The design at the center of the study is a narrow slanted groove, a hybrid between the two conventional options that dominate thick-plate work. Traditional V-shaped or bevel grooves are forgiving but voracious: their wide openings demand large volumes of filler wire and heavy heat input, which drives up cost and accumulates thermal energy in the joint. Narrow-gap I-grooves sit at the opposite extreme, consuming minimal filler metal, but in horizontal welding they are notoriously prone to defects such as lack of penetration and solidification cracking. The slanted groove threads the needle. Its cross-sectional area falls between the two conventional geometries, cutting filler consumption well below bevel levels, while its inclined walls reshape the weld bead to suppress the cracking mechanism that plagues I-grooves.

The cracking problem is rooted in bead geometry. When the height-to-width ratio of a weld bead exceeds roughly one, the last-to-solidify liquid at the weld centerline becomes starved, unable to feed the shrinkage strains concentrating there. Columnar grains grow along the centerline, shrinkage stresses build, and hot cracks can tear through the semi-solid metal. Lowering that ratio below one improves liquid feeding and suppresses cracking. The slanted groove achieves exactly this by tilting the groove walls at 35 and 37 degrees, so the wire sits nearly parallel to the groove surface rather than the horizontal plane. That orientation places the welding position between conventional horizontal and flat welding, boosting penetration on the upper sidewall, which gravity and arc forces normally shortchange in horizontal work.

To test the concept, the researchers welded two 36-millimeter-thick plates of SN490B structural steel, each measuring 133.26 by 250 millimeters, using CO2-shielded arc welding with YGW18 wire in thirteen passes, with no preheating or post-weld treatment. Two transverse webs and a backing strip, all of the same steel, mimicked the restraint of a real structure. A thermocouple recorded the temperature history near the weld line throughout the process, and after welding the team measured angular distortion across four transverse sections using a flat reference plate and magnetic blocks. The average total transverse bending angle came out at 0.68 degrees, comfortably inside the one-degree acceptance limit for angular distortion in welded construction.

Mapping the residual stresses demanded heavier instrumentation. The team used the contour method, in which the specimen is sliced down the middle with wire electro-discharge machining, releasing the stress perpendicular to the cut and causing the surface to deform. A Keyence VR-5200 structured-light system scanned that deformed surface with ten-micrometer precision, and the measured displacements were fed into a finite element model to reconstruct the internal stress field. Because the contour method alone captures only one stress component, the researchers combined it with X-ray diffraction on electropolished measurement lines, an approach known as the extended contour method, to recover the full three-dimensional residual stress state on the cut surface.

The measurements told a consistent story. Longitudinal residual stress, running along the weld line, was high and tensile throughout the weld layers and the adjacent heat-affected zone, peaking at roughly 650 megapascals in the molten zone on the surface path, a consequence of constrained longitudinal shrinkage and heat accumulation inside the narrow groove. Moving away from the weld, the stress fell and turned compressive, and through the thickness it was highest near the top surface, where the final passes were deposited, declining toward the bottom. Transverse stresses were lower overall but still showed pronounced tensile peaks in the weld zone, with oscillations along the thickness path that trace the sequential thermal cycles of the thirteen individual passes.

On the computational side, the team built a three-dimensional thermo-elastic-plastic finite element model in JWRIAN, an in-house welding simulation code developed at Osaka University. The model contained about 61,000 nodes and 56,000 hexagonal solid elements, finely meshed in the weld zone and coarsening outward. An uncoupled thermal-mechanical scheme first computed the temperature history using a prolate-spheroid heat source with temperature-dependent material properties, then applied that history as a thermal load in an elastic-plastic large-deflection analysis. The simulated weld pool geometry matched the macro-etched cross-sections, and the calculated temperature at the monitored point tracked the measured curve closely across all thirteen passes.

One refinement proved decisive for stress prediction. Vickers hardness testing showed the molten zone to be harder than the base metal, while the heat-affected zone differed only slightly. The team translated those hardness ratios directly into yield-strength variations, raising the molten zone’s yield stress by roughly twenty percent across the temperature range while leaving the heat-affected zone essentially unchanged. Incorporating this hardness-based yield strength significantly improved the agreement between predicted and measured residual stresses in both the longitudinal and transverse directions, a practical demonstration that microstructural data can sharpen welding simulations without exotic material testing.

The simulated distortion also matched experiment, with a predicted average angular distortion of 0.53 degrees against the measured 0.68 degrees. Intriguingly, both revealed that the distortion is not symmetric about the weld line: the acute-angle side of the slanted joint rotated more than the obtuse side, because the inclined geometry converts symmetric shrinkage into asymmetric angular rotation, unlike conventional grooves. The finite element results further showed peak tensile longitudinal stress near the final passes of about 700 megapascals, compressive stresses of roughly minus 70 to minus 90 megapascals at mid-thickness to satisfy equilibrium, and Von Mises equivalent stress approaching the material’s yield strength of 458 megapascals near the last few passes.

Taken together, the results argue that the narrow slanted groove delivers a rare combination in thick-plate welding: sound welds free of the defects that plague I-grooves, filler consumption far below bevel-groove levels, distortion within standard acceptance limits, and residual stresses that are now quantitatively predictable. For industries joining thick steel in the horizontal position, from shipyards to offshore construction, the study offers both a practical groove design and a validated simulation workflow, complete with a hardness-informed material model, that could move straight from the laboratory into fabrication planning.

Subject of Research: Residual stress and deformation in horizontal multi-pass welding of thick steel plates with a narrow slanted groove

Article Title: Horizontal welding deformation and residual stress of narrow slanted groove for thick plates

Article References: Nour, M., Rashed, S., Ma, N., Agano, Y., Okumura, T., & Shibahara, M. (2026). Horizontal welding deformation and residual stress of narrow slanted groove for thick plates. Advanced Materials Joining, 1(1), Article 16. https://doi.org/10.1007/s44500-026-00020-1

Image Credits: AI Generated

DOI: 10.1007/s44500-026-00020-1

Keywords: welding, thick steel plates, narrow slanted groove, residual stress, angular distortion, contour method, X-ray diffraction, finite element analysis, multi-pass welding, solidification cracking, SN490B steel, hardness

The trouble with fusion welding aluminium begins with the metal’s own physics. Aluminium conducts heat rapidly, melts at a relatively low temperature, and reacts eagerly with oxygen, all of which conspire against conventional arc and laser welding. When a molten weld pool solidifies, it can crack under solidification shrinkage, trap hydrogen-driven porosity, fail to fuse completely with the base metal, undercut at the weld toe, burn through thin sections, or entangle slag and oxide fragments. These macroscopic defects reduce the effective cross-section of a joint and act as stress concentrators that invite crack initiation under cyclic loading. Beneath the visible damage, the microstructure suffers too: strengthening precipitates such as the beta-double-prime and beta-prime phases in 6xxx-series alloys, or Al2Cu in 2xxx alloys, dissolve or coarsen during the thermal cycle, alloying elements segregate to grain boundaries, and the heat-affected zone widens as grains coarsen, sapping strength according to the well-known Hall–Petch relationship.

The review documents how these problems vary by alloy chemistry. AA6061 proves highly susceptible to cracking under constrained strain conditions, while AA2219 resists cracking better thanks to a finer eutectic network that feeds liquid to grain boundaries during solidification. In Al–Mg–Si alloys, magnesium and silicon segregate to grain boundaries, and in some welds zinc segregates even more prominently, rendering joints vulnerable to intergranular stress-corrosion cracking and solidification cracking. Coarse Al–Fe–Si intermetallic particles in AA6061 fusion welds help nucleate cracks by decohering from the matrix. Micro-porosity forms during the liquid-to-solid transformation as local pressure drops from solidification contraction outpace the supply of liquid metal. Engineers have long fought back by optimising welding parameters, but the review’s central message is that optimisation alone cannot erase defects that are baked into the physics of melting.

Enter friction stir processing, a technique derived from friction stir welding, which The Welding Institute invented in the early 1990s. Where fusion welding melts metal, FSP never lets the workpiece breach its solidus. A hardened, non-consumable rotating tool with a shoulder and pin plunges into the material and traverses along a planned path. Friction at the shoulder-workpiece interface, which the review notes supplies roughly seventy percent of the total heat, and plastic dissipation around the pin soften the metal without melting it. The process unfolds in four stages: plunging, dwelling, travelling and retracting. The intense, simultaneous heat and severe plastic deformation drive dynamic recrystallization, replacing coarse dendritic fusion-zone structures with fine, equiaxed grains that can measure only a few micrometres or even sub-micrometres when parameters are balanced correctly.

Because the material never melts, FSP sidesteps the entire class of solidification defects. The review shows that it eliminates or substantially reduces porosity, hot tears, solidification cracks, shrinkage cavities and micro-segregation, redistributes strengthening precipitates, reduces residual tensile stresses and narrows the effective heat-affected zone. The processed region divides into characteristic zones: a stir zone of dynamically recrystallised fine grains, a thermomechanically affected zone with partial recrystallisation, a heat-affected zone subject only to thermal exposure, and the untouched base metal. Achieving this outcome depends on a delicate three-way balance between rotational speed, traverse speed and tool geometry. Moderate rotational speeds paired with intermediate traverse speeds consistently yield refined grains and uniform particle distribution, while excessive speeds overheat the material and trigger post-weld annealing that coarsens grains and erodes strength.

The evidence compiled in the review is striking. FSP applied to TIG-welded AA2024 eliminated solidification cracks and porosity while producing ultrafine, equiaxed microstructures with substantially improved tensile strength and hardness. On TIG weldments of AA7020, hardness and strength rose 118.5 percent over the untreated weld and 103 percent over the base alloy itself. TIG-welded AA6061-T6 gained 47 percent in tensile strength and 10 percent in microhardness after FSP. In AA7075 TIG joints, tensile strength climbed from 228 to 320 megapascals, accompanied by a dramatic rise in coincidence site lattice boundaries and high-angle grain boundaries that confirmed dynamic recrystallization at work. FSP on AA5052 TIG welds produced three-micrometre grains with 52 percent high-angle boundaries, delivering gains of 50 percent in hardness, 42 percent in yield strength and 25 percent in ultimate tensile strength.

Multipass processing amplifies these benefits. In dissimilar AA8011-H14 and AA5083-H321 TIG joints, the dendritic fusion-zone morphology vanished after a single pass, and by three passes the stir zone held ultrafine grains averaging 3.42 micrometres, with ultimate tensile strength rising from 79.82 megapascals in the unprocessed weld to 126.92 megapascals. Researchers have even used FSP to embed reinforcing particles directly into weld zones: adding alumina particles to TIG-welded AA5083 boosted yield strength by 29 percent, ultimate tensile strength by 18 percent and impact energy by a remarkable 56 percent, effectively converting a repaired weld into an in-situ metal-matrix composite. Scandium-modified filler combined with FSP on marine-grade AA5083 reduced grain size to two micrometres and pushed strength to 331 megapascals with 20.5 percent elongation, surpassing the base metal.

The technique performs equally well on MIG and cold metal transfer welds. FSP of AA6082-T651 T-fillet MIG welds cut grain size by 96 percent, improved average hardness by 37 percent and yield strength by 9 percent, and extended corrosion-fatigue life to roughly eight hundred thousand cycles thanks to the elimination of porosity. On dissimilar AA5083-H321/AA5356 arc welds, FSP erased coarse constituent phases and raised ultimate tensile strength from 259 to 306 megapascals. Compared directly against post-weld heat treatment on AA6082-T6 MIG joints, FSP achieved 99 percent joint efficiency versus 85 percent for heat treatment, with a 305 megapascal tensile strength and 23 to 24 percent hardness gains, though the thermomechanical route sacrificed about 7 percent elongation, a trade-off the authors flag as a matter of tailoring process choice to service requirements. Corrosion resistance improves as well; FSP of AA2219-T6 TIG welds cut corrosion rates from 25 to 4 mils per year by eliminating copper-depleted regions and refining AlCu2 eutectic particles.

The review concludes that friction stir processing has matured into a highly efficient, sustainable post-weld treatment, generating no harmful gases, radiation or excessive noise and consuming far less energy than conventional routes. Optimal parameters for TIG-weld repairs cluster between 600 and 1300 RPM rotational speed and 30 to 100 millimetres per minute traverse speed, with tool shoulder diameter, pin profile, the shoulder-to-pin diameter ratio and axial forging force all playing decisive roles. The authors chart future opportunities that read like a roadmap for the next decade: coupling FSP with ultrasonic vibration or electromagnetic assistance, designing novel scroll and triflute tool geometries, deploying real-time monitoring with force, torque and acoustic emission sensors, applying machine-learning-based optimisation across long weld seams, and embedding ceramic or nano-reinforcements such as silicon carbide, alumina, TiB2 and graphene to create composite weld regions. For an industry racing to build lighter, stronger, greener structures, the message is clear: the humble rotating tool may be the weld doctor aluminium has been waiting for.

Subject of Research: Friction stir processing as a post-weld treatment for improving fusion-welded aluminium alloy joints

Article Title: Advancement in fusion welded aluminium alloy joints by friction stir processing technique: a critical review

Article References: Reyaz, M. S. B., Imam, M., Anshari, M. A. A., & Shah, M. S. (2026). Advancement in fusion welded aluminium alloy joints by friction stir processing technique: a critical review. Discover Industrial Chemistry and Materials, 1(1), Article 5. https://doi.org/10.1007/s44508-026-00005-y

Image Credits: AI Generated

DOI: 10.1007/s44508-026-00005-y

Keywords: friction stir processing, aluminium alloys, fusion welding, TIG welding, MIG welding, dynamic recrystallization, post-weld treatment, grain refinement, solidification cracking, porosity, heat-affected zone, mechanical properties