Papers by Author: Bruno de Meester

Abstract: Welding cheap and ductile 6xxx Al alloys with high strength 2xxx Al alloys is desirable for instance in specific aeronautical applications. These alloys present different rheological behaviors and melting temperatures which affect the ability to produce sound dissimilar friction stir welds. Dissimilar friction stir butt welds made of 2014-T6 and 6061-T6 Al alloys were performed with various welding parameters including shifts of the tool from the initial separation between the plates to be welded and placing one alloy either on the advancing, or on the retreating side of the weld. Temperature measurements during welding, mechanical characterization (transverse tensile tests and hardness profiles) and macrographic observations were performed. Macrographies on sections perpendicular to the welding direction reveal different metal flow patterns in the weld nugget. If the 2014 alloy is placed on the advancing side of the weld, an abrupt transition between the weld nugget and the 6061 alloy is observed on macrographs leading to premature fracture in tension. Dissimilar welds are cooler on the 6061 side of the weld, i.e. the weakest side of the weld, than the corresponding 6061 similar weld, limiting the growth of the hardening precipitates. This leads thus to higher strength of the dissimilar welds. Dissimilar welds with the weld center shifted towards the 2014 alloy present lower temperatures than unshifted welds on the 6061 side of the weld, also leading to higher strength.

Abstract: A friction stir weld in 6005A-T6 aluminum alloy has been prepared and analyzed by micro-hardness measurements, tensile testing and scanning electron microscopy (SEM). The locations of the various weld zones were determined by micro-hardness indentation measurements. The flow behavior of the various zones of the weld was extracted using micro-tensile specimens cut out parallel to the welding direction. The measured material properties and weld topology were then introduced in a fully coupled micro-mechanical finite element model, accounting for nucleation and growth of voids as well as void shape evolution. The model shows satisfactory preliminary results in predicting the tensile behaviour of the weld and the true strain at fracture.