SURFACE CHARACTERIZATION OF THIN-LAYERS OF ALUMINUM-OXIDE

Thin oxide layers of commercial pure aluminium (1100-Al) and AlZnMgCu alloy (7075-Al) were characterized after oxidation in a 2.45 GHz micro wave discharge in oxygen plasma at low temperature (400 +/- 50 degrees C). The composition and structure of the oxide layers were studied by Auger electron spectroscopy (AES) and Fourier transform IR (FTIR) spe ctroscopy. In addition, atomic force microscopy (AFM) and micro-indent ation techniques were used for surface topography observations and for the evaluation of the coating-surface deformation response. It was fo und that the 1100-Al layer was composed of duplex sublayers, namely an external gamma-Al2O3 layer followed by an interdiffused Al-O sublayer . Under similar oxidation conditions the oxide structure of 7075-Al al loy was mainly composed of Mg-O. The surface features largely depended on the plasma processing parameters. The oxide-substrate composite la yer was characterized by higher microhardness values up to about twice that of an untreated substrate. The microhardness value was mainly de termined by the oxide composition, microstructure and thickness. An in dentation dimensional effect (IDE) was evident in the treated sample, and was confirmed by microscale measurements. The chemical and structu ral characterization of the oxide layers is presented and discussed wi th emphasis on the role of processing and micro-alloying effects on th e fine layer characteristics.