Effect of discharge parameters on surface integrity and microstructure in electro discharge layering of Ni–Cr composite coating on AA2024 aluminium alloy
摘要
In the present research, an attempt was made to create a nickel–chromium (Ni–Cr) composite layer on AA2024 aluminum alloy using electrical discharge layering (EDL). The electrode was fabricated with a composition of Ni50:Cr50 under a compaction pressure of 400 MPa using the powder metallurgy method. During the EDL process, various parameters such as discharge current (I) − 3 A, 5 A, 7 A; pulse-on time (Ton) − 25 µs, 50 µs, 75 µs; and pulse-off time (Toff) − 4 µs, 6 µs, 8 µs, were regulated to improve the deposition rate (DR) and surface roughness (SR). The microstructure and elemental composition of the Ni–Cr coating were analyzed using a scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS), respectively. The results revealed that the DR increased with higher levels of I, Ton, and Toff. The highest DR of 0.435 g/min was achieved at 7 A, 75 µs, and 6 µs, while the lowest SR of 3.59 µm was recorded. SR increased with rising Ton and Toff values but decreased with increasing I. SEM analysis indicated the formation of larger craters at 7 A due to higher energy sparking. At a Ton of 25 µs, shallow craters were observed, whereas, at 75 µs, globular structures were formed, attributed to enhanced energy absorption. EDS analysis confirmed the presence of elements from both the AA2024 alloy and the electrode. The percentages of electrode elements in the coating were 34.32% Ni and 28.64% Cr. This study concluded that the composite electrode and optimal parametric settings play a crucial role in enhancing DR and SR.