The relation between heat treatment and corrosion behavior of Mg-Gd-Y-Zr alloy

The corrosion behavior of Mg-7Gd-3Y-0.4Zr (GW73K) was investigated in as-cast (F), solution-treated (T4) and peak-aged (T6) conditions using immersion tests and electrochemical measurements in NaCl solution (5 wt.%). Microstructure analyses were carried out on GW73K after different heat treatments by optical microscope (OM), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM) and X-ray diffraction. It is found that GW73K alloy exhibits higher corrosion resistance in T4 than in F and T6 conditions due to the fully dissolution of cathodic coarse (Gd + Y) rich eutectic compound. The corrosion products of GW73K have different morphologies for F, T4 and T6 conditions. The product for F is less uniform and compact than T4 and T6, and it has been founded that GW73K-T6 had two different morphologies owing to the presence of β'. The results of polarization curves also confirm that proper heat treatment is beneficial to improve the corrosion resistance of GW73K alloy by transforming the microstructures.