Zn-Al-Mg Plated Steel Microstructure for Corrosion and Formability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Coated steel products with high Mg concentration in the coating layer suffer from poor processability due to exfoliation during processing and reduced corrosion resistance in environments where water is likely to accumulate.
Innovation Solution
A coated steel product with a Zn-Al-Mg alloy layer containing specific elemental compositions and a controlled average value of Zn/Al/MgZn2 ternary eutectics, along with an optional Al-Fe alloy layer, is manufactured by precise cooling rates and surface roughness control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Mg concentration in the coating layer is increased to improve corrosion resistance, then the corrosion resistance is improved, but the coating layer exfoliates during processing and processability deteriorates
Solution Approach 1:
The patent optimizes the Mg concentration parameter within a specific range (3-12.5 mass%) rather than using high concentrations, and controls the cumulative circumferential length parameter of Al crystals (88-195 mm/mm2) to achieve the desired balance between corrosion resistance and processability
Solution Approach 2:
The patent uses a composite coating layer containing multiple elements (Zn, Al, Mg, and optional Sn, Bi, In, Ca, Y, La, Ce, Si, Cr, Ti, Zr, Mo, W, Ag, P, Ni, Co, V, Nb, Cu, Mn, Li, Na, K, Fe, Sr, Sb, Pb, B) working together to achieve both improved corrosion resistance and acceptable processability
2Reliability
If the Mg concentration in the coating layer is increased to improve corrosion resistance, then the corrosion resistance is improved, but corrosion resistance becomes poor in environments where water is likely to accumulate
Solution Approach 1:
The patent controls the Mg concentration within a moderate range (3-12.5 mass%) and optimizes the cumulative circumferential length of Al crystals (88-195 mm/mm2) to prevent excessive intermetallic compound formation that would harm corrosion resistance in water accumulation environments
Solution Approach 2:
The patent introduces optional elements (Sn: 0.01-3 mass%, Bi: 0.01-5 mass%, In: 0.01-2 mass%) that specifically improve corrosion resistance in water accumulation environments by forming protective local phases without compromising overall coating integrity
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 provides excellent processability and corrosion resistance even in environments where water accumulation is likely, by minimizing local corrosion and intermetallic compound cracking.
Implementation Method 1
the coating layer in the vicinity of such portions dissolves out before corrosion of the base steel, and the dissolved coating component forms a protective film
Implementation Method 2
cooled down in a temperature range of from 450° C. to 395° C. at an average cooling rate of from 5 to 20° C./s, cooled down in a temperature range of from 395° C. to 340° C. at an average cooling rate of 3° C./s or less, and cooled down in a temperature range of from 340° C. to 280° C. at an average cooling rate of from 10 to 20° C./s
Data Source
AI summary
Provided are a coated steel product in which a coating layer has a predetermined chemical composition, and in a backscattered electron image of a Zn—Al—Mg alloy layer, obtained by polishing a surface of the coating layer to ½ of a layer thickness, and observing the surface at a magnification of 100× with a scanning electron microscope, Zn/Al/MgZn2 ternary eutectics are present, and an average value of a cumulative circumferential length of the Zn/Al/MgZn2 ternary eutectics is from 100 to 300 mm/mm2 and a method of manufacturing the coated steel product.