Influence of Grain Refinement and Residual Stress on Corrosion Behavior of AZ31 Magnesium Alloy Processed by ECAP in RPMI-1640 Medium

Influence of grain refinement and residual stress on corrosion behaviour of AZ31 magnesium alloy processed by equal-channel angular pressing (ECAP) in vitro environment has been investigated. Microstructure of magnesium alloy has been obtained by ECAP process on the different temperature conditions. RPMI-1640 medium was adopted in the immersion test to investigate the effect of the carbonate buffer system and the organic compounds on the degradation behavior of AZ31 magnesium alloy. Additionally, the residual stress of ECAP processed (ECAPed) samples measurement by X-ray diffraction (XRD) was carried out. The results of XRD investigated that residual stress of the sample increases as the forming temperature decreases. The experimental results investigated that the organic compounds which are generated on the sample surface by corrosion reaction works as effective barrier to inhibit corrosion. Besides, the grain refinement and the crystal defects, which were induced by strain, promoted development and growth of pitting corrosion. However, the corrosion resistance of the ECAPed sample processed above the re-crystallization temperature was exceeded as-received sample. Furthermore, the corrosion resistance is expected to be improved by reducing defects via subsequent aging. This study is significant for applying the magnesium alloy in the biomedical implant material.