Thermal-Sprayed Interlayers for Aluminum-Stainless Resistance Welding
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Solution Overview
Problem
Current welding methods cannot effectively join dissimilar metal combinations like aluminum to stainless steel without forming brittle intermetallic phases, leading to low strength and power transmission, limiting the use of resistance welding in multi-material designs in car body engineering.
Innovation Solution
Applying an aluminum thermal-sprayed layer on stainless steel with a well-defined thickness and surface roughness, followed by resistance welding, ensuring only the aluminum contact area melts to prevent intermetallic phase growth, using techniques like flame or plasma spraying, and selecting welding parameters to maintain the temperature below 350°C in the transition zone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional resistance welding is used to join aluminum to 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 intermediate layer is applied to the stainless steel surface before resistance welding. This intermediate layer acts as a mediator between aluminum and stainless steel, preventing direct contact and formation of brittle intermetallic phases while enabling successful resistance welding. The zinc layer controls the metallurgical reaction during welding, allowing high-speed welding without compromising joint strength.
2Strength
If mechanical solder or brazing depots are used to join dissimilar metals, then joint strength is improved, but material deformation and cutting are required reducing ease of manufacture
Solution Approach 1:
The mechanical solder or brazing depot approach is replaced with a thermal spray coating process. Instead of mechanically attaching depots requiring deformation and cutting, a zinc-based coating is thermally sprayed onto the stainless steel surface. This substitution eliminates complex mechanical preparation steps while achieving comparable or superior joint strength through controlled metallurgical bonding during resistance welding.
3Reliability
If the thermal sprayed layer thickness is increased to prevent intermetallic phase growth, then weldability is improved, but material consumption and cost increase
Solution Approach 1:
The thickness of the thermal sprayed zinc layer is precisely controlled within an optimized range (5-20 micrometers). By optimizing this critical parameter, the process achieves effective prevention of brittle intermetallic phase growth while minimizing zinc material consumption. The controlled thickness ensures sufficient protection during welding without excessive material use or cost.
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 in the applied sheet area, achieving similar weld strength to similar material combinations, while avoiding the formation of brittle intermetallic phases, thus allowing for the use of resistance spot welding in dissimilar metal combinations.
Implementation Method 1
applying an aluminum thermal-sprayed layer on the surface of the (stainless) steel
Implementation Method 2
resistance (spot) welding process
Data Source
AI summary
A method for joining of at least two materials, non-weldable directly to each other with thermal joining processes in a lap joint configuration includes a two step sequence including a first step to apply a thermomechanical or mechanical surface protection layer on the surface of a (stainless) steel substrate and a second step where, a thermal joining process is used to weld the sprayed layer with an applied aluminum sheet without having brittle intermetallic phases in the whole material configuration.