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High-resolution transmission electron microscopy (TEM), X-ray diffractometer (XRD), and hardness test were used to study the evolution of long plate-shaped S′ phase in the spray-formed fine-grained Al−Cu−Mg alloy during aging after rapid cold punching deformation. Results show that the long plate-shaped S′ phase in the extruded Al−Cu−Mg alloy undergoes evident distortion, brittle failure, separation and redissolution, during rapid cold punching deformation, leading to the transformation of long plate-shaped S′ phase into short rod or even redissolution and disappearance, causing the matrix to become a supersaturated solid solution. After the aging treatment, the reprecipitation of the phases occurs, and these aging phases are mainly long plate-shaped and granular. The incompletely dissolved S′ phase acts as nucleation core, promoting uphill diffusion of the surrounding solute atoms. The S′ phase gradually grows with increasing the aging time. The completely dissolved S′ phase forms the incoherent equilibrium phase with the matrix to reduce its free energy. After rapid cold punching, the aging response of the deformed Al−Cu−Mg alloy is accelerated, and the hardness of the alloy is substantially increased.

High-angle annular dark-field scanning transmission electron microscopy and selected area electron diffraction techniques were used to study the mechanism that underlies the influence of rapid cold-stamping deformation on the fracture behavior of the elongated nanoprecipitated phase in extruded Al−Cu−Mg alloy. Results show that the interface between the long strip-shaped S′ phase and the aluminum matrix in the extruded Al−Cu−Mg alloy is flat and breaks during rapid cold-stamping deformation. The breaking mechanisms are distortion and brittle failure, redissolution, and necking. The breakage of the long strip S′ phase increases the contact surface between the S′ phase and the aluminum matrix and improves the interfacial distortion energy. This effect accounts for the higher free energy of the S′ phase than that of the matrix and creates conditions for the redissolution of solute atoms back into the aluminum matrix. The brittle S′ phase produces a resolved step during rapid cold-stamping deformation. This step further accelerates the diffusion of solute atoms and promotes the redissolution of the S′ phase. Thus, the S′ phase necks and separates, and the long strip-shaped S′ phase in the extruded Al−Cu−Mg alloy is broken into a short and thin S′ phase.

High-resolution transmission electron microscopy (TEM), X-ray diffractometry (XRD), energy dispersive spectroscopy (EDS) and hardness test were used to study the re-dissolution and re-precipitation behavior of nano-precipitates of the spray-formed fine-grained Al−Cu−Mg alloy during rapid cold stamping deformation. Results show that the extruded Al−Cu−Mg alloy undergoes obvious re-dissolution and re-precipitation during the rapid cold-stamping deformation process. The plastic θ′ phase has a slower re-dissolution rate than the brittle S′ phase. The long strip-shaped S′ phases and the acicular θ′ phases in Al−Cu−Mg alloy after three passes of cold stamping basically re-dissolved to form a supersaturated solid solution. A large number of fine granular balance θ phases precipitate after four passes of rapid cold-stamping deformation. Rapid cold stamping deformation causes the S′ phase and θ′ phase to break and promote the nano-precipitate phases to re-dissolve. The high distortion free energy of the matrix promotes the precipitation of the equilibrium θ phase, and the hardness of the alloy obviously increases from HB 55 to HB 125 after the rapid cold stamping process.

The evolution of nanoprecipitated phases in Al–Cu alloys under severe plastic deformation (SPD) is summarized in this study. SPD at room temperature induces the precipitation of Al–Cu alloys to dissolve, leading to the reformation of supersaturated solid solution in the aluminum matrix. In the process of SPD or aging treatment after the SPD, the reprecipitated phases are precipitated from the aluminum matrix and the mechanical properties of the alloys are remarkably improved. The mechanism and system of the redissolution of the precipitation phases and the effects of redissolution and reprecipitation on the microstructure and properties of Al–Cu alloys are comprehensively analyzed. The development and future of redissolution and reprecipitation of nanoprecipitated phases in Al–Cu alloys are also described.

The microstructures and interface structures of basalt particle reinforced 7A04 Al matrix composites (BP/7A04 Al) were analyzed by using OM, TEM, SEM and EDS, and the mechanical properties of 7A04 Al alloy were compared with those of BP/7A04 Al matrix composites. The results show that the basalt particles are dispersed in the Al matrix and form a strong bonding interface with the Al matrix. SiO2 at the edge of the basalt particles is continuously replaced by Al2O3 formed in the reaction, forming a high-temperature reaction layer with a thickness of several tens of nanometers, and Al2O3 strengthens the bonding interface between basalt particles and Al matrix. The dispersed basalt particles promote the dislocation multiplication, vacancy formation and precipitation of the matrix, and the precipitated phases mainly consist of plate-like η (MgZn2) phase and bright white band-shaped or ellipsoidal T (Al2Mg3Zn3) phase. The bonding interface, high dislocation density and dispersion strengthening phase significantly improve the mechanical properties of the composites. The yield strength and ultimate tensile strength of BP/7A04 Al matrix composites are up to 665 and 699 MPa, which increase by 11.4% and 10.9% respectively compared with 7A04 Al alloy without basalt particles.

The microstructure evolution of spray formed and rapidly solidified Al−Cu−Mg alloy with fine grains during rapid cold punching and recrystallization annealing was investigated by transmission electron microscopy (TEM). The results show that the precipitates of fine-grained Al−Cu−Mg alloy during rapid cold punching and recrystallization annealing mainly consist of S phase and a small amount of coarse Al6Mn phase. With the increase of deformation passes, the density of precipitates increases, the size of precipitates decreases significantly, and the deformation and transition bands disappear gradually. In addition, the grains are refined and tend to be uniform. Defects introduced by rapid cold punching contribute to the precipitation and recrystallization, and promote nucleation and growth of S phase and recrystallization. Deformation and transition bands in the coarse grains transform into deformation-induced grain boundary during the deformation and recrystallization, which refine grains, obtain uniform nanocrystalline structure and promote homogeneous distribution of S phase.

Transmission electron microscopy (TEM), electron backscattered diffraction imaging (EBSD) and X-ray diffractometry were used to analyze the microstructure and texture characteristics of Al−9.8Mg−1.5Li−0.4Mn alloy cross-rolled and extruded plates, and the tensile properties and deep drawing performance were measured. The results show that the occurrence of dynamic recrystallization was promoted, the grains were refined and the preferred orientation of the recrystallized grains was improved by large strain cross rolling. Compared with CBA and CCB rolling methods, CBB rolling method significantly reduced the orientation density of the typical Brass texture {110}〈112〉 in the extruded plates. The orientation densities of Copper texture {112}〈111〉 and Brass texture {110}〈112〉 on the β orientation line in the CBB rolled plates were the lowest, and there were no typical texture features in the plates. Meanwhile, better deep drawing could be gained in the CBB rolled plates, and the mechanical properties of the 0°, 45° and 90° directions were basically the same. The tensile strength, yield strength and elongation at room temperature for the CBB rolled plates were 617 MPa, 523 MPa and over 20.1%, respectively. The deviation of the mechanical properties at different directions was less than 3%.

The flow stress behavior of spray-formed Al-9Mg-1.1Li-0.5Mn alloy was studied using thermal simulation tests on a Gleeble-3500 machine over deformation temperature range of 300-450 °C and strain rate of 0.01-10 s−1. The microstructural evolution of the alloy during the hot compression process was characterized by transmission electron microscopy (TEM) and electron back scatter diffractometry (EBSD). The results show that the flow stress behavior and microstructural evolution are sensitive to deformation parameters. The peak stress level, steady flow stress, dislocation density and amount of substructures of the alloy increase with decreasing deformation temperature and increasing strain rate. Conversely, the high angle grain boundary area increases, the grain boundary is in serrated shape and the dynamic recrystallization in the alloy occurs. The microstructure of the alloy is fibrous-like and the main softening mechanism is dynamic recovery during steady deformation state. The flow stress behavior can be represented by the Zener-Hollomon parameter Z in the hyperbolic sine equation with the hot deformation activation energy of 184.2538 kJ/mol. The constitutive equation and the hot processing map were established. The hot processing map exhibits that the optimum processing conditions for Al-9Mg-1.1Li-0.5Mn alloy are in deformation temperature range from 380 to 450 °C and strain rate range from 0.01 to 0.1 s−1.

The extrusion preform of the spray-formed 5A12 Al alloy was hot rolled using high reduction rolling technology. By means of transmission electron microscopy (TEM), electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS), the microstructure evolution was studied and the strengthening and toughening mechanism was thereby proposed. The results indicate that discontinuous and continuous dynamic recrystallization occurred during the hot rolling deformation of the spray-formed 5A12 Al alloy. The grain size was significantly refined and the micro-scale grains formed. Partial dynamic recrystallization leads to a significant increase of dislocation density and cellular structure. The Mg atoms were distributed in the Al matrix mainly in the presence of solid solution rather than the formation of precipitate. High solid solution of Mg atoms not only hindered the dislocation motion and increased the density of dislocation, but also exhibited a remarkable solid solution strengthening effect, which contributes to the high strength and high toughness of the as-rolled sheets. The tensile strength and elongation of spray formed 5A12 Al alloy at room temperature after 3 passes hot rolling were 622 MPa and 20%, respectively.

Hot deformation behavior of extrusion preform of the spray-formed Al–9.0Mg–0.5Mn–0.1Ti alloy was studied using hot compression tests over deformation temperature range of 300–450 °C and strain rate range of 0.01–10 s−1. On the basis of experiments and dynamic material model, 2D processing maps and 3D power dissipation maps were developed for identification of exact instability regions and optimization of hot processing parameters. The experimental results indicated that the efficiency factor of energy dissipate (η) lowered to the minimum value when the deformation conditions located at the strain of 0.4, temperature of 300 °C and strain rate of 1 s−1. The softening mechanism was dynamic recovery, the grain shape was mainly flat, and the portion of high angle grain boundary (>15°) was 34%. While increasing the deformation temperature to 400 °C and decreasing the strain rate to 0.1 s−1, a maximum value of η was obtained. It can be found that the main softening mechanism was dynamic recrystallization, the structures were completely recrystallized, and the portion of high angle grain boundary accounted for 86.5%. According to 2D processing maps and 3D power dissipation maps, the optimum processing conditions for the extrusion preform of the spray-formed Al–9.0Mg–0.5Mn–0.1Ti alloy were in the deformation temperature range of 340–450 °C and the strain rate range of 0.01–0.1 s−1 with the power dissipation efficiency range of 38%–43%.

Effects of specific pressure and the dual refiner of Al-5Ti-1B and Al-10RE on microstructure of the hollow 2024 aluminum alloy drive shaft prepared by squeeze casting in express locomotive were investigated in this paper. With the increasing specific pressure, the ɑ-A1 primary grains became rounder and smaller. With the specific pressure up to 120 MPa, the average grain size of the ɑ-A1 primary grains and the average equivalent roundness were 38 μm and 0.75 respectively. When the dual refiner was adopted, the average grain size of the alloy decreased obviously with a lower mass fraction of A1-5Ti-1B and a higher mass fraction of Al-10RE. However, no obvious change was detected in the average equivalent roundness. The roundness value ranged from 0.62 to 0.72. With the dual refiner of 1wt% Al-5Ti-1B and 3wt% Al-10RE, the average grain size of the alloy and the average equivalent roundness were 26 μm and 0.71 respectively.

Effects of casting temperature and RE refiner on microstructure of the hollow Al-Zn-Mg-Cu alloy drive shaft prepared by squeeze casting ( in express locomotive) were investigated in this paper. As the casting temperature increase from 720°C up to 780°C, the average grain size of the α-A1 primary grains increased from 32μm up to 51μm, and the average equivalent roundness changed irregularly. Meanwhile the variation range was not big and the roundness value ranged from 0.63 to 0.72. With the casting temperature up to 780°C, the average equivalent roundness was 0.71. When the refiner was adopted, the average grain size of the alloy decreased obviously. However, no obvious change was detected in the average equivalent roundness, which ranged from 0.73 to 0.78. With the refiner of 3wt% Al-10RE, the average grain size of the alloy and the average equivalent roundness were 35μm and 0.77, respectively.