Effect of grain size and twins on corrosion behaviour of AZ31B magnesium alloy

Grain refining is a promising approach to improve mechanical properties of magnesium alloys, but how grain size and twins affect corrosion behaviour is not well understood. In this work, corrosion resistance of AZ31B alloy with different grain sizes is studied in 3.5% NaCl solution using immersion testing, evolved hydrogen gas measurement and potentiodynamic polarisation measurement. Intra-granular corrosion was predominant and the existence of twins further accelerated the corrosion. The effect of grain size was more pronounced in the corrosion of the untwinned microstructure. The corrosion rate significantly increased as the average grain size increased from 65 to 250 μm.