Original title: Phase stability and mechanical response of Ag-interlayered Al/Cu resistance spot-welded joints
Shuang Lin, Kyubok Lee, Jiahui Ye, Ho Kwon +5 · September 2026
Joining aluminum and copper is vital for building battery packs. However, welding them creates brittle aluminum-copper compounds, like Al2Cu and Al4Cu9, which make the connection weak. Scientists often guess how to fix this by adding extra metals between the pieces. Here, researchers inserted a thin silver layer between aluminum and copper before welding. The silver changes how the metals mix during melting and cooling. Instead of brittle aluminum-copper compounds, the weld forms a ductile aluminum-silver solid solution, keeping copper out of the mix. Atoms in this new mixture slide rather than crack under stress. The researchers confirmed this by testing both the structure and the physical strength of the joint. Adding silver raised the joint's nominal strength from 47.9 to 67.4 MPa. Ultimately, using silver replaces brittle compounds with tougher materials, creating significantly stronger metal joints.
Imagine two different-colored clays that don't stick well together. Normally when you press them, a hard, crumbly crust forms at the seam. Now suppose you roll a thin layer of a third, softer clay between them. That soft layer spreads smoothly and bonds to both sides, while also keeping the hard crust from forming. In this paper, the silver interlayer acts like the soft clay, preventing the brittle aluminum-copper crystals from forming and resulting in a stronger weld.
Battery packs rely on joints between aluminum and copper, but these welds are brittle and prone to failure. By adding a silver interlayer, engineers can more than double the joint strength. This work gives manufacturers a predictive tool to choose the right interlayer, replacing trial-and-error with science.
The workflow is demonstrated only for a silver interlayer. The study does not test other interlayer materials or different joint geometries. The nominal strength improvement (from 47.9 to 67.4 MPa) is reported, but fatigue or impact properties are not evaluated. The predictive framework requires validation across a wider range of alloy systems.
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Phase stability and mechanical response of Ag-interlayered Al/Cu resistance spot-welded joints — Shuang Lin, Kyubok Lee, Jiahui Ye et al.
Abstract licence: CC0
Explanation generated by Synthesis from the abstract — it is not the original paper. This is a preprint, so it hasn't necessarily been peer reviewed.