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Commonly used commercial cast aluminum alloys for the automotive industry are viable for temperatures only up to 250 °C, despite decades of study and development. Affordable cast aluminum alloys with improved high-temperature mechanical properties are needed to enable the next generation of higher efficiency passenger car engines. Metastable θ′ (Al2Cu) precipitates contribute to strengthening in Al–Cu alloys, but above 250 °C coarsen and transform, leading to poor mechanical properties. A major challenge has been to inhibit coarsening and transformation by stabilizing the metastable precipitates to higher temperatures. Here, we report compositions and associated counter-intuitive microstructures that allow cast Al–Cu alloys to retain their strength after lengthy exposures up to 350 °C, ∼70% of their absolute melting point. Atomic-scale characterization along with first-principles calculations demonstrate that microalloying with Mn and Zr (while simultaneously limiting Si to

The development of through-thickness texture gradient during continuous cast (CC) processing of AA 5052 aluminum alloy was investigated by X-ray diffraction. The CC slab and the hot bands after each of three rolling passes were obtained from an industrial CC processing operation. The results show that a through-thickness texture gradient exists near the surface after the first pass. The subsurface layer exhibits a very weak texture, while the center layer shows the β fiber rolling texture. After the third pass, a strong β fiber rolling texture is obtained at different through-thickness layers. The roll-gap geometry does not produce any shear deformation at the intermediate layer. After recrystallization annealing, the through-thickness texture gradient still exists in the AA 5052 aluminum alloy sheets. As the measured position moves towards the center from the surface, the cube recrystallization texture strengthens.

The texture evolution of continuous cast (CC) AA 3105 aluminum alloy during cold rolling was investigated by X-ray Bragg diffraction. The influence of the precipitation state on the texture evolution during rolling was determined. The results show that the precipitates in a CC AA 3105 aluminum alloy affect the texture evolution during rolling. As the amount of precipitates increases and the size of precipitates decreases, the rate of disappearance of the cube, r-cube, and remainder components and the rate of formation of the β fiber decrease. The presence of large precipitates in a CC AA 3105 aluminum alloy hardly affects the texture evolution.

The effect of initial cube and rotated cube (r-cube) textures prior to cold rolling on the recrystallization and recrystallization texture of cold rolled AA 5182 aluminum alloy was investigated in detail. The transformation kinetics of recrystallization texture during isothermal annealing was quantified by the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation. The results show that AA 5182 aluminum alloy with different initial cube and r-cube textures exhibits almost the same recrystallization kinetics and recrystallized grain size. The apparent activation energy for recrystallization was estimated from both hardness and texture data to be 230 kJ/mol. The recrystallization texture of AA 5182 aluminum alloy with initial cube and r-cube textures is characterized by the R and cube components. As the annealing temperature increases, the volume fraction of the R component decreases, whereas the volume fraction of the cube component increases. The initial cube and r-cube textures affect the recrystallization texture of AA 5182 aluminum alloy. The AA 5182 aluminum alloy with an initial cube texture exhibits stronger R and Goss components as well as weaker cube and r-cube components than the alloy with an initial r-cube texture after complete recrystallization.

Industrially produced continuous cast (CC) aluminum alloys AA5182 and AA5052 were heat-treated at a low temperature of 182 °C for different times (30 and 100 h). Samples from the hot band (hot band in continuous cast process is produced through hot rolling of the materials at relatively high temperatures, usually from 490 to 310 °C) and the heat-treated materials were prepared for microstructure examination, chemical composition analysis, electrical resistivity testing and tensile testing. Particle structures of CC5182 alloy show precipitation along the grain boundaries after this low temperature heat-treatment. The particles were identified by SEM analysis to be Mg precipitates (Mg 2 Al 3 ). Due to the Mg precipitation, electrical resistivity, elongation and ultimate tensile strength decreased. As the interaction between Mg solute atoms in solid solution and mobile dislocations decreases due to precipitation, the magnitude of the stress drop in the serrations decreases and the critical strain for the onset of serrated yielding increases in CC5182 alloy. These phenomena do not occur in CC5052 alloy since precipitation either does not occur or is much weaker in this alloy. An inverse serrated yielding behavior, which is characterized by an increase in the critical strain for the onset of serrated yielding with a decrease in strain rate, occurs in CC5182 alloy but not in CC5052 alloy. This inverse behavior is believed to be related to precipitation during tensile deformation in CC5182 alloy.

AA 5182 aluminum alloy with a strong cube texture was cold rolled to different reductions at an angle of 22.5° to the prior rolling direction. The texture evolution at this new rolling direction was investigated by X-ray diffraction. The rotation paths and stability of the 22.5° ND rotated cube orientation were determined based on the variation in the three-dimensional orientation distribution function (ODF) with rolling reduction. The results show that most of the grains with the 22.5° ND rotated cube orientation are directly rotated to the β fiber along different rotation paths, but there are a few grains moving through the cube orientation to the β fiber. The {0 0 1} oriented grains possess the lowest stability during rolling, and the stability increases as the initial orientation changes from the {0 0 1} orientation to the {0 0 1} orientation along the ϕ1 axis.

Continuous cast (CC) AA5182 Al alloy with the precipitation of Mg2Al3 and of MnAl6 was cold rolled to 70% reduction and then isothermally annealed in a salt bath at three temperatures (316, 343, and 371 °C) for different times. Texture evolution during recrystallization was investigated. It was found that the recrystallization textures of the material with intense Mg2Al3 precipitation along the grain boundaries exhibited weaker Cube, Goss and R/β fiber components than those of the material with the more uniform fine MnAl6 precipitates. The opposite was true in the cold rolled condition, i.e. the material with MnAl6 precipitation had weaker Cube, Goss, and R/β fiber components in the cold rolled condition than the material with intense Mg2Al3 precipitation. Thus, recrystallization textures of material with Mg2Al3 precipitation were weaker than material with MnAl6 precipitation. This is due to the fact that large Mg2Al3 particles favor the nucleation of randomly oriented grains. When subjected to formability tests, the material with prior Mg2Al3 precipitation displayed a lower anisotropy in tensile yield strength, ultimate tensile strength, elongation, and strain hardening exponent than material with prior MnAl6 precipitation. This is in accord with the texture results which indicated that the recrystallization textures of material with an initial Mg2Al3 precipitation were closer to those of a perfectly random sample than those of material with an initial MnAl6 precipitation. On the other hand, the elongation and Olsen values were lower and the surface quality after bending tests was worse for material with Mg2Al3 precipitation. This is due to the non-uniform distribution of Mg2Al3 particles which precipitated primarily along the grain boundaries and caused an earlier formation and coalescence of the microvoids around the grain boundary precipitates. The forming limit diagrams (FLD) correlated well with the tensile, Olsen and bending results.

Industrially produced DC AA5182 was cold-rolled to different reductions, and then annealed at 589 K for 3 h. The annealed and the cold-rolled samples were further heat-treated at 455 K for 100 h. Serration behavior during each stage of the process was investigated. It was found that a decrease in the grain size of recrystallized material results in an increase in both Luders elongation and serration frequency or the number of serrations within a fixed strain range. For differently treated materials, serration behavior is different. In the completely recrystallized materials, serration intensity is initially low and increases in magnitude with increase in strain. The increase is fast at first, then the rate of increase decreases until the magnitude becomes a plateau. For cold-rolled and recovered materials, serration starts abruptly and is high in magnitude when it first appears. For highly cold-rolled materials this behavior is more obvious and the magnitude is almost a constant during the whole serration process for the 80 and 90% cold-rolled materials. Both the dislocation density and Mg concentration in solid solution have an effect on serrated yielding and a decrease of each or both results in a decrease of the intensity of serrated yielding. Negative strain rate sensitivity is manifested with an increase in the ultimate tensile strength (UTS) when the strain rate decreases. The tensile elongation does not follow commonly accepted behavior and displays an increase when the serration intensity is most intense.

The recrystallization behaviors of direct chill cast (DC) and continuous cast (CC) AA5052 hot bands and cold-rolled hot bands with and without preheating at 454 °C for 4 h were compared. The particle structures of DC and CC AA5052 hot bands and preheated hot bands were investigated. It was found that the differences in recrystallization behaviors between DC and CC AA5052 hot band materials were related to the differences in particle structures between DC and CC AA5052 materials. CC AA5052 hot band contained more Mg 2 Si particles than DC AA5052. Particle stimulated nucleation (PSN) occurred and resulted in weak recrystallization textures for CC hot band and its cold-rolled hot band. At the same time, DC AA5052 hot band and its cold-rolled hot band recrystallized faster due to the enhanced stored energy of the Mg-rich solid solution. If DC and CC AA5052 hot bands were preheated at 454 °C for 4 h before cold rolling, the Mg 2 Si particles dissolved, and thus the DC and CC materials had similar particle structures and similar recrystallization behaviors for the cold-rolled preheated DC and CC materials. Therefore, preheating CC AA5052 hot band decreased the structural differences that caused different behaviors in subsequent processing between DC and CC AA5052 materials.

The effect of pre-treatment on recrystallization and recrystallization textures of cold rolled continuous cast (CC) AA 5182 aluminum alloy as well as on the earing behavior was investigated. The progress of recrystallization was tracked by means of measurements of tensile properties. The texture of cold rolled and annealed samples was determined by X-ray diffraction. The results show that the recrystallization temperature of cold rolled CC AA 5182 aluminum alloy without pre-treatment is about 24 °C higher than that of the alloy with pre-treatment. The recrystallization textures of cold rolled CC AA 5182 aluminum alloy are characterized by the R, cube and Goss orientations. The recrystallization textures of cold rolled CC AA 5182 aluminum alloy without pre-treatment exhibit stronger cube and Goss components and a weaker R component than those of the alloy with pre-treatment. The deformed and recovered samples without pre-treatment possess a significantly higher 45° earing than the samples with pre-treatment, while the recrystallized samples without pre-treatment possess a slightly lower 45° earing than the samples with pre-treatment.

The recrystallization and recrystallization textures in cold-rolled direct chill cast (DC) and continuous cast (CC) AA 5182 aluminum alloys were investigated. The recrystallization behavior of cold-rolled DC and CC AA 5182 aluminum alloys was evaluated by tensile properties. The evolution of recrystallization textures in cold-rolled DC and CC AA 5182 aluminum alloys was determined by X-ray diffraction. The results showed that the recrystallization temperature of cold-rolled DC AA 5182 aluminum alloy was somewhat lower than that of cold-rolled CC AA 5182 aluminum alloy. The resulting recrystallization textures of cold-rolled AA 5182 aluminum alloy were characterized by the strong R orientation and the cube orientation with strong scattering about the rolling direction towards the Goss orientation. CC AA 5182 aluminum alloy showed slightly weaker recrystallization textures than DC AA 5182 aluminum alloy.

Industrially produced hot bands of continuous cast (CC) and direct chill (DC) cast AA 3105 aluminum alloy were cold rolled to different reductions from 10 to 90%. Macrotexture evolution of the deformation texture in the CC and DC materials was investigated by using three-dimensional orientation distribution functions (ODFs) that were determined by X-ray diffraction. The electron backscatter diffraction (EBSD) technique was adopted to investigate micro- and mesotexture during the early stages of cold rolling (≤40%). Results showed that the macrotexture evolution for CC and DC materials during cold rolling follows the same path. α and β fibers become developed beyond 50% cold rolling in both CC and DC materials. The highest intensity along the β fiber (skeleton line) is located between the Copper and the S orientations in both materials. There exists a path by which Cube orientation (0 0 1)[1 0 0] transforms to the Brass orientation (0 1 1)[2 1 1] through the CubeND orientation (0 0 1)[1 1 0] after certain cold rolling reductions. In both CC and DC materials, a cell structure develops with the indication of increasing coincidence site lattice (CSL) ∑1 boundaries during the early stages of cold rolling while high-angle boundaries (HABs) are randomized over the misorientation angle. There is no evidence for the development of twin boundaries in both CC and DC materials when the cold rolling reduction is less than 40%. Cold rolling texture itself is not responsible for the different recrystallization behaviors that cause different earing behaviors between CC and DC aluminum alloys.

The effect of different thermal treatment temperatures (from 472 to 783 K) on the characteristics of serrated yielding of three commercial aluminum alloys, AA5052, AA5754 and AA5182, was investigated. In the high temperature treatment range, the stress drop (Δ σ ) decreases with increasing thermal treatment temperature. This is the result of an increase in grain size as the thermal treatment temperature increases and can be explained from the solute–dislocation interaction model. For these alloys without any thermal heat treatment after cold rolling and those with a 472 K heat treatment after cold rolling, there is a critical strain before the onset of serrated yielding. The critical strain is larger for those after 472K heat-treatment as compared to those without heat-treatment. This result can be explained by the precipitation of Mg atoms from the solid solution when heat-treated at 472 K.

The hot bands of direct chill cast (DC) and strip cast (SC) AA 5182 aluminum alloys were annealed at 454 °C for 3 h, and then cold rolled to different reductions. The ODFs of the cold rolled samples were determined by X-ray diffraction in order to compare the texture evolution of DC and SC AA 5182 aluminum alloys during rolling. The texture volume fractions were computed by a new method, in which the Euler space representing all possible crystallographic orientations in rolling was subdivided into the cube, r-cube, Goss, r-Goss, β fiber, and random orientation regions based on the slip pattern combined with the characteristics of microstructure and texture. Empirical formulae of the texture volume fractions and true strain were constructed to predict the texture of cold rolled DC and SC AA 5182 aluminum alloys. The results show that the processing method (DC vs. SC) strongly affects the texture after annealing at 454 °C and the texture evolution during the subsequent rolling.

Texture, microstructure and formability were studied in direct chill (DC) cast and strip cast (SC) Al–Mg alloys (AA5754 and AA5182) and were found to largely depend on the production processes (DC versus SC) and chemical compositions. DC hot bands are usually fully recrystallized and thus have strong recrystallization textures while SC hot bands have deformation structures and thus strong deformation textures. It is difficult to obtain strong recrystallization textures in SC hot band materials with elevated temperature annealing. However, annealed SC5754 hot bands have stronger recrystallization texture components than annealed SC5182 hot bands. This is due to the fact that a stronger dynamic precipitation occurs in SC5182 hot bands during annealing. As a result, annealed SC5754 hot bands have small 90° earing while SC5182 hot bands have both 90° earing and 45° earing after annealing. Cross rolling of materials with a deformation structure causes a significant texture change in the final cold rolled samples while it causes no texture change in materials with a recrystallized structure. Compared to samples after straight rolling, cross rolling reduces the volume fraction of the deformation texture components (especially the copper component) with little change in recrystallization texture components. Al–Mg alloys are strong and difficult to work. However, the workability can be significantly improved after annealing at an elevated temperature.

A possible source mechanism for non-basal 〈c+a〉 slip dislocations is proposed based on the formation of an attractive junction between glissile 〈a〉 and sessile c dislocations from the prism plane into a pyramidal plane. The driving force for the junction formation, which comes from the long-range elastic interaction between c and 〈a〉 dislocations, is relatively large in most hexagonal close-packed (hcp) metals. Beryllium, which has an unusually low Poisson's ratio, is an exception to this rule. The cross-slip process is energetically unfavorable in Mg and Ti, from a viewpoint of the change in anisotropic elastic line tension, but it becomes favorable in Ti at elevated temperatures above 300°C. Discussion is given on intrinsic stacking fault energies and kinetic aspects of the cross slip.