Improved corrosion resistance achieved in a friction stir processed Mg-5Zn-0.3Ca alloy with fragmented precipitates

The microstructure of an as-cast Mg-5Zn-0.3Ca alloy was significantly modified by friction stir processing, which improved the alloy's corrosion resistance. In electrochemical results, the corrosion current density of the FSPed sample at the open circuit potential in 3.5 wt% NaCl aqueous solution decreased to 4.3 μA/cm2 (about 1/7 that of the as-cast sample). The improved corrosion resistance was attributed to the weakening of galvanic corrosion caused by precipitate fragmentation. In addition, a large number of fine cathodic precipitates tended to accumulate on the corroded surface, thereby forming a denser deposition layer and enhancing the shielding effect against corrosion propagation.