Effect of Heat Treatment on Corrosion and Electrochemical Behaviors of Mg-3Nd-0.2Zn (wt.%) Magnesium Alloy

Corrosion behavior of Mg-3Nd-0.2Zn (NZ) alloy was investigated in as-cast (F), solution-treatment (T4) and peak-aged (T6) conditions in 5% NaCl solution by immersion test and electrochemical measurement. It was found that NZ alloy exhibits better corrosion resistance in T4 temper than it does in the other two conditions due to the less microgalvanic corrosion between second phase and matrix in T4 condition. Both the corrosion resistance of NZ-T4 and that of NZ-T6 are higher than that of commercial AZ91D ingot. It is discovered by FE-SEM that the corrosion product of NZ-T6 after immersion test is uniform and compact, which is composed of fine needle-like compounds and small particles. The result of XRD indicates that the corrosion products are mainly Mg(OH)2 with a few of MgC12 coexisted. Both the solution treatment and aging can decrease the cathodic current density and increase the charge transfer resistance of NZ alloy.