Enhanced corrosion resistance of AZ31 magnesium alloys through the use of high-purity raw magnesium

Poor corrosion resistance is a critical barrier to the widespread application of magnesium alloys. Statistically, the literature reported that approximately 70% of as-cast AZ31 magnesium alloys exhibit corrosion rates exceeding 1 mm·y⁻¹ in 3.5 wt.% NaCl solution, which is unacceptable for industrial use. Furthermore, there is a considerable discrepancy in the corrosion rates reported by different studies (as-cast alloys ranging from 0.4 to 215 mm·y⁻¹). These phenomena may be attributed to the uncontrollable content of impurity elements in commercial magnesium alloys, which fluctuate widely between batches. In the present work, we prepared as-cast AZ31 magnesium alloys with different impurity contents using two different purities of raw magnesium (Mg-99.9% and Mg-99.99%). The impact of impurity contents on the corrosion resistance of AZ31 magnesium alloys was then analyzed. The AZ31 magnesium alloy prepared with 99.99% raw magnesium showed superior corrosion resistance compared with that prepared with 99.9% raw magnesium, with a reduction in corrosion rate by approximately 98% and a decrease in the fluctuation range of corrosion rate by 91%. Thus, enhancing the purity of raw magnesium is an effective method to improve both the corrosion resistance and consistency of magnesium alloys.