Electrodeposition of nanocrystalline Au-Cu alloy coatings with high hardness and corrosion resistance for electronic contact application

Au-Cu nanocrystalline coatings were prepared by direct current electrodeposition. The Au-Cu alloy coatings exhibit 3-fold higher hardness than commercially used Au-Co hard gold or 6-fold higher hardness than the pure Au coating. The ultra-high hardness originates from the synergistic effect of the solid solution and nanocrystalline grain boundary strengthening. Au-Cu coatings also presented excellent corrosion resistance, wear resistance, and low contact resistance comparable to those of Au-Co coatings based on industrial standard test specifications. By replacing hard gold with an Au-Cu alloy coating that contains 46% Cu (at.%), the use of Au can be reduced by 33%.