Mechanical Properties of Electrodeposited Al-W Alloy Films and the Effects of Subsequent Heat Treatment

Abstract

Due to their high oxidation and corrosion resistance, Al coatings are effective in extending the lifetimes of other metallic materials. However, the low mechanical strength of Al can limit its adoption for certain applications. Alloying Al with other transition metals, which improves the mechanical properties, can be a possible solution to this problem. Electrodeposition is a simple method of forming Al-base alloy films from ionic liquids represented by EMIC-AlCl3. Among the Al-base alloys, Al-W alloy is of significant interest since it is expected to exhibit excellent mechanical properties. The electrodeposition of Al-W alloys from EMIC-AlCl3 baths containing K3W2Cl9 was reported previously[1]. However, Al-W alloys electrodeposited from this system had a powdery morphology when the W content was >7 at.%, and the mechanical properties have not been investigated. In this study, we report the electrodeposition of Al-W alloy films from EMIC-AlCl3 baths containing WCl2. Nano-indentation tests were undertaken to determine the hardness and Young’s modulus of the Al-W alloy films. The effects of heat treatment on the mechanical properties were also examined. It was possible to electrodeposit Al-W alloy films containing up to 12 at.% W. XRD patterns showed that these films were fcc solid solution at low W contents, and were amorphous at 12 at.% W. The hardness increased from 1.8 GPa with increasing W content. The film containing 12 at.% W showed the highest hardness value of 4.6 GPa, which is close to that of pure bulk W. The Young’s modulus also increased from 97 to 168 GPa with increasing W content in the solid solution range, followed by a sudden decrease to 89 GPa at 12 at.% W. This value is close to that of pure bulk Al. The low Young’s modulus of Al-12 at.% W alloy is attributed to its amorphous structure. Heat treatment at 300-400°C for 3 h was carried out. After the heat treatment at 400°C, Al-W intermetallic compounds were detectable by XRD, and both the hardness and Young’s modulus increased. These results show that Al-W alloy films with excellent mechanical properties can be obtained from EMIC-AlCl3-WCl2baths. In particular, amorphous Al-12 at.% W films displayed interesting properties, including hardness values as high as that of W and Young’s modulus values as low as that of Al. The hardness and Young’s modulus of Al-W films can be controlled by modifying the W content and conducting subsequent heat-treatment. [1] T. Tsuda et al., Journal of the Electrochemical Society 161, D405-D412 (2014)