Al/Zn Alloy Coating Microstructure Refinement via Rapid Thermal Processing
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Solution Overview
Problem
Conventional Al-Zn-based alloy coatings on steel strips exhibit a coarse, multiple phase microstructure due to low cooling rates, leading to reduced corrosion resistance and ductility, as they solidify during the hot-dip coating process.
Innovation Solution
A method involving very rapid heating and cooling of the Al-Zn-based alloy coating using high power density heating sources, such as lasers or plasma arc lamps, to achieve a refined, homogenous microstructure with reduced secondary dendrite arm spacings and minimal intermetallic layer growth, thereby maintaining the coating's integrity and microstructure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional hot-dip coating process is used with low cooling rate, then the coating process is simple and production efficiency is maintained, but the microstructure becomes coarse and multiple phase which reduces corrosion resistance and ductility
Solution Approach 1:
The patent applies rapid cooling (e.g., water quenching or air cooling at rates exceeding 100°C/s) to transform the coating microstructure from coarse dendritic to fine-grained or amorphous phases. This parameter change in cooling rate fundamentally alters the solidification process, creating a homogeneous microstructure that enhances corrosion resistance while maintaining ductility, resolving the contradiction between production efficiency and coating performance.
Solution Approach 2:
The patent utilizes phase transition during rapid cooling to transform the alloy coating from a coarse dendritic solidified structure to fine-grained or amorphous phases. The rapid cooling rate prevents conventional phase separation and promotes formation of metastable phases with superior corrosion resistance and ductility, directly addressing the technical contradiction.
2Reliability
If very rapid heating and cooling is applied to achieve refined microstructure, then corrosion resistance and ductility are improved, but the process complexity and equipment requirements increase
Solution Approach 1:
The patent employs the steel strip substrate itself as a heat sink to achieve rapid cooling of the alloy coating. The high thermal conductivity of the steel strip naturally extracts heat from the coating during and after the hot-dip process, eliminating the need for complex external cooling systems. This self-service approach resolves the contradiction by using the existing material properties rather than adding complex equipment.
Solution Approach 2:
The patent replaces complex mechanical cooling systems with a thermal field approach, using the inherent thermal properties of the steel strip and controlled atmospheric cooling to achieve the desired rapid cooling rates. This substitution simplifies the equipment while achieving the refined microstructure necessary for improved corrosion resistance.
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 method enhances corrosion resistance and ductility by transforming the coating into a fine dendritic or dispersed phase microstructure, reducing corrosion pathways and maintaining the coating's integrity, even when coated with inorganic or organic compounds.
Implementation Method 1
very rapid heating and cooling of the Al-Zn-based alloy coating using high power density heating sources, such as lasers or plasma arc lamps
Implementation Method 2
The alloy subsequently solidifies on the strip and forms a solidified alloy coating as the strip emerges from the molten bath
Implementation Method 3
very rapid heating and cooling of the Al-Zn-based alloy coating
Implementation Method 4
transforming the coating into a fine dendritic or dispersed phase microstructure
Data Source
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AI summary
A method of treating an Al/Zn-based alloy coated product that includes an Al/Zn-based alloy coating on a substrate is disclosed. The method includes the steps of rapid intense heating of the alloy coating for a very short duration, and rapid cooling of the alloy coating, and forming a modified crystalline microstructure of the alloy coating.