Microstructure and mechanical properties of Al-Si-Ni coating on Cu-Cr substrate prepared by multi-permeation and friction stir processing

The surface of copper-chromium alloy was processed by Al-Si-Ni multi-permeation and friction stir processing, and the microstructure and mechanical properties of the surface layer were tested by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), microhardness tester and friction testing machine. The results show that Al, Si and Ni elements are fully permeated into the surface of copper-chromium alloy after multielement co-infiltration and friction stir processing. In the observation of the microstructures, we found that the reticular structure is fragmented and distributed in the stir zone region. Microstructure becomes finer and grains refinement. The micro hardness of the copper-chromium alloy increased to 129 HV, 44.9% higher than that of the original matrix. The main reasons of microhardness enhancement are solid solution strengthening, fine grains strengthening and dispersion strengthening. The friction test results show that the friction coefficient is basically stable at 0.69 and the wear mass is only 0.0017 g after 10  min of friction test. The improvement of wear resistance was attributed to the increase of microhardness of the alloy surface.