ABSTRACT
For precipitation-strengthened Al alloys, the interfacial segregation behavior of alloying elements plays an important role in controlling the effectiveness of precipitation strengthening. In this work, the adhesion work (Wad) and interfacial energy (γ) of the η(0001)/Al(111) interface were studied to gain an insight into the interface properties between the precipitate η and the Al matrix. Additionally, we examined the impact of the segregation behavior of alloyed elements on the bonding strength of the interface. The computed values for Wad and interfacial energies indicated that the T6S3 terminated configuration represents the interfacial structure with the highest stability across all models analyzed. Focusing on the T6S3 interface, the assessed segregated energies (Eseg) disclose that the segregation ability of elements from strong to weak exhibits the order of Ti > Sc > Zr > Y > Ta > Nb > Lu > Hf > Mo > V > W, while Cr and Mn elements are not easy to segregate at the interface. Sc, Ti, V, Cr, Mn, Zr, Nb, Mo, Hf, and Ta preferentially occupy Al atoms, whereas Y and Lu predominantly inhabit Mg atoms. Relative to the clean interface, the electron cloud enrichment at the interface after alloying element X (Zr, Sc, Ti, W, Hf, Mn, Y, Lu and V) doping is weakened, and the ion interaction among interface atoms is enhanced. After doping alloying element X (Nb, Mo, Ta, and Cr), the degree of electron cloud enrichment at the interface is obviously enhanced, and the covalent interaction among interface atoms is enhanced. This suggests that the introduction of alloyed elements through doping can augment the bond strength at the interface between the precipitated phase and matrix, thereby reinforcing the strength and toughness of 7xxx series alloys.
ABSTRACT
In this paper, a one-step hot extrusion dual-stage solution treatment method is employed to fabricate high-strength and tough T-shaped complex cross-section 7055 (Al-Zn-Mg-Cu-Zr) alloy profiles, and a detailed investigation is conducted on the microstructure and mechanical properties. The results indicate that the comprehensive mechanical properties of the 7055 aluminum extruded alloy using the two-stage solution aging treatment are excellent. This is particularly evident in the balance between strength and ductility, where outstanding strength is accompanied by a plasticity that is maintained at 13.2%. During the extrusion process, the deformation textures are mainly composed of brass and copper, forming a 15.1% recrystallization texture Cube. In addition, the equilibrium phase η(MgZn2) precipitated in the grain is the main strengthening phase, and there are large discontinuous grain boundary precipitates at the grain boundary, which hinders the grain boundary dislocation movement and has great influence on the mechanical properties of alloy materials.
ABSTRACT
Hot extrusion forming is one of the best cost-effective processing methods to obtain high-strength aluminum alloys. In order to obtain high performance 2024 aluminum alloy for the aero and automobile industries, this research comprehensively uses heat treatment and reverse isothermal extrusion technology to prepare 2024 alloy. The effects of homogenization, extrusion and post-extrusion annealing treatment on the microstructure and mechanical properties of 2024 aluminum alloy were discussed in detail. The results indicate that the grain refinement of the extruded alloy material is significant. The coarse eutectic microstructure at the grain boundaries was refined, and these grains tended to be uniformly distributed after the annealing treatment. Extruded 2024 aluminum alloy material mainly has S (Al2CuMg) and Al7Cu2Fe second phases. The appearance of a large number of S phases led to a significant improvement in the properties of the alloy with an increase in tensile strength and elongation of 176% and 547%, respectively. In addition, EBSD analysis showed a significant meritocratic growth in the extrusion direction with the appearance of Copper {112} <111> rolling weaving, which led to process hardening and the strength improvement of the alloy.
ABSTRACT
A new welding method, flux bands constricting arc (FBCA) welding, is proposed to compensate for the shortage of insufficient weld width of laser welding T-joints in high steel sandwich panels. The arc behavior (arc burning position, arc shape, arc heat, and arc stability) before and after sticking the flux bands (GMAW and FBCA welding) to the ultra-narrow gap groove was tested. Results indicate that flux bands have solid-wall constricting effect (SWCE) and thermo-compression effect (TCE) on the arc and self-producing slag and gas function in FBCA welding. In ultra-narrow gap groove, the arc burning position climbing up phenomenon (APCP) occurs without flux bands. The SWCE of flux bands on the arc effectively suppresses the APCP because of the insulation of flux bands. In the FBCA welding process, the effective heating area of the arc is increased by at least 5 mm2 compared with that in GMAW. When the groove gap decreases, flux bands not only compress the arc from an inverted bell shape to a rectangular shape, but also make the 660 °C isotherm on the core-plate to increase from 3 mm to 8 mm. In the end, the proportion of unstable arc burning time is reduced by 86.85%, the fluctuation of arc voltage and welding current are also significantly reduced by the flux bands because of their SWCE on the arc.
ABSTRACT
The effects of CeO2 on the microstructure and synthesis mechanism of Al-Ti-C alloy were investigated by quenching experiment method, while using Al powder, Ti powder, graphite powder, and CeO2 powder as main raw materials. The results showed that the addition of CeO2 was favorable for promoting the formation of TiC particles in Al-Ti-C systems. With CeO2 contents increasing, the distribution of TiC particles were more homogeneous, and the rare earth phase Ti2Al20Ce was formed. CeO2 had little effect on the synthesis of Al3Ti particles in Al-Ti-C systems, but had a significant effect on the synthesis of TiC particles. In the Al-Ti-C system, TiC is mainly formed by the reaction of dissolved [Ti] and solid C in the melt. While in the Al-Ti-C-Ce system, CeO2 reacts with C and O2 to form CeC2 firstly, and then CeC2 reacts with dissolved [Ti] to form TiC. Based on thermodynamic calculation and microstructure analysis in the process of reaction, a macroscopic kinetic model of Al-Ti-C-Ce system reactions was proposed in this paper.
