Surface and subsurface characteristics of wire-electrical discharge machined Al-alloy and composite: a fundamental study on the role of machining variables

For hard-to-machine materials like discontinuous particulate reinforced Al-matrix composites, wire-electrical discharge machining (wire-EDM) is increasingly preferred for manufacturing intricately shaped parts with high dimensional accuracies and surface finishes. The wire-EDM process involves a large number of machining variables apart from parameters associated with the workpiece, dielectric, and electrode; therefore, research on wire-EDM is often performed on the basis of the design of experiments, which is somewhat limited the fundamental understanding of the role of various influencing variables. The current experimental research reports the influences of major wire-EDM machining variables on the surface and subsurface characteristics of 20 vol% in-situ Al3Fe reinforced Al–2Mg alloy in reference to the unreinforced matrix alloy. The cutting velocity (CV), kerf width (KW), surface roughness (SR), and surface chemistry (SC, = ΣO + Zn + Cu) of the composite and base alloy have been determined over a wide range of peak current (IP, 70–150 A), pulse-on time (TON, 5–25 μs), pulse-off time (TOFF, 51–63 μs), servo voltage (SV, 40–80 V), wire feed rate (WFR, 6–10 m min^{− 1}) and wire tension (WT, 4–12 N), varying one parameter at a time and keeping all others constant at their mid-levels. The surface and subsurface of the wire-EDMed composite and alloy specimens have been extensively characterized employing FESEM coupled with EDS microanalyses, including the change in surface chemistry due to the in-situ oxidation and transfer of elements from the brass wire electrode, while a noncontact optical profilometer has been employed to determine the surface roughness. The CV, KW, and SR are found to increase monotonically with increasing IP and TON but decreasing TOFF, while the reverse trend has been observed for SC; these influences are more pronounced for base alloy over composite except for SR. Higher SV diminishes CV and markedly raises SC; in contrast, enhanced WT decreases only KW, and greater WFR increases SC only. Variations in the mechanisms of material removal and, subsequently, the alterations in the surface and subsurface of machined alloy and composite have been proposed.