In-situ microscopy for studying the cathodic poisoning effect in Mg alloys produced by HEBM

Mg has attracted many researchers due to its unique characteristics of low density and high strength to weight ratio. However, the poor corrosion resistance of Mg in an aqueous electrolyte has limited its potential in many structural applications. The problem of the immediate reaction of Mg with water leading to an increased rate of hydrogen evolution (HE) with immersion time, is well known. The addition of cathodic poisoning elements decreases the HE either by decreasing the water-dissociation reaction or minimizing the hydrogen recombination reaction. In previous studies, the effect of Ge addition has been shown with the help of potentiostat based tests. A visual investigation during the immersion could help reveal specific regions that are affected by decreased HE. This could supplement in unraveling the associated corrosion minimization mechanism. The present work tests the influence of Ge addition to Mg-10Al alloy by high energy ball milling (HEBM). The work aims at studying the decrease in corrosion rate due to Ge addition and the decrease in HE. For these studies, immersion tests were performed in 0.01 M NaCl solution for Mg-based HEBM alloy prepared by Al and Ge binary additions and Mg-10Al-xGe (x=2,5) ternary alloy. Alloy samples were studied using in-situ optical microscopy, surface profilometry and scanning electron microscopy (SEM). Among binary systems, it is evident that Mg-5Ge showed much lower HE than Mg-10Al alloy. The ternary alloy showed lesser HE than the Mg and Mg-10Al alloy. The corrosion behavior will be compared qualitatively using optical and SEM results. Additionally, surface roughness and average depth will be used for quantitative comparison of the corrosion response for mentioned alloys. This study shows a real-time corrosion behavior comparison of alloys in terms of HE problem and also contributes to corrosion studies of Mg-Al-Ge based alloys.