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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]

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 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]