Characterisation of Surface Coatings Produced by Plasma Electrolytic Oxidation on Locally Available Aluminium Alloys

This study characterises ceramic coatings produced by plasma electrolytic oxidation (PEO) on AA1100 and AA6061 aluminium alloy substrates to evaluate the potential for implementing PEO surface treatment in Nigerian light manufacturing and automotive component industries. PEO produces hard, wear-resistant alumina-based ceramic coatings directly on aluminium surfaces and is being increasingly adopted in the global automotive and aerospace sectors as an alternative to hard anodising. Coating specimens are produced in silicate-based and phosphate-based electrolyte systems at varied current densities (50, 100, and 150 mA/cm2) and treatment durations (10, 20, and 30 minutes). Coating morphology and composition are characterised by SEM-EDX, XRD, and cross-sectional TEM. Coating thickness, microhardness, porosity, and adhesion strength are measured by callipers, Vickers microhardness testing, image analysis, and scratch testing respectively. Tribological performance is evaluated by pin-on-disc wear testing against a steel ball counterface. Salt spray corrosion resistance is assessed per ASTM B117. Findings reveal that silicate-based PEO coatings at 150 mA/cm2 and 20 minutes treatment time produce the optimal combination of hardness (1,450 HV), wear resistance, and porosity on AA6061. Corrosion resistance is improved by three orders of magnitude relative to bare alloy. The study documents PEO process parameters transferable to Nigerian laboratory-scale implementation. Keywords: plasma electrolytic oxidation, aluminium alloy, surface coating, wear resistance, corrosion.