Effect of multi-pass friction stir processing on the microstructure evolution and corrosion behavior of ZrO2/AZ31 magnesium matrix composite

Most of magnesium matrix composites processed by traditional technique have poor anti-corrosion and biological performance, because of uneven microstructure, especially for nonuniform distribution of reinforced particles. Friction stir processing (FSP) can be used for preparing magnesium matrix composites with refine grains and uniform distribution of reinforced particles. In this paper, multi-pass FSP is employed to fabricate the ZrO2 particles reinforced AZ31 magnesium composites. The results showed that the microstructure of the composites become more homogeneous with the increase of FSP pass. The grain size is refined from 10 μm of basal metal (BM) to 8.2 μm of two-pass FSP (FSP-2P) and 4.5 μm of four-pass FSP (FSP-4P), respectively. The ultimate tensile strength, yield strength and elongation of BM is 283 MPa, 137 MPa and 15.5%. The mechanical properties are improved with the increase of FSP pass. The ultimate tensile strength, yield strength and elongation of FSP-4P is 328 MPa, 160 MPa, and 11.5%, respectively. Moreover, the corrosion resistance is arranged in the following order: FSP-2P < BM < FSP-4P. The cell activity of FSP-4P is higher than that of FSP-2P sample, which is similar to BM.