To facilitate the manufacturing of the thin-walled components of 2219 aluminum alloy, the quenching–forming–aging (Q–F–A) process has been increasingly utilized. However, natural aging (NA) after quenching significantly affects the cold forming performance of this alloy. In this study, experiments are conducted to investigate the effect of NA time on the cold forming performance of 2219 aluminum alloy. The results indicate that NA can weaken the Portevin–Le Chatelier (PLC) effect, thereby reducing its influence on the cold forming performance of the alloy. The PLC effect becomes indistinct when the aging time reaches 2 years. The yield strength of 2219 aluminum alloy increases monotonically with aging time, while the elongation first increases rapidly and then decreases. After an aging time of 2 years, the yield strength increases by 28.6% from that of newly quenched alloys. The strain hardening index and hardening coefficient indicate that short-term NA (less than 4 days) increases the work hardening rate, while long-term NA reduces it. Microstructural analysis shows that the strengthening effect of NA on 2219 aluminum alloy is mainly due to the growth of G.P. zones and the precipitation of θ″ phases. The NA precipitation behavior can also cause the aggregation of solute atoms and weaken the PLC effect.

Cyclic heat treatment is an effective approach for enhancing the mechanical properties of 18Ni(C250) maraging steel, and the selection of cyclic heat treatment temperature is a key factor. In this study, a cyclic heat treatment process with a two-step solution treatment is employed to investigate the influence of cyclic heat treatment temperature, specifically the first solution treatment temperature (920 °C, 950 °C, and 980 °C), on the microstructure and mechanical properties of 18Ni(C250) maraging steel. The results indicate that with an increase in the cyclic heat treatment temperature, the average grain size of the 18Ni(C250) maraging steel decreases initially and then increases. When the cyclic heat treatment temperature reaches 950 °C, the grain size is at its minimum, exhibiting optimal grain uniformity. Additionally, the increase in cyclic heat treatment temperature results in a reduction in the size of martensitic lath with the same orientation inside the grains, along with an increase in the relative quantity of low-angle grain boundaries. Furthermore, the volume fraction and size of retained austenite show a monotonous increase with the rise in the temperature of the cyclic heat treatment, and the rate of increase becomes notably larger when the temperature is raised from 950 °C to 980 °C. Based on the observed microstructural changes, the variation in the mechanical properties of the 18Ni(C250) maraging steel was analyzed. Specifically, as the cyclic heat treatment temperature increases, the tensile strength of the 18Ni(C250) maraging steel initially increases and then stabilizes, while the elongation and fracture toughness exhibit a monotonic increase.

The quenching-spinning is an emerging process for achieving high-performance manufacturing of 2219 aluminum alloy thin-walled components. However, quenching-induced distortion in 2219 aluminum alloy blanks critically influences the formation laws during spinning process, necessitating process optimization for high-accuracy forming. Through integrated finite element (FE) simulation and experimental validation, this study investigates the distortion characteristic during immersion quenching and their effects on the geometric accuracy of thin-walled components, followed by spinning process optimization. The quenching process causes significant bending distortions in the circular blanks, and the distortion mode is depended on the immersion rate. A higher immersion rate generates saddle-shaped distortion mode, whereas a lower rate produces shovel-shaped profiles with greater distortion degree. Comparative forming analyses show that saddle-shaped blanks reduce flange fluctuation and improve circumferential stress uniformity, indicating better process stability. As a result, the component-mandrel gap after forming is smaller when using saddle-shaped blanks, and the roundness is noticeably better. Installation orientation optimization demonstrates that mounting the saddle-shaped blank with its concave surface toward the mandrel for spinning process can reduce the component-mandrel gap and increase roundness. Parameter optimization identifies that the maximum negative deviation ratio has the greatest effect on the spinning accuracy, followed by the roller nose radius, roller feed ratio, and roller oblique angle. Experimental results confirm the reliability of the optimized process for achieving components with high accuracy.

This study investigates the acoustic emission (AE) response and damage mode characteristics of ±45° glass fiber-reinforced polymer (GFRP) composites used in wind turbine blade shear webs under quasi-static tensile loading. It aims to establish the relationship between AE features and three typical damage mechanisms—matrix cracking, interfacial debonding, and fiber fracture—to support damage assessment and structural health monitoring. Quasi-static uniaxial tensile tests with synchronous AE monitoring are conducted on specimens with three orientations (0°, 45°, and 90°). AE features are selected using correlation analysis and principal component analysis, and the HAC-initialized K-means clustering method is employed for damage mode identification. The optimal number of clusters is determined to be three, according to the Davies–Bouldin index (DBI) and the Silhouette index (SI). The resulting low-, mid-, and high-frequency clusters are associated with matrix cracking, interfacial debonding, and fiber fracture, respectively. These interpretations are further supported by wavelet-based time–frequency analysis and microscopic fracture surface observations.