Spiral Oscillation Laser for Improving Formation And Mechanical Properties in High-speed Welding of Medium-thick Plates

01 Paper Introduction
Al-Mg-Er-Zr alloy, with its low density, high specific strength, and excellent corrosion resistance, has become a key alternative material for lightweight shipbuilding. However, welding of medium-thick plates often suffers from defects such as humping, porosity, and joint softening, which severely limit its engineering application. Although conventional laser-arc hybrid welding can improve gap tolerance, the molten pool tends to collapse under high-speed full penetration conditions, and conventional oscillation modes may lead to penetration loss due to energy homogenization. Meanwhile, the precipitation behavior and strengthening mechanisms of microalloying elements Er and Zr during welding remain unclear. Therefore, it is essential to investigate high-speed spiral oscillation laser-arc hybrid welding, including the regulation of weld formation by oscillation parameters, optimization of microstructure through microalloyed filler materials, and clarification of strengthening mechanisms, to provide an efficient and high-quality welding solution for marine medium-thick aluminum alloy plates.

02 Overview
This study focuses on 6 mm thick marine-grade Al-Mg-Er-Zr alloy and adopts a high-speed spiral oscillation laser-arc hybrid welding process. The effects of oscillation diameter, frequency, and filler materials on weld formation are systematically compared. Grain evolution, Mg segregation, and precipitation characteristics are analyzed using OM, EBSD, and TEM. In-situ tensile deformation is monitored using DIC technology, and the contributions of different strengthening mechanisms are quantitatively calculated. The study reveals the intrinsic mechanisms behind improved weld formation and enhanced mechanical properties, ultimately identifying optimal process parameters that balance weld quality and mechanical performance.

03 Results and Discussion
Figure 1 investigates the effects of oscillation diameter and frequency on weld formation in Al-Mg-Er-Zr alloy, analyzing defect distributions such as spatter (S), humping (H), and undercut (U). Without oscillation, severe spatter, continuous humping, and edge undercut are observed. At an oscillation diameter of 2 mm and frequency of 250 Hz, uniform fish-scale-like double-sided weld formation is achieved. When the diameter is <2 mm, laser-arc coupling becomes unstable; when >2 mm, excessive molten pool disturbance occurs; and when frequency <250 Hz, insufficient upward vortex flow fails to suppress molten pool collapse. Thus, 2 mm diameter and 250 Hz frequency are identified as the optimal parameter combination for stable high-speed welding.

Figure 2 compares grain morphology and orientation under conventional laser-arc hybrid welding (LAHW) and oscillating laser-arc hybrid welding (OLAHW) using 5183 and 5E61 fillers via EBSD analysis. LAHW with 5183 filler produces a mixed structure of coarse equiaxed grains in the center and columnar grains in the fusion zone. Using 5E61 filler results in fully equiaxed grains. With OLAHW and 5E61 filler, grains are further refined, and the maximum pole density decreases to 1.40, indicating significantly weakened texture. The results confirm that Er-Zr microalloying provides heterogeneous nucleation sites for grain refinement, while laser-induced stirring further homogenizes grain distribution.

Figure 3 presents real-time longitudinal strain distribution during tensile testing of LAHW and OLAHW joints using digital image correlation (DIC). In LAHW joints, localized strain concentration appears as early as 0.2% strain, with deformation concentrated in the upper weld region, eventually leading to necking fracture. In contrast, OLAHW joints exhibit more uniform strain distribution, lower peak strain, and a broader deformation-affected zone extending to the base material and lower weld region. Spiral oscillation welding delays localized deformation through microstructural homogenization, significantly enhancing plastic deformation capability.

Figure 4 quantitatively evaluates the contributions of solid solution strengthening, grain boundary strengthening, dislocation strengthening, and precipitation strengthening to yield strength. Both joints show similar contributions from dislocation strengthening (43.68 MPa) and precipitation strengthening. In OLAHW joints, Mg solid solution strengthening increases from 50.22 MPa to 79.98 MPa, while grain boundary strengthening slightly decreases due to minor grain coarsening. The calculated values show less than 2% deviation from experimental results. Laser stirring suppresses Mg segregation and precipitation, increasing Mg content in solid solution, which is the key mechanism for improved yield strength.

04 Conclusion
Under optimal parameters of 250 Hz oscillation frequency and 2 mm diameter, defect-free double-sided weld formation of 6 mm plates is achieved at a welding speed of 3 m/min. The spiral oscillation mode maintains high energy density at the weld center without requiring additional power input. Er-Zr microalloyed filler combined with laser stirring produces a fully equiaxed grain structure, suppressing Mg segregation and coarse precipitation. The joint yield strength increases by 10.5%, elongation improves by 21.7%, and strength reaches 95% of the base material. This process effectively resolves key challenges in high-speed welding of medium-thick aluminum alloys, such as poor weld formation and joint softening. High-performance joints are achieved without post-weld heat treatment, while welding efficiency is more than doubled compared to conventional methods, significantly reducing shipbuilding costs and promoting large-scale application of Al-Mg-Er-Zr alloys in lightweight ship structures.

References: https://doi.org/10.1016/j.msea.2026.149999

**--Cite the article published by 高能束加工技术 on April 20th, 2026, in the WeChat public account "High-Energy Beam Processing Technology and Applications."