Studies on adhesion strength and corrosion behavior of ZnO-Mg coated on AISI 4140

The electrolytic ZnO based alloy coating with admixed interfacial blend of Mg have been successfully coated on medium carbon steel (AISI 4140) substrate by spray coating technique over a range of applied current density and dwell time. The structural and morphological properties of the coated samples are characterized using Optical Microscope (OM), Scanning Electron Microscope (SEM), X-ray Diffraction Analysis (XRD) and Energy Dispersive Spectroscopy (EDS) analysis. The adhesion test was carried out using scratch testing. The corrosion behavior is evaluated in a chloride environment (NaCl) by Tafel exploration as a function of coating thickness. The results revealed that the introduction of ZnO-Mg particles increases the adhesion strength of the AISI 4140. During scratching, cracks parallel with the scratch channel, external transverse cracks, adhesive spalling, and complete breaking of the coating within the scratch channel were observed. The acquired results exhibit that the introduction of ZnO - Mg coating improves corrosion resistance of AISI 4140 in NaCl solution. Equally, deposition thickness significantly affected the adhesion and corrosion properties. Increasing the coating thickness from 30 µm to 90 µm leads to decreasing the adhesion and corrosion properties.