Friction stir welding of as-extruded Mg-Al-Zn alloy with higher Al content. Part II: Influence of precipitates

Extruded Mg-Al-Zn (AZ80) plates were subjected to friction stir welding at a welding speed of 100 min.min(-1) and a tool rotation rates of 800 rpm. Different heat treatments were conducted before or after welding with the aim to evaluate the influence of precipitates on the weld properties. The welding joint with the solution treatment before welding exhibited enhanced ductility and decreased yield strength due to the dissolution of beta-Mg17Al12 and the coarsening of grains. After aging at 180 degrees C for 16 h, a banded structure consisting of different densities of discontinuous beta-Mg17Al12 precipitates was observed in the nugget zone of both joints with or without the solution treatment before welding. The yield strength of the joint without the solution before welding increased by 30% after aging, with the elongation being decreased. The fracture behavior of the aged joints was closely related to the banded structure where the crack propagated more easily along the coarse discontinuously precipitated bands. (C) 2014 Elsevier Inc. All rights reserved.