Hot-dip zinc-based plated steel sheet
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Solution Overview
Problem
Zinc-based plated steel sheets, particularly hot-dip galvanized steel sheets, experience excessive oxidation during hot pressing, leading to reduced metal zinc in the plating layer and compromised corrosion resistance at uncoated portions, which is not suitable for critical applications like joint reinforcement or spot-welded areas.
Innovation Solution
A hot-dip zinc-based plated steel sheet with a surface treatment layer containing granular oxides that have a standard free energy of formation between that of zinc oxide and aluminum oxide, along with specific content ranges of phosphorus, vanadium, copper, aluminum, and chromium compounds, to suppress zinc oxide production and enhance corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a zinc-based plated steel sheet is hot pressed to achieve high mechanical strength, then the mechanical strength is improved, but excessive zinc oxide is formed on the surface reducing corrosion resistance
Solution Approach 1:
A surface treatment layer is applied in advance to the zinc-based plated steel sheet before hot pressing. This surface treatment layer contains elements that will form protective oxides during the hot pressing process, preventing excessive zinc oxide formation and maintaining corrosion resistance at the heated surface where mechanical strength is enhanced.
Solution Approach 2:
The steel sheet structure is made composite by adding a surface treatment layer containing multiple elements (such as Al, Si, Ti, Mn, Cr, P) on top of the zinc-based plating layer. This composite structure allows the surface treatment layer to control oxidation behavior during hot pressing, suppressing excessive zinc oxide formation while maintaining the high mechanical strength achieved through heat treatment.
2Ease of operation
If the steel sheet is heated to high temperature for hot pressing to improve moldability, then shape fixability is improved, but scales are produced on the surface requiring descaling processes
Solution Approach 1:
The surface treatment layer is applied in advance to prevent scale formation during the hot pressing process. By having this protective layer in place before heating, the steel sheet surface is protected from oxidation and scale formation, eliminating the need for subsequent descaling processes and maintaining high productivity.
Solution Approach 2:
The surface treatment layer converts the potentially harmful oxidation process into a beneficial effect. During hot pressing, the surface treatment layer oxidizes preferentially to form a protective barrier that prevents excessive zinc oxide formation and scale production, while the oxidation itself is controlled to be beneficial rather than harmful.
3Object-affected harmful factors
If a thick zinc oxide layer is formed on the heat-treated steel material, then the surface is protected from oxidation, but coating film adhesiveness and post-coating corrosion resistance are adversely affected
Solution Approach 1:
The surface treatment layer changes the oxidation parameters by controlling which elements oxidize preferentially. By containing elements with appropriate oxidation potentials (Al, Si, Ti, Mn, Cr, P), the surface treatment layer ensures that these elements oxidize instead of zinc, forming a thin, controlled oxide layer that protects from excessive oxidation while maintaining good coating film adhesiveness and post-coating 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 solution effectively reduces zinc oxide formation during hot pressing, maintaining sufficient metal zinc in the plating layer and improving corrosion resistance at uncoated areas, making it suitable for applications requiring high durability and resistance.
Implementation Method 1
the surface treatment layer contains more than or equal to 0.1 g/m2 and less than or equal to 1.2 g/m2 of granular oxide per one surface on a metal basis in which, in a temperature range of 900 to 1300 K, standard free energy of formation (ΔG0) of oxide is smaller than standard free energy of formation (ΔG0Zn) of zinc oxide
Implementation Method 2
In the hot pressing method, a material to be molded is once heated to high temperature, the steel sheet softened by heating is pressed to be molded, and then cooling is performed
Implementation Method 3
the mechanical strength of the material can be enhanced by the quenching effect by the cooling after molding
Data Source
AI summary
A hot-dip zinc-based plated steel sheet includes: a base steel sheet that is a metal substrate; a hot-dip zinc-based plating layer provided on the base steel sheet; and a surface treatment layer formed on at least one surface of the hot-dip zinc-based plating layer, in which the surface treatment layer contains more than or equal to 0.1 g/m2 and less than or equal to 1.2 g/m2 of granular oxide per one surface on a metal basis in which, in a temperature range of 900 to 1300 K, standard free energy of formation (ΔG0) of oxide is smaller than standard free energy of formation (ΔG0Zn) of zinc oxide and larger than standard free energy of formation (ΔG0Al) of aluminum oxide at an identical temperature, and the granular oxide has a particle size of more than or equal to 3 nm and less than or equal to 100 nm.