Surface characteristic and corrosion resistance of different plasma-sprayed coatings (Zn, Al6061and Zn/23Al) on S960 high strength steel with subsequent micro-shot peening

Abstract

The pure Zn, Al6061 alloy and Zn/23Al coatings were prepared on S960 high strength steel by plasma spraying method respectively, then these coatings were treated with subsequent micro-shot peening. The surface characteristics including surface morphology, micro-hardness, and residual stress were characterized, and the corrosion resistance of the coatings was evaluated by an electro-chemical test, salt spray test and immersion corrosion, respectively. The results showed that the coatings were densified and the surface micro-hardness was improved in the range of HV 20–30 after the micro-shot peening treatment. Taking Al6061 alloy coating as an example, after micro-shot peening, the surface residual stress changed from tensile stress (17 MPa) to compressive stress (−102 MPa). The corrosion testing results showed that the corrosion resistance of Zn coating could be improved by adding Al element and micro-shot peening in the polarization tests. According to EIS results, the impedance of Zn, and Al6061 alloy coatings were improved after micro-shot peening in 3.5 wt% NaCl solution, while the charge transfer resistance of Zn/23Al coating was decreased. In the neutral salt spray test and immersion test, the corrosion resistance of the three coatings was enhanced by micro-shot peening, and the shot-peened Zn/23Al coating illustrated the best corrosion resistance. The improved corrosion resistance of the Zn/23Al coatings can be ascribed to the densification of micro-shot peening and the addition of Al.