Effect of microstructure evolution on corrosion of different crystal surfaces of AZ31 Mg alloy in a chloride containing solution

The crystallographic basal plane dominated rolling surface (RS) of AZ31 Mg alloy has higher corrosion resistance in a chloride containing solution than its prismatic plane dominated cross-section surface (CS). The microstructures of these two surfaces with different crystallographic orientations evolve at 450 °C, resulting in larger grains, less twins, and more Al8Mn5 particles. Among these changes, the precipitated Al8Mn5 intermetallic phase during heat-treatment is responsible for the reduced corrosion resistance of the RS and CS surfaces. The electrochemical galvanic effect of the intermetallic particles suppresses the influence of crystallographic orientation and leads to a diminished difference in corrosion behavior between the RS and CS surfaces.

► We measure different corrosion rates of AZ31 rolling and cross-section surfaces. ► We measure increased corrosion rates of AZ31 after heat-treatment. ► The corrosion rate difference of these two surfaces decreases after heat-treatment. ► Grain orientations are responsible for different corrosion behavior of the surfaces. ► The growth of intermetallic particles deteriorates the corrosion performance.