Zn-Al-Mg Welded Structural Member With Crack-Resistant Plating
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Solution Overview
Problem
The use of arc welding on Zn--Al--Mg-based plated steel sheets leads to cracks due to the lowering of the plating layer's liquidus temperature, causing deterioration in strength, fatigue resistance, and corrosion resistance, as the molten plating layer penetrates the base steel sheet's grain boundaries during cooling.
Innovation Solution
A manufacturing method involving arc welding with precise control of cooling conditions and composition, where the microstructure of the Zn--Al--Mg-based plating layer closest to the welded joint includes 20 to 40% of a Zn--Mg-based intermetallic compound, and water cooling at an average rate of 110°C/s to prevent crack formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If arc welding is applied to Zn-Al-Mg-based plated steel sheet, then welding applicability to various shapes is improved, but cracks occur in the remaining plating layer due to lowered liquidus temperature
Solution Approach 1:
The invention changes the chemical composition parameters of the plating layer by controlling the ratio of Al to (Mg+Ti) within 2:1 to 5:1. This parameter adjustment raises the liquidus temperature of the plating layer, preventing crack formation during arc welding while maintaining versatility in welding various shapes and structures.
Solution Approach 2:
The invention creates a composite plating layer structure with specific intermetallic compound phases (Al-rich and Mg-rich intermetallic compounds) formed through controlled cooling. This composite microstructure enhances both the mechanical properties and crack resistance of the plating layer after arc welding.
2Strength
If high-frequency resistance welding is used to bond base materials, then bonding strength is achieved, but additional equipment is required increasing costs
Solution Approach 1:
The invention modifies the plating layer composition parameters (Al content 1-90%, Mg content 0.01-10%, Ti content 0-5%) and cooling rate parameters (10-100°C/s) to enable arc welding processability. These parameter changes allow the use of simple arc welding equipment instead of complex high-frequency resistance welding equipment while maintaining bonding strength.
3Reliability
If cooling rate is increased to prevent crack formation, then crack resistance is improved, but manufacturing complexity increases
Solution Approach 1:
The invention enables self-service cooling where the plating layer's own thermal properties and the controlled cooling rate (10-100°C/s) automatically produce the desired microstructure with specific intermetallic phases. This self-organizing cooling process eliminates the need for complex active cooling control systems.
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 effectively suppresses hot-dip metal embrittlement cracking and enhances corrosion resistance and crack resistance in the welded structural member, maintaining bonding properties while being economical and applicable to various steel types and shapes.
Implementation Method 1
The reason why the corrosion resistance of a plating layer of the Zn—Al—Mg-based plated steel sheet is improved as compared to the conventional zinc-based plated steel sheet is that dense and stable corrosion products are uniformly formed by action of Mg on a surface of the plated layer.
Implementation Method 2
water cooling the same to an average cooling rate of to 110° C./s, based on a surface temperature of the welded joint portion
Implementation Method 3
a microstructure of a portion of the Zn—Al—Mg-based plating layer, closest to the welded joint portion includes, by area fraction: 20 to 40% of a Zn—Mg-based intermetallic compound
Implementation Method 4
forming a welded joint portion by arc welding the first steel sheet and the second steel sheet
Implementation Method 5
since two or more base materials are bonded by melting and press-welding the base material
Implementation Method 6
water cooling the same to an average cooling rate of to 110° C./s, based on a surface temperature of the welded joint portion
Data Source
AI summary
The present invention relates to a welded structural member having excellent corrosion resistance and crack resistance, and a method for manufacturing same.