Dual-phase titanium alloys, such as Ti-6Al-4V, are widely used in aerospace, biomedical, and marine applications owing to the desirable combination of their mechanical properties and relatively low density. However, the low thermal conductivity and high chemical reactivity of titanium alloys severely restrict the performance of conventional machining processes, particularly in achieving fine surface finishes and dimensional accuracy for geometrically complex components. Wire electrical discharge machining (WEDM), which leverages controlled electrical discharge erosion, overcomes the precision limitations of traditional methods through non-contact material removal. However, improper selection of electrical parameters will not only increase the thickness of the recast layer and heat-affected zone with mechanical property mismatches relative to the bulk material, but also deteriorate kerf flatness and reduce machining efficiency. The work aims to investigate the effect of WEDM parameters on the surface quality and machining efficiency of Ti-6Al-4V alloy, and elucidate the mechanical properties of machined surfaces under optimized conditions. To achieve systematic evaluation, an orthogonal experimental design was implemented with four controlled factors of pulse width, discharge gap, power amplifier tube number, and wire speed. Three performance metrics including kerf flatness, recast layer thickness, and machining time were selected as evaluation criteria. Range analysis was conducted to determine the hierarchical significance of parameter effects. Optimized parameter combinations were identified based on orthogonal experimental results. Nanoindentation tests were performed on samples processed with optimized parameters to evaluate the hardness gradients across the recast layer, heat-affected zone, and bulk material, with testing positions strictly confined to identical α/β lamellar colonies to eliminate crystallographic anisotropy effects. The results demonstrated that pulse width and tube number had a more significant effect on the machining indices of Ti-6Al-4V alloy than discharge gap and wire speed. Although a trade-off relationship between surface quality and machining efficiency was identified, parameter optimization enabled three combinations achieving satisfactory coordination. Group 8 exhibited the best kerf flatness, Group 10 reached the shortest machining time, and Group 11 yielded the smallest recast layer thickness. Nanoindentation results revealed that the hardness of the recast layer was consistently higher than both the heat-affected zone and bulk material, measuring approximately 1.2 to 3.9 times that of the bulk material. Compared to the bulk material, the hardness of the heat-affected zone initially increased and then decreased with the increasing power amplifier tube numbers, while its areal extent expanded proportionally with tube numbers. Additionally, within the same colony, the recast layer and heat-affected zone exhibited greater hardness dispersion, whereas the bulk material remained relatively stable. This study indicates that the recast layer thickness is dominated by the pulse width, and the machining efficiency is determined by the tube number mostly in WEDM of Ti-6Al-4V alloy. Several optimal WEDM parameter combinations can be obtained through orthogonal experiments, allowing prioritization of precision or productivity based on application requirements. The recast layer, which exhibits brittleness and microstructural incompatibility with the bulk material, requires removal during post-processing. Although the heat-affected zone retains a microstructure similar to the bulk material, the significant hardness fluctuations necessitate concurrent removal. These findings provide practical guidance for selecting WEDM parameters to achieve precision and productivity in titanium alloy machining, particularly for safety-critical components demanding stringent surface integrity standards.
Key words
titanium alloy /
WEDM /
orthogonal experiment /
recast layer /
hardness
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Funding
National Natural Science Foundation of China (52101013); Natural Science Foundation of the Hebei Province (E2022202004)
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