Hot-dip Al-plated Steel Sheet Fine Spangle Formation
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Solution Overview
Problem
The challenge in producing hot-dip Al-based alloy-coated steel sheets with fine spangles is the difficulty in achieving stable and uniform formation due to the precipitation of high-specific-gravity substances like Ti, TiC, and TiB2 in the coating bath, and the insufficient effect of B and aluminum boride in forming a beautiful surface appearance.
Innovation Solution
Incorporating both boron (B) and potassium (K) into the coating bath at specific concentrations, with B at not less than 0.005 mass % and K at not less than 0.0004 mass %, to enhance the formation of dense spangle nuclei and achieve a beautiful surface appearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high-specific-gravity substances like Ti, TiC, and TiB2 are added to the coating bath to form spangle nuclei, then the number of spangle nuclei increases, but these substances precipitate into the bath bottom due to high specific gravity, making uniform dispersion difficult
Solution Approach 1:
The patent introduces boron (B) as an intermediary substance that forms fine spangle nuclei through chemical reaction with aluminum in the coating bath. Unlike high-specific-gravity substances (Ti, TiC, TiB2) that precipitate due to gravity, boron has comparable specific gravity to aluminum (2.7 vs 2.7), allowing it to remain uniformly dispersed throughout the bath without settling. This intermediary approach solves the contradiction by providing a substance that both increases spangle nucleus quantity and maintains uniform distribution stability.
2Manufacturing precision
If B and aluminum boride are added to the coating bath, then spangle formation is improved, but the surface appearance beauty is insufficient compared to using Ti-based substances
Solution Approach 1:
The patent changes the concentration parameters of boron and potassium in the coating bath to optimize both spangle formation and surface appearance. By controlling boron concentration at 0.003-0.03 mass% and potassium concentration at 0.0001-0.005 mass%, the invention achieves fine spangle formation while maintaining beautiful surface appearance. This parameter optimization allows the use of boron (which provides uniform dispersion) to achieve results previously only attainable with Ti-based substances, thus resolving the contradiction between spangle formation quality and surface appearance beauty.
3Manufacturing precision
If more spangle nuclei are formed to reduce spangle size, then each spangle becomes minute, but stable and uniform formation becomes difficult due to precipitation of additives
Solution Approach 1:
The patent uses boron as an intermediary substance that does not precipitate due to its specific gravity matching aluminum. This ensures stable and uniform formation of fine spangles throughout continuous production. The boron remains dispersed in the coating bath, continuously providing nucleation sites for fine spangle formation without the reliability issues caused by precipitation of high-specific-gravity additives.
Solution Approach 2:
The patent optimizes the concentration parameters of boron and potassium to achieve stable fine spangle formation. By setting boron concentration at 0.003-0.03 mass% and potassium concentration at 0.0001-0.005 mass%, the invention ensures consistent nucleation and growth of minute spangles throughout continuous production, resolving the reliability issue while maintaining manufacturing precision.
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
This approach results in a hot-dip Al-based alloy-coated steel sheet with stably formed fine spangles and improved corrosion resistance, suitable for industrial continuous production with a low-cost method.
Implementation Method 1
a primary dendrite arm grows from the spangle nucleus. Subsequently, a secondary dendrite arm develops from the primary dendrite arm. Growth of such dendrite arms stops due to a collision between adjacent spangles.
Implementation Method 2
the nucleus of the spangle (i.e., spangle nucleus) occurs. Then, a primary dendrite arm grows from the spangle nucleus.
Implementation Method 3
a primary dendrite arm grows from the spangle nucleus. Subsequently, a secondary dendrite arm develops from the primary dendrite arm.
Data Source
AI summary
Provided is (i) a hot-dip Al-based alloy-coated steel sheet which includes a coated layer having a surface on which fine spangles are stably and sufficiently formed and which has a beautiful surface appearance due to the fine spangles thus formed on the surface of the coated layer, and (ii) a method of producing such a hot-dip Al-based alloy-coated steel sheet. The hot-dip Al-based alloy-coated steel sheet includes: a substrate steel sheet; and a hot-dip aluminum-based alloy coated layer which is formed on a surface of the substrate steel sheet and which contains boron at an average concentration of not less than 0.005 mass % and contains potassium at an average concentration of not less than 0.0004 mass %.