The effects of the Cu content on the microstructure and strengthening mechanisms of the Al-Mg-Si-xCu alloys were systematically investigated using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), transmission electron microscopy (TEM), and mechanical tensile tests. The results show that, the strengthening mechanisms change with the Cu content. For as-quenched alloys, solution strengthening (σ_SS) is predominant when the Cu content ≥2.5 wt.%, and of equivalent importance as grain size strengthening (σ_H-P) when the Cu content ≤1.0 wt.%. With respect to peak-aged alloys, precipitation strengthening (σ_ppt) is predominant when the Cu content ≥2.5 wt.%, but σ_SS becomes predominant when the Cu content is 4.5 wt.%. As the Cu content increases from 0.5 to 4.5 wt.%, the main type of precipitates in alloy tends to change from a β″ phase to Q′ phase, and then to a θ′ phase. Among the three types of precipitates, θ′-precipitate causes the largest increase in yield strength (σ_0.2) and the largest decrease rate in elongation. β″-precipitate leads to the smallest increase in σ_0.2 and the smallest decrease rate in elongation. The increase of Cu content reduces Si solubility in the Al matrix and thus decreases the nucleation rate of β″ phase during subsequent aging.

Laminated composites have emerged as a prominent research focus in materials science due to their ability to combine the advantageous characteristics of constituent metallic elements synergistically. This study presents an innovative fabrication approach for multilayer metal composites utilizing high-temperature torsion processing. The effects of different torsion temperatures and torsion angles on the organization and properties of 1060 aluminum alloy/stainless steel laminated composites were also investigated by mechanical tensile property tests, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and electron backscatter diffraction (EBSD) analyses. The results showed that with the increase of torsion temperature, the maximum torque (Τ _b) of the material showed a decrease, the maximum tensile strength (σ _th) of the material decreased (above the theoretical σ _th of 295.9 ± 4.7 MPa), and the maximum ductility (δ) increased. Among them, the σ _th of the laminated composites reaches up to 360.4 ± 9.9 MPa, while the δ increases from 30.4 ± 5.1% to 75.4 ± 6.1% during the torsion process from 20 °C to 500 °C of the laminated composites. It can be seen that the torsion-molded composites have the advantages of high strength, high elongation, and excellent interfacial bonding properties.

In this study, a combination surface modification technique integrating high-speed cutting and solid projectile entrained water jet (HSC-SPEWJ) was employed to strengthen the surface of a 7075-T6 aluminum alloy. By combining analyses of surface morphology, microhardness, residual stress, transmission electron microscopy (TEM), and numerical simulation, the evolution of surface properties and the underlying microstructural transformation mechanisms during the combined modification process were systematically investigated. The results indicate that, after samples after HSC machining, the sample surface was mainly characterized by machining feed marks accompanied by localized plastic deformation. Following the introduction of SPEWJ surface modification, the surface morphology was dominated by uniformly distributed plowing grooves, while localized impact pits and irregular damage features were significantly reduced. As the jet pressure increases from 5 MPa to 11 MPa, the surface residual compressive stress increases from −176.57 MPa to −300.85 MPa, and the depth of the compressive residual stress layer increases from 247.87 μ m to 375.39 μ m. In contrast, both microhardness and residual compressive stress show a negative correlation with the jet standoff distance. Compared with single HSC and SPEWJ treatments, the HSC-SPEWJ combined modification significantly enhances the surface strengthening effect of 7075-T6 aluminum alloy, increasing the surface microhardness to 188.46–207.22 HV, corresponding to improvements of approximately 10.37%–21.36% and 4.13%–14.49% relative to single HSC and single SPEWJ, respectively. Finite element simulations indicate that the water jet impact induces stress superposition within the cutting-induced plastic layer and promotes stress propagation toward deeper regions. TEM analyses reveal that a high density of dislocations with a non-uniform distribution is formed during the samples after HSC machining stage, whereas SPEWJ surface modification facilitates dislocation multiplication and rearrangement, leading to a more homogeneous plastic deformation behavior.