Achieving brittle-intermetallic-free and high-conductivity aluminum/copper joints using nickel-phosphorus coatings

Nannan Chen, Hongliang Wang, Pawan Veeresh, Jingjing Li, Jay Oswald, Liang Xi, Sean Wagner, Ryan Sekol, Vic Liu, Ke Wang, Thomas Perry, James Schroth

Research output: Contribution to journalArticlepeer-review

Abstract

Mechanical degradation due to brittle intermetallic compounds (IMCs) formed at the faying interface is a predominant deficiency in dissimilar metal joints. In copper/aluminum (Cu/Al) joints, additional defects (such as partially-bonded interfaces, porosity and cracks) lead to further weakened strength and lowered electrical conductivity. In this study, nickel‑phosphorus (Ni-P) coatings are deposited on Al to address these issues. With the aid of Ni-P coatings, the detrimental Cu-Al IMC is eliminated, a donut-shaped weld with a partially-bonded interface is evolved into an hourglass-shaped weld with a fully-bonded interface, while the porosity and cracks are inhibited. Numerical simulations indicate that, during the welding without Ni-P coating, the Al oxide aggravates the inhomogeneity of heat generation at the Cu/Al interface, promoting the formation of donut-shaped weld and defects. Microstructural characterization suggests that the Ni-P coatings obstruct the Cu-Al interdiffusion which results in CuAl2-free interfaces, while the amorphous Ni-P convert into eutectic microstructure composed of nanocrystalline Ni and fine Ni3P grains through a solid-state transformation. Using the Ni-P coatings, joints gain an improvement of 140% in lap-shear peak load and a 25-fold increase in lap-shear maximum elongation, as well as an 84% reduction in electrical resistance.

Original languageEnglish (US)
Article number109435
JournalMaterials and Design
Volume199
DOIs
StatePublished - Feb 1 2021

Keywords

  • Dissimilar metal joining
  • Interface
  • Ni-P coating
  • Numerical simulation
  • Transmission electron microscopy

ASJC Scopus subject areas

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering

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