Al-Fe Hot-Stamped Coating Structure to Suppress Plating Cracks
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Hot stamping of aluminum plated steel sheets often results in cracks in the aluminum plating layer, leading to reduced post-painting anticorrosion properties due to the brittleness of the intermetallic compound and electropositive potential differences, and existing methods either require additional elements or fail to prevent crack propagation.
Innovation Solution
Controlling the mean linear intercept length of crystal grains in the intermetallic compound phase to 3-20 µm and forming a ZnO lubricating film on the aluminum plating layer surface to arrest crack propagation and improve formability, while maintaining stable spot weldability by controlling the thickness deviation of the Al-Fe alloy layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If aluminum plated steel sheet is used for hot stamping to suppress scale formation, then heating process is improved, but cracks form in the aluminum plating layer due to brittleness of intermetallic compound
Solution Approach 1:
The patent controls the composition parameters of the aluminum plating layer, specifically limiting Al-Fe alloy content to 5-20 mass% and adding 0.01-2.0 mass% Si to modify the intermetallic compound structure. This parameter optimization reduces brittleness while maintaining scale suppression during hot stamping.
Solution Approach 2:
The patent creates a composite plating structure with multiple layers including an Al-Fe-Si intermetallic compound layer and an Al-Si alloy plating layer. This composite structure combines the scale suppression capability of Al-Fe compounds with the crack resistance of Si-modified phases.
2Strength
If severe forming operation is applied during hot stamping to achieve high strength, then tensile strength is improved, but cracks propagate in the aluminum plating layer
Solution Approach 1:
The patent optimizes the crystal grain size of the Al-Fe intermetallic compound phase to 3-20 µm through controlled heating and cooling parameters. This grain size control allows the plating layer to withstand severe forming operations while achieving 1000 MPa or higher tensile strength in the steel sheet.
Solution Approach 2:
The patent adds Si to the aluminum plating layer beforehand to create a more ductile intermetallic compound structure. This pre-modification cushions against the stresses of severe forming operations, preventing crack initiation and propagation during hot stamping.
3Ease of operation
If aluminum plating layer is heated to austenite region to improve formability, then steel sheet formability is improved, but intermetallic compound becomes more brittle
Solution Approach 1:
The patent adds Si to the aluminum plating layer, which modifies the intermetallic compound formation during heating. The Si-containing phases remain relatively ductile even at austenite temperatures (800-950°C), allowing severe forming operations while maintaining reduced brittleness compared to conventional Al-Fe plating.
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
Prevents crack propagation in the aluminum plating layer, enhancing post-painting anticorrosion properties and productivity, and stabilizing spot weldability, resulting in high-strength parts with 1000 MPa or more tensile strength.
Implementation Method 1
heating the steel sheet to the 800°C or higher austenite region, then forms it by a die when hot
Implementation Method 2
TRIP (transformation induced plasticity) steel which utilizes the martensite transformation of residual austenite
Implementation Method 3
forming a ZnO lubricating film on the aluminum plating layer surface to arrest crack propagation and improve formability
Data Source
Figure 1
Figure 2
Figure 3(a)~3(d)
AI summary
A hot stamped high strength part in which the propagation of cracks which form at the plating layer at the time of hot stamping when hot stamping aluminum plated steel sheet is suppressed and the post painting anticorrosion property is excellent even without adding special ingredient elements which suppress formation of cracks in an aluminum plating layer is provided. A hot stamped high strength part which is excellent in post painting anticorrosion property, which hot stamped high strength part has an alloy plating layer which includes an Al-Fe intermetallic compound phase on the surface of the steel sheet, wherein the alloy plating layer is comprised from phases of a plurality of intermetallic compounds, a mean linear intercept length of crystal grains of a phase containing Al: 40 to 65 mass% among the phases of the plurality of intermetallic compounds is 3 to 20 µm, an average value of thickness of the Al-Fe alloy plating layer is 10 to 50 µm, and a ratio of the average value of thickness to the standard deviation of thickness of the Al-Fe alloy plating layer satisfies the following relationship: 0<standard deviation of thickness/average value of thickness ≤0.15.