Improving weld formability by a novel dual-rotation bobbin tool friction stir welding

doi:10.1016/j.jmst.2017.11.001

Abstract

Abstract:

A novel dual-rotation bobbin tool friction stir welding (DBT-FSW) was developed, in which the upper shoulder (US) and lower shoulder (LS) have different rotational speeds. This process was tried to weld 3.2 mm thick aluminum-lithium alloy sheets. The metallographic analysis and torque measurement were carried out to characterize the weld formability. Experimental results show that compared to conventional bobbin tool friction stir welding, the DBT-FSW has an excellent process stability, and can produce the defect-free joints in a wider range of welding parameters. These can be attributed to the significant improvement of material flow caused by the formation of a staggered layer structure and the unbalanced force between the US and LS during the DBT-FSW process.

Key words: Bobbin tool friction stir welding, Dual rotation, Material flow, Microstructure, Microhardness

F.F. Wang, W.Y. Li, J. Shen, Q. Wen, J.F. dos Santos. Improving weld formability by a novel dual-rotation bobbin tool friction stir welding[J]. J. Mater. Sci. Technol., 2018, 34(1): 135-139.

Figures/Tables 6

Fig. 1. (a) Details of the welding tool and (b) schematic of DBT-FSW.

Fig. 2. OM images of: (a) BT-FSW joint; (b) DBT-FSW joint; (c) typical void defect exhibited in BT-FSW; and typical microstructure on the AS of (d) DBT-FSW and (e) BT-FSW.

Fig. 3. Welding parameters windows of (a) BT-FSW and (b) DBT-FSW.

Fig. 4. (a) Layer structure at the run-out of the DBT-FSW joint; (b) measured torque of the welding tool; and illustration for material flow in (c) BT-FSW and (d) DBT-FSW.

Fig. 5. Microstructures in the SZ along the weld center line of DBT-FSW joint: (a) 0.2 mm; (b) 1.35 mm; (c) 1.81 mm; (d) grain size and fraction of HAGB.

Fig. 6. Microhardness distribution on the cross-section of typical DBT-FSW joint.

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