Zn-Al-Mg Plated Welded Joint for Back Bead Rust Resistance
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Solution Overview
Problem
Existing welded joints of Zn--Al--Mg-based hot-dip plated steel sheets face issues with red rust resistance and coating adhesion in the heat-affected zones, particularly at the back bead surface, which are not adequately addressed by prior technologies.
Innovation Solution
A welded joint design where the non-heat-affected zone of the steel sheets has a specific chemical composition (Al: 5.0% to 40.0%, Mg: 3.0% to 15.0%, Fe: 0.01% to 15.00%, and a remainder of Zn with an Mg--Zn phase area ratio of 5% or more, ensuring excellent coating adhesion and red rust resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If arc welding is performed on Zn-Al-Mg-based hot-dip plated steel sheets, then joining strength is achieved, but red rust resistance and coating adhesion deteriorate in the heat-affected zone of the back bead surface
Solution Approach 1:
The invention applies local quality by specifying different chemical composition requirements for different regions of the plating layer. The plating layer is divided into a heat-affected zone and a non-heat-affected zone, each with tailored Al and Mg concentration ranges to optimize both welding performance and corrosion resistance in their respective locations.
Solution Approach 2:
The invention utilizes parameter changes by controlling the chemical composition parameters (Al concentration: 5-40 mass%, Mg concentration: 3-15 mass%) of the plating layer to achieve the desired balance between weldability and corrosion resistance. The specific concentration ranges are optimized to prevent excessive alloying during welding while maintaining protective properties.
2Strength
If arc welding is performed on Zn-Al-Mg-based hot-dip plated steel sheets, then joining strength is achieved, but coating adhesion deteriorates in the heat-affected zone
Solution Approach 1:
The invention applies local quality by specifying different chemical composition requirements for different regions of the plating layer. The plating layer is divided into a heat-affected zone and a non-heat-affected zone, each with tailored Al and Mg concentration ranges to optimize both welding performance and coating adhesion in their respective locations.
Solution Approach 2:
The invention utilizes composite materials by creating a multi-layered plating structure with a Zn-Al-Mg-based alloy plating layer containing specific Fe-Al-based alloy layer. This composite plating system provides both good weldability and maintained coating adhesion after welding.
Data Source
AI summary
A welded joint 10 is a welded joint 10 in which a first steel sheet 1 and a second steel sheet 2 having a plating layer 4 at least on a part thereof are welded, in a back surface A of a surface having the weld bead portion 3, Expression (1) is satisfied, where L0 is a horizontal length of an observation field and L is a surface unevenness length of the plating layer 4 in the observation field, and an area ratio of an Mg—Zn phase in the plating layer 4 of the region from a starting point to a position 1,000 μm away from the starting point is 5% or more.(L−L0)/L0×100≥3 (1)