Extrusion experiments and 3D numerical modeling were conducted to investigate the dynamic recrystallization and welding quality of a 6063 aluminum alloy hollow square tube extruded by a porthole die at the ram speeds of 3 mm/s, 7 mm/s, 9 mm/s and 11 mm/s. The results showed that average grain size of hollow square tube extruded at the ram speed of 7 mm/s was the smallest. The profile extruded at the ram speed of 3 mm/s exhibited the highest expansion ratio. Dynamic recrystallization (DRX) fractions were highly variable at different ram speeds. DRX fractions in the matrix zones were higher than those in the welding zones, resulting in smaller grain sizes in the matrix zones. Mechanical properties in the welding zones and matrix zones was different. A local strain concentration would occurred during expansion, which would affect the welding quality. Finally, it was found that the uniform microstructure near the welding line would also affect the welding quality.

The influence of artificial aging time on the microstructures and mechanical properties of the 6063 aluminum alloy profile extruded by porthole die was investigated through hardness testing, expansion testing, scanning electron microscope (SEM), and transmission electron microscope (TEM). The results showed that the artificial aging time had a significant impact on the size, morphology, distribution of precipitated phases, and mechanical properties of the porthole die extruded 6063 aluminum alloy profiles. As the artificial aging time increased, the second phase particles gradually precipitated, and the precipitation strengthening gradually enhanced, resulting in an increase in the hardness of the profile. The hardness of the welding zone was lower than that of the matrix zone. Compared with the precipitation in the matrix zone, the size and distribution of the precipitates were uneven, and the time for the precipitation was long in the welding zone due to the influence of grain size. The width of the precipitate free zone (PFZ) in the welding zone was greater than that in the matrix zone. The expansion ratio decreased with the increase of aging time, which indicated that the artificial aging treatment was adverse to the plastic deformation ability of the profiles.

Based on the first principles, the structural stability, mechanical characteristics, electronic structure, and thermodynamic properties of AlCu₂M (M = Ti, Cr, Zr, Sc, Hf, Mn, Pa, Lu, Pm) are investigated. The calculated results indicate that the AlCu₂Pa crystal structure is more stable and that AlCu₂Pa should be easier to form. All of the AlCu₂M compounds have structural stability in the ground state. Elastic constants are used to characterize the mechanical stability and elastic modulus, while the B/G values and Poisson ratio demonstrate the brittleness and ductility of AlCu₂M compounds. It is demonstrated that all computed AlCu₂M compounds are ductile and mechanically stable, with AlCu₂Hf having the highest bulk modulus and AlCu₂Mn having the highest Young’s modulus. AlCu₂Mn has the highest intrinsic hardness among AlCu₂M compounds, according to calculations of their intrinsic hardness. The electronic densities of states are discussed in detail; it was discovered that all AlCu₂M compounds form Al-Cu and Al-M covalent bonds. Additionally, we observe that the Debye temperature and minimum thermal conductivity of AlCu₂Mn and AlCu₂Sc are both larger than those of others, indicating stronger chemical bonds and higher thermal conductivities, which is consistent with the elastic modulus results.

Hot compression tests for Al-Mg-Si aluminum alloy were performed on Gleeble-1500 at the deformation temperatures of 300~500℃ and strain rates of 0.01-10 s-1. It was found that the flow stress curves exhibit continuous flow softening after reaching the peak value. Microstructure observations indicate that dynamic recovery is the dominant restoration mechanism during the deformation. Continuous flow softening is considered to arise mainly due to thermal softening by deformation heating and microstructural softening by dynamic grain boundary migration. The effect of deformation heating on flow stresses was corrected with the measured instantaneous sample temperature. The dynamic grain boundary migration rate was calculated based on the measured grain thickness. A modified Laasraoui-Jonas model was developed through introducing the flow softening item induced by dynamic grain boundary migration. The predicted flow stresses overall agree well with the experimental data.

This paper investigates the low-altitude air traffic control in joint radar and communication (JRC) networks. Small base stations (SBSs) apply JRC technology to serve unmanned aerial vehicles (UAVs) by sensing UAVs and transmitting the sensing information to the macro base station (MBS), which assists for low-altitude air traffic control. We formulate this control problem as a service strategy optimization problem, where SBSs need to perform multiple sense and communication operations within each scheduling period. The goal is to maximize the network service profit, which is obtained from serving UAVs by SBSs. We prove that the objective function of the optimization problem is submodular and then propose a greedy-based service algorithm to solve it efficiently with low complexity. The proposed algorithm provably achieves at least $1 - \frac{1}{{\sqrt e }}$ of the optimum value. Simulation results show that our proposed algorithm performs close to the optimal solution with different system parameters.