Joining low-Si 5B06 Al alloy to steel is limited by brittle Fe-Al intermetallic compounds. Here, a Si-rich 4043 Al interlayer (4.5 wt.% Si) was locally introduced between 5B06 Al alloy (0.24 wt.% Si) and 316L stainless steel during wire-based friction stir additive manufacturing. Compared with a direct 5B06/316L joint showing interfacial cracking, the 5B06/4043/316L joint exhibited a sound interface, a retained Si-rich transition region, and a locally observed ∼200 nm reaction layer. Transmission electron microscopy/energy-dispersive X-ray spectroscopy revealed interfacial Si enrichment and supported the local identification of α-Al 15 (Fe, Mn) 3 Si 2 -type reaction products. The 5B06/4043/316L joint exhibited an ultimate tensile strength of 230 ± 10 MPa and a fracture strain of 3.7 ± 0.5%, reflecting the combined effects of the interlayer design, including Si-assisted interfacial reaction and transition-region modification.
Low-temperature toughness of coarse-grained heat-affected zone (CGHAZ) is investigated with varying C and Nb contents, focusing on mitigating CGHAZ embrittlement without sacrificing the mechanical performance of as-rolled plates. Higher Nb promoted deformation-induced ferrite transformation in as-rolled plates, whereas in the CGHAZ, lower C produced degenerated pearlite instead of martensite–austenite (MA) constituents. Such phase transformations reduce the size and volume fraction of MA constituents, decrease potential crack-initiation sites, and enhance crack-propagation resistance. Consequently, the 6C–2Nb steel exhibited lower ductile-to-brittle transition temperatures of −73 °C and −30 °C in as-rolled plates and CGHAZ, respectively, compared to −46 °C and −16 °C for 7C–1Nb steel. This study proposes a microstructural approach to overcome the traditional ultimate tensile strength–toughness trade-off while preserving the matrix structure.
Laser stake welding of hidden T-joints requires precise lateral beam positioning relative to the concealed web sheet. Existing monitoring approaches based on optical coherence tomography, camera vision with neural networks, or spectroscopy involve substantial hardware costs, extensive training data, or limited temporal resolution. This study presents a plasma voltage sensing approach using a voltage divider circuit with an external copper electrode. Experiments on S355 steel demonstrate that electrode positioning critically determines measurement capability. A leading electrode configuration yields clearly separated voltage distributions for weld-in (μ = 0.988 V) and weld-through (μ = 0.169 V) conditions, enabling threshold-based classification. The sensor offers a cost-effective alternative to established monitoring technologies for industrial beam positioning control.
In this study, high-frequency circular oscillating laser is employed to achieve a more uniform energy distribution and a Ti interlayer is used to suppress the continuous and excessive formation of brittle Al–Mg intermetallic compounds (IMCs). The results show that the joint interface exhibits an optimal “U-shaped” morphology at 3.0 kW with the Ti interlayer melting uniformly. The interface is primarily composed of a 6-μm Al–Mg IMCs layer and a 23-μm Al–Ti IMCs layer. During shear tests, fracture occurs along the Al–Ti IMCs layer. At 3.5 kW, the Ti interlayer is completely penetrated, and the interface transforms into an “n-shaped” configuration consisting of an α-Mg + Al 12 Mg 17 eutectic phase and a dispersed mixture of Al–Ti IMCs. Fracture occurs at the Mg-side fusion line. Neither joint exhibits large-area, single-phase Al–Mg IMCs. Instead of occurring at the conventional Al–Mg interface, fracture is shifted to the Mg-side fusion line, allowing both joints to achieve reliable strengths of ≥2.5 kN.
After the addition of rare earth (RE) elements to the Mg–Ca treated steel, the mean size of inclusions increases from roughly 1 μm to 2 μm, whereas the number density declines from 533 mm −2 to 174 mm −2 . In Mg–Ca treated steel, intragranular acicular ferrite (IAF) constitutes the predominant microstructure, occupying approximately 60% of the area. Following RE addition, the IAF fraction falls to 15%, while widmanstätten ferrite (WF) and bainitic ferrite (BF) become the dominant microstructures. After impact testing at −20 °C, the fracture mode changes from ductile–brittle fracture in the Mg–Ca treated steel to cleavage fracture in the Mg–Ca–RE treated steel, and the impact energy value decreases from 252 J to 33 J.
