Features of structure formation processes in AA2024 alloy joints formed by the friction stir welding with bobbin tool

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 2 2021 Ta b l e 1 Chemical composition of AA2024 alloy Fe Si Mn Ti Cu Mg Zn Others Al ≤0,5 ≤0,5 0,3-0,9 ≤0,15 1,4-2,0 1,2-1,8 ≤0,25 ≤0,15 The rest Fig. 1. Schematics ( a ) and the image ( b ) of the BFSW process with “bobbin tool” ( c ) a b c in Fig. 2), in the boundary sub-shoulder zone of the joint, and between the effect zones of the pin and the shoulder of the welding tool (BDR in Fig. 2), were selected for the study. Several cross sections of the welded joint were also studied (TD 1...3 in Fig. 2). For macro- and microstructure analysis, the samples were mechanically ground and polished, followed by chemical etching with Keller´s reagent (2 ml HF, 3 ml HCl, 5 ml HNO 3 , and 190 ml H 2 O) and examined with the Altami MET-1C optical microscope. Grain sizes were determined by the random secant line method. Microhardness measurements were performed according to GOST 9450-76 using the Duramin 5 hardness tester at a load of 50 gs. A four-sided diamond pyramid was used as an indenter. The data obtained were processed and visualized using the software package Origin.