The objective of this work is to settle the problem of adhesion between hard films and soft metal substrates. Hard Ti-Si-N films were deposited onto soft Al substrates with a double target magnetron sputtering system. The composition, structure, surface morphologies and mechanical properties were characterised by electron probe microanalyser, X-ray diffraction, atomic force microscope, scratch test and nanoindentation respectively. The as-deposited films had good adhesion to the Al substrates and had a smooth and lustrous surface. The maximum hardness of the films achieved was as high as 27?2 GPa at the Si target power of 80 W.