Xiwu Li’s research while affiliated with General Research Institute for Nonferrous Metals (GRINM) and other places

The number of fasteners used in aircraft is vast, reaching millions. Aluminum alloy wire for fasteners has become a focus of research. In this study, the Al-Zn-Mg-Cu alloy wire was prepared by hot rolling and extruding methods. A comparative analysis of microstructure and mechanical properties was examined. Results indicated that the hot rolling technique yields a more homogeneous microstructure and enhances the stability of mechanical properties. Following solution treatment and aging, a significant quantity of nano-sized strengthening η′ phases developed within the alloy. This led to improvements in both strength and elongation relative to the cold-deformed state. Consequently, the hot rolling method emerges as the most effective approach for the industrial production of alloy wire for fasteners.

This article investigates the effects of different aging regimes on the microstructure, mechanical properties, and impact toughness of Al-Zn-Mg alloys. The mechanisms by which microstructural changes influence mechanical properties and impact toughness are discussed. In an overaged condition, as aging temperature is elevated and aging time extends, intragranular precipitates become coarser, and the density of precipitates decreases, leading to a decline in yield and tensile strength properties. However, it narrows the strength gap between intragranular and intergranular regions, enhancing the impact toughness. The appearance of the equilibrium η phase and the expansion of PFZ are also reasons for the improved impact toughness of the alloy.

Al–Zn–Mg–Cu alloys are widely used in aerospace, with recrystallization significantly influencing their stress corrosion resistance. This study examines the impact of recrystallization morphology on corrosion resistance in a high‐alloying Al–Zn–Mg–Cu alloy, focusing on lath‐shaped and equiaxed recrystallized grains. The findings reveal that, at the same recrystallization fraction, the equiaxed sample has a 2.83 times higher corrosion current density and a 1.15 times higher stress corrosion cracking susceptibility index than the lath sample. However, its critical stress intensity factor is only 89.3% of the lath alloy's. Lath recrystallization demonstrates superior stress corrosion resistance due to larger grain sizes, wider grain boundary precipitate spacing, lower Zn and Mg content, and higher Cu content. Finite element simulations and in‐situ tensile tests show that the equiaxed sample experiences more stress concentration and cracking at grain boundaries under the same applied stress. These results provide insights into optimizing the stress corrosion resistance of Al–Zn–Mg–Cu alloys.

Solid-state additive manufacturing (SSAM) is an emerging technology that offers a unique approach by avoiding the melting and solidification of metals during the fabricating process. As a result, it eliminates common solidification related defects like porosity and cracking. This method is characterized by low residual stress, low distortion, and the formation of fine equiaxed grain structures, making it particularly advantageous for fabricating large-scale components in sectors like aerospace, aviation, and rail transportation. This review explores the fundamental principle and recent development of solid-state additive techniques, namely, friction stir additive manufacturing (FSAM), additive friction stir deposition (AFSD), friction and rolling-based additive manufacturing (FRAM), and wire-based friction stir additive manufacturing (W-FSAM). Furthermore, the advantages, challenges, and future trends of these SSAM techniques are reviewed. A comprehensive review of the characteristics and current research trends in solid-state additive manufacturing methods is crucial for driving further advancements in this technology.

The 7085 aluminum alloy with a low Cu content is an important lightweight structural material in the aerospace field due to its advantages of low density, high specific strength, and high hardenability. However, like other high-strength Al-Zn-Mg-Cu alloys, this alloy is susceptible to stress corrosion cracking (SCC). Additionally, the lower Cu content may increase its tendency toward SCC, potentially impacting the safe use of this alloy. Therefore, this study investigated the effects of aging treatment processes on the mechanical properties and SCC resistance of 7085 aluminum alloy. And the factors affecting the properties of the alloy were analyzed by optical microscope (OM), scanning transmission electron microscope (STEM), and energy-dispersive X-ray spectroscopy (EDS) analyses. The results indicated that increasing the secondary aging temperature and adding a tertiary aging step can significantly reduce the alloy’s susceptibility to SCC while meeting the mechanical performance requirements. The reduced SCC sensitivity was mainly attributed to the increased spacing of grain boundary precipitates, a wider precipitate-free zone at the grain boundaries, and a higher Cu content in the grain boundary precipitates.

In the current study, the effects of extrusion and annealing treatment on the peripheral coarse grain (PCG) structure were investigated. The results showed that the edge of profiles recrystallized during the extrusion process, the grain size was in the range of 2-5 m and the degree of recrystallization had obvious heterogeneity along the extrusion direction, showing two kinds of recrystallization microstructure. The thickness of recrystallized microstructure at the head of the profile was 2 mm and there were obvious boundaries. The thickness of recrystallized microstructure at the tail reached 13 mm and there was no obvious boundary. The recrystallized grains grew abnormally to form PCG structure during the solution process. The PCG structure was significantly reduced when the extrusion ratio decreased from 20 to 14. The higher the extrusion temperature reached, the more serious the PCG structure was. The suitable annealing regime is 350°C/5h.