Zn-Based Coating With Diffusion Barrier for Hot Forming
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Solution Overview
Problem
Current Zn-based coatings for steel substrates face challenges in high temperature processes and environments due to zinc diffusion, evaporation, micro-crack formation, liquid metal embrittlement, and oxidation, limiting their effectiveness in hot forming operations and high-temperature applications.
Innovation Solution
A Zn-based coating with elevated melting temperatures, such as Zn-Sr, Zn-Ca, or Zn-Mn coatings with specific content ranges, combined with a diffusion barrier layer like tungsten or conductive oxides, and an evaporation/oxidation barrier layer, to prevent zinc diffusion and evaporation while maintaining cathodic corrosion protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Zn-based coatings are used for corrosion protection, then cathodic corrosion protection is provided, but zinc diffusion into the substrate occurs at high temperatures
Solution Approach 1:
A diffusion barrier layer comprising at least one of tungsten, tantalum, niobium, hafnium, or their oxides is introduced between the steel substrate and the Zn-based coating. This intermediary layer prevents zinc diffusion into the substrate while allowing the Zn-based coating to maintain its cathodic corrosion protection function, thus resolving the contradiction between corrosion protection and zinc loss.
2Productivity
If high temperature hot forming operations are performed, then forming operations can be carried out, but zinc evaporation occurs reducing coating weight
Solution Approach 1:
The diffusion barrier layer also acts as an evaporation barrier, preventing zinc from evaporating during high temperature hot forming operations. This allows the coating to withstand the high temperatures required for hot forming while maintaining sufficient zinc weight for corrosion protection.
3Productivity
If high temperature processes are applied, then hot forming operations are enabled, but micro-crack formation due to solid metal induced embrittlement occurs
Solution Approach 1:
The diffusion barrier layer prevents direct contact between the Zn-based coating and the steel substrate at high temperatures, eliminating the mechanism that causes solid metal induced embrittlement. This allows hot forming operations to proceed without micro-crack formation, maintaining the strength and integrity of the steel blank.
4Reliability
If Zn-based coatings are used, then cathodic corrosion protection is provided, but liquid metal embrittlement can occur during hot pressing
Solution Approach 1:
The diffusion barrier layer prevents liquid Zn-phases from penetrating between steel substrate grain boundaries during hot pressing operations. This intermediary barrier eliminates the risk of liquid metal embrittlement while preserving the cathodic corrosion protection provided by the Zn-based coating.
5Productivity
If high temperature operations are performed, then hot forming is enabled, but oxidation of the Zn-based coating occurs
Solution Approach 1:
The diffusion barrier layer acts as a protective barrier that prevents oxidation of the Zn-based coating during high temperature hot forming operations. This intermediary layer allows the coating to withstand high temperatures without forming thick oxide layers that would compromise corrosion protection.
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 solution enables Zn-based coatings to withstand high temperatures, reduce micro-crack and liquid metal embrittlement risks, and maintain effective corrosion protection, making them suitable for hot forming and high-temperature applications without significant zinc loss or oxidation.
Implementation Method 1
a diffusion barrier layer between the substrate and the Zn-based coating, wherein the diffusion barrier layer prevents diffusion of zinc from the Zn-based coating into the substrate
Implementation Method 2
the Zn-based coating has a melting temperature above 600°C... reduce evaporation of the Zn-based coating
Implementation Method 3
not a cathodic corrosion protection such as provided by Zn-based coatings
Data Source
AI summary
The invention relates to a steel substrate provided with a Zn-based corrosion resistant coating, wherein the Zn-based coating has a melting temperature above 600°C which makes it suitable for forming operations at elevated temperatures.