Zn-Al-Mg Alloy Coating for Welding LME and Blowhole Reduction
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Solution Overview
Problem
Current methods for welding zinc-coated steel products face challenges with liquid metal embrittlement (LME), blowhole formation, and deterioration of corrosion resistance at welding heat affected zones due to thermal evaporation of zinc, despite previous attempts to address these issues.
Innovation Solution
A metallic coated steel product with a Zn--Al--Mg alloy layer having a specific chemical composition and structure, including a Zn--Al--MgZn2 ternary eutectic structure, which reduces LME and blowhole formation and enhances corrosion resistance at welding heat affected zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If zinc-coated steel products are welded to improve corrosion resistance, then corrosion resistance is improved, but liquid metal embrittlement and blowhole formation occur due to thermal evaporation of zinc
Solution Approach 1:
The patent changes the chemical composition parameters of the zinc coating by controlling the ratios of Zn, Al, and Mg elements, and by controlling the phase composition (MgZn2 phase area fraction of 45-75%, total MgZn2 and Al phases of 70% or more). This compositional parameter change reduces thermal evaporation of zinc during welding, thereby reducing liquid metal embrittlement and blowhole formation while maintaining corrosion resistance.
Solution Approach 2:
The patent creates a composite zinc alloy coating system containing Zn, Al, and Mg elements with specific phase distributions. The composite structure includes MgZn2 intermetallic phase and Al phase in controlled proportions, which provides both corrosion resistance and reduced harmful effects during welding by modifying the thermal behavior of the coating.
2Reliability
If zinc coating is applied to steel products to improve corrosion resistance, then corrosion resistance is improved, but welding performance deteriorates due to thermal evaporation of zinc
Solution Approach 1:
The patent modifies the compositional parameters of the zinc coating, specifically controlling Zn content (44.90-79.90%), Al content (15-35%), and Mg content (5-20%), along with the phase distribution (MgZn2 phase area fraction 45-75%). These parameter changes reduce zinc thermal evaporation during welding, improving weldability while preserving corrosion resistance.
3Reliability
If conventional zinc coating is used on steel products, then corrosion resistance is improved, but production cost increases due to complex welding and plating processes
Solution Approach 1:
The patent merges the corrosion protection function and weldability improvement into a single zinc alloy coating application. By incorporating Al and Mg elements in specific proportions with controlled phase distribution, the coating simultaneously provides corrosion resistance and reduces harmful thermal evaporation effects during welding, eliminating the need for separate post-weld plating operations.
Solution Approach 2:
The patent changes the coating composition parameters to achieve multi-functionality. The specific compositional ranges and phase distributions enable the single coating to provide both corrosion protection and improved welding performance, simplifying the overall production process by eliminating the need for separate welding and plating stages.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed solution significantly reduces LME and blowhole formation while improving corrosion resistance at welding heat affected zones, providing better weldability and corrosion protection compared to existing zinc-coated steel products.
Implementation Method 1
decrease in bond strength due to blowhole formation by thermal evaporation of Zn, and deterioration of corrosion resistance at areas around and behind welded zones due to thermal evaporation of Zn
Implementation Method 2
LME is considered to be mainly caused by a zinc plating component remaining in a molten form on the surface of the heat affected zone of the base material near a welded zone and infiltrated into grain boundaries in the welded zone
Data Source
AI summary
Provided is a metallic coated steel product which is less likely to experience LME and blowhole formation and is likely to exhibit an improved corrosion resistance at welding heat affected zones. The metallic coated steel product is a hot-dip metallic coated steel product including a steel product and a plating layer that is provided on a surface of the steel product and includes a Zn—Al—Mg alloy layer. In a cross-section of the Zn—Al—Mg alloy layer an area fraction of MgZn2 phase is from 45 to 75%, a total area fraction of MgZn2 and Al phases is not less than 70%, and an area fraction of Zn—Al—MgZn2 ternary eutectic structure is from 0 to 5%; and the plating layer has a predetermined chemical composition.