Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. In particular, it can be used to join high-strength aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding. FSW is considered to be the most significant development in metal joining in a decade. Recently, friction stir processing (FSP) was developed for microstructural modification of metallic materials. In this review article, the current state of understanding and development of the FSW and FSP are addressed. Particular emphasis has been given to: (a) mechanisms responsible for the formation of welds and microstructural refinement, and (b) effects of FSW/FSP parameters on resultant microstructure and final mechanical properties. While the bulk of the information is related to aluminum alloys, important results are now available for other metals and alloys. At this stage, the technology diffusion has significantly outpaced the fundamental understanding of microstructural evolution and microstructure–property relationships.

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Friction Stir Welding and Processing

Recent advances in friction-stir welding : Process, weldment structure and properties

The comprehensive body of knowledge that has built up with respect to the friction stir welding (FSW) of aluminium alloys since the technique was invented in 1991 is reviewed The basic principles of FSW are described, including thermal history and metal flow, before discussing how process parameters affect the weld microstructure and the likelihood of entraining defects After introducing the characteristic macroscopic features, the microstructural development and related distribution of hardness are reviewed in some detail for the two classes of wrought aluminium alloy (non-heat-treatable and heat-treatable) Finally, the range of mechanical properties that can be achieved is discussed, including consideration of residual stress, fracture, fatigue and corrosion It is demonstrated that FSW of aluminium is becoming an increasingly mature technology with numerous commercial applications In spite of this, much remains to be learned about the process and opportunities for further research a

Friction stir welding of aluminium alloys

Microstructural investigation of friction stir welded 7050-T651 aluminium

https://apps.dtic.mil/sti/pdfs/ADA414407.pdf

Continuous dynamic recrystallization during friction stir welding of high strength aluminum alloys

Microstructural aspects of the friction-stir welding of 6061-T6 aluminum

Residual microstructures, including dynamic recrystallization and grain growth structures and a wide range of precipitation phenomena associated with a friction-stir-weld in a thin 6061-T6 aluminium plate have been systematically investigated utilizing light metallography and transmission electron microscopy. In this rather remarkable process, a hard steel head pin rotating at 400 r.p.m. was advanced into a solid 6061-aluminium plate at a traverse velocity of approximately 2 mm s−1 to produce a solid-phase weld in its trailing side. Maximum work-piece temperatures did not exceed 425°C and there was no melt evidence. Dynamic recrystallization associated with the solid-state plastic flow therefore seems to provide the process mechanism. Weld zone hardnesses averaged roughly 55 Vickers hardness number (VHN) in contrast to the base plate or work-piece hardness of 110 VHN. Precipitation microstructures ranged from continuous to discontinuous coherent zones (∼2 nm thick) coincident with {1 0 0} planes, semicoherent and non-coherent needles and plates characteristic of Widmanstatten structures coincident with {1 1 0} planes, and a range of homogeneous precipitate particles often intermixed with these microstructures in the effective heat-affected zone (HAZ′) connecting the friction-stir-weld zone with the unaltered work piece microstructures. © 1998 Chapman & Hall

A TEM study of precipitation and related microstructures in friction-stir-welded 6061 aluminium

Dynamic recrystallization in friction-stir welding of aluminium alloy 1100

The microstructures of friction-stir welded aluminum alloys (1100 and 6061) are dominated by dynamic recrystallization. Friction-stir welding of 6061 aluminum to copper produced a complex, intercalated microstructure which was also dominated by dynamic recrystallization. The friction-stir welding process is characterized by extreme plastic deformation in the solid state; there is no associated melting.

Friction-stir welding: microstructural characterization

In order to obtain the pure shear deformation characteristics along the circumferential direction of tubes, a circumferential shear test for thin-walled tubes is proposed in this paper. The experimental device consists of a tubular sample and two cylindrical mandrels with shear plates. The torque along the circumferential direction was applied to the tubular sample by the two shear plates to make the pre-set shearing zone of the sample under a circumferential pure shear stress state. The two cylindrical mandrels support the inner wall of the tube to avoid buckling so that the pure shear stress state can be maintained during the whole deformation process. A 5052 aluminum alloy tube with an outer diameter of 50 mm and a wall thickness of 1.2 mm was used in the test. It is shown through simulation and experiment that shear deformation is concentrated in the pre-set shearing zone. This test can be used to obtain the circumferential pure shear stress-strain relationship.

G. Liu

Papers

Microstructural aspects of the friction-stir welding of 6061-T6 aluminum

A TEM study of precipitation and related microstructures in friction-stir-welded 6061 aluminium

Dynamic recrystallization in friction-stir welding of aluminium alloy 1100

Friction-stir welding: microstructural characterization

Circumferential pure shear test of thin-walled aluminum alloy tubes