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In this work, the precipitation behavior and recrystallization behavior of highly alloyed Al-Zn-Mg-Cu alloy with different Zn/Mg ratio were investigated using optical microscope, scanning electron microscope, X-ray diffraction, transmission electron microscope and tensile test. The results indicated that the primary phase increases with Zn/Mg ratio dropping, which increases the nucleation particles and refines the grains. The real solidification path is between Lever law and Scheil model, which is closer to Scheil model. The precipitates are η′ when Zn/Mg ≥ 4.19 in T6 temper. However, it is the co-precipitation of η' and T' when Zn/Mg < 4.19 and the fraction of η' decreases from 100 to 7.6% as Zn/Mg ratio decrease from 4.19 to 1.91. In addition, the impact of residual eutectic phase in a low Zn/Mg ratio alloy on recrystallization behavior and mechanical properties was discussed. Grain boundary primary phases in low Zn/Mg alloys are difficult to completely dissolve during the solid solution. Interestingly, the particle stimulated nucleation occurs preferentially around the second phase and gradually extends to the center of the grain, and there are still low angle grain boundaries in the center of larger original grain. When Zn/Mg > 1.91, the tensile strength increases with Zn/Mg ratio dropping. After Zn/Mg ≤ 1.91, the tensile strength decreases slightly due to the residual second phase. [ABSTRACT FROM AUTHOR]

The quality of extruded profiles depends largely on accurate constitutive models and thermal processing maps. In this study, a modified Arrhenius constitutive model for homogenized 2195 Al-Li alloy with multi-parameter co-compensation was developed and further enhanced the prediction accuracy of flow stresses. Through the processing map and microstructure characterization, the 2195 Al-Li alloy could be deformed optimally at the temperature range of 710~783 K and strain rate of 0.001~0.12 s−1, preventing the occurrence of local plastic flow and abnormal growth of recrystallized grains. The accuracy of the constitutive model was verified through numerical simulation of 2195 Al-Li alloy extruded profiles with large shaped cross-sections. Dynamic recrystallization occurred at different regions during the practical extrusion process, resulting in slight variations in the microstructure. The differences in microstructure were due to the varying degrees of temperature and stress experienced by the material in different regions. [ABSTRACT FROM AUTHOR]

This study systematically investigated the performance and microstructure characterization of cryogenic rolling (CR) and room-temperature rolling (RTR) Al–Mg–Si alloys. The result showed that the hardness of the CR alloys decreased at the early aging stage, but that the hardness of the RTR alloys increased at the early aging stage. Retrogression phenomena were apparent in the CR alloys at the early aging stage. Despite undergoing the same solid solution treatment, a few substructures were still observed in the CR alloys, and the degree of recrystallization in the CR alloys was significantly inferior to that in the RTR alloys. After aging for 50 h, the strength and precipitates' density in the CR 75 alloy were higher than that in the other alloys; this indicated that the substructures were beneficial to precipitation and precipitate growth. A precipitation strength model was employed to illustrate the precipitation contribution at different aging stages. The results showed that the CR 75 alloy obtained the strongest precipitation strengthening. [ABSTRACT FROM AUTHOR]

The thermal deformation behavior of as-forged Al–Zn–Mg-(Cu) aluminum alloy at strain rate 0.001–1 s−1, temperature 663–783 K and deformation degree 0–60% was studied by isothermal compression test, and an accurate strain-compensated Arrhenius constitutive equation was established. Based on the microstructure characteristics of compressed specimens, the effects of strain rate, temperature and strain on dynamic recrystallization (DRX) behavior and substructure evolution were determined. The results show that the alloy undergoes discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX) and geometric dynamic recrystallization (GDRX) simultaneously at high temperature and low strain rate (743 K, 0.001–0.01 s−1), where CDRX includes microshear band assist (MSBA), homogeneous increase of misorientation (HIM) and progressive lattice rotation near grain boundaries (LRGB). However, with decreasing temperature and increasing strain rate, GDRX basically disappears, and DDRX becomes the main DRX mechanism. At medium to high strain rate (0.1∼1 s-1), high-density dislocations accumulate at the grain boundaries and numerous microshear bands form inside grains during the early deformation stage. The misorientation angles of these pre-existing geometrically necessary boundaries gradually increase with temperature and strain, ultimately transforming into subgrains and DRX grains. [ABSTRACT FROM AUTHOR]

The effects of homogenization annealing processes on twin-roll casting (TRC) Al-Mg-Si plates have been studied, the transformation of β -AlFeSi phase to α -AlFeMnSi phase and the recrystallization behavior have been discussed, and the uniformity of the plate has been evaluated. The results show that the hardness from the surface to the center is wildly fluctuating in the TRC plate, the recrystallization level and the morphology of second phases are different between the surface and the center. It indicates that the uniformity of TRC plate needs to improve. After the homogenization annealing process, the uniformity of the plate improves observably. When the homogenization annealing process is 540°C×7 h, the microstructure and properties of TRC Al-Mg-Si plate are uniform, the hardness from the surface to the center fluctuates smoothly, coarse lamellar β -AlFeSi phases have basically transformed into spherical α -AlFeMnSi phase, recrystallization level in the surface is in consistent with that in the center basically. As homogenization annealing temperature rises, the hardness from the surface to the center starts to fluctuate unsteadily. It is concluded that spherical α -AlFeMnSi phases initiate to coarsen, resulting in obvious fluctuations of Mg, Si and Fe elements. the recrystallization levels of the surface and the center are approximate when the process is 560°C×7 h, but the grains have significantly coarsened. • The microstructure characterization of TRC plate has been evaluated by statistical methods. • The uniformity in normal direction has been evaluated. • The microstructure evolutions of TRC plate during homogenization annealing have been clarified. [ABSTRACT FROM AUTHOR]

The complex section cylindrical part with thin-wall and high-rib was obtained through integral-accuracy-extrusion, and the microstructure evolution, recrystallization behavior, texture configuration and strengthening and toughening mechanism were investigated. Samples of different positions all exhibit the microstructure of predominant elongated grains along extrusion direction (ED) surrounded by fine equiaxed grains, but the width of elongated grains in the rib is higher than that in the thin-wall. Except for particle-stimulated nucleation (PSN) mechanism due to the MgZn2, the dominant recrystallization mechanism of all samples should be discontinuous dynamic recrystallization (DDRX), and the parent grains with the orientation of (001)//ED are more susceptible to recrystallization than other orientations. Additionally, more prone to continuous dynamic recrystallization (CDRX) results in a higher recrystallization fraction and a lesser average grain size in the thin-wall. Samples in the rib are dominated by strong copper-type texture, showing the feature of deformation texture; as for sample in the thin-wall, a high strength of Cube texture is displayed. The ultimate tensile strength (UTS) of the sample in the rib is 20 MPa higher than that in the thin-wall, which is mainly attributed to texture strengthening caused by hard orientation grains with smaller Schmid factor (SF), but the elongation of sample in the thin-wall is 30% higher than the rib (15.1% vs 11.6%), showing a superior plasticity, which is related to higher SF, higher recrystallization fraction and more homogeneous microstructure. This research will theoretically guide the manufacture of high-performance complex section Al–Zn–Mg–Zr cylindrical part with thin-wall and high-rib. [ABSTRACT FROM AUTHOR]

Heterogeneous bimodal microstructure and its formation mechanism of Mg-Gd-Y-Zn-Zr alloy during isothermal compression at 450 °C and 0.001 s−1 was investigated in detail. Based on microstructure analysis, Mg-Gd-Y-Zn-Zr alloys with bimodal grain size distribution and bimodal texture distribution were obtained by uniaxial isothermal compression. There were more heavily bimodal levels in grain size and texture at true strain greater than 0.8. There was a significant inhomogeneous plastic deformation between and within the grains in Mg-Gd-Y-Zn-Zr alloy during the deformation, which is attributed to the difference the grain orientation and a large number of intergranular block-shaped LPSO phases. Further studies revealed that particle-stimulated nucleation (PSN) caused by a large intergranular LPSO phases and continuous dynamic recrystallization (CDRX) developed layer by layer toward the grain interior were the main grain refinement mechanisms. This PSN and CDRX mechanism contributed to the fine grains in bimodal grain size distribution and the random texture in bimodal texture distribution. However, the original coarse grains with basal orientation were preserved during deformation due to smaller plastic deformation and energy storage. Meanwhile, grain boundary segregation and intragranular lamellar LPSO precipitate promoted CDRX by retarding DDRX. In addition, the grain boundary pinning effect dominated by grain boundary segregation and intragranular lamellar LPSO precipitate hindered the coarsening of fine DRXed grains, which was the ultimate guarantee for the formation of bimodal microstructure. Ultimately, inhomogeneous plastic deformation, DRX, and grain boundary pinning effect were demonstrated as the necessary conditions for the formation of heterogeneous bimodal microstructure during thermal deformation of Mg-Gd-Y-Zn-Zr alloy. [Display omitted] • The inhomogeneous plastic deformation is a prerequisite for the formation of heterogeneous bimodal microstructure. • The PSN and CDRX are directly contributing to the heterogeneous bimodal microstructure. • Grain boundary pinning promotes heterogeneous bimodal microstructure by inhibiting coarsening of DRXed grains. [ABSTRACT FROM AUTHOR]