Stoichiometry of unbalanced magnetron sputtered Al–Mg alloy coatings

Abstract

Abstract Numerous Al–Mg coatings were prepared by unbalanced magnetron sputtering with a range of substrate bias voltages. The coatings were deposited from circular planar targets, composed of sequential sectors of Al and Mg, bonded to a directly cooled copper backing plate. The chemical composition of the coatings was found to be significantly affected by preferential resputtering of Mg due to ion bombardment. X-ray diffraction indicated that all coatings were extremely fibre textured. Some dramatic changes in d -spacing of the coating were observed for only small increments in the bias voltage. This indicates a transition in crystal structure induced by preferential resputtering. Extremely high amounts of argon were also detected in the coatings which contained a Mg-rich cph structured phase. Very little argon was detected in any of the Al-rich fcc coatings, even with high substrate bias voltages (−200 V). The burial of argon in the cph structured Al–Mg coatings is not purely an ion implantation phenomenon, but is controlled by microstructural entrapment or alloying effects. It is concluded that ion-assisted deposition of Al–Mg alloy coatings should be treated with some caution, because of these difficulties with the control of stoichiometry.