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In this work, the deformation behavior of Al-8.1Zn-2.0Mg-1.0Cu-0.2Ag-0.15Zr alloy was studied under isothermal compression, with strain rate and temperature in the range of 0.001 s−1−10 s−1and 330 °C−450 °C, respectively. First, it was found that the deformation temperature significantly affected the dynamic recrystallization (DRX) and phase transformation behaviors of this alloy. At 330 °C, discontinuous dynamic recrystallization (DDRX) and arched grain boundaries were observed, whereas dislocation entanglements dominated continuous dynamic recrystallization (CDRX) was notably detected at 370 °C. Temperatures exceeding 410 °C facilitated the CDRX behavior, as polygonal chain-like subgrains and block-like dislocation loops were found within the new grains. High deformation temperatures also resulted in the amalgamation and growth of adjacent subgrains. Moreover, we found the Ag-containing phase spheroidized and grew at high temperatures, while the deformation had little effect on the Al3Zr. Strain rate also significantly affected the deformation behavior of this alloy. Samples deformed at 0.001 s−1exhibited prolonged deformation time with clear dynamic recovery (DRV) and DRX. At 1 s−1, irregular dislocation distribution was observed, while at 10 s−1, shear band formation induced by deformation instability was evident. Furthermore, the deformation induced η′/matrix interfacial transformation from Zn clusters to a Zn–Mg common interface. Particularly, the precipitation order at grain boundary was proved to be Zn atomic clusters → Zn, Mg atomic clusters (GP zone) → η′ (MgZn2).

In this work, a qualitative and quantitative investigation on inclusions in molten Al–Mg, Al–Cu, and Al–Zn–Mg–Cu alloys, and the evolution behavior of inclusions in these three alloys during off-line and on-line purification steps were studied via the porous disc filtration technique. It was found that the removal of oxide from 2219 and 5A06 aluminum alloys melt via furnace refining is difficult, both of which can only remove the oxide by about 27 %, whereas the furnace refining can remove oxide from 7A04 aluminum alloy melt effectively, it can reduce the oxide by 55 %. Moreover, we determined that the furnace refining and degassing can reduce the boride content in 5A06 aluminum alloy effectively, but the boride content in 7A04 and 2219 aluminum alloy varied little after these two purification processes. Also, the furnace refining and on-line degassing were found to increase the carbide in 7A04 aluminum alloy, which was not found in the other two alloys. Further, we correlated the relationship between the slopes of the melt mass-time curves of the filtrates and the inclusion content for 2219, 5A06, and 7A04 aluminum alloys, which implies a higher concentration of inclusion possesses a lower slope for the melt mass-time curves of the filtrates. The obtained result could offer some guidelines for the production of high-quality ingot for the studied three alloys.

Three relatively novel initial microstructures of Mg–Gd–Y–Zn–Zr alloy were regulated by heat treatment, the deformation behavior of long period stacking ordered (LPSO) phases with different morphology and distribution and their role on recrystallization during thermal deformation were systematically investigated. The interdendritic block-shaped LPSO phases exhibit higher deformation resistance, and shearing, bending, kinking, tearing, dissolution, together with the breaking of plate-shaped lamellae produced by dissolution, are the main deformation mechanisms for them to coordinate deformation. As for the lamellar LPSO phases, deformation behaviors such as shearing, bending, kinking and breaking mainly occur. The interdendritic block-shaped LPSO promote recrystallization through the particle-stimulated nucleation (PSN) mechanism, and the PSN effect is enhanced with the increasing phase fraction, also, the broken block-shaped LPSO have better PSN effect. Recrystallized grains tend to nucleate at the kink of lamellar LPSO and form recrystallized grains bands along the kink bands; the fragmented fine lamellae have better PSN effect, promoting numerous recrystallization nucleation in the severely deformation zone, meanwhile, the joint pinning effect of the fragmented lamellae and precipitates β-phase results in the smaller recrystallized grains size. However, the intragranular continuous large-sized lamellar LPSO strongly pin the dislocation movement and hinder migration of recrystallized grain boundaries along the basal plane and c-axis of lamellar LPSO, making it difficult to achieve extensive lattice rotation, which is not conducive to the recrystallization nucleation. The most remarkable work in this paper is that we clarified the mechanism of different LPSO phases, especially lamellar LPSO phase, on recrystallization behavior, and these findings will provide microstructure regulation guidance for thermal-deformed Mg–Gd–Y–Zn–Zr alloys containing LPSO.

The formation conditions and influence mechanisms of the heterogeneous bimodal microstructure of Mg-9.8Gd-3.5Y-2.0Zn-0.4Zr alloy were systematically studied by thermal compression experiments in the range of 0.001–1.0 s−1and 350–500 °C. Combined with the microstructural characterization, the inherent relationships between the grain structure and the deformation parameters are deeply analyzed. The results indicate that heterogeneous bimodal microstructures composed of fine dynamically recrystallized (DRXed) grains with random orientation and coarsely deformed grains with basal orientation can only be formed under deformation conditions of 40.51 < lnZ < 46.33. This mainly stems from the dominant continuous dynamic recrystallization (CDRX) and particle stimulated nucleation (PSN) mechanisms under this deformation condition. However, dynamic recovery (DRV) and discontinuous dynamic recrystallization (DDRX) dominate isothermal compression process with lnZ > 47.41 and lnZ < 39.74, which eventually lead to unimodal distributions of deformed grains and DRXed grains, respectively. Furthermore, results reveal that deformation parameters have a strong influence on the long-period stacking order (LPSO) phase and grain boundary (GB) segregation. The lamellar LPSO phases and grain boundary co-segregation of Zn, Y, and Gd atoms jointly promote CDRX and inhibit DDRX by preventing GB migration under the condition of 40.51 < lnZ < 46.33, which is ultimately beneficial to the development of heterogeneous bimodal Mg-Gd-Y-Zn-Zr alloy.

Medium temperature compressions were implemented in the range of 433–593 K and 0.001–5 s−1to reveal the workability and dynamic restoration mechanisms of quenched Al-6.2Zn-2.1Mg-0.15Zr alloy. The activation energy evolution with processing parameters was inspected through the modified kinetic equation that derived by integrally considering the strain and deformation parameters, and the results suggested activation energies decreased with the increasing strain rate and deformation temperature while less affected by the increase of strain at a specific strain rate condition. The 3D processing map was constructed to optimize the processing regions, in which two unstable domains yielded by distinct microscopic instabilities were marked whilst the safe working regions could be identified at 533–593 K, 0.001–0.1 s−1with dissipation efficiency >20%. The microstructural evolution of the compressed specimens was examined, and the results confirmed different types of dynamic recovery (DRV) involving dislocation migration and rearrangement were dominate restoration process during the compression. Also, the microstructures of the specimens deformed at unstable domains were characterized, the results revealed fluctuating flow localization, micro cracking and particles debonding as well as dynamic strain aging were responsible for compression failure.

The precipitation thermodynamics and kinetics of the second-phase of the as-quenched Al–Zn–Mg–Cu–Sc–Zr–Ti alloy was investigated by hardness measurements, electrical conductivity, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The results show that: 1) Both the GP zone and η′ phases are strengthening phases, and the strengthening effect of the η′ phase is dominant. The η phase decrease the hardness but increase the electrical electrical conductivity at high temperature. 2) The activation energy of GP zone, η′ phase and η phase are 118.80  kJ· mol−1, 105.74  kJ· mol−1and 273.78  kJ· mol−1respectively. The precipitation formulas are simulated and the precise equations are obtained, which match with experimental values well.

In this study, we investigate the through-thickness shear texture F{111}<112> and r-cube {001}<110> of the AA6016 twin-roll cast sheet under asymmetric rolling (ASR) via simulation and experiments and its recrystallization behaviors after annealing at 330 °C for 60 min. ASR can be achieved by controlling the velocity ratio of the upper and lower rollers to 2.0. Finite element (FE) simulations in case of ASR are used to determine the shear strain through the sheet thickness. Polycrystal simulations are conducted based on the FE results to predict the shear texture. Subsequently, the crystallographic texture of the sheet obtained with unidirectional ASR processes is evaluated. The experimental results show that the F-texture is obtained and that the inhomogeneity was distributed. The F-texture intensity of the sample near the lower roller (sample A) was greater than that of the sample near the upper roller (sample B). The simulation results are in good agreement with the measured results. However, the simulation results obtained with respect to the r-cube texture are greater than the measured results, resulting in considerable deviation. Further, the different recrystallization behaviors of the F-oriented grains (F-grains) are determined based on the sheet thickness. The F-grains associated with sample A can be obtained based on the rolling texture contributed by continuous recrystallization, whereas those associated with sample B can be achieved via discontinuous recrystallization. A considerably inhomogeneous microstructure and texture are observed through the sheet thickness after annealing.

In this study, properties of low-index L12-Al3Nb/Al such as structure stability, thermodynamic, strength, electron properties, unstable stacking fault energy, plasticity, and fracture behavior of interface (L12-Al3Nb(001)/Al(001), L12-Al3Nb(110)/Al(110), and L12-Al3Nb(111)/Al(111)) were systematically studied. The results showed that the structure of the strongest interfaces of L12-Al3Nb(001)/Al(001), L12-Al3Nb(110)/Al(110), and L12-Al3Nb(111)/Al(111) were stacked similar to bulk L12-Al3Nb or Al, with maximum work of adhesion of 2.80 J/m2, 2.99 J/m2,and 1.74 J/m2, respectively. The maximum computed theoretical tensile strength of L12-Al3Nb (001)/Al(001), L12-Al3Nb (110)/Al(110), and L12-Al3Nb (111)/Al(111) interfaces were 18.71 GPa, 16.85 and 11.88Gpa respectively, for the rigid scheme; and 8.91 GPa, 8.52 GPa and 6.98 GPa respectively, for the full-relaxed scheme. Meanwhile, the interfaces were virtually prone to break on the Al side on full-relaxed stretching. Moreover, the partial density of states of the interface indicated that hybridization occurs among the Al-s, Al-p, Nb-s, Nb-p, and Nb-d orbitals, forming s-p-d hybrid orbital. Finally, based on the unstable stacking fault energy and Rice ratio, the interfaces have high plasticity once subjected to shear stress in the <100 > , <110 > , <-110 > , or <11−2> directions, which elucidate the interface properties and understand the underlying mechanism between L12-Al3Nb and Al alloys, thereby provide vital information to guide designing of novel Al alloys.

To better understand the enhanced formability of Al–Mg–Si alloy automotive outer panels by introducing shear texture F{111}<112> orientations, we investigate the shear texture evolution of a twin-roll casting AA6016 sheet with an initial R-cube and E texture during asymmetric rolling (ASR). The macro-textures of the sheet with a deformation of 30%, 50%, and 85% are studied using X-ray diffraction. Results show that the initial R-cube evolved to Dillamore/copper with the increase in strain, whereas the initial E texture is weakened accompanying the enhancement of the F texture during ASR. Moreover, the local recrystallization textures are analyzed using the sheet that has been annealed at 330°C at different times via the ex-situ electron backscatter diffraction. The F texture is dominant for the ASR sheet, which could be attributed to the rapid nucleation and grain growth of grains with F orientation (F-grains). Furthermore, the spatial relationship at 19.7° [1¯10]between the grain with copper orientation and F-grains is another important reason to promote the F orientation development. Finally, the formability of the ASR sheet is found to significantly improve.

In order to obtain the high-temperature flow behavior of Cu-0.5Cr-0.1Zr alloy more accurately, the hot compression test of Cu-0.5Cr-0.1Zr alloy was performed at the strain rates from 0.001 to 1.0 s−1and the deformation temperatures from 600 to 750 °C on a Gleeble-3800 thermo-simulation machine. The results show that the high-temperature flow stress and dynamic recrystallization behavior of Cu-0.5Cr-0.1Zr alloy are affected by strain rate and temperature. The peak stress is obvious under the condition of high temperature and low strain rate, and the flow stress curve shows a clear dynamic recrystallization phenomenon. On the contrary, there is no obvious peak stress at the low temperature and high strain rate, and dynamic softening behavior is mainly based on dynamic recovery. The high-temperature flow stress of Cu-0.5Cr-0.1Zr alloy is expressed as a result of multiple stress actions, such as work hardening, dynamic recovery softening, and dynamic recrystallization softening. The thermal deformation activation energy of this alloy can be calculated as 244.94 kJ/mol. The relationship between the critical stress and the critical strain of dynamic recrystallization and the Zparameter was established through the cubic linear fitting of the work hardening rate curve. Based on the stress–dislocation relation and kinetics of dynamic recrystallization, the constitutive equations before and after critical strain of Cu-0.5Cr-0.1Zr alloy were developed. The predicted stresses of the established DRX constitutive model agree well with the experimental stresses.

ABSTRACTThe uniaxial tensile tests of Hastelloy C-276 were performed under elevated temperature and strain rate. Considering the effects of different deformation parameters, the flow behaviour, microstructure and fracture characteristics were analysed based on the experimental data. From the rheological curves, the typical characteristics of dynamic recrystallisation were observed at a relatively high deformation temperature and low strain rate. Optical microstructures show that the degree of dynamic recrystallisation increases with an increase in temperature. The SEM micrographs show that the amount of precipitates increases with an increase in deformation temperature. Examination of the fracture morphology at high magnifications revealed that the coalescence of microscopic voids is responsible for the fracture failure.

The uniaxial tensile tests of Hastelloy C-276 were performed under elevated temperature and strain rate. Considering the effects of different deformation parameters, the flow behaviour, microstructure and fracture characteristics were analysed based on the experimental data. From the rheological curves, the typical characteristics of dynamic recrystallisation were observed at a relatively high deformation temperature and low strain rate. Optical microstructures show that the degree of dynamic recrystallisation increases with an increase in temperature. The SEM micrographs show that the amount of precipitates increases with an increase in deformation temperature. Examination of the fracture morphology at high magnifications revealed that the coalescence of microscopic voids is responsible for the fracture failure.

ABSTRACTThe influence of Al–Ti–B grain refiners on the microstructures of Zr-containing Al–Zn–Mg–Cu alloy was investigated by optical microscopy and scanning electron microscopy, as well as through tensile and hardness tests. A poisoning effect occurred when the grain refiner was added to the Zr-containing alloy, and the grain size increased significantly. The precipitates in the alloy without the grain refiner were finely distributed, while the phases of the alloy with the Al–Ti–B refiner agglomerated at the grain boundaries, decreasing both the hardness and elongation. The addition of the grain refiner to the alloys markedly increased their hardness and elongation, when coupled with slow cooling, although the peak stress also decreased slightly.

The influence of Al–Ti–B grain refiners on the microstructures of Zr-containing Al–Zn–Mg–Cu alloy was investigated by optical microscopy and scanning electron microscopy, as well as through tensile and hardness tests. A poisoning effect occurred when the grain refiner was added to the Zr-containing alloy, and the grain size increased significantly. The precipitates in the alloy without the grain refiner were finely distributed, while the phases of the alloy with the Al–Ti–B refiner agglomerated at the grain boundaries, decreasing both the hardness and elongation. The addition of the grain refiner to the alloys markedly increased their hardness and elongation, when coupled with slow cooling, although the peak stress also decreased slightly.

Abstract

In this work, the homogenized Al–Li alloys were compressed at different strains (20%–80%) under medium (370 °C) and high temperatures (470 °C), and their microstructures were characterized by SEM, EBSD, and TEM. The evolution of dynamic precipitation (DPN) during thermal deformation and its effect on microstructure and flow behavior were investigated. The results show that obvious flow softening appears with the increase of strain at medium temperature deformation while not at high temperatures, associated with the reduction of solid solution strengthening caused by DPN and the fragmentation of T1precipitates with large aspect ratios. The T1precipitates undergo fragmentation, dissolution and re-precipitation to develop two types of T1bands. Deformation at medium temperatures, DPN inhibits dislocations and (sub)grain boundary movement, and mainly dynamic recovery (DRV) accompanied by little dynamic recrystallization (DRX) occurs. The fine secondary phases at high temperatures are dominated by the pre-existing Al3Zr phase, and some precipitates are observed until 80% strain, however, DPN has little influence on precipitation hardening and DRX and occurs later than DRX. DRX mechanism changes from CDRX (20–60%) to CDRX and GDRX (80%) with strain at high temperatures. Furthermore, the deformed grains tend to develop in <101>//CD (compression direction) fiber texture during deformation, and the texture strength increases with increasing strain and decreasing temperature.

The present study designed a set of extrusion dies with unequal bearing lengths to investigate the extrusion deformation behavior of 2195 Al-Li alloy. With the standard deviation of the velocity field (SDV) and extrusion force as optimization objectives, the extrusion process parameters (billet temperature, die temperature and extrusion speed) were optimized using Taguchi method and orthogonal test. The results indicate that billet temperature is the most significant factor affecting SDV and extrusion force, with a range of 1.287 and 7.076, respectively. Furthermore, the optimal extrusion parameters were determined as billet temperature 420 °C, die temperature 410 °C and extrusion speed 0.2 mm/s, resulting in the SDV value of 0.3345 and the extrusion force of 17.059 MN. The grains on the extruded profile were flattened and elongated both in the extrusion direction and cross-section, showing obvious <111>∥TD and <100>∥TD preferred orientation, and discontinuous dynamic recrystallization (DDRX) and geometric dynamic recrystallization (GDRX) mostly occurred, but no significant differences in grain size were observed, thus verifying the accuracy of the numerical simulation. Additionally, the ultimate tensile strength, yield strength and elongation of the extruded profile reached 437.1 MPa, 345.9 MPa and 11.7%, respectively.

Cryogenic rolling is a promising method to improve the mechanical properties of Al–Mg–Si alloys. In this paper, the effect of artificial aging treatment on the mechanical properties and microstructures of cryogenic rolled Al–Mg–Si sheet is investigated. The hardness and yield strength of cryogenic rolled alloys decrease at the early aging stage, but the hardness and yield strength of room temperature rolled alloys increase at the early aging stage. Besides, substructures (such as dislocations) are observed in cryogenic rolled alloys but not in room temperature rolled alloys after solution treatment, the degree of recrystallization in the cryogenic rolled alloy is inferior to that in room temperature rolled alloy. The differences lead to the difference in strength between cryogenic rolled alloys and room temperature rolled alloys at the early aging stage. A precipitation mechanism is proposed to explain how these substructures promote precipitate nucleation and growth during artificial aging treatment. Based on the precipitation strengthening theory, a precipitation model is used to explain the strengthening contribution from precipitation during aging treatment, the capacity of precipitation strengthening in cryogenic rolled alloy is much higher than that in room temperature rolled alloy.

This study comprehensively investigated the co-segregation behavior of Mg, Zn, and Cu atoms at the Al Σ3(111)[110] symmetrical tilt grain boundary (GB) and its strengthening effect on the GB strength by first-principles calculation. The atoms of the three elements had a strong tendency to segregate at the GB based on the calculation of the segregation energy. The order of their co-segregation was Mg, Zn, and Cu, respectively. The change of the bond lengths between atoms near the GB increased/decreased the charge density attributed to the different atomic radii of the elements. The separation energy and tensile strength of the Al Σ3(111)[110] GB decreased with the preferential segregation of Mg first, then continued decreasing with the co-segregation of Zn, and finally increased with the co-segregation of Cu, decreasing overall. These results suggest that the co-segregation behavior of Mg, Zn, and Cu atoms at the Al Σ3(111)[110] symmetrical tilt GB embrittles the GB and reduces the mechanical properties of the alloy. Besides, O and H atoms further reduce the strength of the GBs co-segregated by Zn, Mg, and Cu.

The influence of Cu content on microstructures and mechanical properties of a highly alloyed Al-10.0Zn-2.6Mg-xCu-0.15Zr alloy with the Cu content in the range of 0 to 3.0 was studied by OM, SEM, TEM, tensile tests, XRD, and DSC. We determined that the Mg(Zn,Al,Cu)2(σ) and Al2Mg3Zn3(T) phases presented in all as-cast alloys, and Al2Cu (θ) phase was found in the alloys with Cu higher than 2.5 wt.%. Also, it is found that the volume fraction of the primary phase increased with the Cu increase. Further, the volume fraction of the residual eutectic phase (REP) increased gradually with the increase of Cu after solid solution, mainly attributed to the low diffusion coefficient of Cu and thus suppressed the dissolution of the second phase. The tensile testing of the aged alloys indicates that the strength of the studied alloys increased significantly with the Cu increase when Cu is lower than 1.0 wt.%, whereas further increase Cu content it decreases. The elongation increases to a peak value fast at low Cu content. After a critical Cu content (1.5 wt.%), a slight decrease is followed. The elongation of highly alloyed Al-Zn-Mg-Cu alloys should consider the coupling effect of grain refinement and REP.

In this work, an Al70Zn10Mg10Cu5Si5medium entropy alloy was for the first time prepared by electromagnetic stirring casting. Electromagnetic casting has little effect on the generated phases in the as-cast alloys, and these phases are mainly composed of the α-Al solid solution, Mg2Si phase, Al2Cu phase, and MgZn2phase. However, the electromagnetic frequency significantly affects the second phase's content, distribution, and morphology, especially for the Mg2Si phase, whose average particle size decreases from 40.0 to 17.7 μm. In addition, the compression mechanical properties were tested at room temperature, and it was found that the hardness, strength, and plasticity were effectively improved by applying a specific electromagnetic frequency. The optimal electromagnetic frequency was 20Hz in this work, under which the corresponding Vickers hardness, ultimate compressive strength δbc, and compressive yield strength δscwere 177 HV, 554 MPa, and 500 MPa, respectively. Moreover, mechanisms on the enhanced mechanical properties for the alloy fabricated with a proper electromagnetic frequency were systematically discussed. This first exploratory study can provide a reference for preparing Al-based medium entropy alloys by electromagnetic stirring casting.