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The local inhomogeneity along the thickness direction of the extruded plate of spray-formed aluminum alloy 7055 were investigated. The thermal extrusion process was simulated by using DEFORM-3D software to understand its formation mechanism. In order to reduce the extrusion-induced inhomogeneity and improve the mechanical properties, the evolution of the secondary phase during different heat treatments and its influence on the peak aged hardness and tensile strength of the alloy were emphatically analyzed. The results show that the strain rate and temperature during the thermal extrusion process tend to decrease from the surface to the center, which leads to the local inhomogeneity of the microstructure and properties in the thickness direction. Such inhomogeneity can be reduced by heat treatments combining long-time or slow-heating solution treatments (F2 and F3) with peak ageing at 120 °C, due to similar content of S (Al2MgCu) phase after solution treatment and η′ phase (peak-ageing) in different regions of the alloy. The alloy solution treated with a slow heating rate (F3) and then peak aged shows highest hardness and tensile strength, because the slow heating process during the solution treatment promotes the precipitation of Al3Zr particles, and there are less S (Al2MgCu) phases after solution treatment which is conducive to the η′ phase precipitation during the subsequent aging process.

This paper reports a quasi in-situ study on the plastic deformation behavior of high purity tantalum, particularly the slip activation and slip transfer, using the electron backscatter diffraction method. We found that the rotation degree of grains is in the range of 0–15°; the rotation axes of slip-activated grains are mainly concentrated in the three corners, while the axes of slip-transfer ones are concentrated near {111} corner in the stereographic triangle. Microstructural parameters including grain size and grain aspect ratio were found to have no apparent relationships with the slip activation or slip transfer process. Most m' factors for the grains underwent slip-transfer are larger than 0.27, and most slip systems involved in the slip-transfer observations are associated with relatively high Schmid factors (SFs), indicating that slip would more easily transfer through the boundaries with large m' factors. In addition, according to the distribution of geometrical necessary dislocation density and the SF of slipping activated grains, we found the slip transfer process is affected by a combination of factors, including the SF, m' factor, and the strain concentration in local regions.

Spray forming is a manufacturing process that enables the production of high-performance metallic materials with exceptional properties. Due to its rapid solidification nature, spray forming can produce materials that exhibit fine, uniform, and equiaxed microstructures, with low micro-segregation, high solubility, and excellent workability. Al-Zn-Mg-Cu alloys have been widely used in the aerospace field due to their excellent properties, i.e., high strength, low density, and outstanding machinability. The alloy manufactured by spray forming has a combination of better impact properties and higher specific strength, due to its higher cooling rate, higher solute concentration, and lower segregation. In this manuscript, the recent development of spray-formed Al-Zn-Mg-Cu alloys is briefly reviewed. The influence of hot working, i.e., hot extrusion, hot forging, and hot rolling, as well as different heat treatments on the property and microstructure of spray-formed Al-Zn-Mg-Cu alloys is introduced. The second phases and their influence on the microstructure and mechanical properties are summarized. Finally, the potential in high-temperature applications and future prospects of spray-formed aluminum alloys are discussed.

The microstructure evolution is very complex during the processing of tantalum sputtering target for integrated circuits, and the deformation mechanisms for this evolution is still unclear. This work aims to investigate the deformation mechanism in a quasi-in-situ way, particularly the activation of slip systems, lattice rotation, and strain concentration, utilizing the electron backscatter diffraction (EBSD) method. We found that the maximal orientation density increased after the deformation, especially the content of both the {111} and {100} components increased while the {110} orientations decreased after the deformation. The lattice rotation leads to misorientation between grain orientations before and after the deformation, and the misorientation axes seem to be randomly distributed during the deformation. The rotation behavior can be adequately described by the activation of both {110} and {112} slip systems, which were found to have no linear relationship with grain size or grain aspect ratio, but are related to the Schmid factors and strain concentration situations. In particular, the inhomogeneous geometrical necessary dislocations distribution indicates the complicated situation of flow stress, and the slip systems activated with smaller Schmid factors are associated with the local heterogeneous strain concentrations.

Compression experiments were designed to examine the intergranular deformation behaviors of 7xxx aluminum alloy at a micro-scale. Band structures formed in grains upon deformation were characterized by electron backscatter diffraction technique, and the local stored energy was analyzed in a quantitative way. In addition, the deformation behaviors of the six pairs of adjacent deformed grains show that, the dislocation slips are transmissible between some pairs of grains but terminated in front of other grain boundaries. Such slip transmission is influenced by the Schmid factor, the strain coordination factor mʹ, and the degree of strain concentration between grains, according to the analysis of kernel average misorientation.

Controlling the formation of the β′ (Al3Zr) phase is pivotal for regulating the recrystallization and thus the mechanical properties of the spray formed 2195 (Al-Cu-Li) alloy. In a conventional “homogenization-extrusion” process, the precipitation of β′ is severely affected by the presence of the T1(Al2CuLi) phase in the as-deposited alloy, leading to an inhomogeneous distribution of the β′ phase. In the present work, we propose a new thermomechanical processing (TMP)—swapping the order of the homogenization and extrusion processes. The microstructures and properties of the new proposed TMP were systematically studied at various stages of the alloy treatment and compared with the out of the conventional TMP. It was revealed that the introduction of the extrusion process on the as-deposited alloy can break the continuous network of primary phases and dissolve the T1 phase, promoting a uniform distribution of the β′ phase during subsequent two-step homogenization. During solution treatment, the new TMP is more effectively in suppressing the formation of a coarse grain layer at sheet surface, while after final peak aging, the new TMP produces a lower alloy strength but a higher elongation, due mainly to the smaller thickness reduction during deformation. The new proposed TMP technique provides a new insight into regulating the mechanical properties of Al-Cu-Li alloys.

The combined effect of adding Sn and natural aging (NA) time on the precipitation and age-hardening rate of the Al-0.4Mg-1.0Si alloy was investigated by a hardness test, electrical resistivity test, differential scanning calorimetry (DSC) analysis, 3-D atom probe (3DAP) analysis, and transmission electron microscopy (TEM). The results showed that the NA of the Al-0.4 Mg-1.0Si alloy was suppressed by adding Sn. This suppression was ascribed to the suppression of the formation of clusters. The short NA time (less than 5 days) had a positive effect on the subsequent artificial aging (AA) in the Sn-added alloys, i.e., a fast AA-hardening rate was achieved. The positive effect of the NA on the AA in the Sn-added alloys increased as the amount of Sn increased, but decreased as the NA time increased. The AA was negatively affected by the NA when the NA time was increased to 14 days. The accelerated AA precipitation of the Sn-added alloys after a short NA time was responsible for the fast AA-hardening rate. This accelerated precipitation was related to the increased amount of retained quenched-in vacancies according to their NA resistivity curves and similarity of the chemical composition between the Sn-containing clusters and β'' phases.

A compression experiment with electron backscatter diffraction (EBSD) measurements was designed to characterize the effect of the microtexture on the grain rotation process. The rotation degrees of more than 180 grains before and after the compression were calculated. Results showed that grains with different crystallographic orientations experienced various rotation degrees. Furthermore, grains in certain microtexture regions also had varying degrees of rotation. The compression led to the lattice rotation and change in orientation of individual grains, but the relative misorientation between grains has not changed much in the microtexture region. The microtexture region, as a whole, participated in the compression process. The similar slipping behavior of the grains in the region promoted the slip transmission between the neighboring grains. Thus, the amount of piled-up dislocations at grain boundaries inside the microtexture region are less than that at grain boundaries outside the microtexture region, leading to a small stored energy density for grain boundaries inside the microtexture region.

Intergranular corrosion is the main corrosion type of Al-Cu-Mg aluminum alloys, which seriously reduce the lifetime of aircraft structural parts. In this paper, the microstructure and the intergranular corrosion behavior of 2024 alloy with varying Cu and Mg content were studied by using a scanning electron microscope (SEM), transmission electron microscope (TEM), and three-dimensional atom probe (3DAP). The results show that nano-scale θ (Al2Cu) and S (Al2CuMg) particles precipitate along grain boundaries after quenching. The nano-cluster is the main strengthening phase in the 2024 alloy after natural aging for 96 h. The intergranular corrosion susceptibility is greatly affected by the presence of θ (Al2Cu) and S (Al2CuMg) phases along grain boundaries. Specifically, Cu-rich precipitates and intermetallics are known to act as local cathodes, which facilitates the action of oxygen reduction and ultimately drives anodic dissolution of the surrounding matrix material. The intergranular corrosion resistance of the alloy decreases with the increase in Cu and Mg contents. The alloy with a lower Mg content shows better corrosion resistance than the commonly used one with a Cu to Mg mass ratio of 2.9. The relationship between the observed corrosion behavior and various contents of Cu and Mg elements is discussed, which has potential to benefit the composition design of 2xxx aluminum alloy with high corrosion resistance.

Al-2.5 wt% Cu alloys with different Sc additions (0, 0.1, 0.3, 0.5 wt%) are studied in comparison to reveal the Sc microalloying effect on precipitation, room temperature mechanical properties, and creep resistance. The results show that the Sc addition into the Al–Cu alloys can effectively promote the precipitation of θ′-Al2Cu, reducing the size and narrow the size distribution. However, the Sc-dependences of mechanical properties at room and at high temperatures are much different. Although the 0.3 wt% Sc addition results in the densest homogeneous θ′-Al2Cu precipitation and hence the highest room temperature strength, the 0.5 wt% addition leads to the most improved creep resistance at 300 °C that is derived from a nanostructural Sc-based hierarchy, i.e., Al3Sc dispersoid/heterogeneous θ′-Al2Cu precipitate units, homogeneous θ′-Al2Cu precipitates, strongest Sc segregation at θ′/matrix interfaces, and Sc clusters. The nanostructural hierarchy with thermally resistant nanostructural features at different length scales provides a new way to develop advanced Al alloys with excellent high-temperature stability and mechanical properties. The strengthening mechanisms at room and high temperatures are respectively discussed. Keywords: Al–Cu alloys, Microalloying effect, Creep resistance, Nanostructural hierarchy

The flow behavior of an Al-Cu-Li-Mg-Ag alloy was studied by thermal simulation tests at deformation temperatures between 350 °C and 470 °C and strain rates between 0.01–10 s−1. The microstructures of the deformed materials were characterized by electron backscattered diffraction. Constitutive equations were developed after considering compensation for strains. The processing maps were established and the optimum processing window was identified. The experimental data and predicted values of flow stresses were in a good agreement with each other. The influence of deformation temperature and strain rates on the microstructure were discussed. The relationship between the recrystallization mechanism and the Zener–Hollomon parameter was investigated as well.