Pitting corrosion behavior and corrosion protection performance of cold sprayed double layered noble barrier coating on magnesium-based alloy in chloride containing solutions

Nitrogen processed, cold sprayed commercially pure(CP)-Al coatings on Mg-based alloys mostly lack acceptable hardness, wear resistance and most importantly are highly susceptible to localized corrosion in chloride containing solutions. In this research, commercially pure α-Ti top coating having good pitting potential(~1293 mV_(SCE)), high microhardness(HV_(0.025): 263.03) and low wear rate was applied on a CP-Al coated Mg-based alloy using high pressure cold spray technology. Potentiodynamic polarization(PDP) curves indicated that the probability of transition from metastable pits to the stable pits for cold spayed(CS) Al coating is considerably higher compared to that with the CS Ti top coating(for Ti/Al/Mg system). In addition, CS Ti top coating was in the passivation region in most pH ranges even after 48 h immersion in 3.5 wt% NaCl solution. The stored energy in the CS Ti top coating(as a passive metal) was presumed to be responsible for the easy passivation. Immersion tests indicated no obvious pits formation on the intact CS Ti top coating surface and revealed effective corrosion protection performance of the CS double layered noble barrier coatings on Mg alloys in 3.5 wt% NaCl solution even after 264 h.