Mechanistic understanding of the corrosion behavior of Mg4Zn0.2Sn alloys: from the perspective view of microstructure

Abstract

The corrosion behavior of as-cast and extruded Mg4Zn0.2Sn (wt.%) alloys was comprehensively compared in 0.5 wt.% NaCl solution. Microstructure and surface chemistry related corrosion performance has been revealed. Zinc-supersaturated solid solution is formed around the intermetallics in the as-cast alloy, but zinc alternately segregates between the α-Mg matrix in the extruded alloy. According to Scanning Kelvin Probe Force Microscopy and immersion tests, micro-galvanic corrosion between the precipitates (intermetallics or impurity particles) or Zinc-rich area and the matrix resulted in severe localized corrosion in both conditions. However, alternation of microstructure induced by extrusion significantly enhanced the corrosion resistance of Mg4Zn0.2Sn alloy.