Reliability Evaluation of Fatigue Characteristics of Magnesium Alloy AZ31B under Corrosive Environment
Satoshi HANAKI, Hiroaki GOTO, Masato YAMASHITA and Hitoshi UCHIDA
Abstract:Magnesium (Mg) alloys have advantages in abundance of natural resources and in ability for recycling. On the other hand, Mg alloys have a disadvantage in poor corrosion resistance. In order to apply the Mg alloys to practical engineering parts, it is important to investigate the mechanical properties of Mg alloys under corrosive environments. In this study, the rotating bending fatigue test for ASTM-AZ31B specimens have been carried out under corrosive environments at room temperature. Silicone rubber was used for covering the circumference of the test specimen and NaCl solution was injected for corrosive environment. Additionally, air was poured into silicone cover to keep the amount of O2 in the solution. Because the fatigue tests resulted in scattered fatigue strength, the S-N curve was calculated by a statistical method. The fatigue strength in 3wt% NaCl solution was decreased in comparison with that in atmosphere and fatigue limit became unclear. Evolution of gas bubbles was dominantly observed during corrosion fatigue test. Measurements of anodic polarization curves showed the corrosion potential lays hydrogen evolution region. Therefore, it is considered that the mechanism of crack propagation has influenced by hydrogen and the decrease of fatigue strength is related to hydrogen embrittlement. The failure modes are classified into three groups from fractographical view point. That is the failure originated from single crack, from plural cracks and from corrosion pits. Among them, the coefficient of variance of fatigue strength distribution became larger in case of the failure originated from plural cracks and corrosion pit. Key Words:Magnesium alloy, Corrosion fatigue, S-N model, Fatigue strength distribution, Fractography