There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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

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

Friction stir welding (FSW) is a widely used solid state joining process for soft materials such as aluminium alloys because it avoids many of the common problems of fusion welding. Commercial feasibility of the FSW process for harder alloys such as steels and titanium alloys awaits the development of cost effective and durable tools which lead to structurally sound welds consistently. Material selection and design profoundly affect the performance of tools, weld quality and cost. Here we review and critically examine several important aspects of FSW tools such as tool material selection, geometry and load bearing ability, mechanisms of tool degradation and process economics.

Review: friction stir welding tools

Surface composites by friction stir processing: A review

Rapid formation of the sigma phase in 304 stainless steel during friction stir welding

Friction stir welding (FSW) was applied to 3 mm-thick Ti–6Al–4V plates under different rotational speeds. Defect-free welds were successfully produced at rotational speeds of 400 and 500 rpm. The base material (BM) had a deformed α/β lamellar microstructure. FSW produced a full lamellar structure with refined prior β grains in the SZ, while the HAZ contained a bimodal microstructure consisting of the equiaxed primary α and α/β lamellar structure within the prior β structure. An increase in rotational speed increased the sizes of α colonies and prior β grains. The SZ exhibited higher hardness than the BM, with the lowest hardness found in the HAZ. Results of the transverse tensile test showed that all welds fractured in the HAZ and that they exhibited lower strength and elongation than the BM. The tensile test for only the SZ showed it to be characterized by higher strength and elongation than the BM.

Microstructural characteristics and mechanical properties of Ti-6Al-4V friction stir welds

In the present study, friction stir welding was applied to commercial purity titanium using a polycrystalline cubic boron nitride tool, and microstructure and hardness in the weld were examined. Additionally, the microstructural evolution during friction stir welding was also discussed. The stir zone consisted of fine equiaxed α grains surrounded by serrate grain boundaries, which were produced through the β → α allotropic transformation during the cooling cycle of friction stir welding. The fine α grains caused higher hardness than that in the base material. A lath-shaped α grain structure containing Ti borides and tool debris was observed in the surface region of the stir zone, whose hardness was the highest in the weld.

Stir zone microstructure of commercial purity titanium friction stir welded using pcBN tool

Corrosion resistance of friction stir welded 304 stainless steel

The present invention is a cooling plate including a groove, which becomes a passage of a coolant, inside a body, wherein one or more fins are provided inside the groove, wherein the groove is covered with a lid having width larger than the groove, wherein the lid is joined to the body by friction stir welding, and wherein a weld bead formed by: the joining is outside the passage, and the weld bead formed by the joining is formed within the body and further, is characterized by a manufacturing method of a cooling plate that has a first groove, which becomes a passage of a coolant, and a second groove, which has width larger than the first groove and receives a lid on the first groove, inside a body, receives the lid on the second groove, and is joined to the body, the manufacturing method of a cooling plate wherein, while the lid and the body are joined together by the friction stir welding owing to insertion of a-rotation tool having a shoulder and a pin, the joining is performed so that a weld bead formed by the joining may become out of the passage, and furthermore, is characterized in that a target for sputtering is joined to the cooling plate.

Satoshi Hirano

Papers

Rapid formation of the sigma phase in 304 stainless steel during friction stir welding

Microstructural characteristics and mechanical properties of Ti-6Al-4V friction stir welds

Stir zone microstructure of commercial purity titanium friction stir welded using pcBN tool

Corrosion resistance of friction stir welded 304 stainless steel

Cooling plate and manufacturing method thereof, and sputtering target and manufacturing method thereof