Corrosion Fatigue of Anodized AM50A Magnesium Die Castings

The increased use of magnesium die-castings in structural automotive components dictates the con-tinuing need for relevant and reliable data. There is virtually no literature relating to magnesium fatigue under corrosion environments. The purpose of the present study is to investigate the effect of an ‘Anomag’ coating on the fatigue and corrosion fatigue performance of magnesium alloys. The coating - ‘Anomag’, is produced by an anodising method and gives excellent corrosion resistance in chemical media. Standard Charpy test specimens of AM50A (50mm × 10mm × 10mm) with smooth surfaces were used for fatigue testing using the three point bending method. S-N curves were determined for uncoated (die cast surface), 5μm and 25μm thick coatings and 5μm and 25μm coatings with organic sealing. The environments adopted were natural seawater, tap water and air. Fatigue test specimens were characterised by X-ray radiography and SEM fractography before and after fatigue testing, respectively. It was found that the fatigue performance of AM50A in seawater was better than in tap water and deionized water environments. It was also showed that there were no negative effects of ‘Anomag’ anodising on corrosion fatigue performance.