Abstract
Extruded and T6 tempered plates of 7042, an Sc modified Al–Zn–Mg–Cu alloy, were joined by friction stir welding (FSW) at a constant weld velocity and various pin rotation speeds (PRSs). At a low PRS, hardness decreased from each edge of the weld to a local minimum at the weld centre, but at a high PRS, the hardness initially decreased from each edge of the weld, but then rose towards the weld centre. The transition in the hardness profile was related to different heating and cooling conditions during FSW. Differential scanning calorimetry of baseline and welded samples revealed that the volume fraction of strengthening particles within the weld regions strongly depended on the weld conditions. For FSW heating rates, secondary phase dissolution/precipitation temperatures are in proximity to the welding temperatures. The maximum welding temperature during FSW increased from ∼250 to 450°C as the PRS increased from 175 to 400 rev min−1.
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