Recast Layer Formation during Wire Electrical Discharge Machining of Titanium (Ti-Al6-V4) Alloy

Titanium alloys, in particularly Ti-6Al-4V alloy is used enormously in many high-tech sectors specially in aerospace industries due to its superior properties. Machining process (for example wire electrical discharge machining) to reshape this alloy affects the integrity of the newly generated surfaces. This experimental study has identified three affected layers using scanning electron microscopy on the cross section of the machined titanium (Ti-6Al-4V) alloy surface generated from wire electrical discharge machining (WEDM). This study also explained the formation mechanism of those three layers as no detail investigation is available in this area so far. It was found that the top flaky layers are formed due to the highest cooling rate at the outermost surface, which is induced due to the low thermal conductivity of the titanium alloy as well as the quenching effect because of the existence of dielectric. The recast layer is formed at a cooling rate lower than that at the outer surface, where the melted material is resolidified very quickly without having any grain boundaries. The heat-affected zone appears at a slightly different color, which does not melt but experience heat treatment during the machining process.