Evaluating the performance of sputter-deposited Aluminium alloy-based coatings on steel in the light of grain orientation, surface roughness, and corrosion behaviour

Abstract

ABSTRACT Magnetron sputtering has been one of the significant processes for developing defect-free uniform coatings for a wide range of materials. Increasing Magnesium (Mg) content in Aluminium (Al)–Mg sputtered coats has been strongly linked to a heightened sacrificial nature. This has directed researchers towards investigating different combinations or compositions of Al-based coats. Sputtered Al coats having minute proportions of Zinc (Zn) and Mg could be promising in terms of offering a corrosion-resistant coating on steel substrates. This has prompted a detailed analysis of three different coatings deposited on 4130 grade IF steel substrates using pure Al, Al–Mg and Al–Zn–Mg as targets by magnetron sputtering. For a fixed deposition time of 10 h, thickness of the coatings were in the order: Al–Zn–Mg > Al > Al–Mg. The coatings were investigated in terms of the microstructure, corrosion behaviour, surface roughness and coating adhesiveness. XRD was conducted to study the evolution of phases with increasing coating thickness. Al–Zn–Mg coating was found to be the most durable one, in terms of corrosion resistance, through EIS and SST and role of surface roughness was identified as a critical controlling factor, which was outweighed by the coating compositions. Although this ternary coating exhibited unsatisfactory performance during bend test, it has been hypothesized that tailoring texture coefficients could be a promising way to attain an optimum combination of oxidation resistance and adhesion.