Corrosion performance of laser-remelted Al–Si coating on magnesium alloy AZ91D

Laser remelting was applied to plasma-sprayed Al–Si coating on magnesium alloy AZ91D to improve corrosion performance. Both salt spray testing and potentiodynamic polarization measurement in 3.5% NaCl solution indicated that laser-remelted Al–Si coating acquired better corrosion resistance than AZ91D and plasma-sprayed Al–Si coating. The decreasing order of the corrosion rates are AZ91D base metal, sprayed Al–Si coating and laser-remelted Al–Si coating. The fine Al–Si eutectic matrix in the laser-remelted microstructure contributed to the improved corrosion performance relative to the AZ91D and the plasma-sprayed coating. The predominant corrosion mechanisms in AZ91D, plasma-sprayed coating and laser-remelted coating are intra-granular corrosion, crevice corrosion and the combined pitting and galvanic corrosion, respectively.

Research highlights
► Laser-remelting changes microstructure of Al–Si plasma-sprayed coating on AZ91D
► Laser-remelted Al–Si coating manifests better corrosion resistance
► Pitting and galvanic corrosion occur at α-Al dendrites of laser-remelted coating
► Refined Al–Si eutectic matrix contributes to the better corrosion resistance