Statistical modelling and analysis of tribological characteristics of electro-discharge deposited Ni-Cr coating on AA2024 using Box–Behnken approach

AA2024 aluminium alloys are widely used in automobile and aerospace applications due to its high-strength weight ratio; however, their low hardness and soft aluminium matrix result in poor wear performance. In this investigation, a Ni-Cr composite coating was deposited on the AA2024 surface using electro-discharge deposition (EDD) at discharge current of 8 A, pulse on-time of 75 μs, pulse off – time of 6 μs, voltage of 40 V, and negative polarity. The Ni80-Cr20 (wt.%) electrode was fabricated through the powder metallurgy route by compacting at 350 MPa and sintered at 900°C, exhibiting a density of 8.26 g·cm−³. The deposited coating exhibited a deposition rate of 14.62 mg/min, surface roughness of 3.42 µm, and layer thickness of 45–55 µm. Microhardness increased from 245 HV to 372 HV, representing an improvement of 52%. Box–Behnken design coupled with RSM was employed to develop mathematical models for wear rate (WR) and coefficient of friction (COF), yielding excellent coefficients of determination (R2) of 99.70% and 98.80%, respectively. Tribological evaluation revealed minimum WR and stable COF under 20 N, 500, and 1.570 m/s. SEM, EDS, and XRD analyses confirmed the development protective NiO and Cr2O3 tribo-oxide layer, which effectively inhibited adhesive and abrasive wear.