The effect of strain rate on mechanical properties and fracture mode of the AZ31 alloy and commercially pure magnesium pre-exposed in a corrosive medium

Abstract

Magnesium alloys are promising materials for aviation, automotive engineering, and medicine, however, due to the low resistance to stress corrosion cracking (SCC), their wide application is limited. To create alloys with high resistance to SCC, a comprehensive study of this phenomenon nature is required. Previously, it was suggested that diffusible hydrogen and corrosion products formed on the magnesium surface can play an important role in the SCC mechanism. However, the contribution of each of these factors to the SCC-induced embrittlement of magnesium and its alloys is understudied. Since the influence of diffusible hydrogen on the mechanical properties of metals increases with the strain rate decrease, the study of the strain rate sensitivity of the SCC-susceptibility of magnesium alloys is a critical task. In this work, the authors studied the effect of the strain rate in the range from 5•10−6 to 5•10−4 s−1 on the mechanical properties, the state of the side and fracture surfaces of the as-cast commercially pure magnesium and the AZ31 alloy before and after exposure to a corrosive environment and after removal of corrosion products. The study identified that the preliminary exposure to a corrosive medium leads to the AZ31 alloy embrittlement, but does not affect the mechanical properties and the fracture mode of pure magnesium. The authors found that the AZ31 alloy embrittlement caused by the preliminary exposure to a corrosive medium appears extensively only at the low strain rate and only if the layer of corrosion products is present on the specimens’ surface. The study shows that a change in the strain rate has little effect on the mechanical properties of pure magnesium. The authors concluded that the main cause of the AZ31 alloy embrittlement after soaking in a corrosive medium is the corrosion products layer, which presumably contains the embrittling agents such as hydrogen and residual corrosive medium.

Keywords

• magnesium alloys
• az31
• pure magnesium
• stress corrosion cracking
• corrosion
• strain rate
• mechanical properties