On the hydrogen state in magnesium alloys after corrosive effect

Abstract

: Low resistance to corrosion and stress corrosion cracking (SCC) hinders the widespread introduction of the magnesium alloys as the construction materials. Considered, that the SCC of the magnesium alloys may be related to the hydrogen fragility. Nevertheless, at the moment, the role of hydrogen in the SCC mechanism of magnesium alloys is not fully evident. In the previous papers, the authors identified that the role of diffusion-active hydrogen in the SCC process of magnesium alloys is highly doubtful: the results both of mechanical tests and gas analysis show that the concentration of diffusion-active hydrogen in tested materials is negligibly small; normally, hydrogen locates in the corrosion products. However, these studies have not identified the influence of external strains on the concentration and state of hydrogen, therefore, it is not clear if the results obtained are typical for SCC only or valid for the corrosion without external load. In this context, the authors set the goal to identify the concentration and the state of hydrogen in magnesium alloys after corrosive action without external strains. Samples of MA14 and MA2-1 alloys and pure magnesium were exposed in a corrosive medium, after which, each sample was divided into two parts: the corrosion products were removed from the first part and left untouched in the second part. Next, the authors studied the samples by gas analysis; and obtained extraction curves and hydrogen concentration values for each of them. The results of the study showed that the removal of corrosion products leads to a strong decline of hydrogen concentration, and at temperatures below 300 °C, it practically ceases. This indicates that most of the hydrogen is in the corrosion products and not in the diffusion-active form in the matrix metal, which is similar to the results obtained when studying the SCC.