Mechanical properties and scratch test resistance of nickel–boron coated aluminium alloy after heat treatments

Electroless nickel–boron deposits were synthesized on aluminium alloys and submitted to heat treatments under neutral (95% Ar + 5% H2) atmosphere. Two set of treatment conditions were used: 1 h at 400 °C and 4 h at 180 °C. Micro- and nanohardness measurements were carried out on the free surface of the sample and on polished cross-sections. A comparative hardness study was conducted to assess the influence of load, indent position (free surface or cross section), and heat treatment on the results of the indentation tests. Scratch tests were made on selected coatings to assess their adhesive properties and scratch resistance. Roughness measurements were carried out on the coatings before and after heat treatments. The samples were also investigated by XRD (X-ray Diffraction), SEM (Scanning electron microscopy) and optical microscopy to link their mechanical properties to their composition, structure and morphology.