Metals

To solve the problems of large deformation and poor welding quality commonly observed during the double-sided welding of Q355 thin plates, this study systematically investigated the effects of single-sided ultrasonic-assisted welding on the weld formation, microstructure, mechanical properties, and residual stresses of the plates, and compared this welding process with conventional ones. Experimental results indicate that ultrasonic assistance is associated with improved weld shape and quality, contributing to a flatter weld surface and more symmetric cross-sectional profile. In contrast to conventional welds, welds produced by single-sided ultrasonic-assisted gas metal arc welding show no obvious oxide inclusions and a reduced tendency for columnar grain growth. In a single tensile test for each welding condition, the measured tensile strength was 552 MPa for conventional welding and 575 MPa for single-sided ultrasonic-assisted gas metal arc welding. These tensile results should be interpreted as indicative trends and require replication to assess scatter and statistical significance. Furthermore, single-sided ultrasonic-assisted gas metal arc welding is associated with lower welding residual stresses, with peak stress values reduced by up to 36.23% along the longitudinal path. This technique provides an engineering reference for improving weld-quality consistency during the double-sided welding of Q355 thin plates without altering the welding specifications.

Nickel superalloy Inconel 718 (IN718) is widely employed in harsh environments with prolonged cyclic stresses in the aerospace and energy sectors, due to its corrosion/oxidation resistance and mechanical strength obtained by precipitation hardening. This work investigates the mechanical behavior in fatigue of IN718 manufactured by Additive Manufacturing (AM), specifically by Laser Powder Bed Fusion (PBF-LB), and compares its results with the material produced by forging and rolling. Samples from both processes were subjected to heat treatments of solution and double aging to increase their mechanical strength. Then, tensile, microhardness, microstructural characterization, and uniaxial fatigue tests were performed (with loading ratio R = −1). The results showed that, although the IN718 produced by AM had higher microhardness and a higher tensile strength limit than the forged and rolled material, its fatigue performance was lower. The S–N curve (stress vs. number of cycles) for the material obtained by PBF-LB demonstrated shorter fatigue life, especially under low and medium stresses. The analysis of the fracture surfaces revealed differences in the regions where the crack initiated and propagated. The shorter fatigue life of the material obtained by PBF-LB was attributed to typical process defects and microstructural differences, such as the shape of the grains, which act as points of crack nucleation.

The stability of the Fe/Zn interface during the hot-dip galvanizing process critically influences the coating’s quality and service performance. In this investigation, the impact of silicon atom positioning on the stability, bonding strength, and electronic structure of the Fe/Zn interface was systematically examined through first-principles calculations grounded in density functional theory, employing the CASTEP software and the GGA-PBE functional. By constructing the FeSi and ZnSi disordered solid solution models, low-energy stable configurations were selected, and 24 ZnSi/FeSi interface models (misfit < 5%) were further established. The interfacial adhesion work, interfacial energy, and electronic structure parameters were systematically calculated. The findings indicate that the position of Si atoms significantly affects interface stability, with Si atoms located on the Zn side exerting a more pronounced influence than those on the Fe side. The interfacial stability is optimal when the Si on the Fe side is far away from the interface and the Si on the Zn side is located at the interface. Notably, the S11Z32 model exhibited the highest adhesion work (4.763 J/m²) and the lowest interface energy (0.022 J/m²). This study elucidates the regulatory role of Si atoms in stabilizing the Fe/Zn interface and provides a theoretical foundation for optimizing the hot-dip galvanizing process and guiding the design of novel materials.