. The yield strength of bimodal size SiCp/AZ91 composite is higher than monolithic micron SiCp/AZ91composite. Both ΔσHall–Petch and ΔσCTE increase as the volume ratio changes from 0:10, 0.5:9.5, 1:9 to 1.5:8.5. Among the composite with different volume ratio, the S-1.5 + 10-8.5 composite has the best mechanical properties. The interface debonding is found at the interface of micron SiCp-Mg. As the increase of volume ratio, the phenomenon of interface debonding weakens and the amount of dimples increases.