Different role of second phase in the micro-galvanic corrosion of WE43 Mg alloy in NaCl and Na2SO4 solution

Effect of the second phase in the micro-galvanic corrosion of a commercial Mg alloy containing rare earth elements, cast WE43 alloy, was investigated in 0.6 M NaCl solution and 0.6 M Na2SO4 solution by scanning electron microscopy (SEM) observations, scanning Kelvin probe force microscopy (SKPFM) analysis, hydrogen evolution, weight loss measurement, and electrochemical techniques. It is confirmed that the second phase of cast WE43 alloy is more active than Mg matrix and exhibits an anodic role in the micro-galvanic corrosion with α-Mg matrix as cathode and dissolves preferentially in Na2SO4 solution, in contrast to the situation in NaCl solution. The corrosion rate of cast WE43 alloy in Na2SO4 solution is much higher than that in NaCl solution, which is different from the conventional wisdom and could be attributed to the different role of the second phase in the micro-galvanic corrosion in two solutions.