Abstract Machining of AA7075-T6 is challenged by high cutting temperature, process instability, and multiple interacting performance responses. This study investigates the effect of deep cryogenic holding time (CHT) on the milling performance of AA7075-T6 through a combined experimental and multi-criteria optimization approach. The material was cryogenically treated at − 146 °C for 12, 24, and 36 h, while untreated specimens were used as the reference condition. Milling experiments were carried out using a full factorial design with cutting speed (200, 250, and 300 m/min), feed per tooth (0.08, 0.10, and 0.12 mm/tooth), and CHT as control factors. Machining performance was evaluated based on the resultant cutting force, vibration, cutting temperature, power consumption, and surface roughness. In addition, microstructural and mechanical changes were examined by X-ray diffraction, SEM/EDS observations, and hardness measurements. The results showed that increasing CHT led to a measurable increase in hardness and induced lattice modifications, which influenced the thermo-mechanical behavior during machining without forming new phases. Among the machining responses, CHT had the strongest effect on cutting temperature and also contributed to a reduction in cutting force, whereas vibration, surface roughness, and power consumption were primarily affected by cutting parameters. Entropy-weighted grey relational analysis identified the optimal condition as 36 h CHT, a cutting speed of 250 m/min, and a feed per tooth of 0.08 mm. Under this condition, cutting force, temperature, and vibration were reduced by 23.7%, 35.0%, and 52.1%, respectively, relative to the reference condition. These findings demonstrate that cryogenic pre-treatment, combined with cutting parameters, can improve milling performance and process stability in AA7075-T6.
Bayram et al. (Mon,) studied this question.