Al-Fe Alloy Plated Steel Sheet for Uniform TWB Weld Hardness
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Solution Overview
Problem
Existing Al-plated steel sheets for hot press forming exhibit poor TWB welding characteristics due to non-uniform hardness in the welding zone, and existing solutions require additional equipment to remove the plating layer, which can compromise corrosion resistance.
Innovation Solution
An Al-Fe alloy plated steel sheet with a specific composition and manufacturing process, including a base steel sheet with controlled alloying and a batch-annealing process to form an Al-Fe alloy layer with uniform hardness, ensuring excellent TWB welding characteristics without removing the plating layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an Al-plated steel sheet is used for TWB welding, then the base material provides sufficient strength, but the welding zone exhibits non-uniform hardness leading to poor welding characteristics
Solution Approach 1:
The patent applies local quality by creating a multi-layered plating structure where the Al-Fe-Si alloy layer (5-15 μm thick) is positioned specifically at the welding zone interface. This localized alloy layer modifies the chemical composition and microstructure only in the welding region, ensuring uniform hardness distribution during TWB welding while preserving the overall strength of the base material. The selective placement of this alloy layer resolves the contradiction between maintaining base material strength and achieving welding zone hardness uniformity.
Solution Approach 2:
The patent employs composite materials by forming a plating layer with a specific Al-Fe-Si alloy composition (Al: 70-90 wt%, Fe: 5-20 wt%, Si: 2-10 wt%) that creates a composite structure at the welding interface. This composite plating layer combines the advantages of aluminum (weldability) with iron and silicon (hardness control), resulting in a welding zone with uniform hardness characteristics. The composite nature of this intermediate layer resolves the hardness non-uniformity issue while maintaining overall structural integrity.
2Reliability
If a plating layer is removed before TWB welding to improve welding characteristics, then welding zone hardness uniformity improves, but corrosion resistance deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the thickness of the Al-Fe-Si alloy layer to be 5-15 μm, which is sufficient to ensure uniform hardness distribution in the welding zone but thin enough to maintain good corrosion resistance. Additionally, the specific compositional parameters (Al: 70-90 wt%, Fe: 5-20 wt%, Si: 2-10 wt%) are optimized to achieve the desired hardness uniformity while preserving corrosion protection. This parameter optimization resolves the contradiction between welding characteristics and corrosion resistance.
Solution Approach 2:
The Al-Fe-Si alloy layer serves as an intermediary between the base steel and the external environment. Instead of removing the plating layer entirely, this intermediate alloy layer is introduced to mediate the welding process by providing uniform hardness characteristics. The intermediary layer performs dual functions: ensuring welding zone hardness uniformity for reliable TWB welding while simultaneously maintaining adequate corrosion resistance, thus resolving the contradiction between these two requirements.
3Reliability
If additional equipment is installed to remove the plating layer before welding, then welding zone hardness uniformity improves, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies preliminary action by pre-forming the Al-Fe-Si alloy layer during the plating process itself, before the welding operation. This alloy layer is created as part of the standard plating procedure through controlled diffusion of Fe and Si into the aluminum plating. By preparing the welding zone with the appropriate alloy composition in advance, during the existing plating step, the need for additional plating removal equipment is eliminated. This preliminary preparation resolves the contradiction between achieving hardness uniformity and avoiding increased manufacturing complexity.
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 uniform hardness in the welding zone, enhancing TWB welding characteristics and maintaining corrosion resistance, thereby improving the manufacturing process for hot press formed parts with tensile strength of 1300 MPa or more and minimal hardness deviation.
Implementation Method 1
an Al—Fe alloy layer which includes, by wt %, aluminum (Al): 40 to 60%, silicon (Si): 2 to 10%, a balance of iron (Fe), and unavoidable impurities, and a fraction of an unalloyed phase is 1 area % or less
Implementation Method 2
batch-annealing the plated hot-rolled steel sheet to satisfy the following Equation 1, where T denotes a heating temperature (° C.), t denotes maintenance time at a heating temperature (hours), and HR denotes a heating rate (° C./hour)
Data Source
AI summary
Provided is an Al—Fe-alloy plated steel sheet for hot forming, having excellent TWB welding characteristics since excellent hardness uniformity of a TWB weld zone after hot forming is obtained by suitably controlling a batch annealing condition, after plating Al, such that an Al—Fe-alloy layer is formed; a hot forming member; and manufacturing methods therefor.