Galvanized Steel Plate Press Formability via Zinc Oxide Layer
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Solution Overview
Problem
Zinc-based coated steel sheets exhibit high sliding resistance during press forming, leading to poor press formability and increased risk of cracking, especially in high-strength steel applications, due to inadequate surface oxide layers and the presence of Al oxides which inhibit zinc oxide formation.
Innovation Solution
A method involving temper-rolling followed by contact with an acidic solution containing NaHF2 or KHF2, and subsequent water-washing and neutralization, forms a zinc-based oxide layer with a crystalline structure, enhancing sliding characteristics without the need for alkali pretreatment or HF addition, which is industrially practical.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a galvanized steel sheet is used, then the coating provides good corrosion resistance, but the sliding resistance during press forming increases due to mold galling
Solution Approach 1:
The patent changes the chemical composition parameters of the coating by controlling the Al content (5-11 mass%) and adding Si (0.1-5 mass%), then modifies the surface chemistry through oxidation treatment to form zinc-based oxides. This transforms the surface properties while maintaining the base coating's corrosion resistance, thereby reducing sliding resistance during press forming.
Solution Approach 2:
The patent creates a composite structure with a zinc-based coating containing Al and Si, topped with a zinc-based oxide layer. This multi-layer composite structure combines the corrosion resistance of the zinc coating with the low friction properties of the oxide surface layer, resolving the contradiction between durability and sliding resistance.
2Strength
If high-strength steel sheets are used to reduce automobile weight, then the strength increases, but the surface pressure during press forming increases causing more severe coating adhesion to molds
Solution Approach 1:
The patent modifies the coating composition parameters (Al: 5-11 mass%, Si: 0.1-5 mass%) and performs oxidation treatment to create a zinc-based oxide surface layer. This surface modification reduces the coefficient of friction and prevents mold galling, allowing high-strength steel to be press-formed without increased coating adhesion problems.
3Manufacturing precision
If Al is added to the galvanizing bath to adjust alloying reaction, then the alloying control improves, but Al oxides form on the surface inhibiting zinc oxide formation
Solution Approach 1:
The patent extracts/removes the harmful Al oxide layer through oxidation treatment that selectively forms zinc-based oxides on the surface. By controlling the oxidation process, the Al oxides are eliminated or transformed, allowing zinc-based oxides to form instead, which provide the desired low friction surface properties.
Solution Approach 2:
The patent changes the surface chemical composition by controlling the oxidation process parameters, transforming the surface from Al-oxide-dominated to zinc-oxide-dominated. This parameter change in surface composition eliminates the harmful effect of Al oxides while maintaining the beneficial alloying structure underneath.
4Manufacturing precision
If an alkali solution is used to remove surface Al oxides before acidic treatment, then the surface activation improves, but the manufacturing process complexity increases
Solution Approach 1:
The patent extracts the harmful Al oxide layer directly during the oxidation treatment step without requiring a separate alkali pretreatment step. The oxidation process selectively removes Al oxides while promoting zinc oxide formation, achieving surface activation in a single step rather than requiring multiple steps including alkali treatment.
Solution Approach 2:
The patent combines the functions of Al oxide removal and zinc oxide formation into a single oxidation treatment step. This merges what would traditionally be separate processes (alkali etching followed by acidic oxidation) into one integrated operation, simplifying the manufacturing process while achieving the same surface activation effect.
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 method results in a zinc-based coated steel sheet with improved press formability and reduced sliding resistance, enabling the formation of a stable zinc-based oxide coating on GI with low surface activity, suitable for complex shapes and high-strength steel applications.
Implementation Method 1
bringing a zinc-based coated steel sheet into contact with an acidic solution containing NaHF2 and/or KHF2 in a total amount of 0.10 g/L to 5.0 g/L
Implementation Method 2
a zinc-based oxide layer is formed on a surface of a zinc-based coated steel sheet
Implementation Method 3
a zinc-based coated steel sheet having a zinc-based oxide layer on a surface of the zinc-based coated steel sheet, wherein the zinc-based oxide layer is formed by a method comprising an oxide layer-forming step
Data Source
Figure 1~3
AI summary
Provided is a method for manufacturing a zinc-based coated steel sheet having excellent press formability. The method includes an oxide layer-forming step of bringing the zinc-based coated steel sheet into contact with an acidic solution, holding the zinc-based coated steel sheet for 1 second to 60 seconds, and then water-washing the zinc-based coated steel sheet and a neutralization step of holding a zinc-based oxide layer formed in the oxide layer-forming step for 0.5 seconds or more in such a state that a surface of the zinc-based oxide layer is in contact with an alkaline aqueous solution, water-washing the zinc-based oxide layer, and then drying the zinc-based oxide layer. The acidic solution contains HF2Na and/or HF2K in a total amount of 0.10 g/L to 5.0 g/L.