Microstructure and Corrosion Resistance of an HVAF-Sprayed Al-Based Amorphous Coating on Magnesium Alloys

An Al86Ni6Y4.5Co2La1.5 amorphous coating was prepared on a ZM5 magnesium alloys substrate by using high-velocity air fuel (HVAF) spray. The coating contained a 75.8% amorphous phase (volume fraction) in addition to the crystallization phases of α-Al, Al4NiY, and Al9Ni5Y3. The microhardness reached 420 HV0.05 for the coating. The coating could endure 500 h neutral salt spray tests without apparent corrosion. Moreover, the coating exhibited a much nobler corrosion potential and two orders of magnitude smaller corrosion current density compared to the substrate. These improvements can be attributed to the compact coating structure and the passive film formed during corrosion.