Hybrid welding of AA5754 annealed alloy: Role of post weld heat treatment on microstructure and mechanical properties

In this paper hybrid welding of the annealed AA5754 alloy was studied and the role of post weld heat treatment (PWHT) on microstructure and mechanical properties was investigated. The microstructure and hardness of the base material and welds were analyzed. Due to the segregation, the lowest microhardness value was observed at the welding centerline. High microhardness was registered in a narrow zone at the interface between the fusion zone and the heat affected zone where the welding cycle promotes both the strengthening by Mg solid solution and the lowest grain size. The hardness of the heat affected zone was higher than that of the base material due to dissolution of soluble particles (Mg2Si and Mg2Al3). PWHT at 350 degrees C increased the microhardness in the fusion zone and the tensile strength with respect to the untreated joint, whereas the strain at fracture was similar showing that the fracturewas promoted mainly by the presence of porosity, coarse grain size and insoluble segregated second phases. (C) 2015 Elsevier Ltd. All rights reserved.