Abstract The directed energy deposition-arc (DED-Arc) process, using high-strength low-alloy (HSLA) feedstock wire, presents a promising solution for fabricating large-scale steel connectors in civil engineering. Due to the use of carbon steel feedstock wire, corrosion protection of the 3D-printed components is necessary. Therefore, this study investigates low-pressure cold spray (LPCS) as a method for applying zinc-based coatings. Two sets of thin walls were 3D-printed: one set uncoated and one set coated with LPCS Zn + Al 2 O 3 coating. This LPCS coating was successfully deposited on untreated and on grit-blasted DED-Arc surfaces. Coating thicknesses exceeding 300 µm as well as electrochemical polarisation analysis confirmed sufficient corrosion resistance of the coated as-built specimens. To evaluate the influence of the surface condition and the coating process on the mechanical behaviour, dog-bone tensile specimens were extracted from the walls, 3D-scanned, and subsequently mechanically tested. Structured-light scanning of the geometry revealed different scatter of the specimens’ thickness based on their orientation with respect to the build direction. Uniaxial quasi-static tensile tests, combined with a four-camera digital image correlation (DIC) system, were performed both on specimens with machined surfaces and with LPCS Zn + Al 2 O 3 coating on the as-built surface. While the machined specimens exhibited nearly isotropic behaviour, the coated as-built specimens showed pronounced anisotropy with comparable mechanical properties to uncoated as-built specimens from literature when excluding the coating thickness from the load-bearing cross-section. The LPCS Zn + Al 2 O 3 coating led to a reduction of the corrosion rate by two thirds compared to uncoated HSLA DED-Arc.

Abstract This study presents a comparative analysis between conventional friction stir welding (CFSW) and flexible ultrasonic-enhanced friction stir welding (FLEX-USE-FSW) applied to 3-mm-thick AA6082-T6 aluminum alloy. A novel ultrasonic system integrated into the tool holder was employed to introduce axial ultrasonic vibrations during welding. Mechanical testing, microstructural characterization, electron backscatter diffraction (EBSD), process force monitoring, and laser vibrometry were conducted to evaluate the influence of ultrasonic excitation on weld quality and process behavior. The results show that ultrasonic assistance reduces axial and traverse forces by up to 20%, broadens the operational window for tensile strength and elongation, and enhances material plasticization. EBSD analysis revealed a higher fraction of low-angle boundaries and modified grain texture in the ultrasonic-assisted stir zone (SZ), suggesting a change in recrystallization dynamics. Cross-sectional imaging indicated a larger and more homogeneous stirred zone in FLEX-USE-FSW, with reduced defect formation at elevated welding speeds. Additionally, laser vibrometry measurements showed improved energy transmission in specimens oriented parallel to the rolling direction. The findings demonstrate that ultrasonic excitation positively affects weld morphology, mechanical properties, and microstructural evolution, particularly under high-speed and low-heat input conditions.

Abstract Applications for additively manufactured (AM) metal parts, particularly via laser-based powder bed fusion (PBF-LB/M), have been growing significantly in industries with high level of requirements such as aerospace, nuclear plant, automotive, energy, and medical industry. However, PBF-LB/M parts often require welding to other components due to their limited size. Thus, the weldability of PBF-LB/M parts is of interest, particularly due to the microstructural differences between PBF-LB/M and conventionally manufactured parts. This study investigates the microstructure and mechanical properties of laser-welded PBF-LB/IN718 and compares the results with laser-welded sheet metal IN718. In addition, the effect of heat treatment before welding on the weldability of PBF-LB/IN718 samples was evaluated. Both the heat-treated and as-built PBF-LB/IN718 welds had lower microhardness at the fusion zone (FZ) than the base metals, whereas the sheet metal IN718 weld showed higher microhardness at FZ than the base metal. This was attributed to the distinct secondary phases and microstructure of the conventional IN718 and PBF-LB/IN718 samples. Nevertheless, the ultimate tensile strength and yield strength of PBF-LB/IN718 welds were higher than the conventional IN718 welds, proving that laser welding is a viable method of joining PBF-LB/IN718 parts. Finally, the fatigue strength of the PBF-LB/IN718 welds, assessed at 10 6 cycles, was inferior to that of the conventional IN718 welds, owning to the defects such as lack of fusion in the base metal of PBF-LB/IN718 samples.

Abstract High-strength low-alloyed (HSLA) steels with yield strength/proof stress ≥ 600 MPa are the basis of modern light-weight steel constructions. Indeed, the economic and ecological benefits strongly depend on their processability in terms of welding. In this context, the use of highly productive welding processes and suitable welding consumables is of vital interest and requires a fundamental understanding of the microstructural changes in the HSLA steel and especially the heat-affected zone (HAZ) of the welded joint. Microalloying elements, such as Ti or Nb, are essential to achieving the desired mechanical properties. To analyse the weldability, three-layer welds were performed using gas metal arc welding (GMAW) and critical microstructures, such as areas of the HAZ that exhibit significant softening or hardening, were identified. The effect of the softened HAZ region on failure was evaluated using cross-weld tensile specimens. Digital image correlation (DIC) was used for in situ monitoring of the development and accumulation of the local strains in different HAZ regions during tensile testing. Using a specially designed mirror system, the local strains of the microstructure zones on the top and bottom of the weld were recorded simultaneously. In addition, the analysis of the local deformation helps to understand the effects of the softened HAZ on the global strain, the reduction in area, the fracture position, and the overall fracture behavior.