Search

Plastic deformation studies of a peak-aged AA6082 alloy by means of tensile tests at 77 K and 295 K, and related microstructure characteristics obtained by Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD), Transmission Electron Microscopy (TEM) and Atom Force Microscopy (AFM), revealed new results. A simultaneous improvement in ductility and strength occurred at 77 K, but not at 295 K. A higher work hardening accompanied by a more homogeneous slip mode explained the improved properties at 77 K. Pre-stretching at these two temperatures and subsequent tensile testing at room temperature revealed a marked yield point. However, pre-stretching at 77 K exhibited a slightly higher room temperature yield strength and ductility than the condition pre-stretched at 295 K. Annealing after pre-stretching improved ductility and reduced the magnitude of the yield point. Pre-stretching at 77 K and subsequent annealing introduced somewhat higher strength and ductility as compared to the counterpart pre-stretched at 295 K. The observed mechanical behaviour and associated phenomena were directly linked to microstructure characteristics such as deformation substructure history, slip localization, dislocation density and the precipitate β ' /β '' ratio. [ABSTRACT FROM AUTHOR]

Mechanical properties at 77 K and 295 K and surface characteristics of an AA6060 alloy have been studied. The alloy exhibited significant differences in mechanical properties and fracture mechanisms at 77 K in comparison with that at 295 K. When the temperature decreases, the yield strength, the ultimate tensile strength and ductility to fracture are drastically increased from 217.2 MPa, 252.4 MPa, 14.5% to 251.6 MPa, 335.9 Mpa, 21.5% respectively, and the average diameter of dimples decreases from ~8 µm to ~3 µm. It is proposed that the changed behavior at cryogenic temperature can be attributed to an increased accumulation of dislocations at low temperature. Detailed inspections of the deformed polished sample surfaces show that slip localization in wide slip-bands is not promoted at 77 K, indicating that crystallographic slip is homogeneous, while activation of surface slip systems forming wide slip bands is much easier at 295 K and therefore the surfaces were deformed more in-homogeneously and localized. The homogeneity in slip behavior introduced more topography at 77 K than observed at 295 K and the enhanced topography might be due to more 3-dimensional (3D) lattice rotation in grains having a high Schmid factor, hence introducing more accumulation of local displacements in the thickness direction. [ABSTRACT FROM AUTHOR]

Nanostructures of three binary Al–Mg alloys and a commercial AA5182 alloy subjected to high pressure torsion at room temperature were comparatively investigated using transmission electron microscopy, high-resolution transmission electron microscopy, and X-ray line profile analysis. Grain size distributions, dislocation densities, and densities of planar defects including stacking faults and microtwins were quantified. The average subgrain size decreased considerably from 120 to 55 nm as the Mg content increased from 0.5 to 4.1 wt%. The average dislocation density in the alloys first increased to a maximum and then decreased as the Mg content increased and the average subgrain size decreased. The role of Mg solute on these features and the refinement mechanisms associated with the typical nanostructures and faults were interpreted. [ABSTRACT FROM AUTHOR]

Abstract: Defects and deformation structures including 0° and 60° full dislocations, 30° Shockley partials, stacking faults and deformation twins in a nanostructured Al–Mg alloy processed by high-pressure torsion were identified using high-resolution transmission electron microscopy. The twinning mechanism previously predicted by the molecular dynamics simulation, i.e., the homogeneous mechanism involving dynamic overlapping of the stacking faults inside grains, was directly verified. A four-layer twin formed by the dynamic overlapping of four stacking faults was experimentally observed. Deformation twins and stacking faults formed by partial dislocations in ultrafine grains were experimentally confirmed. These results suggest that partial dislocation emissions from grain boundaries could become a deformation mechanism in ultrafine-grained aluminum during severe plastic deformation. [Copyright &y& Elsevier]

Abstract: The precipitation behavior during equal-channel angular pressing (ECAP) performed at room temperature and 175°C in an Al–Mg–Si alloy has been investigated. Dynamic precipitation was in fact observed during severe plastic deformation at both temperatures and reasons for dynamic precipitation were analyzed and compared with that in conventional static aging. The interaction between precipitates and dislocations was investigated and strengthening mechanisms were discussed. [Copyright &y& Elsevier]

Abstract: Deformation structures of a commercial Al–Mg–Si alloy (6082) processed by equal-channel angular pressing at room temperature were characterized by transmission electron microscopy. Deformation twins, which have never been observed in coarse-grained aluminium, were experimentally confirmed together with numerous other features. The possible roles of twinning and different grain boundary structures on the severe plastic deformation (SPD) mechanisms, including grain refinement, were discussed. [Copyright &y& Elsevier]

Abstract: The mechanical properties of a wide range of aluminium alloys are compared after being subjected to severe plastic deformation (SPD), i.e. equal channel angular pressing (ECAP). Alloys involved are AlMg, AlMn, AlMgSi, and AlMgSc. The effect of SPD on mechanical properties is mostly beneficial with age-hardenable alloys, whereas non-age-hardenable alloys tend to be relatively less reacting to SPD as compared to conventional processing. Finally, some challenges in regard to commercialization will be discussed briefly. [Copyright &y& Elsevier]

Abstract: Deformation banding and accompanying texture component rotations towards more stable orientations played an important role to grain sub-division and during the development of new high angle grain boundaries. The low energy dislocation structure (LEDS) approach predicted deformation band size in close correspondence to the present observations, and the proposed grain refinement mechanism. Formation of twin boundaries seemed to play an important role at strains beyond two. [Copyright &y& Elsevier]

Aluminium alloys processed by wire arc additive manufacturing (WAAM) exhibit a relatively coarse microstructure with a columnar morphology. A powerful measure to refine the microstructure and to enhance mechanical properties is to promote grain refinement during solidification. Addition of ceramic nanoparticles has shown great potential as grain refiner and strengthening phase in aluminium alloys. Thus, an Al-Mg alloy mixed with TiC nanoparticles was manufactured by the novel metal screw extrusion method to a wire and subsequently deposited by WAAM. Measures to restrict oxidation of magnesium during metal screw extrusion were examined. Purging of CO2 gas into the extrusion chamber resulted in a remarkable reduction in formation of MgO and Mg(OH)2. TiC decomposed to Al3Ti during WAAM deposition, leading to a significant grain refinement of 93% compared to a commercial benchmark. The presence of remaining TiC nanoparticles accounted for an increased hardness of the WAAM material through thermal expansion mismatch strengthening and Orowan strengthening. Exposure of TiC to moisture in air during metal screw extrusion increased the internal hydrogen content significantly, and a highly porous structure was seen after WAAM deposition. [ABSTRACT FROM AUTHOR]

The PLC band parameters are studied in an AA2219 aluminium alloy using a newly developed laser speckle technique for the direct observation of PLC bands. It is observed that though the magnitude of serration is larger in the solution treated condition, the PLC bands are brighter and sharper in the as-received condition. The band multiplicity is much greater, and band width and band velocity are much lower in the as-received condition as compared to the solution-treated condition. Band angle is not affected by the specimen condition. The specimen orientation, on the other hand, does not make much difference in the mechanical properties, serration characteristics and PLC band parameters of the AA2219 alloy tested in the solution-treated condition. The serration characteristics and PLC band behaviour are also found to be similar in the AA5082, AA7020 and AA2219 alloys tested in the solution-treated condition. These various effects are explained by solute content and microstructure of the material. [Copyright &y& Elsevier]

A newly developed laser speckle technique was used in situ during tensile testing to directly observe PLC bands. Some of the observations are quite different from those hitherto reported. Effect of strain, strain rate, specimen thickness and ageing on band width, band velocity and band angle was studied. All the trends are in accordance with previous studies except that band width is found to increase with strain and reach a plateau. The effect of ageing temperature and time on band parameters is reported for the first time. It is found that different types of precipitates obtained at different ageing temperatures affect PLC band behaviour in somewhat different manner. [Copyright &y& Elsevier]

Wire and arc additive manufacturing (WAAM) of metallic materials is expected to become part of the new industrial revolution. The possibilities for complex designs and superior mechanical properties can in many cases replace traditional manufacturing processes such as casting. In order to benchmark the properties of aluminium WAAM components, a comparative study was performed with two different casting techniques: permanent casting with steel mould and sand mould casting. Aluminium-silicon alloys with near eutectic composition were used for the comparison. Porosity levels, secondary dendrite arm spacing, grain size distribution, tensile strength and microhardness were considered for the comparison. The WAAM material exhibited superior mechanical properties originating from a finer dendritic and eutectic microstructure compared with the castings. A slight anisotropy in tensile ductility was observed in the WAAM material, probably due to a coarse microstructural zone between individual beads. All investigated materials had low levels of porosity, < 1% by area fraction. The comparative study has shown that WAAM of aluminium-silicon alloys is well suited for high-integrity applications. [ABSTRACT FROM AUTHOR]

Microstructure, mechanical properties and wear resistance in an ultrafine-grained Al–Mg–Si alloy fabricated utilizing a combination of equal channel angular pressing (ECAP) and dynamic aging were investigated in this paper. The results indicated that the grain size of the ECAP alloy was significantly refined, i.e., to ~239 nm after three ECAP passes. Meanwhile, the yield and tensile strength of the ECAPed material reached 340 MPa and 445 MPa, respectively, while maintaining a significant uniform elongation of 14%. Wear resistance results demonstrated that the wear rate, wear depth and width of the ECAPed material decreased in comparison with the solution-treated (SST) and peak-aged (T6) conditions under a load range of 5–25 N. The adhesive wear that occurs in the undeformed specimens at 10 N does not appear in the ECAPed specimen at the same load, indicating that the ECAPed specimen delay the appearance of more serious wear mechanisms under certain loads. The cooperative interaction of high density nano-scale β" precipitates and dislocations resulted in a combination of super-high strength and good work hardening ability which suppressed the extension of cracks between the friction layer and the plastic deformation zone. As a consequence, the combination of ECAP and dynamic aging brings a significant improvement for antifriction performance of the 6061 aluminum alloy. Image 1 • Super-high strength and high ductility achieved in an Al–Mg–Si alloy. • Cooperative interaction of nano-scale β" precipitates and dislocations verified. • Enhanced wear resistance resulted via super-high strength and good work hardening rate. [ABSTRACT FROM AUTHOR]

Abstract Al-Mg alloys are a series of low cost and low density Al alloys, which show remarkable strengthening during deformation. In this work, study of commercial purity Al, Al-0.5Mg and Al-4.1Mg alloys was carried out to investigate the effect of Mg on materials strengthening. Slight solid solution strengthening by Mg addition is found in the as-cast alloys. While further significant strengthening effect is achieved in the alloys produced by high pressure torsion. An extraordinarily high strength of ~800 MPa is achieved in the Al-4.1Mg alloy, as a result of deformation induced ultrafine grains, high density stacking faults and Mg segregation. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

The present work revealed that equal-channel angular pressing (ECAP) deformation combined with appropriate annealing could represent as an efficient route to modify immiscible as-cast microstructure of a monotectic Al–8Bi alloy by a complete redistribution of immiscible Bi particles and grain refinement of alloy matrix. Especially, we found that the mean size of Bi particles in the 4-pass ECAPed Al–8Bi sample decreases after annealing at 200 °C for 8 h, due to inverse coarsening driven by the reduction of elastic energy and interfacial energy induced by morphology change and spatial distribution of Bi particles. [ABSTRACT FROM AUTHOR]

Exploring the redistribution mechanism of Mg from the perspective of experimental observation has been a long-term yet challenging attempt in Al-Mg alloys. Here we demonstrate a simple but effective approach to obtain non-uniform Mg solute distribution (i.e., Mg-enriched/depletion zones) around typical grain boundaries (GBs) in a nanocrystalline Al-8 Mg alloy. This abnormal segregation was detected by both high-angle annular dark-field scanning transmission electron microscopy and atom probe tomography. The results show that local strain and GB migration during deformation leads to spatially inhomogeneous Mg solute distribution around the GBs. Both the non-uniform distribution and the broadened GBs can hinder GB migration and dislocation motion, thus enhance the strength. An inhomogeneous solute distribution mechanism of Mg atoms is proposed based on the extensive investigations. This study may help with developing new strengthening mechanisms of nanocrystalline materials. [Display omitted] • Atomic-scale non-uniform Mg solute distribution near typical GBs successfully explored in a nanocrystalline Al-8 Mg alloy. • Both local strain and GB migration lead to spatially inhomogeneous Mg solute distribution around the GBs. • The non-uniform Mg solute distribution (i.e., Mg-enriched/depletion zones) expands the width of GBs. • Both the non-uniform distribution and the broadened GBs hinder GB migration and dislocation motion thus enhance the strength. • A new inhomogeneous solute distribution mechanism of Mg around the GBs proposed. [ABSTRACT FROM AUTHOR]

Cyclic extrusion and compression (CEC) was implemented to process the Mg-Gd-Y-Zr alloy. Microstructure characters, including the matrix grain, precipitates and texture evolution, were tried to correlate with the mechanical performance of the post-processed alloy. Results show that after 14 passes of CEC, the average grain size of GW102K is greatly refined to ~100–200 nm. Secondary-phase particles are broken due to the occurrence of tension tearing and shearing fracture. Quantitative texture analysis elucidates that CEC weakens the initial fiber texture of the extruded GW102K. Unlike most of the severe plastic deformed Mg alloys, the CEC processed GW102K alloy follows the normal Hall-Petch equation, which is closely associated with the disintegrated texture as well as the nanoscale second-phase particles. A considerable increase in elongation is witnessed and the introducing of rare-earth elements (RE) is found to change the deformation mechanisms of the Mg alloy by facilitating non-basal slip systems, twinning and shear bands. [ABSTRACT FROM AUTHOR]

Peak-aged AA6082 flat extrusions were cryorolled at liquid nitrogen temperature to three different thickness reductions, the reductions were 21%, 42% and 85%, respectively. Microstructure and plastic deformation behaviors of the initial as well as the rolled materials were studied by means of scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and tensile tests at room temperature. The initial material showed fibrous grain structure. After cryorolling to 21% thickness reduction, grains in the alloy were obviously elongated and importantly, microband traces were detected in selected grains. More detailed information was obtained in the alloy after 42% thickness reduction. Here, numerous microbands aligned along slip planes with the highest resolved shear stress, producing fragmentation of grains, while rests of elongated grains were microband-free. A cryorolling strain of 85% has been found to be desirable for producing a hierarchical microstructure in the materials volume, featuring nano- and ultrafine grains with size <100 nm coexisted with micro-sized grains. The development of hierarchical microstructure could be considered as a consequence of the intersection between families of microbands. As a result, both the strength and uniform elongation of the severely cryorolled alloy, i.e. 85% thickness reduction, were more superior to other rolled alloys. Therefore, this study revealed that the single processing procedure, i.e., cryorolling, can be utilized to tailor for desired properties in favor of both strength and ductility for peak-aged AA6082 extrusions. [ABSTRACT FROM AUTHOR]

Al-Mg alloys with high Mg contents have attracted considerable interest given enhanced strength and simultaneously reduced density by high Mg solute concentrations. In the present study, we proposed a strategy of strengthening Al‐10wt%Mg binary alloy via heavy cryogenic rolling at liquid nitrogen temperature. Both cryogenic plastic deformation and a high concentration of Mg solute effectively suppress dynamic recovery during rolling, creating nanoscale and ultra-fine laminated grains containing a high density of dislocations in a nearly single-phase solid solution. The as-rolled Al‐10wt%Mg exhibits an average 0.2% offset tensile yield strength of 619 MPa, and average engineering and true ultimate tensile strengths of 689 and 726 MPa, accompanied by average uniform elongation of 5.3% exceeding the threshold value of 5% required for structural engineering applications. The high strength stems from enhanced solid-solution strengthening of a high concentration of Mg solute, significant grain boundary strengthening of nanoscale and ultra-fine laminated grains, and strong dislocation strengthening. The appreciable ductility can be primarily attributed to a high concentration of Mg solute that can retard dynamic recovery processes during tensile testing by impeding dislocation motion, thus enhancing dislocation accumulation and work-hardening ability. A high concentration of Mg solute combined with cryogenic plastic deformation to a high strain magnitude provides a new avenue to achieve ultrahigh strength and good ductility in non-age-hardened Al-Mg alloys. • High Mg containing Al-Mg alloy was processed by cryogenic rolling to high strain. • High Mg content, cryogenic temperature and high strain yield ultra-high strength. • A high concentration of Mg solute enhances dislocation storage and work-hardening. [ABSTRACT FROM AUTHOR]

Bulk nanostructured (NS) metallic materials usually have high strength but extremely low ductility. In this study, we successfully prepared a bulk NS binary Al–7 Mg alloy possessing both high strength and high uniform ductility, approaching ∼600 MPa and ∼14%, respectively, by utilizing room temperature equal channel angular pressing (ECAP) combined with inter-pass annealing. The mechanism that governs the high ductility in the alloy and especially the role of the high Mg solute concentration was explored in terms of microstructure analysis. [ABSTRACT FROM AUTHOR]

In the present investigation, both static and dynamic precipitations of an Al–Mg–Si–Cu aluminum alloy after solid-solution treatment (SST) were comparatively analyzed using differential scanning calorimetry (DSC). Dynamic aging was performed in the SST alloy through equal channel angular pressing (ECAP) at different temperatures of room temperature, 110, 170, 191 and 300 °C. For comparison, static artificial aging was conducted in the SST alloy at 191 °C with two aging times of 4 and 10 h. The DSC analyses reveal that the dynamic precipitation has occurred in the ECAPed samples, while the activation energies associated with the strengthening precipitates in the dynamic samples are considerably higher than the energies in the SST and static aged samples. The higher activation energies are probably attributed to the smaller grains and higher dislocation density developed after ECAP. The results in the present investigation allow the prediction of the type of the dynamic precipitates to influence the strength of the ultrafine grained alloy during ECAP at various temperatures. [ABSTRACT FROM AUTHOR]

Achieving high strength and uniform deformation simultaneously in Al alloys processed by severe plastic deformation (SPD) remains a challenging task as these alloys usually possess high strength but very limited uniform deformability, i.e.<∼4%. In the present work, however, high strength (∼507 MPa) and large uniform elongation (∼11%) were achieved simultaneously in a binary Al alloy by using room-temperature equal-channel angular pressing (ECAP) and a high solute Mg content. Detailed characterization by electron backscattered diffraction (EBSD), conventional transmission electron microscopy (TEM) and delicate ASTAR-TEM orientation imaging has been carried out to reveal the microstructure evolution. It was found that it was difficult to form well-developed substructures in Al–7 Mg deformed by 1 pass or 2 passes of ECAP, in contrast to the pure Al and dilute Al–Mg alloys deformed under similar conditions, where well-aligned subgrains and cells are frequently formed. As a result, a bimodal grain structure, i.e. ultrafine/fine grains with mean sizes of < ∼500 nm were developed accompanied by micron-sized grains having a high dislocation density after 3 passes. The high strength is due to a combination of strengthening by the high density of dislocations, ultrafine grains and high solute Mg content. The high uniform elongation is due primarily to the enhanced work hardening resulted from the high solute Mg content and the bimodal grain structure, while the dynamic strain aging effect is supposed also to contribute to the high ductility. Most importantly, the present work revealed that inhomogeneous deformation during SPD introduced by high solid-solution contents can be utilized as a strategy to generate desirable bimodal grain structure, gaining both a high strength and high uniform ductility. [ABSTRACT FROM AUTHOR]

Abstract: The deformation behavior of a soft particle containing Al–8Bi hypermonotectic alloy during equal-channel angular pressing was studied. The size, shape and distribution of soft Bi particles are substantially modified via shearing, fragmentation, coalescence and ripening. It is found that the soft Bi particles have a strong influence on promoting refinement of Al grains via particle stimulated continuous dynamic recrystallization. The present work provides an effective methodology to obtain monotectic aluminium alloys with well-dispersed soft phase particles. [Copyright &y& Elsevier]

Abstract: Metallic materials processed by severe plastic deformation generally possess very high strength but a rather low uniform elongation, usually <5%. In the present Al–7Mg alloy processed by room temperature equal channel angular pressing combined with inter-pass annealing, impressive combination of high ductility (elongation~14.5%) and high strength (UTS~600MPa) was achieved. The high ductility was rationalized by an enhanced work hardening originated from the pronounced dynamic strain aging effect and a bimodal grain structure. The high strength was mainly due to a prominent grain refinement and high dislocation density. [Copyright &y& Elsevier]

Abstract: The annealing response in a binary Al–7Mg alloy processed at room temperature by equal channel angular pressing (ECAP) has been investigated via X-ray diffraction (XRD), electron-probe micro analysis (EPMA) and electron backscattering diffraction (EBSD). After ECAP and subsequent annealing, Mg remains mainly homogeneously distributed in solid solution. A bimodal structure with ultrafine grains accompanied by micrometer-sized crystallites was developed after 3 passes. Upon annealing at ~275°C for 96h, extensive recovery was observed in the as-deformed material, leading to a relatively uniform microstructure; at ~300°C a discontinuous recrystallization initiated in less than 30s with subsequent grain growth clearly evident. Such remarkable thermal stability, i.e., slower recovery and recrystallization kinetics, of the present material, in contrast to other severely deformed commercial pure Al and Al–Mg alloys, is due mainly to the presence of high Mg solid solution contents, the formation of the bimodal structure consisting of both coarse crystallites and ultrafine grains. In addition, the possible Mg-containing precipitates during annealing might also retard the recrystallization kinetics. [Copyright &y& Elsevier]

• The superplastic response is studied in an Al–7Mg alloy with multi-scale microstructural heterogeneities. • The Al–7Mg exhibits enhanced thermal stability and superplasticity of ∼523% at 573 K and 1 × 10−3 s−1. • Enhanced thermal stability owes to cooperative effects of bimodal grain structure and mg segregation along GBs. • The high superplasticity is due to a cooperated mechanism involving dislocation slip accommodated by CDRX and GBS. Achieving high superplasticity in single-phase Al alloys remains a challenge, since the fine-grained structure required for superplastic deformation coarsens rapidly in the absence of dispersed second-phase particles during tensile deformation at elevated temperatures. This paper concentrates on the superplastic response of a high solid solution Al–7Mg alloy processed by equal-channel angular pressing (ECAP) under uniaxial tension. The ECAP-processed Al–7Mg alloy features multi-scale microstructural heterogeneities including a bimodal grain structure and Mg solute segregation along grain boundaries (GBs) of nano/ultrafine grains. To identify effects of multi-scale microstructural heterogeneities on superplastic deformation behavior of the high solid solution Al–7Mg alloy, microstructural evolutions are studied systematically by combing electron backscatter diffraction (EBSD), ASTAR-transmission electron microscopy (TEM) orientation imaging and atom probe tomography (APT). During deformation at the optimal tensile condition of 573 K and 1 × 10−3 s−1, the heterogeneous microstructure evolves to a stable uniform fine grain structure via continuous dynamic recrystallization (CDRX), and impressive superplasticity of ∼523% elongation is achieved. The high superplasticity is discussed in terms of the cooperated mechanism by dislocation slip accommodated by CDRX at the early tensile deformation stage and grain boundary sliding (GBS) at the late deformation stage. Our findings show that the evolution of microstructural heterogeneities in high solid solution Al–Mg alloys can be regulated, favoring for superplastic deformation, which offers an alternative strategy for developing low-cost Al alloys for enhanced mechanical properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The evolution of microstructure and texture of an extruded GW102K Mg alloy processed by cyclic extrusion and compression (CEC) at 450°C were investigated. Tensile tests were performed at room temperature and strain rate 5×10−3 s−1. The results show that the microstructure was effectively refined, and the initial fiber texture became disintegrated and developed a new texture after 14 CEC passes. It was found that the strength and ductility were simultaneously increased compared with the as-extruded alloy. In particular, the elongation and yield strength were related in a line relationship having a positive slope. As the texture changed and texture intensity decreased, substantial grain refinement was observed. The hard second-phase particles were considered to be responsible for the uncommon properties of the GW102K alloy processed by CEC. [Copyright &y& Elsevier]

Abstract: Electron Backscatter Diffraction (EBSD), transmission electron microscopy (TEM) and optical microscopy (OM) are employed to characterize the microstructure evolution of AZ31, AZ61 and AZ91 Mg alloys during cyclic extrusion compression (CEC). The results show that CEC is an efficient grain refinement method for magnesium alloys. The most effective CEC pass is the first pass. There exists a critical CEC pass for three Mg alloys and beyond this critical pass the grain size and the homogeneity of microstructure retains almost constant. With increasing CEC passes, the fraction of low angle grain boundaries (LAGBs) tends to decrease and the average misorientation angle increases. Typical network shape structure of fine grains is obtained in the microstructure of AZ31 Mg alloy with fewer Mg17Al12 particles after CEC 7 passes. The microstructure of the different Mg alloys at the same number of passes becomes more homogeneous as Mg17Al12 particles increase from AZ31, AZ61 to AZ91. The Mg17Al12 particles promote increases of the fraction of high angle grain boundaries (HAGBs), the dislocation density, the refinement process of coarse grains at initial CEC pass, and the texture randomization and delay the formation of network shape structures. [Copyright &y& Elsevier]

Abstract: The microstructure and texture development of an extruded ZK60 Mg alloy during cyclic extrusion and compression (CEC) at 230°C was investigated. Tensile tests were performed at room temperature at a strain rate of 1×10−3 s−1. The results show that the microstructure was effectively refined by the CEC processing. The initial fiber texture became disintegrated during CEC processing and developed a new texture. After CEC 4-passes, the elongation-to-failure significantly increased almost three times compared with that of as-extruded alloy. Texture change and grain refinement were considered to be responsible for the large tensile ductility in the CEC processed ZK60 alloy. Furthermore, the smaller intensity of texture of CEC processed specimen may be another reason for the large ductility. [Copyright &y& Elsevier]

Processing of aluminum alloys by wire arc additive manufacturing (WAAM) gained significant attention from industry and academia in the last decade. With the possibility to create large and relatively complex parts at low investment and operational expenses, WAAM is well-suited for implementation in a range of industries. The process nature involves fusion melting of a feedstock wire by an electric arc where metal droplets are strategically deposited in a layer-by-layer fashion to create the final shape. The inherent fusion and solidification characteristics in WAAM are governing several aspects of the final material, herein process-related defects such as porosity and cracking, microstructure, properties, and performance. Coupled to all mentioned aspects is the alloy composition, which at present is highly restricted for WAAM of aluminum but received considerable attention in later years. This review article describes common quality issues related to WAAM of aluminum, i.e., porosity, residual stresses, and cracking. Measures to combat these challenges are further outlined, with special attention to the alloy composition. The state-of-the-art of aluminum alloy selection and measures to further enhance the performance of aluminum WAAM materials are presented. Strategies for further development of new alloys are discussed, with attention on the importance of reducing crack susceptibility and grain refinement. [ABSTRACT FROM AUTHOR]

Experimental evidence demonstrated that equal channel angular pressing (ECAP) at cryogenic temperature, in comparison with ECAP at room temperature, led to promoted strength-ductility synergy in an Al-2.5wt.%Cu alloy. The simultaneous improvement is related to microstructural hierarchy of multimodal grains, low angle grain boundaries, and inter/intragranular precipitates, which was tuned by aging treatment in match with the low-temperature ECAP. The artificial aging could maintain multimodal grain size distribution, introduce a large number of low angle grain boundaries and produce intragranular precipitates to improve strength/ductility. A minor 0.3wt.% Sc addition was effective in optimizing the precipitations and further boosting the strength/ductility combination. The underlying mechanisms for higher strength and greater ductility were rationalized in terms of the low-temperature ECAP. [Display omitted] [ABSTRACT FROM AUTHOR]

The effect of Zr and Er on the microstructure, electrical conductivity and mechanical properties of Al-0.4Fe alloy was investigated using optical microscope (OM), scanning electron microscope (SEM), electron back-scattered diffraction (EBSD), transmission electron microscope (TEM) and energy dispersive x-ray spectroscopy (EDS). It is revealed that both of the Zr and Er could inhibit the recrystallization process of Al-0.4 wt %Fe alloy due to the formation of Al 3 Zr or Al 3 Er particles. Zr is more recrystallization-resistant than Er due to the preferential precipitation of Al 3 Zr. Both of the Zr and Er could modify the morphology of Al 3 Fe particle from needle-like to sphere-like or rod-like, which reduce the negative effect of Al 3 Fe phase. Zr could significantly refine dendrites of the Al-0.4Fe alloy, while Er shows a negligible effect on dendrite refining due to the delayed formation of Al 3 Er during solidification. However, the low solubility of Er is beneficial for strength and electrical properties of Al-0.4Fe alloy. In consideration of strength and electrical conductivity, the Al-0.4Fe-0.2Er is selected as the best alloy among the four alloys, which shows a yield strength of 145 MPa, elongation at fracture of 8% and electrical conductivity of 61.2 %IACS after cold-rolling. The results provide an insight in design high strength, high conductive aluminum conductor material. • The coarse needle-like Al 3 Fe phases could be modified into sphere- and rod-like small particles by Zr and Er additions. • Synergetic improvement of strength and conductivity in Al-0.4Fe-0.2Er alloy is gained. • Co-adding Zr and Er improves recrystallization resistant capability of the Al-0.4Fe alloy better than the single one. [ABSTRACT FROM AUTHOR]

Cast Al–Mg alloys with high Mg content have attracted considerable interest as a result of exceptionally low mass density and enhanced Mg solid-solution strengthening effect. However, poor ductility in this class of cast Al–Mg alloys originating from the increased amount of brittle Al 3 Mg 2 phase presents a challenge. This work aims to improve ductility of a cast Al-10 wt%Mg alloy by prolonging time and/or increasing temperature during solid-solution treatment, hence minimizing the amount of the Al 3 Mg 2 phase. The amounts of Al 3 Mg 2 decrease and the concentrations of solute Mg increase with prolonging time and/or increasing temperature, improving both ductility and strength. Solid-solution treatment at 425 °C for 9 h or at 438 °C for 3 h induces complete dissolution of the Al 3 Mg 2 phase, achieving an average uniform elongation of ~27% accompanied by an average 0.2% offset yield strength of ~186 MPa. The mechanisms improving both ductility and strength are discussed. [ABSTRACT FROM AUTHOR]

An Al-0.4Fe-0.15Zr-0.25Er alloy was processed by high pressure torsion (HPT) at room temperature in order to explore the evolution of property, microstructure and texture during HPT. The evolution of microstructure revealed by electron back-scattered diffraction (EBSD), transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS). The microhardness increases with increasing strain up to 60 HV at a strain of about 12, and then decreases slightly to a steady stage. HPT processing leads to a significant increase (>100%) in microhardness at expense of a slight reduction (<3%) in electrical conductivity. The synchronous improvement in microhardness and electrical conductivity is obtained after aging. A significant decrease from 40 μm to 600 nm in grain size is observed after HPT deformation for 5 turns and beyond. HPT processing might accelerate the dissolution of the Al 3 (Zr,Er) precipitate. The A- {111} <110>and C- {001} <110> texture components are dominating after 0.25 turn. After 1 turn, the A and C components weaken, and the {112} <111> new component appears. The texture is weak and close to random due to recovery and recrystallization after 5 turns and beyond. • HPT processing leads to a significant increase in microhardness at expense of a slight reduction in electrical conductivity. The synchronous improvement in microhardness and conductivity is obtained after aging. • The grain size was significantly decreased from 40 μm to 600 nm by HPT. HPT might accelerate the dissolution of the Al 3 (Zr,Er) precipitate. [ABSTRACT FROM AUTHOR]