Thermal-Sprayed Interlayers for Aluminum-Stainless Resistance Welding
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Solution Overview
Problem
Current welding methods fail to effectively join dissimilar metal combinations like aluminum and stainless steel due to the formation of brittle intermetallic phases during resistance welding, resulting in low strength and power transmission.
Innovation Solution
Applying an aluminum thermal-sprayed layer on stainless steel with a well-defined thickness and surface roughness, followed by resistance spot welding, ensuring only the aluminum contact area melts to prevent intermetallic phase growth, using techniques like flame or arc spraying.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional resistance welding is used to join aluminum and stainless steel, then welding speed and productivity are improved, but brittle intermetallic phases form between the metals reducing joint strength
Solution Approach 1:
A zinc-based interlayer is applied to the stainless steel surface before welding. This interlayer acts as a mediator between the aluminum and stainless steel, preventing direct contact and intermetallic phase formation while enabling resistance welding to proceed at high speed without compromising joint strength
Solution Approach 2:
The surface properties of the stainless steel are changed by applying a zinc-based coating layer with specific thickness (5-50 μm) and composition. This parameter change modifies the welding interface characteristics, allowing aluminum to weld to the coated steel without forming brittle intermetallic phases
2Strength
If mechanical solder or brazing depots are used to join dissimilar metals, then joint strength can be improved, but deformation and cutting of the material are required increasing process complexity
Solution Approach 1:
The mechanical joining methods (soldering, brazing, deformation, cutting) are replaced by a thermal spray coating process followed by resistance welding. This substitution eliminates the need for mechanical material modification while achieving comparable or superior joint strength through a simpler two-step process
3Ease of manufacture
If aluminum thermal spray is applied on stainless steel to prevent intermetallic formation, then weldability is improved, but the surface roughness and transition resistance must be precisely controlled
Solution Approach 1:
Instead of precisely controlling the aluminum spray parameters to achieve specific surface roughness values, the invention changes the approach by using a zinc-based interlayer with a broader acceptable thickness range (5-50 μm). This parameter change relaxes the manufacturing precision requirements while maintaining weldability and preventing intermetallic phase formation
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 enables high power transmission and fracture behavior focused on the applied sheet area, achieving strength comparable to similar welds while avoiding intermetallic phase formation, thus making previously unweldable combinations weldable with improved corrosion resistance.
Implementation Method 1
applying an aluminum thermal-sprayed layer on the surface of the (stainless) steel
Implementation Method 2
resistance (spot) welding process
Implementation Method 3
the resistance welding can be carried out for instance by spot welding
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a method for joining of at least two materials, non-weldable directly to each other with thermal joining processes in a lap joint configuration, where a two step sequence is used consisting of a first step to apply a thermomechanical or mechanical surface protection layer on the surface of a (stainless) steel substrate (1) and a second step where, a thermal joining process is used to weld the sprayed layer (2) with an applied aluminum sheet (3) without having brittle intermetallic phases in the whole material configuration.