Zn-Al-Mg Hot-Dip Steel Coating for White Surface and Corrosion Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Zn—Al—Mg-based hot-dip plated steel sheets used in industries like automobiles and building materials require a surface appearance closer to white to minimize visible defects while maintaining excellent corrosion resistance.
Innovation Solution
Adjusting the chemical composition of the hot-dip plated layer to increase the ratio of the [Zn phase] to the total of the [Al/MgZn2/Zn ternary eutectic structure] and [Zn phase] to 20% or more, with specific Al and Mg content ranges, and optionally incorporating additional elements like Si, Ni, Ti, or others, to achieve a white appearance and enhanced corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Al and Mg are incorporated into the hot-dip galvanized layer to improve corrosion resistance, then corrosion resistance is improved, but the surface external appearance becomes satin-like and less white
Solution Approach 1:
The invention changes the compositional parameters by strictly limiting Al to 3-11 mass% and Mg to 1-10 mass%, and critically controls the microstructural parameter by ensuring the [Zn phase] area fraction is 70% or more. This parameter optimization resolves the contradiction by achieving the desired white appearance while maintaining adequate corrosion resistance through the synergistic effect of controlled Al-Mg composition and dominant Zn phase structure.
Solution Approach 2:
The invention applies local quality by creating a specific microstructural distribution where the [Zn phase] dominates the surface layer (70% or more area fraction), while Al and Mg are present in controlled amounts. This localized phase distribution ensures the surface exhibits white appearance characteristics while the underlying structure maintains corrosion resistance properties.
2Reliability
If various phases and microstructures are present in a mixed state in the hot-dip plated layer, then corrosion resistance is improved, but the surface has a satin-like external appearance
Solution Approach 1:
The invention applies homogeneity by establishing a dominant [Zn phase] structure that occupies 70% or more of the area fraction in the hot-dip plated layer. This creates a homogeneous microstructure that uniformly reflects light, producing the desired white appearance while the controlled presence of Al and Mg phases maintains corrosion resistance through their protective characteristics.
3Illumination intensity
If the ratio of [Zn phase] to total plating microstructure is increased to improve appearance, then surface appearance closer to white is achieved, but corrosion resistance may be compromised
Solution Approach 1:
The invention creates a composite plating structure where the dominant [Zn phase] (70% or more area fraction) provides the white appearance, while controlled amounts of Al (3-11 mass%) and Mg (1-10 mass%) phases contribute to corrosion resistance. This composite microstructure successfully combines the aesthetic benefits of high Zn phase content with the protective properties of Al-Mg alloying elements.
Data Source
AI summary
A Zn—Al—Mg-based hot-dip plated steel sheet includes a hot-dip plated layer formed on a surface of a steel sheet, in which the hot-dip plated layer contains, as an average composition, Al: 5 to 22 mass % and Mg: 1.0 to 10 mass %, with a remainder including Zn and impurities, and in a case where a 5 mm square cross section parallel to a surface of the hot-dip plated layer is exposed at any position of a 3t/4 position, a t/2 position, and a t/4 position from the surface with a thickness of the hot-dip plated layer represented by t, a ratio (B/A (%)) of an area fraction B of a [Zn phase] to a total area fraction A of a [Zn phase] and an [Al/MgZn2/Zn ternary eutectic structure] of a plating microstructure in at least one cross section is 20% or more.