The corrosion fatigue resistance of an electrolytically-plated magnesium alloy

Magnesium alloys are known to be susceptible to corrosive environments, and a protective barrier coating of nickel, which is electrochemically much more noble than magnesium, offers the promise of reducing the effects of corrosion on mechanical properties such as resistance to cyclic loading. This paper describes the fatigue behavior of electrolytically nickel-plated AZ31–Mg alloy cyclically tested both in laboratory air and in a corrosive environment (3% NaCl). The fatigue lifetimes, the crack initiation and the propagation behaviors of both plated and unplated specimens were studied in order to determine the effect of a nickel coating. In air, the nickel plating was detrimental because of the easy nucleation of fatigue cracks at depressions in the coating which resulted from the plating process. However, in 3% NaCl, the fatigue properties of plated specimens were markedly superior to those of unplated specimens due to their good resistance to corrosion. Further improvement in the fatigue lives of Ni-plated specimens is expected if the plating process can be modified to eliminate the formation of defects such as surface depressions.