Yan Shi

This paper investigated the microscopic corrosion evolution process and corrosion channel propagation mechanism of high-nitrogen austenitic stainless hybrid welds in Cl ^- environment. By employing step interrupted method of polarization test in 3.5 wt.% NaCl, combined with transmission electron microscopy, scanning electron microscopy, and energy dispersive x-ray spectroscopy, the localized corrosion path was identified. It indicated that the corrosion evolution process was induced by ferrite dendrites, originating at the phase boundary and propagating through dendritic detachment channels. The nanoscale Cr-depleted zone formed on the ferrite side of the austenite/ferrite interface was the main reason for promoting the channels propagation. The severe pitting evolution and exacerbation of the HNS weld microstructure were induced by dendrite detachment followed by the Cr-depleted channel effect.

The welded joints exhibited highly complex corrosion mechanisms under the combined action of applied stress and flow erosion. This paper used a stress-flow erosion coupling test device to study the stress-erosion corrosion mechanism of laser-arc hybrid welded HNS. The results indicated that localized stress concentration induced the generation of dislocations within the material, which lowered the activation energy required for metal dissolution and promoted the occurrence of pitting corrosion. The flow erosion accelerated the removal of corrosion products from within the pits, which promoted the propagation of the pits. The study proposed a pitting acceleration kinetic model to calculate the acceleration factor of stress-erosion corrosion relative to static corrosion.

Copper exhibits a significantly higher absorptivity (approximately 45%) for green lasers (wavelength 515 nm) compared to traditional infrared lasers (5%–10%). This characteristic shifts the melting mode from an unstable keyhole regime to a stable conduction regime, which enhances melt pool stability, reduces spattering and porosity, and widens the process window. To further investigate the influence of this property on the laser powder bed fusion of pure copper, this study establishes a coupled DEM–CFD model to systematically analyze the effect of process parameters on the forming process. The results indicate that for single-track formation, a linear energy density below 0.28 J mm ⁻¹ tends to cause defects such as balling and discontinuity in the melt tracks. Within the range of 0.28–0.39 J mm ⁻¹ , balling and discontinuity are notably reduced, but track distortion becomes more likely. At 0.39–0.5 J mm ⁻¹ , the tracks become continuous with significantly fewer defects. When the linear energy density exceeds 0.5 J mm ⁻¹ , the phenomenon of ‘bulging head and sunken tail’ intensifies, leading to instability in track morphology. In multi-track overlapping, a scanning spacing of 100 μm helps avoid heat accumulation (compared to 60 μm) and surface depression (compared to 140 μm). Furthermore, the surface topography of a formed layer affects the uniformity of subsequent powder spreading, and insufficient laser power may result in a shallow melt pool that fails to bond adequately with the underlying layer, leading to interlayer lack-of-fusion defects. This study provides a theoretical basis for optimizing process parameters and achieving high-quality additive manufacturing of pure copper.

This study numerically investigated the thermal performance of a rectangular channel incorporating scale-inspired biomimetic protrusion structures with micro-grooves on their surfaces. A three-dimensional numerical model was established and validated against experimental data under identical geometric parameters and boundary conditions, demonstrating good agreement in terms of outlet temperature and pressure drop over a wide range of Reynolds numbers. The effects of groove depth on friction factor, Colburn factor, and overall performance evaluation criterion (PEC) were systematically analyzed to elucidate the underlying flow and heat transfer mechanisms. The results indicated that the introduction of biomimetic grooves significantly modified the flow structure and thermal boundary layer development, thereby enhancing fluid mixing and heat transfer. However, excessive groove depth intensified flow separation and pressure loss, leading to performance deterioration. An optimal groove depth of 0.6 mm (approximately 40% of the fin height) was identified, which achieved the best balance between heat transfer enhancement and flow resistance. The findings provide theoretical guidance for the biomimetic surface design of high-efficiency heat exchangers.

To achieve high-strength connections for aluminum alloy components produced via Laser Powder Bed Fusion (LPBF) additive manufacturing, this study concentrates on LPBF-formed AlSi10Mg specimens. A single-factor variable approach was employed to conduct continuous laser welding experiments across two distinct parameter ranges: one characterized by high power and high speed, and the other by low power and low speed. Based on the previously discussed welding process parameters and informed by the mechanisms underlying weld porosity formation, this study conducts experimental investigations into various laser welding techniques. These techniques include pulsed laser welding, laser welding conducted under vacuum conditions, repetitive laser welding, ultrasonic-assisted laser welding, ultrasonic-assisted repetitive laser welding, and laser powder filling welding. The study ultimately showed that the pulsed laser filling powder welding process can achieve a high-quality connection for 5 mm thick LPBF-formed AlSi10Mg test specimens. The porosity of the weld is 2.2%, which is significantly lower than that observed in other laser welding processes. Furthermore, the tensile strength of the welded joint reaches a maximum of 267 MPa, which is 75.4% of the base metal’s strength. It plays a significant role in promoting the advancement and application of advanced manufacturing technologies.

This paper analyzed the microstructure and properties of 6061 aluminum alloy laser weld seam, which focused on the effect of laser defocusing amount(LDA) on weld morphology, microstructure, and corrosion resistance. The microstructure and corrosion behavior were studied by scanning electron microscope (SEM), and electrochemical testing system. It indicated that corrosion behavior respectively correlated with the precipitated phase and LDA. Experiments confirmed that with the LDA set to +0.4 mm, the laser focal spot expands, and the weld seam microstructure exhibit better corrosion resistance,reaching the corrosion resistance of 63.23% of the BM. The precipitation of Mg₂Si phases and the corrosion pits reduced to minimum levels by micro-galvanic corrosion. The weld width and the number of surface defects could be optimized by LDA adjustment. And the large LDA value coarsening the grain structure, dendrite spacing, and Mg₂Si precipitates.