Investigating Effect of ECAP Process on Corrosion Behavior of WE43 Magnesium Alloy in Simulated Body Fluid

Corrosion of WE43 magnesium alloys after equal-channel angular pressing (ECAP) process with one pass (1P), two pass (2P), three pass (3P) and four pass (4P) were investigated as a function of immersion time in 37 +/- 2 degrees C simulated body fluid (SBF) to imitate body corrosion environment utilizing AC electrochemical impedance spectroscopy (EIS), Potentiodynamic polarization (PDP) curves, SEM and optical microscopy techniques in addition to EDS analysis. Among the samples, 2P and 3P samples illustrated better corrosion resistance not only among all the samples but also as a function of elapsed immersion time in SBF media. Better corrosion resistance was related to precipitation of beta particles with fair and large volume fraction which served as cathodic reaction sites. Uniform distribution of the reactions not only reduce the severity of micro-galvanic corrosion but also by passing immersion time, anodic reaction dissolved magnesium substrate next to and around beta phase and separate them from the surface which resulted loss of cathodic sites and reduction of corrosion. Additionally, the morphology of the beta phase was changed from needle-like in 1P & 2P samples to spherical one in 3P & 4P samples. It is believed diminished corrosion resistance of 4P samples not only among the ECAPed samples but also as a function of immersion time, were related to coarsening of spherical beta phase. In another word, corrosion reactions amplified and continued while separation of the phase from the surface was delayed due to its larger size.