Resistance Welding with Interlayer Dilution for 7075 Aluminum
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Solution Overview
Problem
Resistance welding of ultra-high strength aluminum alloys, such as 7075 aluminum alloy, results in weld nuggets with poor mechanical properties due to the dissolution of local strengthening precipitates, leading to brittle intermetallic compounds and reduced cross-tension strength.
Innovation Solution
Incorporating an intermediate material between workpieces during resistance welding, which has a lower concentration of alloying elements than the workpieces, to form a weld nugget with reduced precipitate-rich phases by diluting the alloying element concentration in the weld pool.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If resistance welding is performed on ultra-high strength aluminum alloys, then the workpieces can be joined, but the weld nuggets exhibit poor mechanical properties due to dissolution of strengthening precipitates and formation of brittle intermetallic compounds
Solution Approach 1:
A filler material with composition different from the base aluminum alloy is introduced into the weld pool. This intermediary material modifies the chemical composition of the weld nugget, suppressing the formation of brittle intermetallic compounds and preventing complete dissolution of strengthening precipitates, thereby improving cross-tension strength while maintaining joint integrity
Solution Approach 2:
The chemical composition parameters of the weld pool are deliberately altered by adding filler material containing specific alloying elements. This changes the solidification behavior and phase formation in the weld nugget, transforming it from a brittle structure to one with improved mechanical properties and controlled precipitate distribution
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
The method enhances the cross-tension strength of weld nuggets by up to 170% by reducing the volume fraction of precipitate-rich phases, thereby improving the mechanical properties of the weld joint.
Implementation Method 1
An electrical current is then passed through the workpieces from one welding electrode to the other. Resistance to the flow of the electric current generates heat within the metal workpieces and at their faying interface.
Implementation Method 2
Upon cessation of the current flow, the molten weld pool solidifies into a weld nugget that forms all or part of a weld joint.
Data Source
AI summary
Methods for resistance welding, resistance-welded assemblies, and vehicles including resistance-welded assemblies are provided. The method includes providing a workpiece stack-up including first and second workpieces and an intermediate material located between the faying surfaces thereof. At least one of the first workpiece and the second workpiece is formed of a first metal alloy with a first concentration of an alloying element, and the intermediate material is formed of a second metal alloy of the first metal and a second concentration of the alloying element that is less than the first concentration. The method includes bringing electrodes into contact with the workpieces, passing an electrical current therebetween to form a molten weld pool, and cooling the molten weld pool into a weld nugget that forms all or part of a weld joint between the workpieces and has a composition that is a mixture of the workpieces and the intermediate material.