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.

/pdf/friction-stir-welding-and-processing-3hu3ejo7ub.pdf

Friction Stir Welding and Processing

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

Sluggish diffusion in Co-Cr-Fe-Mn-Ni high-entropy alloys

The objective of this review is to study interfacial reactions between pure Sn or Sn-rich solders, and common base metals used in Pb-free electronics production. In particular, the reasons leading to the observed interfacial reactions products and their metallurgical evolution have been analyzed. Results presented in the literature have been critically evaluated with the help of combined thermodynamic–kinetic approach based on the concept of local equilibrium and microstructural knowledge. The following conclusions have been reached: Firstly, the formations of intermetallic compounds in solid/liquid reaction couples are primarily controlled by the dissolution processes of base metals. Other factors that need be considered are the thermodynamic driving force for the formation of intermetallic compounds, their structures and concentration profiles in liquid. Secondly, annealing of solder interconnections in solid state can drastically change the microstructures formed in the solid/liquid reactions, especially if only one of the components in the solder takes part in the interfacial reactions. Thirdly, additional elements can have three major effects on the binary reactions between a base metal and Sn: (i) they can increase or decrease the reaction/growth rates, (ii) the additives can change the physical properties of the phases formed, and (iii) they can form additional reaction products or displace the binary equilibrium phases by forming new reaction products. Finally, if the local stable or metastable equilibrium is established at the interface, stability information together with kinetic considerations can provide a feasible approach to analyze interfacial reactions, which can have significant impact on the reliability of soldered electronics assemblies.

Interfacial reactions between lead-free solders and common base materials

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

Effects of intermetallic compound on the electrical and mechanical properties of friction welded Cu/Al bimetallic joints during annealing

The joint properties of copper by friction stir welding

Interfacial reaction in steel–aluminum joints made by friction stir welding

Microstructural investigation of friction stir welded pure titanium

The joint characteristics of friction-stir-welded A356 alloys, especially concerning the improvement of mechanical properties at the weld zone, were observed with various FSW (friction stir welding) speeds. The microstructures of the weld zone are composed of SZ (stir zone), TMAZ (thermo-mechanical affected zone) and BM (base metal). The BM shows the hypoeutectic Al–Si dendrite structure. The microstructure of the SZ is very different from that of the BM. The eutectic Si particles are dispersed homogeneously in primary Al solid solution. TMAZ, where the original microstructure was greatly deformed, is characterized by dispersed eutectic Si particles aligned along the rotational direction of the welding tool. These regions are mainly formed at the advancing side and the upper region of the retreating side. The mechanical properties of the weld zone are greatly improved in comparison to that of the BM. The hardness of the weld zone shows more uniform distribution than that of the BM because some defects are remarkably reduced and the eutectic Si particles are dispersed over the SZ. The tensile strength of the SZ is also greatly elevated and shows over 178 MPa, i.e. almost 120% that of the BM. Therefore, the FSW is well applied to the joining of the cast Al alloys.

Seung-Boo Jung

Papers

Effects of intermetallic compound on the electrical and mechanical properties of friction welded Cu/Al bimetallic joints during annealing

The joint properties of copper by friction stir welding

Interfacial reaction in steel–aluminum joints made by friction stir welding

Microstructural investigation of friction stir welded pure titanium

The improvement of mechanical properties of friction-stir-welded A356 Al alloy