Plastic flow behaviour and formability of friction stir welded joints in AZ31 thin sheets obtained using the "pinless" tool configuration

The plastic flow behaviour and formability of friction stir welded AZ31 magnesium alloy sheets, 1.5 mm thick, were widely investigated. Flow curves were obtained in extended ranges of temperature (250-350 degrees C) and strain rate (10(-3)-10(-1)s(-1)) by means of uniaxial tensile tests; furthermore, forming limit curves were determined using the hemispherical punch method at 350 degrees C, with a constant cross-head speed of 0.1 mm/s. The results were compared with those obtained on the base material, under the same experimental conditions. It has shown that the flow stress and ductility levels of joints are lower than those of base material; however, as temperature increases and strain rate decreases, the peak flow stress of the welded joint tends to be similar to the one of the base alloy. Finally, formability of the friction stir welded blanks, evaluated in terms of forming limit curves, is lower than the one of the base material. (C) 2011 Elsevier Ltd. All rights reserved.