Microband evolution during large plastic strains of stable {1 1 0}〈1 1 2〉 Al and Al–Mn crystals

The deformation microstructures of Al and Al–Mn {1 1 0}〈1 1 2〉 single crystals have been characterized after room temperature channel-die compression up to true strains of 2.1. The evolution of local misorientations and microband structures were quantified by high-resolution electron backscatter diffraction in a field emission gun scanning electron microscope and their alignments compared with the traces of active slip planes and macroscopic shear stress planes. During plane-strain compression these “Brass” oriented crystals remain stable in terms of the final, average, orientation, with a small orientation spread. However, the microband alignment varies with strain and also with solute content. There is a general tendency for the microbands to be both crystallographic and non-crystallographic at low strains, then crystallographic, and finally mixed again at high strains (with some lamellar banding).     

Electrochemical assessment of laser heat treatment of an Al–Zn–Mg–Cu alloy

The effect of laser heat treatment on the corrosion properties of the 7075 aluminum alloy was studied electrochemically. Laser retrogression and re-aging (LRRA) is proposed to replace the retrogression treatment of retrogression and re-aging. Transmission electron microscopy was used to analyze the microstructure of the alloy. The corrosion of the alloy treated using different LRRA parameters was analyzed by scanning electron microscopy. Using the polarization and electrochemical impedance spectroscopy measurements, it was concluded that the best corrosion resistance was obtained by the alloy treated at 2 mm/s with a laser power of 650 W. The spacing between the precipitate-free zone and grain boundary precipitates increased. It is proved that the laser process can effectively improve the corrosion resistance of the 7075 alloy.     

Coherency loss of Al3(Sc,Zr) precipitates by deformation of an Al–Zn–Mg alloy

Al alloys with additions of Sc and/or Zr exhibit a reasonably stable grain structure due to a uniform distribution of coherent Al₃(Sc,Zr) precipitates that forms at temperatures >300 °C. These precipitates are stable up to the solution treatment temperature and are able to pin subgrain and grain boundaries, inhibiting grain coarsening. The crystallographic structure of these precipitates presents a L1₂ superstructure coherent with the face-centred cubic Al matrix. Changes in the orientation relation between precipitates and the matrix are described in deformed, recovered and partially recrystallized samples of extrusions of AW7010 (AlZn6Mg2Cu2). The coherency of the intracrystalline Al₃(Sc,Zr) precipitates present in the extrusions is lost by severe deformation performed by an equal channel angular pressing process, which produced a fine-grained microstructure. The deformed sample recovers, forming a subgrain structure with restored coherency of the Al₃(Sc,Zr) precipitates. Rapid heating to 470 °C causes partial secondary recrystallization, which transforms the precipitates within the recrystallized grains into incoherent groups of particles that maintain their original orientation with each other.     

Plastic deformation behaviors of a Mg–Ce–Zn–Zr alloy

The stress–strain behaviors of a Mg–2.8%Ce–0.7%Zn–0.7%Zr (wt.%) alloy with various strain rates at different deformation temperatures were investigated. It is found that the alloy can be extruded at 623 K with σ_0.2=222.4 MPa, σ_b=257.8 MPa and δ=12.0%. The working hardening, the dynamic recovery and the dynamic recrystallization play important roles to affect the plastic deformation behaviors of the alloy at different temperature regions, respectively.     

Influence of equal-channel angular pressing on precipitation in an Al–Zn–Mg–Cu alloy

Processing by equal-channel angular pressing (ECAP) affects the morphology of η precipitates in an Al–Zn–Mg–Cu (Al-7136) alloy. It is shown by transmission electron microscopy that ECAP changes the orientation of precipitates and this influences the atomic configuration and the interfacial energy at the η/α-Al interfaces. Consequently, η precipitates adopt an isotropic growth mode and evolve into equiaxed particles. A three-dimensional atom probe analysis demonstrates that large η precipitates formed in different numbers of ECAP passes are of similar composition. The coalescence of smaller precipitates, rather than the fragmentation of larger precipitates, dominates the precipitate evolution.     

Stress relaxation behavior of an Al–Zn–Mg–Cu alloy in simulated age-forming process

The stress relaxation behavior of age-forming for an Al–Zn–Mg–Cu alloy was studied using a designed device that can simulate the age forming process. The mechanism of stress relaxation was also revealed through calculating thermal activation parameters and analyzing the microstructures. The results suggested that the stress relaxation behavior of the Al–Zn–Mg–Cu alloy in the simulated age-forming process can be divided into three stages according to the stress level. The three stages of stress relaxation are: (i) the initial high stress stage, (ii) the subsequent middle stress transition stage and (iii) the last low stress equilibrium stage, respectively. The deformation activation energies are 132 kJ/mol in the initial high stress stage, 119 kJ/mol in the subsequent middle stress transition stage and 91 kJ/mol in the last low stress equilibrium stage, respectively. The analysis of the thermal activation parameters and microstructures revealed that dislocation creep was the dominant deformation mechanism in the initial and subsequent stages of the stress relaxation; whereas diffusion creep is the mechanism in the last stage of the stress relaxation. Additionally, a special threshold stress phenomena was present in the stress relaxation of the age-forming process, which was scribed to the interaction between precipitation and dislocation in the Al–Zn–Mg–Cu alloy     

The effect of zirconium addition on microstructure and properties of ball milled and hot compacted powder of Al–12 wt% Zn–3 wt% Mg–1.5 wt% Cu alloy

Elemental powders of the composition Al–12 wt% Zn–3 wt% Mg–1.5 wt% Cu with addition of 1 and 2 wt% Zr were ball milled in a planetary high-energy ball mill and then hot pressed in vacuum under 600 MPa pressure at 380 °C. The effect of ball milling and hot pressing on the microstructure was investigated by means of X-ray diffraction measurements (XRD), light microscopy, analytical and scanning transmission electron microscopy (TEM). Ball milling for 80 h leads to homogenous, highly deformed microstructure of aluminium solid solution with grain size below 100 nm. In the powder with zirconium addition, some part of the Zr atoms diffused in aluminium up to 0.3 wt% Zr. The remaining was found to form Zr-rich particles identified as face centered cubic (fcc) phase. Good quality samples without pores and cracks obtained by hot pressing composed of grains and subgrains of size below 200 nm. The particles of MgZn₂ phase were identified which were located mainly between compacted particles of milled powder. Hot pressed powder showed Vickers microhardness of about 195 HV (0.2 N) and ultimate compression strength in the range 611–658 MPa in the compression test. Addition of zirconium had no influence on the strength of the compacted powders.     

Stress-driven migration of symmetrical 〈1 0 0〉 tilt grain boundaries in Al bicrystals

Stress-induced migration of planar grain boundaries in aluminum bicrystals was measured for both low- and high-angle symmetrical 〈1 0 0〉 tilt grain boundaries across the entire misorientation range (0–90°). Boundary migration under a shear stress was observed to be coupled to a lateral translation of the grains. Boundaries with misorientations smaller than 31° and larger than 36° moved in opposite directions under the same applied external stress. The measured ratios of the normal boundary motion to the lateral displacement of grains are in an excellent agreement with theoretical predictions. The coupled boundary motion was measured in the temperature range between 280 and 400 °C, and the corresponding activation parameters were determined. The results revealed that for mechanically induced grain-boundary motion there is a misorientation dependence of migration activation parameters. The obtained results are discussed with respect of the mechanism of grain-boundary motion.     

Influence of Nd and Y on texture of as-extruded Mg–5Li–3Al–2Zn alloy

Mg–5Li–3Al–2Zn alloys with the additions of Y and Nd were prepared using induction melting furnace under the atmosphere of pure argon; then they were extruded. The textures of the as-extruded alloys were analyzed by pole figures and electron backscatter diffraction. Results show that the addition of a small amount of Nd can weaken the basal texture. The further increase of Nd content has no corresponding further influence on texture. When a small amount of Y is used to replace Nd, the basal texture can be further weakened and the prismatic slip system can be further activated. In the alloy of Mg–5Li–3Al–2Zn–1.2Y–0.8Nd, the basal textures almost vanish.