Effect of grain size and residual stress on the corrosion resistance of friction stir spot welded AZ31B joints

Abstract

Localized corrosion at the weld periphery of AZ31B friction stir spot welds has been associated with the formation of a galvanic cell between the stir zone material and the adjacent base metal. However, this explanation did not take into account the effects of residual stress and grain growth in material adjacent to the stir zone region. In this study, the influence of microstructural changes on the electrochemical characteristics of FSSW joints is investigated using a combination of microcapillary polarization, stress relief heat‐treatment and micro‐hardness testing. It is confirmed that residual stress has no significant effect on the corrosion resistance properties of completed joints. Also, based on a detailed examination of the electrochemical characteristics of materials in the stir zone, TMAZ and HAZ regions, grain growth had negligible influence on the corrosion resistance properties.

Evaluation of corrosion resistance of multipass friction stir processed AZ31 magnesium alloy

“…Owing to the effect of microgalvanic corrosion, pitting corrosion occurred in the corrosion surface. Similar results can be found in many previous studies regarding the corrosion behavior of Mg–Al–Zn alloys …”

“…According to previous studies, the effect of grain boundaries on the corrosion resistance of Mg alloys is highly dependant on the residual stress in the testing samples. Some studies suggested that the corrosion resistance of Mg alloys would be reduced if large residual stresses remain after grain refinement .…”

“…Although previous studies consistently reported that the decrease in grain size is beneficial to the corrosion resistance of Mg alloys, residual stress and dislocation density are detrimental to the corrosion resistance . Some studies found that, if large residual stresses or high dislocation densities remain after grain refinement, the corrosion resistance of Mg alloys would be reduced, even if the grain size has decreased . As is known, grain refinement by thermomechanical processing may result in high residual stresses.…”

“…The limitation of low corrosion resistance significantly restricts the application of Mg alloys. Moreover, many factors have an impact on the corrosion resistance of Mg alloys, including precipitate particles, grain boundaries, dislocation density, and residual stresses . Although previous studies consistently reported that the decrease in grain size is beneficial to the corrosion resistance of Mg alloys, residual stress and dislocation density are detrimental to the corrosion resistance .…”

The Influence and Mechanism of Residual Stress on the Corrosion Behavior of Welded Structures

“…Numerous studies have indicated that residual tensile stress can not only increase the susceptibility of welded structures to corrosion cracking and the growth rate of corrosion cracks, but can also decrease their corrosion resistance [12][13][14][15] . Compared with studies of residual tensile stress, reports on the influence of residual compressive stress on the welded structures' corrosion behavior are few.…”