Details

Autor(en) / Beteiligte

• Chu, Q.
• Li, W.Y.
• Wu, D.
• Liu, X.C.
• Hao, S.J.
• Zou, Y.F.
• Yang, X.W.
• Vairis, A.

Titel

In-depth understanding of material flow behavior and refinement mechanism during bobbin tool friction stir welding

Ist Teil von

• International journal of machine tools & manufacture, 2021-12, Vol.171, p.103816, Article 103816

Ort / Verlag

Elmsford: Elsevier Ltd

Erscheinungsjahr

2021

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Bobbin tool friction stir welding (BT-FSW) is a promising solid-state welding process for fabricating closed or hollow profiles due to its self-supporting nature, which is achieved using a combined tool consisting of two shoulders and a penetrating pin, releasing the backing plate. The joint reliability is mainly affected by its macro-/micro-features including geometric defects and non-uniform grains. However, the underlying thermo-physical process has not been fully understood to clarify how the defects form and grains evolve during welding and how to control them. In this paper, a 3D thermo-mechanically coupled Eulerian-Lagrangian model was developed to analyze the material flow behavior and help understand the defect forming mechanism and recrystallization behavior during BT-FSW of aluminum alloy, wherein tracing particles were specially embedded. The calculated results revealed a complex material migration in the domain driven by the rotating tool. The flow behavior in horizontal/vertical directions at local regions was asynchronous, and eventually converged on the advancing side (AS) to normally form a sound joint, where the combined effects of shearing and squeezing of the material flow throughout thickness affected the morphology of S-line defect. In addition, the non-uniform thermo-mechanical cycling caused an abrupt change in grain structure near the TMAZ/SZ-AS transition region due to the combined continuous and discontinuous dynamic recrystallization, and geometrical effect of strain. The final joint failure was the result of competition between the two softening regions, S-line defect and TMAZ/SZ-AS. These can be applied for further fundamental investigation of parameter optimization or welding structure design, and promote the exploration of post-processing methods to improve the joint performance. [Display omitted] •Grain refinement was dominant by CDRX, together with geometrized requirement of strain and discontinuous recrystallization.•The flow behavior was non-simultaneous throughout the joint, with preferential movement near shoulders.•The convergence of multiple material flow strands seriously affected the macrostructural features and crystal orientation.•The incompatibility of plastic deformation exacerbated local stress concentration to boost fracture initiation.