Rapid solid-state thermal diffusion fabrication of MgZn intermetallic layer for hardening surface and improving corrosion resistance of AZ31 alloy

Magnesium (Mg) alloy is an engineering material with tremendous application potential in fields such as transportation, aerospace, electronic instruments, and biomaterials. Nonetheless, the poor abrasion and corrosion resistance hinder the further application of Mg alloy in the field of industrial manufacturing. Solid-state thermal diffusion (SSTD) is regarded as an strategy for creating intermetallic thermal diffusion layers (TDLs) on the surface of Mg alloy, providing protection against wear and corrosion. However, traditional SSTD is a high-temperatures and time-consuming heat treatment process. During the process, Mg alloy may undergo grain coarsening and phase transformations, leading to a degradation in mechanical properties. Additionally, the long-term high-temperature heat treatment will inevitably increase energy consumption and production cost. The present study introduces a solid-state pressure-assisted thermal diffusion (SSPTD) process with the goal of efficiently fabricating MgZn intermetallic TDLs on the surface of AZ31 alloy at relatively lower temperatures. As a result, MgZn intermetallic TDLs with an outer diffusion layer (ODL) and an internal diffusion layer (IDL) were successfully fabricated on the AZ31 alloy at the average fabrication rate (AFR) of 0.6–3 × 103 μm/h. When the SSTPD treatment was conducted at 360 °C for 60 min under 10 MPa, the surface microhardness of the sample was increased by up to 3.6 times compared to that of the AZ31 alloy, and the corrosion current was reduced by about 74 %. However, the decline in the microhardness and corrosion resistance took place when the sample was subjected to the SSPTD treatment under the condition of higher temperature and pressure (e.g., 400 °C@30 MPa). The degradation in performance was primarily attributed to the increased formation of α-Mg phases and phase transition defects (e.g., cracks and shrinkage cavities) within the TDLs during the SSPTD treatment.