ZnAlMg Coated Sheet Flexibility via Nickel-Free Composition
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Solution Overview
Problem
Galvanized metallic coatings with zinc, aluminum, and magnesium (ZnAlMg) suffer from cracking when severely bent, and the addition of nickel, while improving cracking resistance, introduces contact corrosion and complicates bath management.
Innovation Solution
A ZnAlMg sheet with a metallic coating comprising 4.4-5.6% aluminum and 0.3-0.56% magnesium, with no nickel, combined with a paint film of melamine cross-linked polyesters or similar polymers, to enhance corrosion resistance and flexibility, reducing cracking upon severe bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If magnesium is added to the metallic coating to improve corrosion resistance, then corrosion resistance is improved, but the coating hardens and cracks appear during severe bending
Solution Approach 1:
The patent changes the chemical composition parameters of the metallic coating by limiting magnesium content to 0.05-2% (down from conventional higher levels) and aluminum content to 3-11%, with zinc as the remainder. This parameter optimization maintains the corrosion resistance enhancement from magnesium while reducing the harmful hardening effect that causes cracking during bending operations.
2Strength
If nickel is added to the metallic coating to improve cracking resistance, then cracking resistance is improved, but contact corrosion accelerates and bath management becomes more complicated
Solution Approach 1:
The patent extracts nickel from the metallic coating composition entirely, achieving cracking resistance through alternative means by optimizing the magnesium and aluminum content ratios and applying a specifically formulated paint layer. This elimination of nickel removes the harmful effect of accelerated contact corrosion while avoiding the complexity of managing nickel in the galvanizing bath.
3Strength
If nickel is added to the metallic coating to improve cracking resistance, then cracking resistance is improved, but the number of elements in the bath increases and bath management becomes more complicated
Solution Approach 1:
The patent removes nickel from the bath composition, simplifying bath management. Cracking resistance is achieved instead through optimized magnesium (0.05-2%) and aluminum (3-11%) content control, combined with a specifically designed paint layer formulation, reducing the number of elements requiring complex management in the galvanizing bath.
4Reliability
If conventional ZnAlMg coating is applied to improve corrosion resistance, then corrosion protection is enhanced, but the coating cracks when the sheet is severely bent
Solution Approach 1:
The patent creates a composite protection system consisting of a metallic coating with optimized composition (zinc as base, 0.05-2% magnesium, 3-11% aluminum) combined with a specifically formulated paint layer. This composite structure maintains the excellent corrosion resistance of the metallic coating while the paint layer provides additional flexibility and crack prevention during severe bending operations.
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 combination of the ZnAlMg coating and paint film significantly reduces cracking and maintains corrosion resistance, with fewer cracks and improved flexibility, while avoiding the drawbacks of nickel addition.
Implementation Method 1
Galvanized metallic coatings comprising essentially zinc and 0.1 to 0.4% by weight aluminum are conventionally used because of the effective protection they provide against corrosion
Implementation Method 2
The addition of magnesium significantly improves the corrosion resistance of steels coated with a metallic coating
Implementation Method 3
deposition of a metallic coating on at least one face by hot-dipping of the substrate in a bath
Implementation Method 4
solidification of the metallic coating
Data Source
AI summary
A process for the manufacture of a pre-painted sheet. The process includes supplying a steel substrate, depositing a metallic coating on at least one face by hot-dipping of the substrate in a bath including 4.4% to 5.25% by weight aluminum and 0.3% to 0.56% by weight magnesium. The rest of the bath includes exclusively zinc, unavoidable impurities resulting from the process and optionally one or more additional elements including Si, Ti, Ca, Mn, La, Ce and Bi. The content by weight of each additional element in the metallic coating is less than 0.3% and the presence of nickel is excluded. The process further includes solidifying the metallic coating, surface preparation of the metallic coating and painting of the metallic coating. The present invention further provides a pre-painted sheet.