Tempering effect on corrosion performance of magnesium alloys for biomedical applications

The corrosion resistances for magnesium alloys AZ80, AE82 and ZM21 treated at 200 and 330°C for 2 hours, and for AZ80 and AE82 at 415°C for 8 hours were investigated using potentiodynamic polarization measurements in simulated body fluid (SBF) solution at 37°C. The morphology and the Volta potential of intermetallic precipitates in AE82 were analyzed by SEM-EDS combined with SKPFM. The heat treatments have little effect on the corrosion of ZM21 alloy, but significantly improve the corrosion resistance of AE82 alloy in the SBF. The corrosion rate of AE82 decreased by about 10% after being treated at 200°C for 2 hours and decreased by 20% after being treated at 415°C for 8 hours. Intermetallics Al-Nd(Y), Al-Mn(Nd,Y), Mg-Al have been detected in the AE82 alloy. Most of Mn and Nd are distributed at aluminum enriched areas. Zn is scattered in the matrix. The potential of intermetallic precipitates Al-Nd(Y) is higher than that of the precipitates Al-Mn. Heat treatment until 415°C cannot melt intermetallic particles, but the : phase building up at grain boundaries provides a barrier against corrosion propagation into the adjacent grains.