This paper presents the results of research into the influence of surface modification of 7075 aluminum alloy with nitrogen ions on the type and quantity of chemical bonds and on the mechanical properties of Si: C:N:H coatings deposited with use of the Micro Wave Chemical Vapor Deposition method. Fourier Transform Infrared Spectroscopy results show that during coating deposition the following chemical bonds are mainly formed: -CH2 in -Si-CH2-Si-, -C=C-, -NH-, -NH2, -CH3, and -CH2-. Their relative proportions are directly linked to the hardness and modulus distribution of the coatings. The modification of Al alloy substrate with N+ ions below 670 K promotes an increase (by a factor of 2) in the formation of -NH-and -NH2 groups relative to -C=C-double bonds and the CH2-group in the -Si-CH2-Si-chain as compared to unmodified samples. However, above 670 K the mechanismchangeswherebymore -C=C-and-Si-CH2-Si-groups are formed as compared to -CH2, -CH3-, -NH-, and -NH2 groups. The change of mechanism determines the hardness of the coatings, which is approximately 8 GPa in the case ofmodification above 670 K, but does not exceed 3 GPa if modification was conducted below 670 K. Still, coatings deposited on substrates modified above 670 K delaminate in scratch tests by propagation of crackswithin the scratch track. This behavior is not observed for coatings deposited below 670 K (on nitrogen-modified substrates). In this case, only plastic deformation in the sample/indenter contact region is present. (C) 2013 Elsevier B. V. All rights reserved.