The influence of the fabrication route on the microstructure and surface degradation properties of Al reinforced by Al9Co2

Abstract

Al-7 (wt. %) Co alloys have been prepared by conventional casting (Cast), vacuum arc melting (VAM) and free sintering (FS), with the objectives to: a) determine an effective fabrication route (in terms of low cost, ease of manufacture and property boosting) and b) exploit the benefits that the combination of a complex metallic alloy (Al9Co2) with Al at the Al-rich end of the Al-Co phase diagram can offer, corrosion- and wear-wise, whilst at the same time, specific weight and raw material costs remain at relatively low levels. All the attained microstructures consist of Al9Co2 in an Al matrix. However, the main microstructural features are strongly affected by the preparation method. The VAM alloy presents the finest microstructure, which is also highly directional. All the microstructures are analytically being discussed and explained with respect to the fabrication method. Porosity and hardness data are correlated with the fabrication route and the corresponding microstructures. All alloys, regardless of the preparation method, exhibit high resistance to localized corrosion in 3.5 wt% NaCl. The potentiodynamic and potentiostatic polarization performances are analysed. The sliding wear resistance of the Al-Co alloys is notably improved as compared to commercially pure Al and common Al-alloys. A wear mechanism is proposed and the role of Al9Co2 is clarified. The superiority of the VAM alloy with respect to the surface degradation behavior is noted and correlated with its microstructure.