SURFACE ANALYSIS OF CHEMICAL CONVERSION AND NICKEL CHROME COATINGS ON ASTM-A516 GRADE-70

Abstract

In this experimental based research study, Chemical conversion coating, Chromium (Cr) and Nickel (Ni) electroplating techniques are being used to deposit anti-corrosion protective layers on ASTM-A516 Grade 17 Steel, which is used in construction and manufacturing industries most commonly in fabrication of large storage tanks. During the process of chemical conversion coating which is also known as passivation, Sodium hydroxide (NaOH) and Sodium nitrate (NaNO3) solution is used as source material to prepare hot alkaline oxide bath solution. After this process outermost surface of sample is converted into magnetite (Fe3O4). This magnetite layer prevents substrate surface from any corrosive attack. ASTM-A516 Grade 17 Steel is electroplated with Ni and Cr in which substrate is taken as cathode and metal to be coated are taken as anode. Chromium tri-oxide and Nickel sulfate are used to prepare electrolytic bath solution for Cr and Ni electroplating respectively. After depositing the coatings, Salt spray test is performed on coated and uncoated samples for weight loss analysis, to evaluate corrosion trends of coated and uncoated samples. The salt spray test serves as a benchmark for comparative analysis of various samples. In this test, samples are placed in a controlled environment with specific temperature and humidity levels and exposed to an atomized 5% NaCl solution. This atmosphere is highly corrosive, leading to surface damage and accelerating the corrosion process. The results exhibit minimum weight loss in dual coated (Ni-Cr) samples which indicates high resistance against corrosion. Coated samples micro structure and surface morphology are studied to further validate result and deduce conclusion. This is done through X-ray diffraction (XRD), Scanning electron microscope (SEM) along with energy dispersive spectrometer (EDS) respectively.