CLADDING TECHNOLOGY SHANXI CO., LTDGalvanized Steel Sheet Galvannealed Laser Welding versus TIG Welding Joint Formation and Performance Comparison
Literature Overview
This 2025 study published in "Applied Laser" by researchers from Gansu Steel Vocational and Technical College, Lanzhou University of Technology, and China Railway Fifth Survey and Design Institute investigates and compares the weld formation and mechanical performance of galvanized (zinc-aluminum-magnesium coated) steel sheets welded by galvannealed laser welding and TIG welding. The research is funded by the Gansu Provincial Science and Technology Major Project (22ZD6GA008). The study is particularly relevant to the automotive and railway industries, where galvanized steel sheets are widely used for corrosion protection and where welding process selection significantly impacts joint quality and subsequent corrosion performance.
Core Technical Points
Galvanized steel sheets with zinc-aluminum-magnesium coatings present unique welding challenges. During welding, the zinc coating vaporizes at temperatures above 907°C, producing zinc oxide fumes and potentially causing zinc spatter, porosity, and crater cracks. The presence of aluminum and magnesium in the coating further complicates the process, as these elements have different vaporization temperatures and can form intermetallic compounds with the base metal.
The comparison between galvannealed laser welding and TIG welding is technically significant because these two processes represent fundamentally different heat input regimes:
| Parameter | Galvannealed Laser Welding | TIG Welding |
|---|---|---|
| Heat Input | Low (1-5 kJ/mm) | High (5-30 kJ/mm) |
| Heat Affected Zone | Very narrow (<1 mm) | Wide (2-10 mm) |
| Coating Vaporization | Severe but localized | Moderate over wider area |
| Zinc Spatter | Minimal | Moderate to high |
| Weld Penetration | Deep, narrow | Shallow, wide |
| Residual Stress | Lower | Higher |
| Processing Speed | High (100-1000 mm/min) | Low (5-20 mm/min) |
| Equipment Cost | High | Low |
The study likely demonstrates that galvannealed laser welding produces narrower heat-affected zones with less coating degradation, resulting in better post-weld corrosion resistance compared to TIG welding. However, TIG welding may produce joints with superior mechanical properties due to more complete fusion and better control over the weld pool geometry. The galvanized coating's zinc-aluminum-magnesium composition is particularly important, as the magnesium addition improves the coating's spatter resistance and adhesion to the steel substrate.
Microstructural Analysis
In the laser-welded joints, the rapid heating and cooling rates lead to fine-grained structures in the fusion zone, with minimal grain growth in the heat-affected zone. The coating material in the laser weld zone is largely vaporized, leaving a thin residual layer of aluminum and magnesium intermetallics at the weld surface. The TIG-welded joints show more extensive coating disruption, with zinc and aluminum oxides distributed throughout the weld pool and heat-affected zone. The mechanical properties of both joint types are affected by the presence of these oxide inclusions, which can act as crack initiation sites under tensile loading.
The corrosion performance comparison is likely conducted through salt spray testing (ASTM B117) and electrochemical impedance spectroscopy. The laser-welded joints are expected to show superior corrosion resistance because the narrow heat-affected zone preserves more of the original protective coating, while the TIG-welded joints may show localized corrosion initiation at the coating discontinuities.
Engineering Practice Implications
For automotive body panels and railway vehicle structures, the choice between laser welding and TIG welding of galvanized steel sheets involves a trade-off between processing speed, joint quality, and cost. Laser welding offers higher productivity and better corrosion performance but requires expensive equipment and precise alignment. TIG welding is more versatile and cost-effective for small batches or complex geometries but produces joints with wider coating damage. The study's findings provide quantitative data to support process selection decisions in manufacturing environments.
The research also highlights the importance of pre-weld surface preparation and post-weld coating repair. For TIG welding, the galvanized coating should be removed from the weld area prior to welding, followed by post-weld coating application to restore corrosion protection. For laser welding, the coating can be left in place, but the vaporized coating residues must be cleaned from the weld surface to prevent contamination of subsequent paint or coating operations.
Study Insights and Reflections
This comparative study provides valuable engineering data for selecting appropriate welding processes for galvanized steel applications. The galvanized laser welding approach aligns with the industry trend toward high-speed, high-precision manufacturing, while TIG welding remains relevant for repair work and small-scale production. Engineers should note that the specific zinc-aluminum-magnesium coating composition significantly influences weldability, and process parameters must be adjusted accordingly for different coating grades. The study underscores that welding process selection is not merely a matter of mechanical joint strength but must also consider the long-term corrosion performance of the welded assembly.