Study on the surface integrity, mechanical and microstructure behaviour of Ni-Cr based coating fabricated through electro discharge coating on AA2024 aluminium alloy

Electro discharge coating (EDC) has attracted significant attention in recent years due to its ability to enhance surface properties, extend component lifespan, and improve performance under extreme environmental conditions. Although extensive research has focused on surface integrity, studies evaluating the mechanical properties of coated surface remains limited. In the present study, AA2024 aluminium alloy was coated using a powder metallurgy electrode composed of Ni80-Cr15-Gr5 via EDC. The effects of current ( I ), pulse-on time ( T on ), and pulse-off time ( T off ) on deposition rate (DR) and surface roughness (SR) were investigated using response surface methodology (RSM). Additionally, microhardness (MH) and adhesion strength (AS) of the coated surfaces were assessed. The results indicated that the DR increased with increasing I , T on , and T off , but decreased at higher levels of these parameters. A maximum DR of 0.354 g/min was achieved at 7A, 20 μs, and 6 μs, while the lowest SR of 4.28 μm was recorded at 3A, 15 μs, 4 μs. The coated surface exhibited a maximum MH of 896.45 HV and AS of 117 N, indicating superior mechanical performance. Scanning electron microscope (SEM) analysis revealed a uniform and well-adherent coating with a layer thickness (LT) of 129.4 μm, while Energy dispersive spectroscopy (EDS) confirmed the presence of Ni (15.8%), Cr (10.95%), and C (7.87%) on the coated surface, validating effective electrode material transfer. However, defect mechanisms such as microcracks, voids, craters, globules, and particle accumulation were observed at higher parameter levels, adversely affecting coating integrity. The findings suggest that the developed composite coating on AA2024 aluminium alloy is suitable for automobile and aerospace applications requiring enhanced wear resistance, hardness, and surface integrity.