Corrosion Performance and Surface Analyses of Laser Cladded Zn-Ni-Fe Coatings on ASTM A29 Steel.

Abstract

The corrosion behaviour of the laser coatings was investigated in 3.65 % sodium chloride solutions at 30°C via potentiodynamic polarization technique. The composition of Zn-50Ni-5Fe at parameters 900 W and 1.2 m/min exhibited enhanced electrochemical performance in 3.65wt.% NaCl solution. Microstructures with unique characteristics and refinement of grain size were observed. The fast solidification of the coating is accounted for this unique features. In terms of corrosion performance, results revealed that increasing the laser scanning speed was beneficial to the property, showing that the corrosion performance became better at higher scanning speeds. At the set laser intensity of 900 W and increased laser velocity, Zn-50Ni-5Fe coatings showed enhanced microstructure. The multiple tracks applied in the direct laser metal deposition (DLMD) process had resulting fields of residual stresses which attributed to the solid-state phase transformation that was a repeated process. The study validated the reliability of optimizing DMLD set parameters for metallurgical and mechanical considerations. These bring improvements in coatings which were laser cladded in terms of their corrosion performance and the dimensional accuracy, by optimizing the processing parameters. The only processing parameters which were varied was the laser intensity and the scanning speed, which were employed to numerically design the DLMD experiment. An empirical method was also developed and was used to validate the results achieved experimentally. The Grey relational model (GRM) used in this research described vividly the influence of optimized factors on the improved corrosion resistance and compared reasonably with the experimental results. In addition, the proposed model has the potential to provide induced corrosion rate predictions of coatings fabrication that are additively manufactured.