Stress corrosion cracking susceptibility of ultrafine grained AZ31

Abstract

In this study, stress corrosion cracking (SCC) behavior of AZ31 magnesium alloy was carried out using slow strain rate testing (SSRT) technique in 3.5 wt% NaCl solution. The influence of microstructural scale on the stress corrosion behavior was investigated in AZ31 alloy with three different mean grain sizes. Single-pass and two-pass friction stir processing (FSP) was employed to obtain fine grain and ultrafine grain microstructures, respectively. For FSP, SSRT specimens were extracted from the processed region. SSRTs were carried out in air and solution at an initial strain rate of 10 -6 /s. A significant decrease in the ultimate tensile strength was observed for FSP specimens tested in chloride solution as compared to specimens tested in air. More than 75 % loss in total elongation was observed for the specimens tested in chloride solution as compared to the ones tested in air. In comparison with base material, lower time to failure was observed for processed samples. The higher SCC susceptibility of processed microstructure is attributed to increased hydrogen adsorption and favorable basal texture.

Corrosion of Ultrafine Grained Materials by Severe Plastic Deformation, an Overview

“…Most of UFG materials in the list are pressed by ECAP, HPT, ARB as the core of SPD technology, but the recent emerging SPD for surface modi cation such as surface mechanical attrition treatment (SMAT), 21,[72][73][74] cryorolling, 75,76) high-power shotblast, [77][78][79][80][81] burnishing, [82][83][84] friction stir processing (FSP) 85,86) are included. However, nanocrystalline metals, which are fabricated by the so-called bottom-up approaches such as magnetron and DC spattering, powder consolidation by high-energy ball milling are excluded in this Better=Corrosion resistance increases with grain size reduction, Worse=Vise versa.…”

Stress Corrosion Cracking Behavior of Fine-Grained AZ61 Magnesium Alloys Processed by Equal-Channel Angular Pressing

“…Besides, grain boundaries, as a kind of crystal defect, stored high energy as well and exhibited unfavourable impact on corrosion resistance to some extent. Diffusion of hydrogen prone to grain boundaries and diffusivity will be accelerated with the increased proportion of grain boundaries per volume of refined microstructure [9].…”

“…However, a conclusion about the effect of grain refinement on SCC has not yet been reached in the limited literature. Argade et al [9] reported that ultrafine grained AZ31 processed by friction stir processing, one of the SPD methods, exhibited higher susceptibility to SCC because of the enhanced hydrogen diffusivity. Lopez et al [10] claimed that an austenitic stainless steel containing 0.97 wt % nitrogen achieved higher resistance to SCC through grain refinement compared to the as-received steel in 30% NaCl solution at 90 • C.…”

Finite Element Based Physical Chemical Modeling of Corrosion in Magnesium Alloys

“…Argade et al [8] studied the mechanism of AZ31 Mg alloy under slow strain rate testing technique. They found that the corrosion of AZ31 is predominantly influenced by its microstructure which results in a favorable texture for increased adsorption of hydrogen.…”