Static and dynamic corrosion fatigue of Mg alloys used in automotive industry

Corrosion fatigue tests were carried out on die-cast and extruded magnesium alloys AZ91D, AZ80, AM50, and ZK60 in air, and NaCl-based and borate solutions. N-sot/N-air ratios (the relative fatigue life) were used for analysis of the corrosion fatigue behavior of Mg alloys in various environments, where N-sol and N-air are the numbers of cycles to failure in the solution and in air, respectively. Extruded ZK60 alloy reveals very high fatigue and corrosion fatigue properties in comparison with other alloys. However, it has the lowest relative fatigue life (N-sol/N-air similar to 10(-3) - 10(-2)) or the highest sensitivity to the action of NaCl-based solutions in comparison with that of AM50 and AZ31 alloys (N-sol/N-air similar to 10(-2) - 10(-1)). Under the same stress, the corrosion fatigue life of extruded alloys is significantly longer than that of die-cast alloys (N-sol for extruded AM50 in NaCl is two to three times longer than that of die-cast AM50). The synergistic effect of corrosion and stress on viscoelasticity of magnesium alloys called corrosion creep is shown. The highest sensitivity to creep in a corrosive environment is observed in the alloy with the highest Al content.