Super corrosion-resistance and self-passivity of a magnetron-sputtered Mg-Y-Al alloy

Abstract

The poor corrosion resistance, particularly the disastrous galvanic corrosion, poses a huge challenge to the application of magnesium (Mg) alloys in industry. To address such a critical issue, this study explored the possibility of fabricating a super corrosion-resistant and self-passive Mg alloy through magnetron-sputtering. The experimental results indicated that the crystallography and microstructure of the magnetron-sputtered ternary alloy Mg-Y-Al could be modified by Y and Al alloying. With the optimized composition around Mg₆₃Y₃₄Al₃, the alloy had a corrosion rate lower than 0.02 mm/year or 5 × 10⁻⁷ A/cm², nearly 1 order lower than those of all the reported Mg alloys. It also had undetectable hydrogen evolution and nearly 100% anodic efficiency. Its passive current density was around ∼2 × 10⁻⁶A/cm², very close to that of a typical stainless steel. This magnetron-sputtered corrosion-resistant self-passive Mg alloy could be deposited on a typical Mg alloy AZ91 as a coating to effectively inhibit the corrosion of the substrate in an artificial seawater. Even in the case that the coating was mechanically damaged, it exhibited a great self-healing behavior and continuously inhibited the corrosion in the damaged area, because a Y₂O₃-rich passive film could be rapidly formed on the surface. The new understanding of the super corrosion resistance and self-passivity of the Mg alloy may be utilized in the development of galvanic-corrosion-resistant Mg alloys, and the high anodic efficiency mechanism may even lay a foundation for the use of some innovative Mg alloys as an anode in battery and as a biodegradable implant in human body.