Mechanical properties and corrosion behaviors of AZ31 alloy with dual-phase glass-crystal coating

A magnesium-based ‘supra-nanometre-sized dual-phase glass-crystal’ (SNDP-GC) coating had been fabricated on AZ31 alloy by magnetron sputtering. Surface mechanical attrition treatment (SMAT) was also introduced to form a gradient structure in order to reduce the hardness mismatch between Mg-based SNDP-GC coating and substrate. Microstructure, mechanical properties and corrosion behaviors of the as-received AZ31 (AR), AZ31 with Mg-based SNDP-GC coating (SC) and AZ31 after SMAT with Mg-based SNDP-GC coating (SSC) were investigated by optical microscope, scanning electron microscopy, transmission electron microscope, X-ray diffraction, Vickers hardness penetrator and electrochemical characterization. Results revealed the Mg-based SNDP-GC coating together with a gradient structure contributed to the improved microhardness. The decreased hardness mismatch between the coating and substrate prevented the delamination of the coating from the substrate. There is a decrease trend in Ecorr in sequence of AR, SC and SSC, while a rise in icorr in the same sequence. Corrosion uniformity was decreased in sequence of AR, SC and SSC, and corrosion cracks exhibited on corrosion products due to formation of galvanic cells and stress concentration. These results indicated the presence of gradient structure and Mg-based SNDP-GC coating led to better mechanical properties but worse corrosion resistance.