Arc Spot Welding of Al-Steel Joints Using a Hollow Steel Intermediary
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Solution Overview
Problem
Existing arc spot welding methods fail to achieve excellent tensile shear strength and cross tensile strength when joining ultra-high tensile steel with aluminum or magnesium alloys, leading to insufficient joint strength in multi-material applications, particularly in transportation equipment where high-strength steel is required.
Innovation Solution
An arc spot welding method using a welding material with 13% or more Ni content, where a steel sheet with a hole is overlapped with an ultra-high tensile steel sheet, and a steel joining auxiliary member with a hollow portion is inserted to fill with weld metal, ensuring a strong bond and improved joint strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional arc spot welding methods are used to join ultra-high tensile steel with aluminum or magnesium alloys, then the welding process is simple and equipment cost is low, but the joint strength (tensile shear strength and cross tensile strength) is insufficient
Solution Approach 1:
A joining auxiliary member made of steel with a specific chemical composition (C: 0.15-0.40%, Si: 0.01-0.50%, Mn: 0.50-2.00%, Cr: 0.05-1.00%, Ni: 0.05-1.00%, Mo: 0.05-0.50%, B: 0.0005-0.0050%, Fe: balance) is introduced as an intermediary between the ultra-high tensile steel and aluminum/magnesium alloy sheets. This auxiliary member facilitates strong bonding between dissimilar materials while maintaining a relatively simple welding process using conventional arc spot welding equipment.
2Strength
If a joining auxiliary member with complex shape (stepped outer shape with shaft and flange portions) is used, then the strength against shear stress and restriction force are improved, but the manufacturing complexity and cost increase
Solution Approach 1:
Instead of using a complex stepped shape, the invention achieves improved shear strength by optimizing the chemical composition parameters of the joining auxiliary member (specific ratios of C, Si, Mn, Cr, Ni, Mo, and B). This allows a simpler cylindrical shape with diameter slightly larger than the hole diameter to provide sufficient shear resistance and restriction force, reducing manufacturing complexity while maintaining strength.
3Strength
If the maximum outer diameter of the shaft portion is made larger than the hole diameter to improve restriction force, then the strength against horizontal shear stress is improved, but the insertion difficulty and assembly complexity increase
Solution Approach 1:
The invention optimizes the diameter of the joining auxiliary member to be only slightly larger than the hole diameter (specifically, the outer diameter is 1.01-1.05 times the hole diameter). This minimal size difference provides sufficient restriction force and shear resistance while ensuring easy insertion and assembly, avoiding the problems associated with excessively large diameter differences.
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 enhances the tensile shear strength and cross tensile strength of dissimilar material joints, enabling the use of inexpensive arc welding equipment to achieve high-strength welds suitable for ultra-high tensile steel and aluminum or magnesium alloys.
Implementation Method 1
a step of joining the first sheet and the second sheet via the joining auxiliary member by using a welding material containing 13 mass % or more of Ni, in which the step of joining the first sheet and the second sheet is a step of melting the second sheet and the joining auxiliary member and melting the welding material to fill the hollow portion of the joining auxiliary member with weld metal
Data Source
AI summary
The arc spot welding method for joining dissimilar materials, in which a first sheet (10) made of an Al-based material or an Mg-based material and a second sheet (20) made of ultra-high tensile steel having a tensile strength of 1180 MPa or more are joined, includes a step of forming a hole in the first sheet (10), a step of overlapping the first sheet (10) and the second sheet (20), a step of inserting a joining auxiliary member (30) made of steel, in which a hollow portion is formed, into the hole of the first sheet (10), and a step of joining the first sheet (10) and the second sheet (20) via the joining auxiliary member (30) using a welding material containing 13 mass % or more of Ni.