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In this study, the microstructure, mechanical, and tribological properties of (Ti42V28Zr15Nb15)100-xAlx lightweight refractory high-entropy alloys (LRHEAs) were systematically investigated. The results show that the single BCC solid solution structure of LHEAs is maintained after the addition of Al elements, and no other phases are formed. The addition of Al elements to the alloys can be reduce density, improve properties, and enhance wear resistance. While the hardness of the alloy increased from about ~ 352 HV to ~ 430 HV, the tensile ductility decreased significantly. The main reason for the increase in hardness is the strong bonding between aluminum atoms and other atoms. On the other hand, the severe impairment of the tensile properties may be due to the decrease in GNDs. Although the addition of Al helps to reduce the coefficient of friction, the wear rate of the alloy increases. [ABSTRACT FROM AUTHOR]

The mechanical anisotropy of selective laser melted (SLM) aluminum alloys resulting from heterogeneous grain structures is still not fully understood due to lacking study of grain orientation related mechanical response. Here, by introducing in-situ EBSD tensile method, the orientation induced anisotropy coefficient Ka related to the deformation-induced grain rotation was revealed by excluding effects of grain size and grain aspect ratio. Compared with traditional mechanical properties models by Taylor factor M, it was found that the orientation <001 > in as-built and <102 > in heat treatment contributed the most yield strength anisotropy, and introducing Ka predicts the mechanical anisotropy more accurately. By introducing in-situ EBSD tensile method, we found the orientation induced anisotropy coefficient can reflect the mechanical anisotropy by excluding effects of grain size and grain aspect ratio. [ABSTRACT FROM AUTHOR]

The intergranular corrosion behaviour of Al-Cu-Li-Sc alloy with different microstructures was systematically investigated in this work. The SKPFM characterisation revealed that the AlCuSc (W) phase has more negative potential compared to the Al matrix and undergoes dealloying in the intergranular corrosion solution. The dealloying rate of the W phase in the corrosive solution is relatively slow, which does not lead to serious pitting characteristics. As denser anodic T1 precipitates formed on low-angle grain boundaries of the partially recrystallised sample will reduce the precipitates on the sub-grain interior, resulting in the low-angle boundary being prone to preferential corrosion and reduced intergranular corrosion resistance. The complete recrystallised sample exhibits corrosion of grain interior and propagates along corroded bands parallel to {111}Al habit planes of T1 precipitates, reducing the expansion rate of corrosion along the grain boundaries. Restraining the IGC along the low-angle grain boundary and inducing crystallographic corrosion to improve the intergranular corrosion resistance. [ABSTRACT FROM AUTHOR]

A change in the heat treatment state of aluminum matrix before anodization was used to change the state of Mg in this work. The effects of Mg on the interface structure of the film/substrate of anodized AA6082 alloys were systematically studied when Mg existed in the state of Mg5Si6, supersaturated solid solution, and atomic clusters or GP zones. The cross-sectional morphology and film/aluminum alloy interface structure of the oxide film were characterized by SEM and HRTEM, respectively, and the reciprocating friction test was used to compare and analyze the effect of different film/aluminum alloy interface structures on the friction resistance of the oxide film. The results show that the state of Mg before anodization plays a key role in the stability of the film/aluminum alloy interface after anodization, which also has an important impact on the wear performance. Before anodization, the anodized AA6082 alloys have the best friction resistance when the Mg exists in atomic clusters or GP zones, follow by the supersaturated solid solution, and the last is the β″ phase. [ABSTRACT FROM AUTHOR]

Microstructures and mechanical properties of Al-5Zn-2.6Mg alloys with 0.24, 0.43, and 0.91 wt.% Cu were studied and the precipitation rate and activation energy at 378, 393, and 408 K were calculated using the Arrhenius equation in this work. The aging reaction rate k increased and the precipitation activation energy Ea decreased from 25.7 to 15.0 kJ/mol. The η' distribution density of the precipitates clearly increased with increasing Cu content. However, the size and number of coarse second phase with Fe and Mn impurities also increased, which increased the tendency for crack initiation and propagation at the grain boundary, resulting in a decrease in dimple area. The fracture morphology transformed from plastic transgranular fracture to brittle intergranular fracture and the elongation of the alloys decreased by 3.8%. The contribution of Cu content to yield strength was predominantly due to precipitation strengthening rather than grain boundary strengthening and solid solution strengthening. The tensile strength of the Al-5Zn-2.6Mg alloys with 0.91 wt.% Cu subject to peak aging at 393 K increased by 10.2%. [ABSTRACT FROM AUTHOR]

Oxide films for Al–Mg–Si alloys with various aluminium oxide contents from 65.99 to 80.97% and thicknesses ranging from 1.7 to 5.1 μm were obtained. The effect of the oxidation reaction interface on the accelerated corrosion behaviour of Al–Mg–Si alloy has been investigated by using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electron probe microanalyzer (EPMA), accelerated corrosion tests and electrochemical tests. Accelerated corrosion tests indicated that incomplete oxide films reduced the corrosion resistance even with increasing oxide film thickness and Al2O3 content in a solution containing 30 g L−1 NaCl and 10 mL HCl (ρ = 1.19 g mL−1). The thicker oxide film effectively inhibited corrosion behaviour, while the thinner oxide film disappeared and its substrate suffered corrosion after immersion for 6 h, corresponding to the dissolution of oxide film and shedding of second-phase practices on interfaces. Accelerated corrosion response of various oxidation reaction interfaces was built by an equivalent electrochemical circuit. [ABSTRACT FROM AUTHOR]

The intergranular corrosion (IGC) resistance of the Al–Mg–Si alloy with low Zn addition treated by the interrupted aging treatment (T6I6) was investigated. The IGC results of the Al–Mg–Si alloy show that IGC resistance is enhanced by T6I6 aging treatment. The EIS results reveal that the T6I6-treated Al–Mg–Si alloy has lower double layer capacitance and higher charge transfer resistance than the T6-treated alloy. The superior IGC performance of the T6I6-treated alloy may be attributed to the finer and more densely distributed precipitates within the grains, smaller and discretely distributed precipitates along the grain boundaries and narrower precipitate-free zones (PFZs) compared to the T6-treated alloy. [ABSTRACT FROM AUTHOR]

The evolution of grain boundary (GB) of an Al–Zn–Mg alloy profile with heterogeneous structures is studied based on in-situ EBSD tensile. This evolution is not only related to its grain boundary misorientation angle (GBMA) and slip transfer parameter (m'/(Δb/b)) but also to the behavior of the geometrically necessary dislocation (GND) tensor in the deformation. The effect of GBMA and m'/(Δb/b) for three types of high angle grain boundary (HAGB) on GND density and back stress has been revealed. The increase of GND density is not obvious near the HAGBs with 45°–55° GBMA of neighboring coarse grains or neighboring fibrous grains. The optimal grain boundary for forming back stress is the HAGBs between coarse grain and fibrous grain, which has 35°–45° GBMA and a low m'/(Δb/b). The back stress is hard to form near these HAGBs with 25°–35° GBMA and a low m'/(Δb/b). Combined with the neighboring grain type, slip transfer and GBMA, the new criterion is proposed to predict GND behavior near HAGBs. [ABSTRACT FROM AUTHOR]

Multilayer brazeable aluminum alloy sheet is prone to collapse during high-temperature brazing process. The sagging resistance of the aluminum composite sheet needs to be further improved for quality control. Effects of annealing and rate of reduction on sagging resistance, microstructure, and Si diffusion of a hot-rolled, four-layered Al clad sheet (4343/3003/6111/3003) were investigated by means of a sagging device, OM, SEM, and TEM. Results showed that once annealed at 360°C, the sagging distance was increased from 3 to 15.7 mm as the reduction rate changed from 10% to 40%. By increasing annealing temperature to 410°C, those were changed from 3.1 to 20.8 mm accordingly. At 360°C/40% and 410°C/40%, specimens exhibited weak sagging resistance, whereas fine recrystallized grains were formed in the core promoting Si penetration along grain boundaries. While the specimens were treated at 360°C/10% and 410°C/10%, better sagging resistance was observed due to the formation of coarse recrystallized grains that can suppress erosion of Si. At the same reduction rate, the sagging resistance was higher for the sample annealed at a lower temperature as more precipitates appeared in the core (at 360°C), thus leading to an increase in strength. [ABSTRACT FROM AUTHOR]

The intergranular corrosion (IGC) behavior of an extruded 6005A alloy profile with the coexisting of peripheral coarse grain (PCG) structure and partial recrystallized grain (PRG) structure was investigated by using an accelerated corrosion test, electrochemical impedance spectroscopy and a quasi in situ examination of IGC process. PCG structure was found to have a unique IGC behavior that pitting corrosion and subsequent IGC are less severe and will not be transformed into intragranular corrosion as they were found in PRG structure. Microstructure characterization reveals that the microstructural differences in grain boundary precipitates, primary α-AlFeMnSi intermetallic particles and grain characteristic between PCG structure and PRG structure are the reason for these phenomena. Further analysis indicates that the grain boundaries decorated with more AlFeMnSi particles and Q phase precipitates are more sensitive to corrosion, where Q phase precipitates are the primary cathodes and the most important factor affecting IGC; AlFeMnSi particles are supposed to initiate pitting corrosion since they are dissolved as anodes in the early stage of corrosion. With the development of corrosion, they are transformed into cathodes and become the bridges of IGC propagation by connecting the Q phase precipitates at grain boundary. In addition, grain characteristic was also found to have great effects on IGC. With the decrease in grain size and the increase in the frequency of high-angle grain boundaries and the dislocation density, corrosion becomes more severe and more likely to be transformed into intragranular corrosion. [ABSTRACT FROM AUTHOR]

The Al-Zn-Mg-Cu alloy with different sub-grains and recrystallized grains was isothermal forged at 400 °C with strain rate of 10−4 s−1, and the grain structures were examined by electron backscatter diffraction (EBSD). The results showed that the coarsening of sub-grains and the formation of recrystallized grains at grain boundaries were the primarily changes of grain structures during isothermal forging. Besides, it found that the coarsening of sub-grains occurred first, and then recrystallization started at grain boundaries when quite a few sub-grains were found within grain interiors. Coarsening of sub-grains was found during isothermal forging of the one containing many sub-grains, and the recrystallization was hindered as strain energy was consumed by such coarsening of sub-grains. But more recrystallized grains were found after isothermal forging of the one containing many fine grains. [ABSTRACT FROM AUTHOR]

Al-1.96Cu-0.24Mg-0.18Ag alloy single crystal with ( 2 ¯ 15) plane orientation has been used to investigate the effect of external stresses (50, 100, 134, 160 and 200 MPa) on the precipitation behavior of Ω, θ′ and S precipitates. The microstructure of the aged specimens was observed by transmission electron microscopy (TEM), selected area electron diffraction (SAED) and scanning transmission electron microscopy (STEM). X-ray elemental mapping under high-angle annular dark-field (HAADF) was used to analyze the elements in the precipitates. TEM images showed that the amount and distribution of the three types of precipitates are different in specimens aged under different external stresses. Along with the SAED and STEM images, the type, amount and distribution of Ω, θ′ and S precipitates were quantitatively measured. Compared to the results on stress-free aged specimen, the amount of Ω precipitates decreases in stress aged samples, while that of the S precipitates increases, and the amount of θ′ precipitates is constant with low value. The orienting effect of stress on Ω precipitates gets serious at 100 MPa, but it decreases at 200 MPa. The orienting effect of stress on S precipitates is quite similar to that in the case of the Ω phase. As the competition of acquiring Mg and Cu atoms between S and Ω precipitates, the orienting effect of stress on S precipitates is serious from 100 to 160 MPa. Both the orienting effect of stress on Ω and S precipitates decreased because of the inhibiting effect of dislocations at 200 MPa. The orienting effect on θ′ variants is different from that of Ω precipitates. It is serious at 50 MPa and gets weaker at 100–200 MPa. [ABSTRACT FROM AUTHOR]

In order to confirm whether the Zener—Hollomon parameter (Z)—recrystallized grain size (d) model obtained from hot compression tests is suitable for the commercial production, the microstructure and mechanical properties of the extruded Mg-8Gd-3Y-0.6Zr alloy plate were investigated. The grain size of the plate has been predicted based on this model. The results indicated that the predicted grain sizes disagree with the measured ones. The static recrystallization should be considered for the center area samples, and the recrystallization mechanism of particle stimulated nucleation (PSN) together with the inhibiting effects caused by precipitated particles should be taken into account for the edge area samples. Precipitation of β phases during extrusion lowered the driving force during ageing, which resulted in the yield strength and ultimate strength of the samples cut from the edge area lower than that of the samples cut from the center area. [ABSTRACT FROM PUBLISHER]

• The effect of twinning and texture on the fatigue properties was studied. • The law of crack propagation during fatigue was studied. • The relationship between grain structure and fatigue resistance was built. • Non-basal planes have better resistance to crack propagation. The fatigue crack propagation behavior of rolled magnesium alloys was studied and compared with as-cast alloys to unravel a relation between the early crack propagation and the fatigue resistance at the microstructural level. Grain structures results indicated that the geometric compatibility of grains and stress component on basal slip planes determine the propagation path of cracks. Twins are usually unfavorable for crack propagation, and the texture changes the stress component distribution in grains under the condition of unchanged loading. Both twins and textures increase the difficulty of crack propagation and improve the fatigue resistance at higher stress level. [ABSTRACT FROM AUTHOR]

Low-cost Si was added to Mg-8Gd-4Y-1Nd alloys to improve their ductility. With the Si increased from 0 to 1.0 wt %, the elongation increased from 8.7% to 17.1% for as-extruded Mg-8Gd-4Y-1Nd alloys. Microstructures results indicated that the formation of GdSi and Y 5 Si 3 intermetallic phases increased significantly with the Si addition, which was shown to promote the random orientation of grain structures. As Si works as substitutional atoms in Mg alloys can decrease the first intrinsic stacking faults (I 1 SF) energy, the pyramidal dislocation was activated during deformation, thus the {0001} Mg basal plane deviate from the extrusion direction and alter to random textures. Activating both the pyramidal and basal slip provided more independent slip systems during deformation and caused more stress accumulation, which exceeded the critical shear stress (CRSS) for tensile twinning. The simultaneous activation of the pyramidal slip and tensile induced twinning improved the ductility of the Mg-8Gd-4Y-1Nd-1.0Si alloy. [ABSTRACT FROM AUTHOR]

In this paper, two high Fe containing Al–Mg–Si–Mn–Fe alloys with Mg, Si and Mn modified were prepared, and their microstructures and mechanical properties were comparatively studied with a common applied alloy. Furthermore, the effects of alloying elements on their microstructures and the corresponding strengthening mechanisms were analyzed. It was found that the two Al–Mg–Si–Mn–Fe alloys exhibited good combination of strength and elongation in spite of their high Fe content. When compared with the common applied alloy, the yield strength of the two alloys was increased by 28 MPa and 50 MPa respectively, whereas the elongation was only slightly decreased. The higher strength of the two Al–Mg–Si–Mn–Fe alloys was mainly attributed to precipitation and solid solution strengthening which were substantially caused by the appropriated proportion of Mg and Si. Owing to the appropriate addition of Mn, no β–AlFeSi phases were found in the alloys, and the detriments of Fe were fully eliminated. The submicron scaled α–Al(FeMn)Si phases slightly improved the yield strength because of their contribution to grain refinement and dispersion strengthening. The results of this paper provide a valuable insight into the strengthening and industrial manufacturing of Al–Mg–Si alloys. [ABSTRACT FROM AUTHOR]

Crushing performance is being widely investigated because it is the key performance indicator of the thin-walled beam structure in automobile safety components. In this study, five kinds of ageing state with different yield strengths were prefabricated with a self-developed KHC63 alloy. Using a rectangular tube profile, the physical relationship between crushing properties and mechanical properties, and the structure of the profile, were studied. According to variation characteristics, the crushing curve was divided into four typical stages: elastic stage, bending stage, compaction stage and folding stage. In the elastic stage, the peak load of the component is related to material elasticity and structure elasticity, and the relationship is approximately linear. In the bending stage, the driving factor of plastic hinge deformation is the bending moment, and it is always constant. In the compaction stage, the crushing curve correlates well with the cosine function. In the folding stage, the crushing process begins to lose stability and is hard to predict. The mathematical relationships between force and displacement were established according to the characteristics of each stage, and the calculated results were close to the measured results except for the folding stage. The deviation of the calculated energy absorption from the measured data in the first three stages is only 4.3%, but it is 10.6% in the folding stage. The calculation method used for the first three stages is, therefore, suitable. [ABSTRACT FROM AUTHOR]

Large number density of coarse precipitates were introduced into the Al–Zn–Mg–Cu alloy by interrupted aging and then over-aging at 300 °C. Both the overaged and homogenized samples were isothermal MDFed at 5 × 10−3 s−1 with temperatures ranging from 300 °C to 450 °C to investigate the effect of high number density of precipitates on the microstructural evolutions. The results showed that the precipitates decreased gradually during MDF of overaged samples at 300 °C and 350 °C while they were almost dissolved at 400 °C and 450 °C. And as the result of that the precipitates could pin dislocations during deformation, and much greater grain refinement was achieved during MDF of overaged samples at 300 °C and 350 °C. • Large number of η precipitates were introduced in the Al–Zn–Mg–Cu alloy by interrupt aging and over-aging. • The introduced high density precipitates expanded the temperature range with significant grain refinement. • The introduced high density precipitates accelerated the grain refinement effect during MDF. • The number density of precipitates decreased gradually during isothermal MDF. [ABSTRACT FROM AUTHOR]

The microstructure evolution and the mechanical behavior of Al–4.8Mg alloy were investigated by means of isothermal compression tests at various temperatures (280–520 °C) and strain rates (0.01–10 s−1). The results shown that there are three main mechanisms of dynamic softening of samples within the range of selected process parameters: dynamic recovery, dynamic recovery + dynamic recrystallization, and dynamic recrystallization, and the equiaxed dynamic recrystallization grain tends to be formed under higher temperature and higher strain rate. In order to accurately describe the dynamic recrystallization condition of Al-4.8Mg alloy under a wide range of hot deformation parameters, an improved dynamic recrystallization critical conditions model is proposed based on deformation activation energy and work-hardening rate. Additionally, a two–stage physically constitutive model considering the influence of work hardening–dynamic recovery and dynamic recrystallization is established. Comparisons between the predicted and experimental data indicate that the proposed model can adequately predict the flow stress in the range of selected process parameters with the average absolute relative error of 4.02%. [ABSTRACT FROM AUTHOR]

The effects of Zn and Mg content in thin-walled square extrusions of Al-Zn-Mg alloys on its crashworthiness were investigated, and the correlation between the crushing properties, mechanical properties, and microstructures of the profiles were investigated. The results showed that the strength and the compression properties were gradually increased with a decrease in the Zn/Mg ratios (from 12.48 to 4.57). When the Zn/Mg ratio is lower (less than 6.29), an increase in the Mg content simultaneously improves the alloy strength and the compression properties. An increase in Zn content (from 5.07 to 6.77) can improve the strength of the alloy however, it does not affect the compression properties. However, the higher Zn contents (6.77%) would lead to cracking in advance during the compressing, which reduces the compression energy absorption capacities of the product. Therefore, in order to obtain higher strength and excellent compression properties, the Zn/Mg ratio should be reduced. For the upper limit, the Zn content should not be too high (less than 6.77), as this may lead to early cracking and failure. For the lower limit, the Mg content should be higher (more than 0.91) to make sure that the alloy has excellent compression properties and higher strength. [ABSTRACT FROM AUTHOR]

The influence of asymmetric cold rolling (ASR) and subsequent ageing on microstructures and mechanical properties of the Al–Cu–Li alloy was investigated systematically in this work. Both the hardness and yield strength increased with the asymmetric cold rolling degree. The peak hardness, yield strength and ultimate tensile strength of aged samples increased from 138 HV, 380 MPa, 430 MPa of the conventional hot rolled sheet (CHR) to 162 HV, 420 MPa and 480 MPa of 90% ASR sheet (ACR90), respectively, while the elongation keeps near 10%. The grain size decreased and the recrystallization degree increased with the asymmetric rolling degree. Textures of four rolled sheets, such as solid solute of conventional hot rolled sheet (CHR), conventional cold rolling with reduction of 50% (CCR50), asymmetric cold rolling with reduction of 50% and 90% (ACR50 and ACR90) were mainly Copper, S, and Brass types along the β fiber. In particular, volume fractions of textures were different, and CCR50, ACR50, ACR90 samples had similar average Taylor factors (M), which was lower than the CHR sample. The number density and the average diameter of T 1 precipitates in matrix increased with the ASR degree. The CHR sample with higher average M value in the tensile direction at room temperature can sufficiently compensates for the loss of strengthening due to less precipitates as compared with the CCR50 sample. The strength of two ASR samples is higher than the CHR sample due to the coupling effect of textures and precipitation strengthening. • The effect asymmetric rolling on the subsequent ageing behaviors has been studied. • The texture and Taylor factor of aged Al-Cu-Li sheets were analyzed and compared. • Amount of T 1 precipitates increasing gradually with asymmetric deformation degree. • The textures and precipitation are the main reasons causing the strength difference. [ABSTRACT FROM AUTHOR]

The Al 3 Zr particles formed in the Al–Cu–Li–Zr alloy during single and double-step homogenization treatments contributed to various microstructures and mechanical properties during the subsequent thermomechanical treatment. Compared with the single-step homogenization treatment (ST), the double-step homogenization treatment (DT) generated higher density and more uniform distribution of β′ (Al 3 Zr) phases, which makes the alloy retain more substructures and improve the initial strength of solid solution. During the ageing process, Al 3 Zr particles induced the T 1 precipitation in grain interior and the width of PFZ get narrowed. Therefore, the strength and toughness of the DT sample improved in peak aged state compared with that of the ST sample. The peak hardness value of DT sample is 167.8 HV, which is higher than that of ST sample with 153.1 HV. Furthermore, the tensile strength and elongation of the DT sample at peak aged state (521 MPa, 556 MPa and 8.8 %, respectively) are higher than those of the STA sample (492 MPa, 535 MPa and 6.7 %, respectively), and the impact toughness of the DTA sample (13.2 J cm−2) is also higher than those of STA sample (9.1 J cm−2). Strength model showed that more uniform distribution of Al 3 Zr phases and substructures improve the initial strength of solid solution state, which increased by 16 MPa in the DT sample compared with the ST sample. The promotion of T 1 precipitation inducing the strength increased by 18 MPa in the DT sample at the peak aged state compared with that of the ST sample. The increase of elongation and toughness contributed from the oriented grains with finer distribution and higher Schmid factor, less grain boundaries precipitates and narrower PFZ width. [ABSTRACT FROM AUTHOR]

The EXCO and IGC corrosion behavior of an extruded rod of Al–Zn–Mg–Cu alloy with gradient granular grain structure were investigated. The corrosion resistance increased gradually from the center to the surface of the extruded rod due to the increase of distance between η precipitates and the decrease of the precipitate length along grain/sub-grain boundary, which is assumed as the result of the gradually decrease of grain/sub-grain size from the center to the surface. • The precipitate distance along grain boundaries increases with the decrease of grain size of the Al–Zn–Mg–Cu alloy. • The precipitate length along grain boundaries decreases with the decrease of grain size. • The corrosion resistance could be improved with the increase of the distance between η precipitates. [ABSTRACT FROM AUTHOR]

The in-situ SEM observations and Line-scanning methods were used to observe the atomic concentration distribution and evolution of main elements in intermetallic phase at different solid solution temperatures. The results indicated that the atomic distribution of main elements in η (MgZn 2), S (Al 2 CuMg), Fe-containing (Al 7 Cu 2 Fe) intermetallic phases are parabolic through these phases, while the non-main elements uniformly distribute in matrix. The results of Differential Scanning Calorimetry (DSC) and Energy Dispersive Spectra (EDS) indicated that the Zn atoms dissolved into the matrix between 245 and 430 °C, under which the process of η phase transits to S phase occurred. The Cu element of S (Al 2 CuMg) phase has an obviously diffusion rate at 450 °C, while the Mg element has an obviously diffusion rate when the temperature is higher than 460 °C. Afterwards the atomic concentration dissolution was modelled by diffusion law, and the model results is corresponding to the linear rule, which agrees with the experiment results. • The in-situ SEM and Line-scanning methods were used to study the intermetallic. • The atomic distribution of elements in phases are parabolic. • The atomic concentration dissolution was modelled by diffusion law. • The diffusion temperature ranges of Zn, Cu and Mg atoms was studied. [ABSTRACT FROM AUTHOR]

The influences of aging treatments on microstructures and the corrosion properties of an Al–Cu–Li alloy were investigated through an immersion test in intergranular corrosion (IGC) solutions, a potentiodynamic polarization test, and electrochemical impedance spectra (EIS), combined with scanning and transmission electron microscopy. The results demonstrated that the Al–Cu–Li alloy displayed outstanding comprehensive mechanical properties and IGC resistance after treating with pre-strain deformation and a double aging process (PDA). Both the PDA and pre-strain followed by creep aging (PCA) treatments significantly increased the number densities of T1 and θ' precipitates in the grain interior. The increase in precipitates in the grain interior greatly reduced the Cu-rich precipitates on the grain boundaries and inhibited the formation of a precipitate-free zone (PFZ). The electrochemical characteristics of the Al–Cu–Li alloy were influenced by the precipitates in the grain interior and grain boundaries. The studied alloy gained high IGC resistance due to the refinement of its microstructure, and the main corrosion mode was intra-granular pitting corrosion; thus, the corrosion diffusion rate was slowed down. [ABSTRACT FROM AUTHOR]

The mechanical properties of Al-Zn-Mg alloys via multi-stage aging treatments were studied to explore the strength-toughness trade-off. The microstructures of aged alloys were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results indicated that large numbers of GP zones and some part of η′ phases were formed during the low-temperature (90 °C) aging at the third-stage aging, which consumed considerable solid solubility. This prevents fast growth and coarsening of precipitates at the fourth-stage aging (150 °C). Finally, the mixed precipitation state of mainly η′ phases and some η phases formed. The grain boundary phase grew insignificantly, which is beneficial to decrease the strength gap between intragranular and grain-boundary. The intragranular equilibrium η phase is beneficial to pin the movement of dislocation, which avoids fracture caused by accumulation of dislocations around the large second-phase and on the grain boundaries. Although the strength of materials decreased slightly, the impact toughness of materials significantly increased due to the positive effect of the intragranular equilibrium η phase. Compared with the conventional retrogression and re-aging (RRA) treatment (120 °C/24 h + 185 °C/105min + 120 °C/12 h), the designed four-stage ageing treatment (FSA) (120 °C/24 h + 185 °C/105min + 90 °C/12 h + 150 °C/12 h) resulted in the decrease of tensile strength and yield strength by only 3% and 4%, respectively, but contributed to the increases of elongation and impact toughness by 15% and 17%, respectively. [ABSTRACT FROM AUTHOR]

• The direct observation of corrosion process is performed by EBSD. • The small grains corrode easily. • There is almost no corrosion attack suffered by the largest grain with (10-10) non-basal orientation. • Under the similar grain size condition, the non-basal plane is more vulnerable to corrosion than the basal plane. The influence of grain size and crystal orientation on the corrosion behavior of as-extruded Mg-6Gd-2Y-0.2Zr alloy is investigated by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD). The EBSD system is used to characterize the grain size, crystal orientation and corroded surface. By investigating the corrosion process of as-extruded Mg-6Gd-2Y-0.2 Zr alloy, we can observe that the smaller grains and (10-10)/(11-20) non-basal planes are more susceptible to corrosion in the aggressive corrosion environment. Furthermore, the relationship between the corrosion rate and grain size is connected with the crystal orientation and whether the passivation occurs. [ABSTRACT FROM AUTHOR]

A new ageing treatment method was developed in this work to improve the strength and ductility of Al–Cu–Li alloy. Al–Cu–Li alloy treated via pre-deformation followed by double ageing process (PDA) exhibited excellent yield strength and ultimate tensile strength of 609 and 629 MPa, respectively, while maintaining higher elongation (11.5%). The precipitates in matrix and sub-grains regions indicated that both the PCA (pre-deformation followed by creep ageing) and PDA treatments increased the precipitation number density and yielded refined precipitates (i.e., T 1 and θ′ precipitates) in the matrix due to the dislocations produced by pre-strain. Uniform and fine strengthening precipitates in the matrix are beneficial to increase the strength of the alloy. In addition, eliminating precipitation free zones, reducing the δ′ precipitation and regulating the T 1 precipitates at sub-grain boundaries further promote the plasticity of aged alloys. When this excellent structure is obtained simultaneously, the alloy can obtain high strength while maintaining high elongation. [ABSTRACT FROM AUTHOR]

An Al-Zn-Mg-Cu alloy was isothermal compressed at temperatures ranging from 300 °C to 450 °C with strain rates ranging from 10−5 s−1 to 10 s−1 to study its deformation and recrystallization behaviors. The evolution of grain structure during the isothermal compression demonstrated that sub-grains found in grain interiors of those deformed with high strain rates from 10−2 s−1 to 10 s−1, were mainly the results of continuous dynamic recrystallization (CDRX), while many recrystallized grains formed at grain boundaries of those deformed with low strain rates from 10−5s−1 to 10−3s−1, were largely believed to be the result of discontinuous dynamic recrystallization (DDRX). Furthermore, two totally different constitutive equations as the result of different dynamic recrystallization mechanisms were proposed. • Two different dynamic recrystallization mechanisms (CDRX and DDRX) occur at different strain rates. • The formation of recrystallized grains at the lower strain rates leads to a rapider decreasing of flow stress. • The activation energy increases when the dynamic recrystallization mechanism changes from CDRX to DDRX. • Two different constitutive equations are constructed at the two different strain rate ranges. [ABSTRACT FROM AUTHOR]

An Al–Zn–Mg–Cu support bracket forging was isothermal precision forged at 400 °C with speeds of 0.1 mm/s, 0.01 mm/s and transient speed changing from 1 mm/s to 0.01 mm/s by finite element simulation and experiment. The stress concentration at high ribs of the simulated forging corresponded to the defects of under-filling and folding of the experimental forging at the speed of 0.1 mm/s while none defects appeared at the speeds of 0.01 mm/s and transient speed. Besides, not only less time was used to finish forging but also much more fine grains and sub-grains were formed in the forging that precision forged at the transient speed as compared with that at the speed of 0.01 mm/s, which leaded to the higher mechanical properties. Furthermore, the resistance to IGC was much better in the forging that precision forged at the transient speed for the particles η distributed along the grain boundaries was much wider. [ABSTRACT FROM AUTHOR]

Grain boundaries in metals would introduce extra nucleation energy to promote the growth of θ′ precipitate during ageing process. The influence of grain boundaries on the distribution behavior of two θ′ precipitates variants (010) and (001) were studied in Al–2Cu alloys bicrystals. Ageing conditions without external stress and with 40 MPa and 60 MPa stresses were conducted to study the effect of grain boundaries on the oriented distribution of two θ′ precipitates variants. The hardness differences between the near grain boundaries area and the single crystal of the bicrystal samples were tested to understand the relationship between microstructures and mechanical properties. Results of transmission electron microscopy (TEM) images showed that the stress-orienting effect on precipitates was inhibited by the grain boundary. TEM images and quantitatively measurement of two θ′ precipitates variants indicated that grain boundaries inhibited the orienting effect of external stresses on the distribution of precipitates. Especially in 60 MPa stress-aged sample, θ′ precipitates near the grain boundary distribute homogeneously and have the same density as in single crystal areas. Hardness difference in stress-aged sample was smaller compared to the stress-free-aged sample. External stresses during ageing also narrowed the PFZ width near grain boundaries. The anisotropy of precipitation strengthening contribution of two θ′ variants were reduced due to the extra energy provided from grain boundaries. The compressive yield strength of Al–2Cu alloys bicrystal increased with the applied stresses during ageing. This work provides new insight into solving the anisotropy problem during stress ageing based on the effect of grain boundaries. Image 1 • Al–2Cu bicrystals were used to study the effect of stress ageing on precipitation. • The orienting degree of (010) and (001) θ′ variants was described quantitatively. • The grain boundaries inhibited the orienting effect of stress ageing. • Hardness lines along the bicrystal were tested to study the hardness differences. • Hardness difference becomes smaller in 60 MPa stress-aged bicrystals. [ABSTRACT FROM AUTHOR]

In this paper, the discharge performance of the Al–Mg–Sn alloy anodes with different Sn content for Al-air batteries is investigated in 4 mol L−1 NaOH solution, and their microstructure, corrosion behavior and discharge properties are discussed in detail. It shows that Sn-rich phases in the Al matrix act as cathode to promote the anode dissolution of the Al matrix and increase the electrochemical activity. The electrochemical impedance spectroscopy (EIS) results reveal that the value of hydroxide film resistance (R c) increases as Sn content increases to 0.5 wt%, indicating that Sn addition can improve the corrosion resistance and therefore reduce the hydrogen evolution rate (HER). As a result, the Al-0.6Mg-0.2Sn alloy shows good discharge performance at low current density and its peak energy density reaches 2858.6 mWh∙g−1 at 20 mA cm−2 with the discharge capacity of 2341.9 mAh∙g−1. The Al-0.6Mg-0.5Sn alloy presents good discharge performance at high current density and its peak anode efficiency reaches 93.21% at 40 mA cm−2. When Sn content is up to 0.8 wt%, excessive Sn-rich phases aggravate the hydrogen evolution corrosion and intergranular corrosion, which results in more weight loss. This is responsible for the unsatisfactory discharge performance of Al-0.6Mg-0.8Sn alloy at all current density. [Display omitted] • Moderate Sn-rich phases improve the discharge performance of Al–Mg–Sn alloy. • Excessive Sn-rich phases deteriorate the discharge performance of Al–Mg–Sn alloy. • Peak energy density of Al-0.6Mg-0.2Sn alloy reaches 2858.6 mWh∙g−1 at 20 mA cm−2. • Peak anode efficiency of Al-0.6Mg-0.5Sn alloy reaches 93.21% at 40 mA cm−2. [ABSTRACT FROM AUTHOR]

To elucidate the effect of solution temperature on microstructures and mechanical properties of the Al-Cu-Li-Sc alloy, the evolution of the second phase and precipitates were analyzed to reveal the strength contribution by dissolving Cu-enriched second phases. It is demonstrated that the diffusion rate of the Cu atom in Cu-enriched second phases, mainly Sc-containing θ (Al 2 Cu) phases, increased with solution treatment temperature, which induced more T 1 (Al 2 CuLi) precipitates formed during the aging process. More 10 at. % Cu atoms in second phases could dissolve into the Al matrix with the solution temperature increased from 490 °C to 520 °C, and these Cu-enriched second phases transformed into near equilibrium Sc-containing θ phases. Increasing the Cu atomic concentration in Al solid solution reduced GPB zones and inhibited δ′ (Al 3 Li) phases, thus improving the precipitation kinetics of the T 1 phase. Less δ′ phase was observed in the sample at peak aging with a solution treatment at 520 °C, and the T 1 phase was dominant. A clear improvement in the peak-aging hardness by 15.5% and yield strength by 19.1% of the sample after solution-treated at 520 °C compared with 490 °C. • The effect of solution temperature on subsequent aging behaviors has been studied. • The diffusion behavior of Cu atoms in the second phase is discussed. • Increasing of Cu atomic concentration in the Al solid solution promotes the precipitation kinetics of the T 1 phase. • Reducing GPB zones and inhibiting δ′ phases, significantly increasing the strength contribution of T 1 phases. [ABSTRACT FROM AUTHOR]

Precipitation strengthening and strain hardening after pre-deformation in low Mg Al–Cu–Li alloys dominated by T 1 phases have been widely studied in recent years due to their excellent mechanical properties. In this study, the aging precipitation behavior and the associated strengthening mechanisms caused by the increasing dislocation density in high Mg Al–Cu–Li alloys were systematically studied. The results showed that the dislocation density change along with the degree of the pre-stretching as well as the precipitation behavior, that is the pre-stretched methods inhibit the development of GPB zones and reduce the total precipitation of T 1 phases to promote the development of S phases. Finally, the fraction of recrystallized zones decreases from 59.3% to 2.8% while the average KAM value increases from 0.62 to 1.40, and the yield strength increases from 500 MPa to 620 MPa. The overall precipitation strengthening increment in the case of multi-phase coexistence is essentially independent of dislocation density, which is mainly a result of the decrease in the strengthening increment for T 1 phases is compensated by the strengthening increment for S phases. Our study is expected to provide theoretical contributions to the development of high-strength and high-toughness Al–Cu–Li alloys. [ABSTRACT FROM AUTHOR]

The precipitation evolution of Al-Mg-Si-Zr alloy samples was observed by transmission electron microscopy. Addition of Zr into the Al-Mg-Si alloys significantly hindered the growth of the Mg/Si particles and had a positive effect on the particle density. The higher the Zr content, the more difficult was the diffusion of the Mg and Si atoms. The sample with 0.13 wt% Zr showed the best combination of electrical conductivity (34.44 MS/m), tensile strength (198 MPa), and elongation of 17.8%. • The effect of Zr on the precipitation behavior of Al-Mg-Si alloy was investigated. • Zr addition could hinder the growth of the Mg/Si particles. • Zr addition had a positive effect on the density of the Mg/Si particles. • The higher the Zr content, the more difficult was the diffusion of Mg/Si atoms. [ABSTRACT FROM AUTHOR]

In the present study, the influence of Zn content on the microstructure and mechanical properties of the Al-Mg-Si alloy is systematically investigated. The results show that the precipitation sequence within the grains of the alloy does not change when Zn content does not exceed 2.0 wt%. The intragranular precipitates are mainly composed of β" precipitates with a small amount of η' precipitates when Zn content reaches 4.0 wt.%. Zn addition does not affect the precipitation sequence along the grain boundaries of the alloy when Zn content does not exceed 1.0 wt.%. But the grain boundary precipitates (GBPs) transform into Zn-rich phases when Zn content increases to 2.0 wt.%. The strength of the alloy firstly gradually improves and then reduces when Zn content increases to 2.0 wt.%. This is mainly due to the effect of Zn content on the distribution of the intragranular precipitates. The strength of the alloy significantly enhances again as a result of the increase of the number density of β" precipitates and the formation of η' precipitates when Zn content reaches 4.0 wt%. [Display omitted] • Zn addition promotes the precipitation behavior of the intragranular precipitates. • The size and type of the GBPs change with the variation of Zn content in the alloy. • Zn content has great effect on the PFZ width. • Zn addition improves the strength mainly due to the high number density of the intragranular precipitates. [ABSTRACT FROM AUTHOR]