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Mechanical property and corrosion behavior of 7A46 aluminum alloy under peak-ageing (T6), double-ageing (DA) and pre-ageing (PA) followed by double-ageing (PA-DA) are systematically investigated. The hardness and strength of aged 7A46 alloy follows an order of T6>PA-DA > DA and the rank of corrosion resistance is PA-DA > DA > T6. The small size and dispersed distribution of matrix precipitates (MPs) lead to the high hardness and strength of T6 alloy, and low hetero-phase potential differences and less formation probability of corrosion galvanic couples enhance the corrosion resistance of PA-DA alloy. Intergranular corrosion (IGC) test results reveal that considerable potential differences promote the formation rate and the quantity of corrosive-batteries between the matrix and grain boundary precipitations (GBPs) or precipitate-free zones (PFZs). The exfoliation corrosion (EXCO) rate and the weight gain trend of corrosion products are related to the oxide film formation rate and corrosion products accumulation. Localized anodic dissolution and hydrogen embrittlement can induce the stress cracking corrosion (SCC). • The strengthen mechanism of 7A46 alloy is studied. • The mechanical strength is related to the small dispersed particles. • The alloy exhibits the best corrosion resistance under PA-DA condition. • The corrosion rate of the alloy under PA-DA condition is lower than that under T6, DA condition. [ABSTRACT FROM AUTHOR]

Abstract The localized corrosion behavior of Al-7.82Zn-1.99Mg-2.41Cu-0.12Zr alloy was investigated. At the early stage of corrosion, the sample surface only suffers slight local pitting corrosion. While as the immersion time extends, intergranular corrosion occurs, accompanied with surface exfoliation. At the initial stage of pitting corrosion, Al and Mg elements in the matrix around Al 7 Cu 2 Fe particles are dissolved preferentially, forming Al and Mg deplete zones. Furthermore, the dissolution of Al and Mg elements triggers the selective dissolution of Al element in Al 7 Cu 2 Fe, remaining Cu-rich and Fe-rich cluster. Atomic force microscopy (AFM) results show that this Cu-rich and Fe-rich cluster has higher potential difference relative to the matrix than the uncorroded Al 7 Cu 2 Fe particle. Highlights • The effects of Al 7 Cu 2 Fe on the localized corrosion behavior of alloy were investigated. • AFM technique was used to measure the potential difference between Al 7 Cu 2 Fe and matrix. • The corroded Al 7 Cu 2 Fe has higher potential difference relative to the matrix than the uncorroded Al 7 Cu 2 Fe. • Pitting corrosion initiation mechanism was studied in detail. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of spray formed ultra-high strength aluminum alloy was investigated by isothermal compression tests at 613–723 K and 0.001–1.0 s −1 . The flow stresses were predicted by using phenomenological model (strain-compensated Arrhenius equation), physical-based model (diffusion model) and artificial neuron network. The predictive ability has been weighed through statistical analysis including relative errors, correlation coefficients and box charts. It has shown the artificial neural network contains the best capability to predict the flow stress over the applied phenomenological and physical-based model. The strain-compensated Arrhenius can track the flow stress well in all processing conditions. Moreover, the diffusion model can well describe the metallurgical mechanisms during deformation by the microstructure observation. [ABSTRACT FROM AUTHOR]

Isothermal hot compression tests of Al-7.82Zn-1.96Mg-2.35Cu-0.11Zr alloy were carried out on a Gleeble-3500 thermo-simulator in the temperature range of 573–733 K and strain rate range of 0.001–1 s −1 . Stress-strain curves show that work hardening effect progressively exceeds softening effect with increasing strain rate. Microstructural evolution shows that two kinds of dynamic recrystallization exist in the hot compression process, which includes continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) and the dominant mechanism is continuous dynamic recrystallization, which occurs under the combined action of progressive subgrain rotation and misorientation increase. Five constitutive models were constructed to describe the hot deformation behavior. Weight optimization model has lower average absolute relative errors (AARE) value of 2.78%, root mean square error (RMSE) value of 2.73 and higher correlation coefficient (R) value of 0.997, and gives weight factors at different temperatures. The revised constitutive model with considering the comprehensive effects of lattice diffusion, grain boundary diffusion and the results of weight optimization gives relatively high prediction precision with AARE value of 4.64%, RMSE value of 4.92 and R value of 0.995, which is second to that of weight optimization model. The main diffusion mechanism is dominated by grain boundary diffusion at 573–693 K and lattice diffusion at 733 K. [ABSTRACT FROM AUTHOR]

The effects of solution treatment on microstructural and mechanical properties of a novel Al–Zn–Mg alloy by microalloying with Sc and Zr were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), transition electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), differential scanning calorimeter (DSC), X-ray diffraction and tensile test, hardness measurement, respectively. The results show that solution treatment had a significantly effect on microstructural and mechanical properties. There exist lots of residual phases along rolling direction before solution treatment. With increasing solution temperature/time, the residual phases are dissolved into α-Al matrix gradually, and the number density of residual phases decreased. After solution treatment at 460°C/60 min and aging treatment at 120°C/24 h, the precipitated phase inside the grains are homogenously distributed η ′ phase; the distribution of η precipitates is discontinuous and coarsened on the grain boundary. With the increase of solution temperature(≤470 °C) or solution time(≤60 min), the precipitated phases inside the grains began to become more diffuse, and the grain boundary precipitated phases also gradually become smaller. When solution temperature further increased to 490 °C or solution time increased to 120 min, the precipitated phases within the grains and on the grain boundary began to coarsen. In addition, there also exists lots of fine Al 3 (Sc, Zr) particles during aging treatment. Both tensile strength and hardness increase first and then decrease with increasing solution temperature or solution time. The optimum solution treatment is 470°C/60 min. The ultimate tensile strength, yield strength and elongation of the aged studied alloys reached a maximum value, 581 MPa, 561 MPa, and 10.1%, respectively. [ABSTRACT FROM AUTHOR]

Microstructural and property evolution of the Al–Zn–Mg–0.10%Sc–0.10%Zr alloy sheet during its preparation were investigated in detail by means of optical microscopy (OM), scanning electron microscope (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), Vickers micro-hardness test and room temperature tensile test. Stress corrosion cracking (SCC) behavior of the Al–Zn–Mg–0.10%Sc–0.10%Zr alloy under different heat treatments was studied using slow strain rate test. The results showed that serious dendritic segregation existed in as-cast condition. The suitable homogenization treatment for Al–Zn–Mg–0.10%Sc–0.10%Zr alloy was 470 °C/24 h. After homogenization treatment, dissoluble Zn and Mg enriched non-equilibrium phases dissolved into α -Al matrix completely. The suitable solid solution-aging treatment for Al–Zn–Mg–0.10%Sc–0.10%Zr alloy was solution treated at 470 °C for 60 min, followed by water quenching and then aged at 120 °C for 24 h. Under this aging temper, the grain structures were composed of sub-grains, η ʹ phases and nanometer-sized, spherical Al 3 (Sc, Zr) particles. Grain boundary precipitates (GBPs) area fraction was found to be an important parameter to evaluate the SCC susceptibility. The improved corrosion resistance from increasing aging temperature or prolonging aging time was due to the discontinuous η precipitates along the grain boundary and the high area fraction of GBPs. The main strengthening mechanisms of Al–Zn–Mg–0.10%Sc–0.10%Zr alloy are precipitation strengthening derived from η ʹ precipitates, dispersion strengthening, sub-grain strengthening and grain refinement caused by coherent Al 3 (Sc, Zr) particles. [ABSTRACT FROM AUTHOR]

2.5 mm thick cold-rolled Al–Zn–Mg–Zr alloy plates with trace amount of Sc were subjected to metal–inert gas (MIG) welding with Al–Mg–Sc as the filler metal. The influence of Sc additions on microstructure and mechanical properties of the welded joints was investigated by means of optical microscopy (OM), scanning electron microscope (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), Vickers micro-hardness test and room temperature tensile test. Experimental results indicated that trace amount of Sc had significant effect on microstructure and mechanical properties of the joints. In both cases, base metal consisted of a typical fiber structure, different width of the equiaxed zones (EQZs) with fine grains were observed in the weld metal at the fusion boundary, fusion zones exhibited dendritic microstructure and average size of Al–Zn–Mg–0.10%Sc–Zr was 120 μm, while in Al–Zn–Mg–0.25%Sc–Zr, grain size decreased drastically to 50 μm. The grain refinement is mainly caused by the extremely fine, coherent Al 3 (Sc, Zr) particles with L1 2 structure, which act as heterogeneous nucleation. The observed grain refinement resulted in an appreciable increase in fusion zone strength and micro-hardness. Tensile strength of Al–Zn–Mg–0.25Sc–Zr alloy welded joint was 460 MPa, approximately 11% higher than Al–Zn–Mg–0.10Sc–Zr alloy welded joint. Micro-hardness in the center of fusion zone rose from 95 HV to 110 HV. The main strengthening mechanisms of Al–Zn–Mg–Sc–Zr MIG welded joints are precipitation strengthening derived from η′ precipitates, dispersion strengthening and fine grain strengthening caused by coherent secondary Al 3 (Sc, Zr) particles. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hot compression test were conducted under different deformation conditions. [•] The dynamic recovery and dynamic recrystallization occurred during hot deformation. [•] ANN model and constitutive equations were established to predict the flow stress. [•] Material constants and Q value in the constitutive equations were calculated. [•] ANN model has a better prediction power than constitutive equations. [ABSTRACT FROM AUTHOR]

• The effects of Sc, Y and Zr on the performances and microstructure evolution of Al-0.7Mg-0.6Si-0.2Ce alloys were studied. • An excellent combination of strength, elongation and electrical conductivity was achieved with the addition of Sc and Y. • The strengthening and electrical resistance mechanism of the studied alloys were revealed by statistical calculation. [Display omitted] In order to achieve the compatibility between excellent mechanical properties and good electrical conductivity of Al-Mg-Si alloys, detailed investigation was carried out to understand the microstructure evolution and their influences on performances of different Al-0.7Mg-0.6Si-0.2Ce-X (X Sc, Y and Zr) alloys prepared by casting, homogenization, hot extrusion, solution and aging treatments. Under aging state, Ce can form a large number of micron-sized AlCeSi and a few AlCeFeSi phase. The strength increased to 334 MPa as a result of decreased grain size and improved precipitation effect and the electrical conductivity increased up to 53.53%IACS because of lower solute Si atoms. The β" precipitates were coarsened and consequently the volume fracture was largely reduced due to the presence of Sc element, leading to the decreased strength of 311 MPa. The more solute Mg, Si and Sc atoms increased the degree of free electron scattering and the electrical conductivity decreased to 51.86%IACS. It is also found that Sc significantly enhanced the elongation of the alloy from 11.8% to 18.0%, which might be attributed to the formation of Al 3 Sc and (Al, Si) 3 Sc phases. The addition of Y raised the electrical conductivity of Al-Mg-Si-Ce alloy to 55.79%IACS by ameliorating the volume fraction and distribution of β" precipitates and decreasing the solute Si atoms. The co-addition of Sc and Y inherited the advantages of such two alloys. The ultimate tensile strength, elongation, electrical conductivity of Al-0.7Mg-0.6Si-0.2Ce-0.2Sc-0.1Y alloy processed by aging treatments is 336 MPa, 19.4% and 53.11%IACS, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A ZK60 alloy was processed by two-step equal channel angular pressing (ECAP) in order to refine the grain size and enhance the mechanical properties. The results show that fine grain size less than 1μm was obtained after the two-step ECAP process, 4 passes at 513K, followed by another 4 passes at 453K. The strength of ZK60 alloy decreased after the single-step ECAP process but recovered after two-step ECAP process. The strength decrease was related to the texture softening. Compared with the single-step ECAP at 513K, the two-step ECAP has significantly improved the yield strength and ultimate tensile strength of the alloy. The mechanism of the notable grain refinement of the ECAP process was mainly attributed to continuous dynamic recovery and recrystallization. [Copyright &y& Elsevier]

The effects of trace Sc and Y on the corrosion behaviors of cold-drawn Al-0.2Ce alloys were revealed by scanning Kelvin probe force microscopy (SKPFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Electron Probe Micro-analyzer (EPMA), and electrochemical measurements. The results showed that the Al 3 Sc particles not only enable the increase of subgrain boundaries in the modified alloy after cold drawing but also improve the morphology and size of the Al 13 Fe 3 Ce phase. SKPFM analysis showed that the enrichment of Y around the Al 13 Fe 3 Ce phase in the modified alloy can decrease its electrochemical inertness and thus reduce the micro-galvanic corrosion susceptibility of the alloy. The results of the electrochemical analysis showed that the individual and composite addition of Sc and Y can improve the corrosion resistance of the cold-drawn Al-0.2Ce alloy. The corrosion potential and current of Al-0.2Ce-0.2Sc alloy are −0.892 V and 0.91 μA·cm−2, while the corrosion potential and current of Al-0.2Ce-0.1Y alloy are −0.918 V and 1.08 μA·cm−2, respectively. It is obvious that Sc element improves the corrosion resistance of Al-0.2Ce alloy more effectively than Y element. The corrosion depth of Al-0.2Ce-0.2Sc-0.1Y alloy was the smallest tested by immersion under the same conditions, and its corrosion potential and corrosion current were −0.842 V and 0.79 μA·cm−2, respectively, corresponding to the best corrosion resistance. The formal mechanism of pitting corrosion in the alloys is also discussed. [Display omitted] • Effect of Sc on microstructure and corrosion of Al-0.2Ce alloy was revealed. • The enrichment of Y atoms around Al 13 Fe 3 Ce can reduce the potential difference. • The corrosion behaviors of pitting corrosion induced by Al 13 Fe 3 Ce was discussed. • The equivalent circuit of the studied alloys was identified. [ABSTRACT FROM AUTHOR]

In ultra-high strength Al-Zn-Mg-Cu alloys, traditional heat treatments such as peak aging, two-stage aging and retrogression and re-aging cannot perfectly balance the relationship between mechanical properties and corrosion resistance and usually consume more time. Based on previous studies, the aim of this paper is to establish a suitable non-isothermal aging method for ultra-high strength Al-Zn-Mg-Cu alloys. In this study, after enhanced solution treatment and aging process with the heating rate of 20 °C/h, the alloy achieves excellent hardness and ultimate tensile strength of 195.7 HV and 680 MPA, respectively. When heating rate increases to 40 °C/h, non-isothermal aging can also ensure the alloy achieve the excellent mechanical properties (195.6 HV, 675 MPA). Similar to mechanical properties, the samples have outstanding resistance to intergranular and exfoliation corrosion, which is in accordance with the results of potentiodynamic polarization and electrochemical impedance spectroscopy tests. Evidences from high resolution transmission electron microscopy show that non-isothermal aging can promote the formation of a large number of smaller GP zones, η' precipitates and few η 2 precipitates inside grains, which greatly strengthens the mechanical properties. Furthermore, the grain boundaries precipitates transform from continuous to discontinuous and precipitate free zones form gradually, which greatly enhances the corrosion resistance. Because of these precipitates inside grains and grain boundaries, the samples with enhanced solution treatment +20 °C/h aging process and both solution treatments +40 °C/h aging process can achieve good mechanical properties closing to T6 state and corrosion resistance similar to T74 state simultaneously with much less aging time. Image 1 • The non-isothermal aging was designed as a novel route for heat treatments of ultra-high strength Al-Zn-Mg-Cu alloy. • An excellent combination of strength-ductility and corrosion resistance was achieved in the studied alloy. • The strengthening and corrosion mechanisms of non-isothermal aging on the studied alloy were discussed systematically. • Precipitation behavior of MgZn 2 strengthening phase was well studied. [ABSTRACT FROM AUTHOR]

The hardening behavior of Al-0.25Sc and Al-0.25–0.12 (wt.%) alloys during isothermal annealing were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), optical microscopy (OM), and hardness measurements. The results show that Sc-containing aluminum alloy contained fine dispersion of spherical secondary Al 3 Sc particles, which developed during the annealing process. Al 3 (Sc, Zr) precipitates in the Al-0.25Sc-0.12Zr alloys are core-shell structure. Different isothermal annealing temperatures can lead to different strengthening effects on the alloys. Al-0.25Sc and Al-0.25Sc-0.12Zr alloys both exhibit obvious annealing hardening behavior, and the ternary Al-0.25Sc-0.12Zr alloy shows better thermal stability than Al-0.25Sc alloy. • The diffusion rate of Sc atoms is inhibited by Zr atoms, which can prevent the coarsening of Al 3 (Sc, Zr). • The hardness decrease in Al–Sc alloy is mainly caused by the coarsening of Al 3 Sc particle. • The radius of the Al 3 (Sc,Zr) particles can maintain their value when annealed at higher temperature (>340 °C) for longer time (∼24 h). [ABSTRACT FROM AUTHOR]

The quench sensitivity of Al–Mg–Si–Mn–Cr alloy was studied through time-temperature-transformation (TTT) and time-temperature-property (TTP) curves. The high quench sensitive region ranges from 250 °C to 430 °C with nose temperature at about 350 °C, where the quenching rate is required to higher than 9 °C/s for avoiding the formation of quench-induced precipitates. B′(Al 3 Mg 9 Si 7) precipitates from the supersaturated solid solution, and gradually transforms to equilibrium β (Mg 2 Si) and excess Si phase with increasing isothermal time at 350 °C. The loss of the solute atoms in matrix results in the reduction of the aging hardening precipitation and the formation of the precipitate-free zones (PFZs) during artificial aging. The nucleation rate of the quench-induced precipitation is studied by nucleation theory, and the phase transformation kinetics is analyzed through Avrami equation. The Al(MnCrFe)Si dispersoids, (sub)grain boundaries and dislocations are the preferential heterogeneous nucleation sites for quench-induced precipitation. • The quench sensitivity of the alloy was studied by time-temperature-transformation and time-temperature-property curves. • The microstructure evolution of the quench-induced precipitate and its effect on mechanical properties were analyzed. • The nucleation rate and phase transformation kinetics of the precipitation were investigated. • The preferential heterogeneous nucleation site for quench-induced precipitation was discussed. [ABSTRACT FROM AUTHOR]

The non-superplastic Al–Zn–Mg alloy sheet produced by a simple traditional thermal–mechanical processing can achieve high superplasticity at the temperatures ranging from 450 to 500 °C and the strain rates ranging from 1 × 10 −3 to 1 × 10 −2 s −1 by low scandium additions in the presence of 0.10% Sc (wt.%). An elongation of 1050% is obtained at 500 °C and 5 × 10 −3 s −1 . Analyses on the superplastic data reveal that the average values of the strain rate sensitivity and the activation energy of the Al–Zn–Mg–Sc–Zr alloy are about 0.5 and 85 kJ/mol −1 , respectively. The microstructural results show that the studied alloy consists of 3.14 μm grains characterized by a high fraction of low angle grain boundaries and strong β-fiber rolling textures. During superplastic deformation, low angle grain boundaries gradually transfer into high angle grain boundaries to sustain grain boundary sliding, and the texture intensity diminishes. Besides, β-fiber rolling textures weaken and cube and random textures are dominant in the superplastic deformed alloy. Superior superplastic ductility of the Al–Zn–Mg–Sc–Zr alloy is ascribed to the coherent 10–20 nm Al 3 Sc x Zr 1− x particles that strongly retard recrystallization grain growth. Analyses of the superplastic data indicate that grain boundary sliding is the predominant deformation mechanism. [ABSTRACT FROM AUTHOR]