Effects of deposition time on surface properties of Co-Ni-Fe alloy synthesised on hex bolts

Abstract

Electrodeposition is one of the methods used to perform a protective coating. It is commonly used in the industry because it capable to produce coating with good properties. The objective of this study is to perform the electrodeposition process of cobalt-nickel-iron (Co-Ni-Fe) alloy coatings onto the mild steel hex bolt (M12 x 50). This study also investigated the effect of deposition time on thickness, hardness, surface roughness and the corrosion rate of the electrodeposited Co-Ni-Fe alloy coating. The electrodeposition was performed on the substrate with four different deposition times: 15, 30, 60 and 120 minutes. The working temperature of the sulphate solution was 60ºC and the current supplied was 1.5 A. All the samples undergone surface properties analysis. For the corrosion rate, it was conducted using the potentiodynamic polarization (PDP) test. There were three types of solution used for PDP; hydrochloric acid (HCL), distilled water and sodium hydroxide (NaOH) with pH 3, pH 7 and pH 9 respectively. Scanning electron microscope (SEM) image showed the thinnest coating was 4.74 µm for deposition time of 15 minutes and the thickest coating with 102.77 µm. The coating hardness decreased as deposition time increased and the lowest hardness obtained was 349.6 HV at 120 minutes deposition time. The surface roughness decreased until 60 minutes of deposition time (1.0279 µm) and started to increase at 120 minutes of deposition time (4.0655 µm). The sample with 60 minutes of deposition time had the lowest corrosion rate in all solution; pH 3 = 0.1311 mmpy, pH 7 = 0.0393 mmpy and pH 9 = 0.0512 mmpy. Therefore, it is proven that deposition time is an important plating parameters that determine the surface properties and subsequently the corrosion resistance of electrodeposited Co-Ni-Fe alloy.