Effect of stand-off distance on the microstructural, mechanical and physical properties of al-zn pseudo-alloy coating prepared via wire arc spray process

Abstract

Protective coating has been one of the most effective corrosion mitigation methods. Therefore, it has been utilized to protect steel substrates for decades. Among various coating techniques, the twin wire arc spray (TWAS) process has been widely adopted in surface engineering to protect components due to its cost efficiency and flexibility. It promotes superior coating quality: low porosity, high hardness, and high adhesion. However, it is crucial to set the proper coating process parameters as coating properties produced via TWAS usually have high roughness and low adhesion to substrates. In this study, two different wires feedstock of Al and Zn were used to produce a pseudo-alloy of Al-50Zn alloy coating on mild steel substrates. In this research, the stand-off distance (SOD) parameter was varied at 100, 150, 200, 250, and 300 mm. The effect on the properties of developed coating layer on microstructure, thickness, hardness, roughness, and adhesion was investigated. The microstructure and morphological analyses were conducted using SEM and the phase analysis using XRD. Results have shown that the samples prepared at 100 mm have demonstrated the best coating quality compared to others and there are pronounced correlations between process parameters and all coating properties. The average thickness of the coating at 100 mm SOD was recorded to be the lowest at 230 μm with the highest hardness and adhesion values, 109 Hv and 8.3 MPa, respectively and the lowest surface roughness of 5.1 microns. Contrasts with coating prepared at 300 mm SOD that has demonstrated poor qualities in both microstructural and mechanical properties.