Surface treatment of heat-treated cast magnesium and aluminium alloys

Modern coating systems deposited on surface layers of structural light materials are currently one of the most important issues in up-to-date material engineering, where vacuum deposition techniques are often used to improve the mechanical and functional properties of produced surface layers. Presented in this paper are gradient and monolithic coating types: Ti/Ti(C,N)/CrN, Ti/Ti(C,N)/(Ti,Al)N, Ti/(Ti,Si)N/(Ti,Si)N, Cr/CrN/CrN, Cr/CrN/TiN and Ti/DLC/DLC deposited onto magnesium and aluminium alloy substrates with the cathodic-arc-evaporation method (Arc PVD) and plasma-assisted process (PA CVD). Additionally, a thin metallic layer - in micrometers- (Cr and Ti) was deposited prior to the deposition of the final gradient coating to improve its adhesion to the substrate. This work presents the investigation results concerning the obtained surface-layer microstructures and mechanical properties of the obtained bi-layer coatings (gradient/multicompound) deposited onto light-alloy substrates using the chosen PVD and CVD methods, especially to meet the requirements needed for light-metal substrates - low temperature and duration. The structure investigations of the deposited coating were performed using a scanning electron microscopy (SEM) and glow discharge optical emission spectrometry (GDOES); the mechanical and functional properties were examined using the ball-on-disk method for the wear-resistance determination, and microhardness tests were performed for the functional usability of the coatings. The main finding is that the fracture morphology is characterized by a lack of columnar structures in the obtained coatings. The metallographic examinations carried out proved that the coatings were deposited uniformly over the whole sample, onto the investigated substrate materials; the measured thickness is characteristic for the produced coating type.It was also found that the particular layers adhere tightly to each other and to the light-metal substrate. The investigation results of the up-to-date PVD methods, together with light alloys, led to obtaining new applications, especially in the automobile and aviation industries.