The effect of Al and Si on development of structure and mechanical properties was studied for arc evaporated Al-Cr-(Si)-N films synthesized from Al-Cr and Al-Cr-Si composite targets. All films show stoichiometric compositions, with a Si content corresponding to the target and a minor loss of Al. The hardness of Al-Cr-N films reaches a maximum for Al/Cr ratios close to the solubility limit of AlN in CrN. The addition of Si results in a further increase of hardness due to solid solution hardening and formation of a nanocomposite structure, which is accompanied by a reduced crystallinity and grain size. Al-Cr-Si-N films with high Si contents show a reduced hardness due to grain boundary sliding promoted by the higher amorphous phase fraction. (C) 2013 Elsevier B.V. All rights reserved.