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The machining residual stress produced in the cutting process of aluminum alloy parts can easily lead to a scrap of the processed parts. In order to reduce the residual stress of aluminum alloy in the milling process, based on the Taguchi-Grey relational approach, the effects of different milling parameters on the residual stress and surface roughness of 2A12 aluminum alloy were studied. To reduce the residual stress and surface roughness of 2A12 aluminum alloy, optimized milling parameters were obtained. To further reduce the milling residual stress of 2A12 aluminum alloy, the samples processed by the optimized milling parameters were treated by cryogenic treatment and artificial aging. The residual stress of the sample was measured by the blind hole drilling method, and the evolution mechanism of the microstructure to reduce the machining residual stress was revealed. The results show that the combination of deep cooling treatment and oil bath aging can effectively reduce the residual stress on the machined surface of the aluminum alloy and facilitate a more uniform distribution of the residual stress inside the specimen. The effect of the coarse second phase on the residual stress in the microstructure is not significant, and the fine and diffusely distributed precipitation phase is beneficial to the reduction of the residual stress in the aluminum alloy.

In this work, β-gallium oxide thin film was investigated for enhancing the optical and electrical properties deposited through physical vapour deposition powered by radio frequency sputtering method at optimized parameters of deposition rate and surface roughness based on Taguchi–grey relational approach. Taguchi L8 (24) orthogonal array DOE were selected based on 2 levels of plasma power (P), working pressure (Pr), standoff distance between target and substrate (D), and deposition time (T). From the analysis of Taguchi–grey relational approach, the optimal parameters were predicted as 'P1-D2-Pr2-T2', which showed good improvement on GRG of 0.0165 over initial parameter settings. Predicted parameters were further validated by depositing thin films for deposition rate and surface roughness by varying plasma power of optimal parameter. On analysis, deposition rate and surface roughness showed better results in case of 75 W, as compared to other plasma power (100 and 50 W). Therefore, β-Ga2O3 thin films deposited at optimal parameter were further investigated for optical and electrical properties. Field-emission scanning electron microscopy results suggested that thin films grown were uniform, dense and defects free. Thin films showed nanocrystalline structure with small peak at 2θ = 38°, oriented in the (–311) plane. The maximum transmittance was obtained as ~63% in the visible 300–900 nm wavelength, while the band energy gap calculated from the Tauc plot obtained was 3.79 eV. The electrical resistivity of the thin films was 1.067 × 104 Ω cm. Thus, all results suggest that thin films grown at optimized parameters enhance the optical and electrical properties and also showed potential to further use for optoelectronics device at short wavelengths. [ABSTRACT FROM AUTHOR]