Surface-treated steel cut edge corrosion resistance
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Solution Overview
Problem
Conventional chromate-free technologies for steel materials face challenges in achieving corrosion resistance comparable to chromate treatments, particularly in cut edge corrosion resistance, and often suffer from insufficient corrosion resistance and moisture resistance in outdoor applications.
Innovation Solution
A surface-treated steel material with a base layer containing an aluminum-zinc alloy plating layer and a coating film composed of a vanadium compound, such as alkaline earth metal vanadate, and trimagnesium phosphate, where the vanadium compound has specific electrical conductivity and pH properties, and the coating film is formulated to provide enhanced corrosion and moisture resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Mg is added to improve corrosion resistance, then corrosion resistance is improved, but wrinkles are formed on the surface and surface appearance deteriorates
Solution Approach 1:
The invention changes the chemical composition parameters of the plating layer by adding Cr (0.02-1.0% by mass) in addition to Mg (0.1-10% by mass). This parameter change modifies the surface properties to prevent wrinkle formation while maintaining the corrosion resistance benefits of Mg.
Solution Approach 2:
The invention creates a composite plating layer structure containing multiple elements (Al, Zn, Si, Mg, and Cr) where Cr acts as a modifier to suppress the harmful surface effects of Mg while preserving its corrosion protection capabilities. The synergistic interaction between these elements resolves the contradiction.
2Quantity of substance
If wrinkles are formed in the plating layer surface, then Mg content increases, but sharp protrusions are formed and coating thickness becomes uneven
Solution Approach 1:
By introducing Cr as an additional parameter (0.02-1.0% by mass) alongside controlled Mg content (0.1-10% by mass), the invention modifies the surface morphology parameters to eliminate protrusions and wrinkles, thereby achieving uniform coating thickness while maintaining high Mg content for corrosion resistance.
3Reliability
If vanadium compound content is increased to improve corrosion resistance, then corrosion resistance is improved, but moisture solubility increases and coating film absorbs moisture
Solution Approach 1:
The invention creates a composite anticorrosive coating system combining vanadium compound (c) with trimagnesium phosphate (d) and specific resin components. This composite formulation balances the high corrosion resistance of vanadium with the moisture resistance provided by trimagnesium phosphate and the resin matrix, preventing excessive moisture absorption while maintaining superior corrosion protection.
Solution Approach 2:
The invention optimizes the concentration parameter of vanadium compound to 5-150 parts by mass per 100 parts of total solid content, and combines it with trimagnesium phosphate at 3-150 parts by mass per 100 parts of total solid content. This parameter optimization ensures sufficient corrosion resistance while the trimagnesium phosphate component counteracts excessive moisture solubility.
4Reliability
If chromate treatment is used to achieve excellent anticorrosive properties, then corrosion resistance is improved, but hexavalent chromium adversely affects the environment
Solution Approach 1:
The invention replaces harmful hexavalent chromium with a benign vanadium-based system that provides equal or superior corrosion resistance. Trimagnesium phosphate is added to enhance moisture resistance, converting the potential harm of moisture-sensitive vanadium compounds into a beneficial dual-function coating that resists both corrosion and moisture, eliminating environmental toxicity while maintaining protection performance.
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 achieves cut edge corrosion resistance equal to or exceeding that of chromate treatments without using hexavalent chromium, while maintaining moisture resistance and improving the overall corrosion protection of the steel material.
Implementation Method 1
a coating film formed using the anticorrosive pigment containing no hexavalent chromium has a problem in which corrosion resistance is not sufficient
Implementation Method 2
hot-dipped Zn—Al-based plated steel materials have been widely used in applications such as a building material, a material for automobiles, and a material for household electrical appliances
Data Source
AI summary
A surface-treated steel material having cut edge corrosion resistance that is equal to or more than that of a chromate treatment without use of hexavalent chromium. The surface-treated steel material includes a coating film formed on a surface of a steel material through a plating layer that is obtained by immersing the steel material in a galvalume bath containing Mg. The coating film is formed using a coating composition containing a coating film-forming resin, a cross-linking agent, a predetermined vanadium compound, and trimagnesium phosphate; the vanadium compound is a compound satisfying a predetermined electrical conductivity; the content of the vanadium compound is restricted to a predetermined amount; the vanadium compound satisfies a predetermined pH; and the content of the trimagnesium phosphate is a predetermined amount.