Galvanized Welded Joint Composition for Better E-Coat Bead Coverage

The patent applies parameter changes by precisely controlling the chemical composition parameters of the plating layer (Al: 2-10 mass%, Mg: 3-15 mass%, Si: 0.01-5 mass%, and balance Zn with specific impurity limits) to prevent Si-based slag formation. This compositional parameter optimization ensures that the plating layer suppresses harmful Si oxide formation during welding while maintaining good electrodeposition coating properties on the weld bead surface.

The patent uses a composite plating layer structure consisting of multiple elements (Al-Mg-Si-Zn system) where each component serves a specific function. The composite nature of this multi-element plating layer allows it to simultaneously provide corrosion resistance, control welding behavior to prevent Si-based slag, and ensure good electrodeposition coating adhesion, resolving the contradiction between welding performance and coating quality.

The patent optimizes parameter ranges for each element in the plating layer to achieve multiple objectives simultaneously. Specifically, Al content is controlled at 2-10 mass% to suppress Si-based slag without excessive oxide formation, Mg is maintained at 3-15 mass% for corrosion protection, and Si is limited to 0.01-5 mass% to prevent harmful slag while allowing beneficial oxidation control. This balanced parameter optimization ensures both good electrodeposition coating properties and maintained corrosion resistance.

The multi-element Al-Mg-Si-Zn composite plating layer provides synergistic effects where Al and Mg contribute to corrosion resistance, controlled Si content prevents harmful slag formation, and the overall composition ensures good electrodeposition coating adhesion. The composite structure allows each element to contribute its strengths while mitigating individual weaknesses, achieving both coating quality and corrosion protection.