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Abstract To obtain the optimal mechanical properties, several processes including spray forming technology, two passes hot extrusion and substantial heating treatments were operated on an Al-Zn-Mg-Cu-Zr alloy. The characterization methods used in this study include tensile tests, X-ray diffraction, differential scanning calorimetry and microstructure observations by optical microscope, scanning and transmission electron microscopy. The typical characteristics were the refined grain, homogeneous precipitates and porosity in the as-deposited pre-forms. The ultimate tensile strength, yield strength, hardness and elongation improved significantly after two passes hot extrusion. A good combination of ultimate tensile strength at 704 MPa and elongation at 9.7% were achieved under peak-aged treatment. The best ultimate tensile strength was obtained at 732 MPa after re-aging and regression. It was main dimple fracture in the extruded and aging treated specimens while brittle fracture for the as-deposited. The secondary phases were main MgZn 2 and Al 3 Zr dispersoids throughout all the states. The contributions of grain boundaries, dislocations, solid-solution and precipitates on the yield strength were analyzed using a quantitative equation. Highlights • The spray forming technology was used to fabricate ultra-high strength aluminum alloy. • The alloy under RRA state obtained the highest ultimate tensile strength of 732 MPa. • The effects of dislocations, solutes and precipitates etc., on yield strength were calculated. • Precipitation was characterized as the main strengthening mechanism for aging states. [ABSTRACT FROM AUTHOR]

Extruded plates of 6005A aluminum alloy with 0.07 wt% Sc (referred to as M6005A alloy) was metal-inert-gas-welded (MIG-welded) with ER5087 filler wire. The microstructure, mechanical properties, and fatigue behavior of the joints were studied. Compared with the base material (BM), recrystallization occurred and the formation of the coarse β' phase was evident in the heat-affected zone close to the weld zone (HAZ 2), which resulted in a significant decrease in the mechanical properties of HAZ 2. However, trace Sc inhibited the growth of the recrystallized grains in the HAZ 2, strengthening the α-AlFeSi and β'′ phases in the BM, which drastically improved the mechanical properties of the BM. In the weld zone (WZ), grains were significantly refined since the presence of Al 3 (Sc, Zr) particles promoted the nucleation of such grains in the WZ, and the particles also promoted the non-uniform nucleation of the α-AlFeSi phase, which significantly improved the mechanical and fatigue properties of the WZ. The hardness distribution of the MIG-welded joint shows a double-W shape. The lowest hardness is 55 HV, observed in the HAZ 2. The ultimate tensile strength (UTS) and conditional fatigue strength (107 cycles) of the MIG-welded joint of M6005A-T6 are 238.5 MPa and 108.2 MPa, respectively, 38 MPa and 13 MPa higher than the those of the MIG-welded joint of 6005A-T6 alloy, respectively. • The 6005A alloy profile, with optimum content of Sc, was welded by MIG welding. • Study on microstructure and properties of welding joint of 6005A alloy containing Sc(referred to as M6005A-T6 alloy). • The mechanism of the effect of Sc on the structure and properties of 6005A welded joint was studied. • M6005A alloy is about to replace 6005A alloy as an important material for high-speed iron‑aluminum. [ABSTRACT FROM AUTHOR]

Mechanical property and corrosion resistance are essential performances in ultra-high strength Al-Zn-Mg-Cu alloys for the aerospace and weapon industries. In this study, the pre-strain and aging treatments were used to enhance such performances of the spray formed ultra-high strength Al-Zn-Mg-Cu alloy. After 2% pre-strain with peak aging (PA) and retrogression and re-aging (RRA) treatments, the ultimate tensile strength, yield strength, and elongation can reach to 774 MPa, 735 MPa, 10.7% and 774 MPa, 747 MPa, 9.4%, respectively. The coarser precipitates of the samples with 4% pre-strain can lead to the slight lower strength compared with the samples with 2% pre-strain. The proper combination of pre-strain and aging treatments can also effectively enhance the stress corrosion resistance of the studied alloy by the following reasons. First, the higher strain concentration degree and dislocation density introduced by pre-strain treatments have high internal energy and provide more stored energy for the growth of the passive film. Second, the spacing of grain boundary precipitates under double aging (DA) and RRA states is larger than that under PA state. The width of uniform precipitation free zone (PFZ) with 2% pre-strain is larger than that with 4% pre-strain. Third, after pre-strain treatments, the cracks perpendicular to the deformation direction can be produced in Al 7 Cu 2 Fe phase, which further breaks up such particles. According to the results of Kelvin probe microscopy, the Al 7 Cu 2 Fe phase with smaller dimension can obtain the lower difference of potential to Al matrix. • The strength and corrosion resistance of the alloy were enhanced by pre-strain. • The pre-strain produced cracks in Al 7 Cu 2 Fe particles and further broke up them. • The pre-strain improved the strain concentration degree and dislocation density. • The effect of precipitation free zone and precipitate is better under 2% strain. • The improvement mechanism of pre-strain treatment was revealed. [ABSTRACT FROM AUTHOR]

Sc-containing Al alloys have excellent mechanical properties, which provide the foundation for their applications. The precipitation of the Al 3 Sc/Al 3 (Sc, Zr) is generally considered to be a key factor for the performance boost. However, the performances of the alloy in different production batches often exhibit unstable and fluctuation, which may be related to the heterogeneous of scandium. Herein, we investigated the precipitation behaviors of Al 3 Sc/Al 3 (Sc, Zr) phases in the Al-0.5Sc and Al-0.5Sc-0.25Zr alloys at 340 °C. Results shown that the high scandium‑zirconium ratio not only lead to the discontinuous precipitation, but also contribute to the abnormal continuous Al 3 (Sc, Zr) precipitation in Al-0.5Sc-0.25Zr alloy. The morphology of abnormal Al 3 (Sc, Zr) is similar to the common secondary Al 3 (Sc, Zr) phase with a coffee-bean like morphology. With the aid of Three-Dimensional Atomic Probe (3DAP), the core-shell structures of Al 3 (Sc, Zr) phases are quantitatively analyzed. In the shell layer of abnormal Al 3 (Sc, Zr) phase, the atomic concentration ratio of Sc to Zr is much higher than the common continuous precipitated Al 3 (Sc, Zr) phase. The abnormal Al 3 (Sc, Zr) phase may be one of the key factors for the structure heredity of Sc-containing Al alloys. [Display omitted] • The discontinuous precipitated Al 3 Sc phases are related to the partial high ratio of Sc/Zr (at.%) in Al alloys. • The discontinuous precipitated Al 3 Sc phases form at the casting process and gradually decompose at annealing process. • The high scandium-zirconium ratio leads to the decrease of coarsening resistance of the secondary Al 3 (Sc, Zr) phase. [ABSTRACT FROM AUTHOR]

The morphology of primary Al 3 Sc phase in Al-2.2Sc(wt%) was found to be influenced by melting condition. Some representative morphology appeared in large quantities at specific melting temperatures, holding times, and cooling rates. Crystallography of primary phases with various morphologies was researched, and the growth processes of the primary phase were investigated. Deformed cubes and dendrite can be developed from cubes, the butterfly-like particles had multiple layers inside, and repeated eutectic reactions were the main reason for the formation of multilayer structures. Al-2.2Sc(wt%) master alloys with different morphologies of primary Al 3 Sc phase can lead to different refining effects, and the mechanical properties of alloys were consequently influenced. The structure heredity of Al Sc master alloy was proved to be existed, and not influenced by prolonging insulation time and sufficient stirring. Unlabelled Image [ABSTRACT FROM AUTHOR]

The existing form of Sc in Si-containing 6xxx-series Al alloys and its role in strength has always been controversial. In this study, isothermal section phase diagram of the Al-0.60 wt%Mg-Si-Sc system at 350 °C was calculated by CALPHAD method and Pandat software, and the results show that Sc exists in Al 3 Sc or V (AlSc 2 Si 2) phases, depending on the contents of Si and Sc. Subsequently, we designed a Al-0.60 Mg-0.75Si-0.05Sc (wt%) Melt Inert Gas (MIG) welded alloy, and investigated its microstructure and mechanical property by tensile tests and electron microscopy. HRTEM and STEM-EDS results show that, Sc exists in the form of core(Sc)-shell (Si) structured (Al, Si) 3 Sc transition phases with the size range of 60–80 nm in the fractured zone (heat affected zone, HAZ) of the welded joints, deriving from equilibrium phase diagram, V (AlSc 2 Si 2) theoretically. The HAZ of the Al-Mg-Si-Sc joint consists of partly recrystallized grains and strong rolling texture, different from the completely recrystallized and coarsened grains in the Al-Mg-Si joint. In addition, the (Al, Si) 3 Sc phases increase the density of β'′ aging strengthening phases and prevent them from coarsening under welding heat cycle. The above positive effects of (Al, Si) 3 Sc particles increase the yield strength, ultimate tensile strength and elongation of Al-Mg-Si welded joints by 31 MPa (20.6%), 41 MPa (21.2%) and 0.8% (12.9%), respectively. [Display omitted] • Clarify the existing form of Sc in metal-inert gas welded Al-Mg-Si alloys. • Investigate the thermal stability of (Al, Si) 3 Sc phases and their effects on microstructure under welding thermal cycle. • Quantify the role of Sc in strength of metal-inert gas welded Al-Mg-Si alloys. [ABSTRACT FROM AUTHOR]

Corrosion behaviour of 2A97-T6 Al-Cu-Li alloy was investigated by anodic polarization, immersion test and quasi-in-situ analysis with corrosion morphology characterized by a range of electron microscopy techniques. It is revealed that selective dissolution of grain interior tends to occur in grains of high stored energies, resulting in corroded bands associated with dense precipitate bands in the alloy. The evolutions of corrosion morphology during immersion test and quasi-in-situ analysis are similar, which both exhibit well-defined crystallographic pits. By contrast, crystallographic feature was less evident for localized corrosion induced by anodic polarization, which may be associated with the extensive Cu re-distribution. • Corroded bands are confined within individual grains of high stored energies. • Corroded bands are related to precipitates. • Cu re-distribution promotes the localized corrosion development but compromises its crystallographic features. [ABSTRACT FROM AUTHOR]