Corrosion behaviour of bulk ultra-fine grained AZ91D magnesium alloy fabricated by equal-channel angular pressing

Effect of microstructure change on corrosion behaviour of equal-channel angular pressed (ECAPed) AZ91D Mg alloy was investigated. The ECAPed alloy with ultra-fine grained (UFG) α-phase matrix and refined β-phase particles displays a significantly lower corrosion resistance, resulting in more pits after in-situ corrosion, higher mass-loss rate immersed in NaCl solution, larger Icorr values in polarization curves and lower fitted Rt values in EIS plots. Two factors weaken the corrosion resistance: the first is the strains-induced crystalline defects providing the α-phase matrix more corrosion activation, the second is the refined β-phase particles losing barrier to the corrosion propagation in α-phase matrix.

Research highlights
► ECAPed UFG AZ91D Mg alloys shows significant weakened corrosion resistance.
► The corrosion behaviours of the ECAPed samples changed into severe uniform corrosion gradually.
► Crystalline defects weakened the corrosion resistance of the α-phase matrix is the first factor.
► Refined β-phase particles losing corrosion barrier in α-phase matrix is the second factor.