Grain structure and impact toughness of Al-Li alloy joints formed by friction stir welding

Abstract

The paper presents the investigation of the grain structure of initial homogeneous aluminum alloy AA8090 and welded specimen using friction stir welding. An optical microscopic study reveals four zones in the welding seam. In order to evaluate deformation and fracture behavior, Charpy V-notch impact tests were performed with the recording of emitted acoustic signals (acoustic emission) and capturing of loading diagrams by the instrumented striker. The formation of a large area of grain boundaries in welded specimen leads to a significant increase in the energy required for the initiation and propagation of a crack under impact loading, while initial alloy demonstrates low impact toughness. Registered acoustic signal was further analyzed by means of wavelet spectrum.