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A novel electromagnetic shocking treatment (EST) is put forward to reduce the stress corrosion cracking (SCC) susceptibility of high-strength aluminum alloys and its fasteners by selectively modifying grain boundary (GB) microstructure. The effect of EST on the microstructure, mechanical properties and SCC susceptibility of T73-Al7075 alloy and its high-lock nuts has been investigated. Mechanical properties, electrochemical performance and constant strain SCC test have been carried out for T73-Al7075 alloy, microhardness test and SCC test under wet-dry cyclic condition have been carried out for its high-lock nuts, as well as microstructure characterizations via SEM, EBSD and TEM have been carried out for T73-Al7075 alloy. Comparing to the received sample, the strength of EST sample basically keep consistent while the elongation increases slightly, besides, the electrical conductivity and electrochemical corrosion performance improves. The SCC susceptibility of T73-Al7075 alloy and its high-lock nuts have been reduced after EST. Microstructure characterization shows that the grain morphology and matrix intragranular precipitate distribution of the EST sample keep almost the same as those of the received sample, which is consistent with the almost unchanged mechanical properties of alloy sample. However, EST induces the transformation of grain boundary precipitates (GBPs) and the formation of stripy/wavy GB as observed experimentally, which indicates that EST promotes nonlinear GB wetting or pre-melting and even grain bridging. The phase transformation and GB complexion transition induced by EST are main factors attributing to the obvious improvement of SCC resistance of T73-Al7075 alloy and its high-lock nuts. It can be deduced that anodic dissolution cracking will be relieved because of the dissolution and coarsening of GBPs. Hydrogen induced cracking and crack propagation can be relieved with the occurrence of grain bridging. They are both beneficial to improve SCC resistance of Al7075 alloys. This work provides a novel EST method to targetedly embellish GB microstructure, optimize GB complexion and connectivity, and then enhance the service performance of solid alloys and even finished parts. [Display omitted] • A novel EST is put forward to improve SCC of T73-Al7075 alloys and its fastener. • EST selectively modifies GBs of Al alloy without losing mechanical properties. • EST promotes GB wetting and grain bridging on nanoscale for Al7075 alloy. • EST improves SCC of T73-Al7075 alloys by embellishing GB complexion. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel method for selectively embellishing GB of solid alloys is presented. • GBPs of Al7075 alloys occur dissolution and coarsening concurrently by EST. • Stripy/wavy GBs are more commonly observed in EST sample. • EST enhances corrosion resistance of Al7075 alloys by embellishing GB. A novel electromagnetic shock treatment (EST) is put forward to selectively modify grain boundary (GB) microstructures and further improve corrosion resistance of T73-Al7075 alloys. Electrochemical tests and GB microstructure characterization by TEM (HRTEM) are conducted. The results show that EST with appropriate electromagnetic pulse energy being utilized can modify GB microstructure and enhance the corrosion resistance of T73-Al7075 alloy. In EST sample, GB precipitates (GBPs) dissolve and coarsen simultaneously, and stripy/wavy GBs with nanometer scale are more commonly observed which indicates that GBs relax within nanometer scale and even promote nonlinear grain bridging. The transformation of GBPs as well as the transition of GB complexions improve the corrosion resistance of EST sample. This provides a promising method to selectively modify GB microstructure instantaneously and improve related properties of solid alloys. [ABSTRACT FROM AUTHOR]

Recently, an efficient integrated forging process has been proposed in which solutionized aluminum alloy extruded bars are directly hot forged and quenched. In this study, the hot deformation behaviors and microstructure evolution of 6082 aluminum alloy extruded bar was investigated via isothermal compression tests under the temperature range of 400–535 ℃ and strain rates range of 0.1–10 s−1 with different strains. The deformation behaviors were described by the established strain-compensated constitutive model and processing maps. The microstructure evolution of the deformed specimens was revealed by electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM). It was found that the Zener-Hollomon (Z) parameter, which involved temperature and strain rate, exerted a considerable influence on the deformation behaviors and microstructure evolution. Deformation-induced extensive dislocations were pinned by the dispersoids and generated cellular substructures under high ln Z (i.e. low temperature or high strain rate), potentially triggering dynamic instability. The tangled dislocations pinned by the insoluble dispersoids continued to overcome the pinning points as ln Z decreased, while the dislocations were consumed by the rotation of subgrain boundaries. As a result, the geometrically necessary dislocation (GND) was decreased with the significant increase of the fraction of high angle grain boundaries (HAGBs). In addition, the stable-end orientations, namely, Brass {011}< 211 > and Goss {011}< 001 > texture components with high Schmid Factors (SFs) are generated during compression, facilitating the dislocation movement and thus promoting the fraction of recrystallization. The above findings demonstrate the foundation for improving forming performance and optimizing the processing parameters for the integrated forging process. • The flow behaviors of solutionzied 6082 aluminum alloy extruded bars were investigated. • The relationship of the dominant softening mechanisms and the Z parameter was revealed. • Evolution of grain boundaries misorientation and geometrically necessary dislocation was illustrated. • The characteristics of grain orientation and Schmid Factors were investigated. [ABSTRACT FROM AUTHOR]

The strength and aging efficiency of precipitation-hardened aluminum alloys are always difficult to be obtained simultaneously. To address this issue, a novel fast-aging process, that is, a two-step aging coupled deformation process, was proposed. The influence of fast-aging parameters on the mechanical behavior of Al–Zn–Mg–Cu alloy was studied, and it was found that secondary aging, pre-aging, and deformation have a major effect, an auxiliary effect, and a coordinating effect, respectively, on the strength of aluminum alloys. Compared to traditional peak strength aging process of the T6 condition, the tensile strengths of the material are improved by 10 MPa (∼1.99%), and the aging time reduced by 89.58%. The continuous growth conditions of the precipitates throughout fast aging were analyzed in detail, and a competitive mechanism for the nucleation and growth of the precipitates in the matrix and on dislocations during secondary aging was proposed. Subsequently, the mechanisms were verified using differential scanning calorimetry (DSC) testing and transmission electron microscopy (TEM) observations. [ABSTRACT FROM AUTHOR]

• Variation of strain rate sensitivity of Al-Zn-Mg-Cu alloy caused by PLC effect was evaluated, especially the new variation trend of strain rate sensitivity in additional region was shown in this paper. • The theory of the dynamic precipitation and the redistribution of solute atoms on dislocation were analyzed, and the competition mechanism between dynamic strain aging stress and dynamic precipitation stress was proposed. • Novel kinetics models were built to accurately describe the strain rate sensitivity and precipitation process. The strain rate sensitivity (SRS) of Al-Zn-Mg-Cu aluminum alloy under the effect of dynamic strain aging (DSA) was investigated in this paper by tensile tests at room temperature after different solution treatments. The experimental results show that for the samples after solution treatments, with the increase of strain rate, the flow stress fluctuates in waveform. The dynamic precipitation and the redistribution of solutes around dislocations due to saturation of solute atoms under DSA were described by interaction between solutes and dislocations in different strain rate ranges. The competition mechanism between DSA stress and dynamic precipitation stress was then put forward and discussed in detail. Finally, a set of kinetics models combined DSA and dynamic precipitation were firstly established, in which the concentration variation of solute atoms in matrix during DSA was taken into account to analyze the coordination between solutes and dislocations, and the mechanism of the dynamic precipitation. [ABSTRACT FROM AUTHOR]

• To mitigate macrosegregation, an oscillating laser was applied for welding. • A nonlinearly moving keyhole was produced, leading to forced convections. • Flow field of weld pool liquid was simulated by lattice Boltzmann modeling in 3-D. • Oscillating laser produced higher flow velocities at the keyhole boundary. • Patterns of Ni and Al distributions in weld seams were elucidated by modeling. For the mitigation of macrosegregations in the weld seams, an oscillating laser was applied in the laser welding of Al-Si coated press-handened steels (PHS) using a Ni foils as a interlayer. As captured by the high-speed camera, the stirring effect of the oscillating laser led to obvious fluctuations of the weld pool liquid, and the weld pool width increased with the oscillation diameter of the laser. The concentration distributions of elements Ni and Al were measured in the weld seams obtained from the laser linear and oscillationn welding. It is indicated that the macrosegregation was migitated through the laser oscillation welding with an increasing diameter. Numerical modeling of the weld pool fluid fields during laser welding was carried out by using a three-dimensional multiphase lattice Boltzmann model. The simulation results for the laser linear welding case showed that the velocity vectors with high magnitudes were symerically perpendicular to the keyhole boundary and pointed to the interior liquid phase in the weld pool. Thus, these forced convections transported the Ni and Al atoms from the weld pool center and surface to the lower part of the weld pool. In the laser oscillation welding case, however, the velocity vectors at the keyhole boundary were asymetrical as the keyhole moves, which were beneficial for efficiently mixing the weld pool liquid. The simulation results provided reasonable explanations for the different patterns of Ni and Al concentration distribuitons in the weld seams obtained from laser linear and oscillation welding. [ABSTRACT FROM AUTHOR]