Machinability of squeeze cast (TiB 2 +CNT)/Al 7075 metal matrix nano-composite during EDM with untreated and cryogenic treated Cu electrodes: A comparative study

Abstract

This paper accentuates investigation of machining responses and surface integrity of (TiB₂+CNT) reinforced Al 7075 metal matrix nano-composite intended for aerospace and automotive applications, which was processed through modified liquid metallurgy squeeze casting route. Microstructure of the developed composite was investigated through scanning electron microscopy, elemental distribution was identified through Energy-dispersive X-ray spectroscopy and mechanical properties were determined following recommended ASTM standards. However, focus was emphasized on exploration of the influence of peak current (I_P), pulse-on time (T_ON), and gap voltage (V_G) on material removal rate (MRR), tool wear rate (TWR), and surface integrity during electrical discharge machining of the hybrid nano-composite with untreated and cryogenic treated Cu tools. MRR, TWR, and average roughness (Ra) of the machined surfaces showed distinctive pattern in their variations when the machining parameters were changed; however, hardness of the machined surfaces did not show any specific trend with respect to the increase of the considered parameters. Cryogenic treated Cu tools outperformed the untreated tools, as perceived from the experimental results. For instance, while machining at T_ON = 100 µs, V_G = 55 V, and I_P = 10 A, maximum MRR for untreated tools was 27.43 mm³/min, and that for cryogenic treated tool was 29.12 mm³/min, leading to an improvement of about 5.8%. But at V_G = 55V, I_P = 4 A, and T_ON = 300 µs, maximum MRR for untreated tools was 16.71 mm³/min, and that for cryogenic treated tool was 18.22 mm³/min, leading to an improvement of about 8.3%. Similarly, at I_P = 4A and T_ON = 100 µs and V_G = 75V, maximum MRR for untreated tools was 14.88 mm³/min, and that for cryogenic treated tool was 22.7 mm³/min, leading to an improvement of about 34.4%. Similar outperformed results for cryogenic treated tools were also achieved while analyzing the experimental results of TWR, surface hardness and Ra. Finally, surface defects were analyzed through SEM at the disparate parametric combinations.