Microstructure and mechanical properties of Ti-6Al-4V laser welds for airplane floor manufacturing application
Résumé
Owing to its high strength-to-weight ratio, corrosion resistance and compatibility with carbon fibre composites, Ti-6Al-4V is a good candidate for the replacement of aluminium alloys in the manufacture of aircraft floor structure, whenever enhanced corrosion resistance is required. However forming and machining of Ti -6Al-4V is not straightforward and the cost of such an alloy makes rail manufacture from machining bars a non-viable solution. A better way to manufacture titanium alloy rails is to divide a rail into several components with fairly simple shape, which can then bejoined before limited machining to obtain the final shape. Laser welding is well suited for joining titanium alloys, as it is fast, precise and generates far less deformations than other welding processes. In this study, a 10kW fibre laser was used for joining two different grades of 5 mm thick Ti-6Al-4V plates. A comprehensive study taking into account on the laser process parameters and characteristics of both grades has been carried out to minimize distortion and to achieve sound and reproducible welds without oxide. The structure of each welded zone was examined both by optical and electron microscopy. Micro texture analyses were performed on samples before and after welding, in order to evaluate texture modifications. Differences in terms of mechanical properties, as shown by uniaxial tensile tests, were interpreted on the basis of base material initial microstructures as well as the microstructure of assemblies.