Metals

Laser powder bed fusion (LPBF) was adopted to manufacture AlSi10Mg, and two post-processing schedules, T4 (510 °C/2 h + water quench) and T6 (T4 + 180 °C/6 h), were applied to elucidate how Si precipitation size controls ductility. The as-built alloy consisted of an α-Al matrix with a grid-like eutectic Si network and achieved UTS > 480 MPa but exhibited build-direction-dependent tensile anisotropy. Heat treatment promoted Si precipitation from the supersaturated α-Al matrix and transformed the eutectic network via fragmentation, spheroidization, and Ostwald ripening, leading to pronounced softening and improved elongation. After T4, the yield strength and UTS decreased by >50%, while elongation increased from 10.9% to 22.27%; T6 provided a slight strength recovery accompanied by a marginal ductility reduction. Mechanistically, a high number density of fine Si precipitates enhances dislocation storage and delays damage accumulation, whereas coarse, non-shearable Si particles intensify local strain gradients, facilitate void nucleation at the matrix/particle interface, and accelerate fracture. Overall, tailoring Si precipitation/coarsening offers an effective route to improve ductility and mitigate anisotropy in LPBF AlSi10Mg.

This study reviews the application of wire arc additive manufacturing (WAAM) technology in maritime engineering and investigates an experimentally driven analytical approach for prediction of thermal distributions based on the Rosenthal solution. Two ER70S-6 low-carbon steel WAAM cylinders were fabricated using gas metal arc welding (GMAW) and plasma arc welding (PAW) processes, with interlayer temperatures of 453 °C and 250 °C, respectively. Accurately measuring the temperature field to tailor the microstructure has long been a challenge. The results indicated a significant deviation between the analytical predictions and the experimental data. To address this discrepancy, a hybrid approach combining analytical and experimental results was implemented. Time intervals between layers, extracted from the experimental data, were incorporated into the Rosenthal equation to improve the accuracy of temperature field predictions. The microstructure at the bottom, middle, and top regions of the WAAM components was examined using optical microscopy. Tensile testing and Vickers microhardness measurements were conducted to evaluate mechanical properties. Scanning electron microscopy (SEM) was used to analyze fracture surfaces and identify fracture modes. The results were consistent with those reported for other ER70S-6 cylindrical WAAM components. This work highlights limitations of the Rosenthal solution and emphasizes the need for thermal models in WAAM applications.

This study investigates the influence of vanadium–nitrogen (V-N) microalloying design on the microstructure and mechanical properties of 700 MPa grade ultra-high-strength steel bars. Through the control of the V/N ratio and cooling rate, a yield strength exceeding 700 MPa was achieved in a steel with a pearlite–ferrite matrix. Microstructural characterization via optical microscopy (OM) and scanning electron microscopy (SEM) revealed that a V/N ratio of approximately 1:10 combined with a rolling cooling rate of 1–3 °C/s resulted in the steel bar exhibiting a yield strength of 774.21 MPa and a tensile strength of 971.13 MPa. The primary microstructure of the steel consisted of ferrite and pearlite. The steel featured fine grains and favorable crystallographic orientations, which contributed to its high yield strength and good ductility. Transmission electron microscopy (TEM) analysis indicated that under hot-rolling conditions, vanadium precipitated predominantly as nano-scale V(C,N) particles. These precipitates were distributed in both the pearlite and ferrite phases, thereby enhancing the tensile and yield strength. Furthermore, the steel with an optimal nitrogen content (0.0166 wt.%) and the finest grain structure (average grain size ≈ 2.618 μm) showed the lowest stress corrosion cracking (SCC) susceptibility, characterized by an elongation loss rate (I_δ) of 12.51%, demonstrating excellent SCC resistance.