Effect of grain size uniformity and crystallographic orientation on the corrosion behavior of Mg-2Zn-1Al bar

In this paper, the effect produced by grain size uniformity and crystallographic orientation on the corrosion behavior of the extruded Mg-2Zn-1Al bar was probed by means of techniques such as OM, SEM, XRD, quasi-situ EBSD (Electron Back Scattered Diffraction), and an electrochemical test. The results obtained revealed a high possibility of corrosion nucleation at the grain boundaries; furthermore, preferential corrosion was exhibited by the coarse grains in comparison to the fine grains. The microstructure composed of bimodal grain size retained a higher corrosion rate than the one with uniform grain size, which is attributable to the increased electrochemical heterogeneity in alloys on a micro-scale and the non-uniformity corrosion product film. Prism-oriented grains tend to corrode preferentially in contrast to the basal-oriented grains. The longitudinal sections of the bar entailing a mixture of both the prismatic and the basal oriented grains, expressed a larger corrosion rate than the transverse sections that only consist of the prismatic planes, which could be attributed to the micro-galvanic corrosion activity triggered by the presence of multiple crystallographic orientations. The grain size uniformity factor tends to produce a more profound effect on the corrosion behavior of the bar than its crystallographic orientation.

Automated summary

This study explored the influence of grain size uniformity and crystallographic orientation on the corrosion behavior of the extruded Mg-2Zn-1Al bar. Results indicated a higher likelihood of corrosion nucleation at grain boundaries and preferential corrosion of coarse grains over fine ones. Additionally, the presence of multiple crystallographic orientations led to greater micro-galvanic corrosion activity.