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

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

Fabrication, properties and application of porous metals with directional pores

Thermal plasma technology for the treatment of wastes: a critical review.

For different tool plunge downforces, the optimum FSW conditions of aluminum die casting alloy were examined. The higher the tool plunge downforce is, the wider the range of the optimum FSW conditions is. The following three different types of defects are formed, depending on the FSW conditions. (1) A large mass of flash due to the excess heat input; (2) cavity or groove-like defects caused by insufficient heat input; and (3) cavity caused by the abnormal stirring. As for the abnormal stirring, it is clearly seen that the shape of the top part on the advancing side in the stir zone is completely different. For this type of defect, the effect of the tool plunge downforce is small, though the size of the defect due to insufficient heat input significantly decreases with the increasing downforce.

Three defect types in friction stir welding of aluminum die casting alloy

The characteristics of the microstructures and mechanical properties of friction stir welds of 60% Cu–40% Zn alloy (60/40 brass) were investigated. The defect-free welds were obtained in a relatively wide range of welding conditions; the tool rotation speed ranged from 1000 to 1500 rpm with a welding speed from 500 to 2000 mm/min, and 500 rpm—500 mm/min. The microstructures of the welds yielded extremely fine grains with some deformed grains in the stirred zone (SZ) and elongated grains in the thermo-mechanically affected zone. The hardness values within the SZ in all welding conditions were much higher than those of the base metal, increased with a decrease in heat input. The generation of refined grains in the SZ was a main factor which caused the hardness increase associated with decreasing heat input. The strengths of the all-SZ showed relative correspondence to the variation of the hardness values in the SZ.

Microstructures and mechanical properties of friction stir welds of 60% Cu–40% Zn copper alloy

In order to clarify the formative mechanism of weld penetration in an arc welding process, the development of a numerical model of the process is quite useful for understanding quantitative values of the balances of mass, energy, and force in the welding phenomena because there is still lack of experimentally understanding of the quantitative values of them because of the existence of complicated interactive phenomena between the arc plasma and the weld pool The present article is focused on a stationary tungsten-inert-gas (TIG) welding process for simplification, but the whole region of TIG arc welding, namely, tungsten cathode, arc plasma, workpiece, and weld pool is treated in a unified numerical model, taking into account the close interaction between the arc plasma and the weld pool Calculations in a steady state are made for stationary TIG welding in an argon atmosphere at a current of 150 A The anode is assumed to be a stainless steel, SUS304, with its negative temperature coefficient of surface tension The two-dimensional distributions of temperature and velocity in the whole region of TIG welding process are predicted The weld-penetration geometry is also predicted Furthermore, quantitative values of the energy balance for the various plasma and electrode regions are given The predicted temperatures of the arc plasma and the tungsten-cathode surface are in good agreement with the experiments There is also approximate agreement of the weld shape with experiment, although there is a difference between the calculated and experimental volumes of the weld The calculated convective flow in the weld pool is mainly dominated by the drag force of the cathode jet and the Marangoni force as compared with the other two driving forces, namely, the buoyancy force and the electromagnetic force

A unified numerical modeling of stationary tungsten-inert-gas welding process

Dissimilar metal joining of aluminum to steel, which is difficult due to the formation of the brittle intermetallic compound at the interface of the welded joint, by DC pulsed MIG arc brazing in a lap joint with the flux cored Al-Si filler wire has been investigated for the application of the weight saving of automobiles. The major compound formed at the interface between steel and weld metal was determined to be Al 7.4 Fe 2 Si as the Al-Fe-Si ternary compound. The composition control of weld metal can suppress the growth of the intermetallic compound layer less than the thickness of 2.5μm. In this condition, the transverse tensile strength of the welded joint was about 80 MPa, 70 % of that of Al base metal due to the fracture at HAZ on the aluminum side. The mechanism of the suppressed growth of the intermetallic compound layer during MIG arc brazing has been discussed.

Dissimilar Metal Joining of Aluminum to Steel by MIG Arc Brazing Using Flux Cored Wire

Numerical modeling of free burning arcs and their electrodes is useful for clarifying the heat transfer phenomena in the welding process and to elucidate those effects which determine the weld penetration. This paper presents predictions for a stationary welding process by the free-burning argon arc. The whole region of the welding process, namely, tungsten cathode, arc plasma and stainless steel anode is treated in a unified numerical model to take into account the close interaction between the arc plasma and the molten anode. The time dependent development of two-dimensional distributions of temperature and velocity, in the whole region of the welding process, are predicted at a current of 150 A. The weld penetration geometry as a function of time is thus predicted. It is shown also that different surface tension properties can change the direction of re-circulatory flow in the molten anode and dramatically vary the weld penetration geometry.

Numerical Study of a Free-Burning Argon Arc with Anode Melting

In order to make clear the physical grounds of the potential drop in front of the anode, namely, the anode fall in atmospheric free-burning argon arcs, the results of experimental measurements of the laser-scattering method and Langmuir-probe method are presented. The experimental results show that the anode boundary layer at low arc currents such as 50 A remarkably deviates from local thermodynamic equilibrium (LTE), whereas the boundary layer at higher arc currents such as 150 A preserves a similar state to the LTE. The Langmuir-probe measurements also show that the anode fall for 50 A is positive, whereas that for 150 A is negative. From these results, an assumption regarding the physical state of the anode boundary layer in the free-burning argon arcs is presented synthetically and it is also concluded that the sign and magnitude of the anode fall in the arcs relate vary closely to the thermal state of the anode boundary layer and that the thermal state should be influenced strongly by the arc current density, namely, the electron number density.

Masao Ushio

Papers

Microstructures and mechanical properties of friction stir welds of 60% Cu–40% Zn copper alloy

A unified numerical modeling of stationary tungsten-inert-gas welding process

Dissimilar Metal Joining of Aluminum to Steel by MIG Arc Brazing Using Flux Cored Wire

Numerical Study of a Free-Burning Argon Arc with Anode Melting

Observations of the anode boundary layer in free-burning argon arcs