Improving corrosion resistance of additively manufactured WE43 magnesium alloy by high temperature oxidation for biodegradable applications

Laser powder bed fusion (L-PBF) has been employed to additively manufacture WE43 magnesium (Mg) alloy biodegradable implants, but WE43 L-PBF samples exhibit excessively rapid corrosion. In this work, dense WE43 L-PBF samples were built with the relativity density reaching 99.9%. High temperature oxidation was performed on the L-PBF samples in circulating air via various heating temperatures and holding durations. The oxidation and diffusion at the elevated temperature generated a gradient structure composed of an oxide layer at the surface, a transition layer in the middle and the matrix. The oxide layer consisted of rare earth (RE) oxides, and became dense and thick with increasing the holding duration. The matrix was composed of α-Mg, RE oxides and Mg24RE5 precipitates. The precipitates almost disappeared in the transition layer. Enhanced passivation effect was observed in the samples treated by a suitable high temperature oxidation. The original L-PBF samples lost 40% weight after 3-day immersion in Hank's solution, and broke into fragments after 7-day immersion. The casted and solution treated samples lost roughly half of the weight after 28-day immersion. The high temperature oxidation samples, which were heated at 525 °C for 8 h, kept the structural integrity, and lost only 6.88% weight after 28-day immersion. The substantially improved corrosion resistance was contributed to the gradient structure at the surface. On one hand, the outmost dense layer of RE oxides isolated the corrosive medium; on the other hand, the transition layer considerably inhibited the corrosion owing to the lack of precipitates. Overall, high temperature oxidation provides an efficient, economic and safe approach to inhibit the corrosion of WE43 L-PBF samples, and has promising prospects for future clinical applications.