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The effects of double-step homogenization processes on the precipitation of Al3Zr dispersoids and the dissolution of the primary phases of 2196 aluminum alloy were studied by optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was revealed that first-step homogenization facilitates the nucleation of Al3Zr, while second-step homogenization results in the dissolution of the primary phases and the growth of Al3Zr dispersoids. The nanosized θ' precipitates formed in the first-step homogenization are dissolved after the second-step homogenization. The optimum homogenization process was selected as 400 °C/10 h + 520 °C/24 h, which effectively dissolves the primary phases and promotes the formation of refined distribution of Al3Zr dispersoids. This phenomenon is mainly caused by the highest nucleation rate of the Al3Zr phase at 400 °C. While reducing the heating rate of the homogenization process can increase the number density of the Al3Zr dispersoids and reduce the precipitate free zone (PFZ), it does not alleviate the inhomogeneity of the Al3Zr precipitation. These results are expected to be meaningful for tailoring the industrial homogenization processing of as-cast Al-Cu-Li alloy. [ABSTRACT FROM AUTHOR]

The precipitate evolution mechanism of the Al-Mg-Si alloys with a Si-rich composition have been a long-term challenge due to the complex transformation paths among multiple precipitates. In the present work, the interactive transformation process of multiple metastable precipitates in a Si-rich Al-Mg-Si alloy were thoroughly studied by atomic resolution high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), in-situ heating TEM and first-principles calculation. It was revealed that the β″ phase transforms simultaneously to various types of precipitates in the over-aged stage. Two different evolution paths are proposed. Firstly, the β″ phase transforms directly to the U1, U2 and β′ phases. Secondly, the U2 phase, as an intermediate phase, transforms to the U1, β′ and B′ phases during the prolonging aging. The formation and evolution of substructures, including the QP lattice and Al–Si columns, are the key for structural transformation of precipitates. During the severe over-aging, the evolution of precipitates is governed by the dissolution of small precipitates (β′ and B′ phases) and the growth of the large ones (U1 phase). These results provide scientific basis for both property improvement of the commercial Al-Mg-Si alloys and development of new 6xxx aluminum alloys. [ABSTRACT FROM AUTHOR]

The precipitation mechanism of the Q phase in Al-Mg-Si-Cu alloys has long been the subject of ambiguity and debate since its metastable phase (Q′) has the same crystal structure and similar lattice parameters as its equilibrium counterparts. In the present work, the evolution of the Q′ (Q) phase during aging is studied by combination of quantitative atomic-resolution scanning transmission electron microscopy and atom probe tomography. It was found that the transformation from the Q′ to the Q phase involves changes of the occupancy of Al atoms in atomic columns of the Q′ (Q) phase. The Al atoms incorporated in the Cu, Si and Mg columns are gradually released into the Al matrix, while mixing between Cu and Si atoms occurs in the Si columns. This transformation process is mainly attributed to the low lattice misfit of the equilibrium Q phase. Besides, the formation of various compositions of the Q phase is due to the different occupancy in the atomic columns of the Q phase. The occupancy changes in the columns of the Q phase are kinetically controlled and are strongly influenced by the alloy composition and aging temperature. [ABSTRACT FROM AUTHOR]

Abstract The orientation relationships (ORs), segregation behavior and morphologies of β' precipitate in an over-aged Al-Mg-Si-Cu alloy are systematically characterized by atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Six different ORs and two morphologies, i.e. rod- and lath-like are revealed for β' precipitates, and Cu segregation at the β′/α-Al interface is observed in all these precipitates. The rod-like β' precipitate has multiple β'-angles ranging from 6.1° to 14.1° and non-uniform Cu segregation at the β′/α-Al interface, while the lath-like β' precipitate has a constant β'-angle of 0° and a periodic Cu segregation. These different ORs are explained to be attributable to the rotation of QP lattice, a near-hexagonal network of Si columns formed within β' precipitates, which causes different lattice matching of β′ with α-Al lattice. These findings provide new insights in controlling the precipitation hardening and mechanical properties of this type of alloys. Highlights • Six different ORs and two morphologies are revealed for β' precipitates. • The multiple ORs of β' are attributable to the rotation of QP lattice. • Cu segregation is observed at the β′/α-Al interfaces. [ABSTRACT FROM AUTHOR]

Solidification microstructure, precipitation microstructure, and mechanical properties of foundry Al-Si-Cu-Hf alloy were investigated to elucidate the role of Hf during the solidification and precipitation processes. In the as-casting condition, α-Al dendrites, eutectic Si phases, and intermetallic compounds (Al 2 Cu, the needle-like β-Fe and Chinese-script α-Fe) were observed in the base alloy. However, no β-Fe was detected in the modified alloy, strongly indicating that Hf addition promotes the formation of the α-Fe phase but suppress the formation of the β-Fe phase. Furthermore, Hf addition can result not only in the formation of Hf-containing intermetallic compounds with different morphologies, which were identified as Si 2 Hf, but also, more importantly, in a significant decrease in the size, number, density, and volume fraction of porosity. After treatment with solution at 520 °C for 20 h, the formation of thermally stable Si 2 Hf precipitate was observed. After aging treatment at 180 °C up to 72 h, a delayed aging hardening was observed, which may be because Hf addition suppressed the formation of θ’ precipitate. Clearly, Hf addition in Al-Si-Cu alloy can modify the solidification microstructure and the precipitation microstructure, which is believed to be beneficial for mechanical properties. Indeed, a significant increase in elongation by 51.4% without a sacrifice of strength was obtained, compared with the unmodified Al-Si-Cu alloy. This investigation highlights the importance of a well-controlled solidification microstructure and precipitation microstructure for the improvement of mechanical properties, in particular to elongation. [ABSTRACT FROM AUTHOR]

The solution heat treatment of AA6014 sheet is important to meet the required dent resistance in assembled automotive structures. In this study, the effect of solution heat treatment conditions on the Mg 2 Si particle size distribution and volume fraction were quantitatively investigated using SEM observations, electrical conductivity, and hardness measurements. Precipitation during artificial aging was studied by DSC analysis. After soaking at 570 °C for 1min, the volume fraction of soluble Mg 2 Si was reduced dramatically from 1.58% to nearly zero. Hardness measurements, EC, and SEM characterization of T4 samples were compared as measures of Mg 2 Si dissolution. [ABSTRACT FROM AUTHOR]

The natural aging (NA) and artificial aging (AA) behavior of Al-Mg-Si-Cu alloys with different Mg/Si ratios and Cu additions were systematically investigated by means of hardness test, atom probe tomography, transmission electron microscopy, and Monte Carlo simulation. The Si-rich low-Cu alloys displayed higher hardness compared to the Mg-rich equivalents because Si atoms play a dominant role in clustering of solute atoms during both natural and artificial aging. In the high-Cu alloys, Cu did not obviously change the cluster distribution during NA, but significantly refines the clusters and precipitates due to the strong interaction of Cu atoms with Mg atoms during AA. In contrast to the low-Cu alloys, the Mg-rich high-Cu alloys exhibit higher hardness in the early and over-aged stages of artificial aging, with similar or slightly higher hardness in the peak aging condition compared to their Si-rich counterparts. Three types of precipitates ( β″, Q′, and L) are favored in the high-Cu alloys. The Mg-rich high-Cu alloy has more L phase, while the Si-rich variant is abundant in Q′ phase. The negative effect of NA on subsequent AA behavior is less dependent on Mg/Si ratio in the high-Cu alloys due to a synergistic action of the residual Si and Cu atoms, but is closely related to Mg/Si ratio in low-Cu alloys. [ABSTRACT FROM AUTHOR]

The morphologies and orientation relationships (OR) of the Q′ phase in an over-aged Al––Mg–Si–Cu alloy were characterized by atomic resolution high-angle annular dark-field scanning transmission electron microscopy. Statistical results revealed that the OR of the rod-like Q′ phase with the Al matrix has a variable angle ranging from ~ 3.4° to 15.5° between ( 11 2 - 0 ) Q′ and (510) α , while the lath Q′ phase has a conventional OR with a constant angle of 11°. Such variations likely to be attributable to the ordering of Si-network in the Q′/β″ phase formed in the peak aging condition. [ABSTRACT FROM AUTHOR]

The natural aging and artificial aging behaviours of Al-Mg-Si-Cu alloys with different Mg/Si ratios and Cu additions were investigated using Vickers microhardness measurements, differential scanning calorimetry (DSC) analysis and transmission electron microscopy (TEM) characterisation. Excess Si and Cu additions enhanced the alloy hardening ability during natural (NA) and artificial aging (AA). Alloys with low Cu and high Si contents exhibited higher precipitation hardening than alloys rich in Mg during artificial aging. In contrast, the alloys with high amounts of Cu were less dependent on the Mg/Si ratio during precipitation hardening due to their similar aging kinetics. The main precipitate phases that contributed to the peak-aging hardness were the L, Q′ and β″ phases. In the over-aging conditions, the alloys rich in Mg and Cu had finer and more numerous precipitates than their Si-rich equivalents due to the preferential precipitation of the L phase. The combination of excess Mg and high Cu resulted in an alloy with a relatively low hardness in T4 temper and a relatively higher hardness after the paint baking cycle. Thus, this alloy has good potential for use in auto body panel applications. [ABSTRACT FROM AUTHOR]

Abstract: One of the main problems of using Al3Zr in order to stabilize the microstructure in aluminium alloys, i.e. to inhibit recrystallization, is that these dispersoids usually are heterogeneously distributed. The areas of low dispersoid number density makes such alloys prone to recrystallization, and in this work it was therefore attempted to generate a homogeneous distribution of Al3Zr by subjecting two Al–Zr–Mn alloys to a homogenization treatment at 630°C in order to remove the microsegregation of Zr, i.e. to ensure that the driving force for dispersoid formation was equal throughout the microstructure prior to precipitation annealing. Homogenized variants were then compared with unhomogenized variants with respect to recrystallization resistance after cold rolling. The results showed, however, that the homogenization treatment led to a reduced structural stability. This was mainly caused by particle stimulated nucleation (PSN) of recrystallized grains in the deformation zones around coarse Mn-bearing phases that developed during the homogenization, and also by a reduced number density of Al3Zr dispersoids. [Copyright &y& Elsevier]

6000-series aluminium alloys with high Cu or excess Si addition were susceptible to intergranular corrosion (IGC). In order to obtain good IGC resistance, four alloys with low/high Cu and various Mg/Si ratios were designed. The corrosion behaviour of four alloys was investigated by accelerated corrosion test, electrochemical test and electron microscopies. It was revealed that IGC susceptibility of alloys was the result of microgalvanic coupling between the noble grain boundary precipitates and the adjacent precipitates free zone (PFZ), which was closely related to a combination of Cu content and the Mg/Si ratio. Excess Mg could improve the IGC resistance of alloys by forming discontinuous precipitates on the grain boundaries. The designed alloy with high Cu and excess Mg has the same corrosion level as the commercial alloy with low Cu and excess Si, which provides possibility for developing new alloy. [ABSTRACT FROM AUTHOR]

The disordered structures of the Q′ and C phases in the over-aged Al–Mg–Si–Cu alloy were studied by the atomic resolution high-angle annular dark-field scanning transmission electron microscopy and density functional theory calculations. A Cu cluster-like zone is found in both the well-ordered and disordered regions of the disordered precipitates, which acts as a stable skeleton of these phases. The statistic result shows that the C phase is more preferential to produce disordered structure than the Q′ phase. The mechanism for forming the highly disordered C phase is attributed to the relatively weak metallic bonding between the Al–Si1 and Mg2–Si1 atoms. [ABSTRACT FROM AUTHOR]

The impact of three main alloying elements (X = Cu, Zn, and Mg) on the precipitation evolution and structural stability of L1 2 -Al 3 Zr dispersoids in heat-resistant Al-X-0.2 wt% Zr alloys (4–5 wt% X) has been thoroughly examined experimentally. In line with earlier predictions, all three elements are found to be effective in promoting L1 2 precipitation during heat treatment at 500 °C, but with clearly different outcomes revealed: Zn is most effective in refining the dispersoid microstructure, Cu is most effective in increasing the L1 2 phase thermal stability, while Mg is promoting the precipitation kinetics the most strongly. These phenomena may be linked primarily to the different partitioning concentrations of the three elements within the L1 2 -Al 3 Zr dispersoids. It is observed that 11 ± 2. (at. %) Cu and 17 ± 2 (at. %) Zn, respectively, are incorporated in the particles, replacing Al atoms, while Mg incorporation appears marginal. The increased precipitation kinetics with Mg addition is evidenced by the dispersoid number density peaking much earlier in this alloy. This beneficial result however is hampered by primary Al 3 Zr particle formation, together notably limiting the number density. Both Cu and Zn can increase the energy barrier to anti-phase boundary (APB) activation, extending the L1 2 stability range. Cu is more effective as the Cu-APB repulsion is almost twice as strong as the Zn-APB repulsion, but theory predicts that this difference may be eliminated with higher Zn incorporation. These findings resolve the fundamental individual influence mechanisms of three key main alloying elements on the precipitation of Al 3 Zr dispersoids, which is essential for regulating the properties of various aluminum alloys. [Display omitted] • Cu, Zn and Mg are effective in promoting L1 2 precipitation during heat treatment. • About 10.6 ± 2.2 (at. %) Cu and 16.5 ± 1.7 (at. %) Zn are incorporated in the L1 2 -Al 3 Zr dispersoids. • Cu is more effective in promoting the stability of the L1 2 phase compared with Zn. [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]

The effect of individual and combined additions of different transition metals (TMs), Mn, Cr, and Ni, on the precipitation of dispersoids and the final mechanical properties of Al–Mg–Si–Cu alloys was systematically studied by scanning electron microscopy, transmission electron microscopy and tensile testing. The various TM additions examined are found to induce notably different dispersoid precipitation behaviors. The combined addition of Mn, Cr produces the highest number density of dispersoids among the three TM-added alloys examined, due to the incorporation of Cr promoting the precipitation of the α-Al(Mn, Cr, Fe)Si dispersoid. By contrast, the combined addition of Mn, Ni slightly suppresses the precipitation of the α-Al(Mn, Ni, Fe)Si dispersoid compared with individual Mn addition. The presence of a fine dispersoid microstructure can moderately increase the strength, and strongly increase the elongation, especially for the case of the combined Mn, Cr added alloy, where the elongation is increased almost threefold compared with the base alloy. An excellent strength-elongation combination, with an ultimate tensile strength of 421.9 ± 2.2 MPa and an elongation of 18.2 ± 3.6, is achieved for this alloy. This property is superior to most reported 6xxx alloys. The main reasons for this result are the presence of a high number density of dispersoids promoting grain refinement, providing high Orowan hardening, and reducing stress concentration on the grain boundary. The findings of this work are expected to provide guidance for developing new Al–Mg–Si–Cu alloys with excellent comprehensive mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract The strain-controlled low cycle fatigue (LCF) behaviour at 300 °C and the microstructure of Al-7Si-0.3Mg casting alloys with additions of Zr and/or Hf are studied. Microstructural characteristics are investigated in detail by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is found that the Zr- and/or Hf-rich primary particles and precipitates form in the alloys and have a significant effect on the fatigue properties. The cyclic softening characteristics are mainly attributed to the combination of the effects of the interaction of dislocations with nanobelt-like precipitates and an over-ageing phenomenon in the Mg 2 Si phase during the LCF test at 300 °C. The dislocations climbed over the nanobelt-like precipitates and tangled around the rectangle-like precipitates. Fatigue cracks initiated from the specimen surface, and crack propagation was characterized by dimple-like features coupled with fatigue striations. The best fatigue resistance of Al-7Si-0.3Mg-0.14Zr-0.44Hf casting alloy is related to the combination of morphological changes of the primary phase, the pinning effect of the Zr + Hf-rich precipitates and the different fracture characteristics. Highlights • Al-Si-Mg alloys with Zr/Hf additions exhibit cyclic softening behaviour at 300 °C. • The dislocations climb over nanobelt-like Zr/Hf-rich precipitates. • The dislocations tangle around rectangle-like Zr/Hf-rich precipitate and Si particles. [ABSTRACT FROM AUTHOR]

The purpose of this work is to explore new possible precipitates, unveil their crystal structures as well as the precipitation sequence in an Al-Si-Mg-Hf heat treated alloy. Precipitates in the Al-Si-Mg-Hf alloy after heat treated at 560 °C for various holding times are investigated by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy dispersive x-ray spectroscopy (EDS). Three kinds of precipitate phases and their crystal structures, i.e., Si 3 Hf (metastable phase, cubic L1 2 structure), Si 2 Hf 2 (metastable phase, tetragonal structure) and Si 2 Hf (stable phase, orthorhombic structure), are identified based on the atomic resolution HAADF-STEM micrographs. The precipitation sequence in the alloy is first proposed as: Si-Hf clusters→Si 3 Hf→Si 2 Hf 2 →Si 2 Hf. This precipitation sequence is further confirmed by the first principle calculation. These results are probably useful for developing new aluminum alloys with high temperature stable strengthening phases in automotive applications. [ABSTRACT FROM AUTHOR]

The effect of homogenization process on the microstructures and mechanical properties of the twin-roll casted (TRC) 8006 alloy strip during various thermomechanical processing was systematically studied by optical microscope, tensile testing, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) characterizations. The results show that the coarse-grained layer is easily activated at the strip surface due to the severe microstructure gradient throughout the entire strip, which is related to the accumulation of high storage energy at the strip surface. With the increasing homogenization temperature, the coarse-grained layer increases and the dendrite network generally dissolves, broken and spheroidized, which produce a fully recrystallized grains with discrete distributed second phase particles after homogenization at 580 °C. After cold rolling and final annealing, depending on the homogenization temperatures, the 1 mm sheets exhibit three- or five- layer sandwich structure. This phenomenon is mainly caused by the uneven distribution of second phase particles and deformation levels at the surface and center regions of the sheets. Increasing the homogenization temperature can reduce the tensile strength but increase the elongation of the 1 mm annealed sheet due to the different grain and second phase distributions. Homogenization of 540 °C/3 h is selected as the optimum process as it provides good combination of high strength, good elongation and rather thin coarse-grained layer. [Display omitted] • The thickness of coarse-grain layer increase and the dendrite network dissolves during homogenization. • Increasing the homogenization temperature can significantly reduce the strength and improve the elongation of the strip. • Homogenization can result in the formation of three- or five- layer sandwich structure after final annealing. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of Al-Cu-Li alloy was studied under plane strain compression in the temperature range of 400–500 °C and strain rate of 0.01–10 s − 1 . The related microstructure was studied by optical microscopy, electron back-scattered diffraction and transmission electron microscope. The results showed that the stress decreased significantly with the increase of temperature and decrease of strain rate. However, stress increase was found after peak stress at strain rate of 0.01 s − 1 and deformation temperature 440–500 °C. Constitutive equation based on the hyperbolic sine equation was established and the apparent activation energy of plane strain compression was estimated to be 226.7 KJ/mol. Precipitates decreased and finally disappeared with decreasing Z value, having an impact on the softening mechanism. Plate-shaped particles and precipitate zones restrained the proceeding of dynamic recovery but increased store energy for discontinuous dynamically recrystallization nuclei. Therefore, recrystallization nuclei more obviously occurred in the sample with higher ln Z value than the one with lower ln Z value at close ln Z value. The microstructure of all deformed specimens was composed of elongated grains and new quasi-equiaxed grains. However, the basic deformation mechanism was dynamic recovery. The mechanism of recrystallization nuclei transformed discontinuous dynamic recrystallization into continuous dynamic recrystallization with the decreasing Z values. [ABSTRACT FROM AUTHOR]

A two-step annealing treatment consisting of a pre-recovery process (450 °C/5 h) and a following recrystallization process (530 °C/15 h) was developed for a cold-rolled twin-roll cast 3003 alloy (Al-1.13Mn-0.45Fe-0.1Si in wt%) sheet. The effects of pre-recovery on recrystallization behavior and mechanical properties were systematically studied. Our results show that fine quasi-equiaxed grains together with very weak ND-rotated cube (001) <310> texture was successfully obtained using the proposed two-step annealing treatment. It is found that pre-recovery stimulates the formation of precipitates-free zones around constituent particles. Within such precipitates-free zones, substantial random oriented sub-grains can readily grow to critical size for nucleation, which contribute to enhanced nucleation without preferential orientation. This is the reason for the formation of fine grains as well as a weak texture in the two-step annealed sheet. The sheets that were subject to this two-step annealing also exhibits an extremely weak mechanical anisotropy with a Δ r value 0.03, much lowe r than that of sample (0.31) subjected to a single-step annealing at 530 °C for 15 h. [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]

The microstructures and mechanical properties of the twin-roll casting (TRC) 8021 alloy strip under different homogenization processes (direct homogenization, cold rolling + homogenization) have been systematically investigated by optical microscope, tensile testing, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) technique. It was revealed that due to the severe microstructural gradient throughout the full strip thickness, the coarse grain layer is readily formed in the strip surface due to the high stored energy involved. Although the introduction of cold rolling before homogenization reduces the strain inhomogeneity in the strip, the rather high deformation level produces fully recrystallized structures after homogenization at 580 °C. After cold rolling and final annealing, recrystallized grains are formed in the interior of the sheets for most the homogenization temperatures. Compared with direct homogenized samples, the average recrystallized grain sizes in the "cold-rolled + homogenized" samples are larger due to the small thickness reduction. Therefore, the combination of cold rolling and homogenization can improve the elongation and decrease the strength of the strip. Homogenization at 530 °C is selected as the optimum parameter for both the two homogenization processes as it provides a good combination of strength and elongation. • Regulating homogenization is essential for improving the microstructural homogeneity of the twin-roll casted alloy. • The combination of cold rolling and homogenization improves the elongation and decrease the strength of the strip. • The introduction of cold rolling before homogenization reduces the strain inhomogeneity in the strip. [ABSTRACT FROM AUTHOR]

Al 3 Zr precipitates in Al-Cu-Zr alloys are investigated using high-resolution transmission electron microscopy. The results show that Cu can effectively stabilize the L1 2 phase and which may originate from Ref. 〈110〉(001) slip systems activated by Cu, that is in good agreement with our first-principles predictions. Moreover, theoretical calculations show that Zn and Ag has same effect as Cu. The ductility can be improved for stabilized L1 2 phase with Cu, Zn and Ag based on the Pugh’s criterion. Rice and Zhou-Carlsson-Thomson criterions are used to reveal the brittle/ductile mechanism using stacking fault energy. Finally, the electronic density of states show that the brittleness of D0 23 -Al 3 Zr is mainly due to the strong covalent bonding between Al and Zr atoms, and the improved ductility is mainly due to the weakened Zr 4 d and Al 3 p covalent interactions with the addition of Cu, Zn and Ag. [ABSTRACT FROM AUTHOR]

Thermal treatments such as pre-aging (PA) of Al–Mg–Si alloy sheet are important and necessary in the industrial production of automotive body panels. Interrupted quenching (IQ) treatments were investigated as a new strategy to improve the performance of Al–Mg–Si alloy during natural aging and paint-bake hardening. Direct comparisons were made to conventional pre-aging treatments for these alloys. The results show that IQ and PA treatments at 100 °C both suppress natural aging and promote precipitation of β″ phase during paint baking. However, the 100 °C IQ process has the potential to reduce the time from 3 h to 45 min. The accelerated formation of Cluster(2) induced by the slow quenching rate is the main reason for high efficiency. IQ treatments at 170 °C produced less and coarser Cluster(2) which did not effectively improve the bake hardening response (BHR) after paint-bake cycle. The main disadvantage of IQ treatments is the precipitation of large quenching-induced precipitates and formation of precipitate-free zones (PFZ) at the grain boundaries which could decrease the fracture toughness of Al–Mg–Si alloys. [ABSTRACT FROM AUTHOR]

Abstract: Specimens of Al–0.2wt.% Sc were solution heat treated and subjected to precipitation heat treatment. Precipitation-hardening response depended on storage time after solution heat treatment. An underaged condition and an overaged condition with equal strengths were found. Transmission electron microscopy indicates that the dislocations pass the precipitates by shearing in the underaged condition, and not in the overaged conditions. Analyses of stress–strain curves show significant differences in work-hardening behaviour between the two conditions. [Copyright &y& Elsevier]

Microstructural evolution of AA2195 aluminum alloy was recorded under different conditions (400–500 °C/0.01–10 s−1) during isothermal compression via metallurgical microscopy, electron backscattered diffraction and transmission electron microscopy/scanning transmission electron microscopy. By means of the dynamic material modeling, the processing map (PM) at the strain of 0.7 was also constructed using flow stress data. It was shown that the unstable criterion was adiabatic shear band (ASB) and flow localization (FL). ASB was easily formed at high strain rates (>1 s−1) due to non-uniform deformation heating. FL was attributed to local coarseness of T 1 precipitates near grain boundaries or inhomogeneous distribution of T 1 precipitates in the matrix. The stability domain showed that the absence of T 1 precipitates contributed to the formation of fine homogeneously distributed continuous dynamic recrystallization (CDRX). In the light of PM and microscopic observation, the optimal processing conditions suitable for AA2195 aluminum alloy were proposed as 475–500 °C/0.01–0.1 s−1 with an exception of 490–500 °C/0.01 s−1. Image 1 • Processing map for AA2195 aluminum alloy is established. • At high strain rates, non-uniform deformation heating induces adiabatic shear band. • Under moderate deformation conditions, the instable criterion is flow localization. • Flow localization is attribute to localized T 1 precipitates. • At the high temperature, the absence of T 1 precipitates makes contribution to CDRX. [ABSTRACT FROM AUTHOR]