Solidification cracking remains a critical challenge in laser welding of 6ⅹⅹⅹ aluminium alloys, particularly in near edge conditions where thermo-mechanical restraint is severe. Existing predictive models often require micro scale calibration or post-test strain measurements, limiting their practical use. This study combines a finite element method (FEM) approach with the classical Rappaz-Drezet-Gremaud (RDG) framework to predict crack susceptibility in 6060-T6 aluminium alloys with varying Cu additions (0–0.6 wt.%) with respect to edge distance (3, 6.5, 10, 13.5 mm). The thermo-mechanical FEM was calibrated against laser experimental weld profiles at different edge distances. The strain rate derived from the FEM formulation within the brittle temperature range (fs = 0.5–0.95) was directly compared to the RDG critical strain rate, computed from the solidification path and mushy zone permeability. Experiments revealed cracks only at 3 mm and 6.5 mm, consistent with FEM–RDG predictions. Statistical analysis showed no significant effect of Cu additions within the investigated range on weld profiles nor crack length, though composition slightly modified the critical strain rate. Microstructural EBSD analysis confirmed that edge distance governs grain morphology, with broader equiaxed zones and coarser grains at short distances. The proposed FEM–RDG framework therefore provides a process-dependent and physics-based criterion for predicting solidification cracking without post-test strain calibration, offering transferable insight into the interaction between restraint, solidification behaviour, and crack susceptibility in laser welding.
Thermal accumulation limits stability and productivity in directed energy deposition–arc with metals (DED-Arc/M), commonly referred to as wire-arc directed energy deposition (WA-DED). This study numerically examined thermal accumulation in WA-DED with solid-contact active cooling (SCAC) and the coupled effects of cooling-block length and heat-transfer conditions for a short-tracking SCAC configuration. A three-dimensional transient heat-conduction model for AZ31 magnesium-alloy thin walls was calibrated using substrate-temperature histories and melt-pool lengths from previous experiments conducted with water-cooled copper blocks covering the full wall length. The so-called volume-averaged stored-thermal-energy density was introduced to evaluate thermal accumulation in the substrate and the deposited wall. The model reproduced continuing temperature increase under natural cooling (NC) and early thermal stabilization under SCAC. Despite its shorter interpass times, SCAC maintained the volume-averaged stored-thermal-energy density at levels comparable to or lower than those during late NC. A parametric study was conducted for a short block tracking the heat source during 24-pass deposition. Block length and the wall–block and block–water heat-transfer coefficients were each varied at three levels. Increasing these factors reduced both the late-stage accumulation rate and final accumulation level. However, stronger water-side cooling had a limited effect under low wall–block heat transfer. Thermal accumulation continued for a 5 mm block even under the strongest heat-transfer conditions, nearly stabilized for a 10 mm block, and slightly decreased for a 20 mm block. The lowest final accumulation level was approximately 94% below the maximum across 27 conditions. Numerical results indicate that short-tracking SCAC requires sufficient wall–block heat transfer, appropriate block length, and water-side heat rejection.
Understanding the mechanical heterogeneity of welded joints in ultra-high-strength steels is critical for predicting their performance and failure behaviour. In this study, digital image correlation was employed to extract local true stress–strain curves for individual sub-zones within laser-welded butt joints of S960MC steel. The local plastic behaviour of the weld metal, coarse-grained HAZ, and sub-critical HAZ was quantified using Voce hardening model, and XRD-based apparent dislocation density, complemented by residual stress measurements. Results confirm pronounced differences in strain hardening capacity among the sub-zones, with the sub-critical HAZ consistently exhibiting the lowest saturation stress and the most rapid exhaustion of its hardening reserve. Notably, the two investigated weld variants exhibited distinctly different failure modes attributed to differences in soft zone geometry, constraint effects, and residual stress distribution. These findings highlight the importance of accounting for local mechanical disparities and constraint effects when evaluating weld performance and predicting failure behaviour in statically loaded joints.
FSX-414 is a cobalt-based superalloy widely used in stationary gas turbine blades due to its high-temperature strength and oxidation resistance. However, service-induced degradation often necessitates repair welding to extend component life. In this study, the effect of filler metal selection on the microstructure and mechanical performance of GTAW-repaired FSX-414 was investigated. Four filler metals, namely FSX-414, HS25, HS188, and Mar-M918, were evaluated under identical welding conditions. The repaired joints were characterized using optical microscopy, SEM/EDS analysis, Vickers microhardness testing, and tensile testing conducted at both room and elevated temperatures. The results showed that filler metal composition significantly influenced dendritic morphology, carbide formation, hardness, and fracture behavior. The average weld metal hardness ranged from 367.5 HV for HS25 to 425 HV for HS188. Mar-M918 exhibited the best tensile performance, with the highest ultimate tensile strength and elongation, whereas FSX-414 showed the lowest values. Fractographic and microstructural observations indicated that variations in carbide precipitation and elemental segregation contributed to the observed mechanical behavior. Overall, Mar-M918 provided the most favorable strength–ductility balance, highlighting the critical role of filler metal selection in repair welding of FSX-414.
The increasing demands for high production rates, reduced costs, and more sustainable aircraft structures encourage the rapid introduction of thermoplastic composites in aerospace applications. A major challenge for their widespread implementation, especially in single-aisle aircraft programs, lies in meeting the required high production rates of up to 80–100 aircraft per month. Fast, automated manufacturing technologies such as thermoforming and welding are therefore essential to enable scalable industrialization. Continuous ultrasonic welding is such a high-speed joining technique. However, for stiff aerospace-grade composites, it remains challenging to achieve uniformly welded seams using current state-of-the-art control methods. This study investigated the potential for improving process robustness and weld quality in continuous ultrasonic welding of CF/LMPAEK adherends made from unidirectional plies by introducing a novel combined power-amplitude control method. Welds were produced using the state-of-the-art constant-amplitude and constant-power control methods, as well as the newly introduced approach, and were compared in terms of power and amplitude responses, heating uniformity, and resulting weld quality. A combined fuzzy power-amplitude control method was developed and implemented. Under the processing conditions investigated in this study, the proposed control method reduced extreme fluctuations in power and amplitude and was associated with improvements in weld strength and weld uniformity. Overall, the findings indicate that combined power-amplitude control is a promising approach for improving the robustness and quality of continuous ultrasonic welding of thermoplastic composites.
