Arc Welded Joint Cleaning for Low-Slag Corrosion Resistance
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Solution Overview
Problem
Conventional techniques for improving corrosion resistance in arc welded joints of steel members, such as those used in automobile chassis, face challenges including slag formation, welding fume adherence, and oxide formation, which compromise the effectiveness of chemical conversion and electrodeposition coatings, leading to reduced strength and increased manufacturing complexity and costs.
Innovation Solution
The method involves reducing slag coverage and oxide formation by using a shielding gas with decreased oxidizing gases, performing arc welding with reverse polarity, and ensuring a cleaning region adjacent to the weld bead toe, along with specific pulse current characteristics to stabilize the arc and promote uniform coating layer formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If zinc phosphate treatment is performed to improve adhesion of electrodeposition coating, then coating film adhesion is enhanced, but corrosion resistance deteriorates due to insufficient formation of chemical conversion coating layer
Solution Approach 1:
The invention optimizes the chemical parameters of the zinc phosphate treatment solution, specifically controlling the zinc ion concentration at 1-10 g/L, phosphate ion concentration at 0.1-5 g/L, and adding fluorine at 10-500 ppm. The zinc-to-phosphate ion concentration ratio is maintained at 1:0.05 to 1:2. These parameter changes ensure sufficient formation of the chemical conversion coating layer with dense crystal grain structure, simultaneously achieving both adhesion enhancement and corrosion resistance.
2Weight of moving object
If high strength steel sheet is used to decrease member thickness and weight, then fuel efficiency is improved, but corrosion resistance of weld decreases
Solution Approach 1:
The invention applies parameter changes to the zinc phosphate treatment solution composition, controlling zinc ions at 1-10 g/L, phosphate ions at 0.1-5 g/L, and fluorine at 10-500 ppm, with a zinc-to-phosphate ratio of 1:0.05 to 1:2. This optimized chemical composition enables the formation of a dense chemical conversion coating layer on high strength steel welds, preventing corrosion even in thin-walled members where weld corrosion resistance is critical.
3Reliability
If plated layer is used to improve corrosion resistance, then corrosion protection is enhanced, but manufacturing cost increases
Solution Approach 1:
The invention extracts and utilizes fluorine (at 10-500 ppm) as a key additive in the zinc phosphate treatment solution. This fluorine addition promotes the formation of a dense, uniform zinc phosphate crystal grain structure during the chemical conversion coating process, achieving plated-layer-level corrosion protection through a more economical zinc phosphate treatment rather than requiring separate plating operations.
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 approach enhances corrosion resistance and maintains joint strength, allowing for the use of high-strength steel sheets while minimizing manufacturing costs and environmental impact, effectively preventing corrosion progression in weld areas.
Implementation Method 1
a cleaning region, in which oxides formed on a surface of the steel sheet are removed due to formation of a cathode spot when the arc welding is performed
Implementation Method 2
formation of a cathode spot when the arc welding is performed
Implementation Method 3
reducing slag coverage and oxide formation by using a shielding gas with decreased oxidizing gases
Data Source
AI summary
Provided are an arc welded joint and an arc welding method. The arc welded joint has a slag-coverage area ratio SRATIO (%) of 15% or less, and a weld bead width ratio WRATIO (%) of 60% or more. The SRATIO is calculated by using an equation SRATIO=100×SSLAG/SBEAD. In this equation, an area of a surface of a weld bead formed by performing arc welding on a steel sheet is defined as a weld bead surface area SBEAD (mm2) and, of the weld bead surface area SBEAD, an area of a region covered with slag is defined as a slag surface area SSLAG (mm2). The WRATIO is calculated by using an equation WRATIO=100×WMIN/WMAX from a maximum value WMAX (mm) and a minimum value WMIN (mm) of a weld bead width in a direction perpendicular to a welding line of the weld bead.