Materials Science Forum Vols. 638-642

Abstract: Friction Stir Welding (FSW) induces thermal residual stresses resulting in distortions in thin-walled structures. In order to understand and quantify this phenomenon, simulations and experiments of FSW on aluminium alloy (AA) 2024-T3 have been performed using different rotational and welding speeds. A sequentially coupled finite element (FE) model was used to study the residual stresses caused by the thermal cycling induced from FSW. The 3D FE model used temperature-dependent mechanical and thermophysical material properties. The predicted longitudinal stresses peaked at ~300 MPa and had a ‘‘W’’ profile with tensile stress peaks in the weld and compressive stresses outside the weld. In the FE model, the influence of process parameters on residual stress distribution was studied. The application of ‘hot’ welding conditions, i.e. low welding speed and high rotational speed, increased the residual stresses significantly, mainly in the transverse direction. Conversely, ‘cold’ welding conditions resulted in lower residual stresses. The magnitude and distribution of the residual stresses predicted by the FE model were validated by neutron diffraction. The results indicate a good agreement between the measured and predicted residual stresses in AA2024-T3.

Abstract: Friction Stir Welding (FSW) is a solid-state joining process whereby no bulk melting of the base material occurs during joining. FSW avoids severe distortion and formation of as-cast coarse microstructure as well as defects arising from melting and solidification during traditional fusion welding processes. The objective of this investigation is to evaluate the effect of joining parameters on the mechanical and microstructural properties of dissimilar aluminium alloys (3 mm thick AA2024-T3 and AA7075-T6 sheets) joints produced by FSW. Microstructural features have been analysed; while mechanical performance has been investigated in terms of hardness and tensile testing. In both welding configurations the boundary between the base materials at the stir zone is clearly delineated, i.e., no material mixing is observed.

Abstract: Spot welding between Al alloy and some kinds of steels by friction stirring was conducted. In the process, a rotating tool was plunged into the Al alloy which was overlapped onto the steel plate, and held at the plunge depth for a few seconds with rotating condition. In this welding, friction stirring was adopted only inside of the Al alloy, and welding between Al alloy and steel is performed by an interaction of stirred Al alloy to the fixed steel surface. Mechanical strength of the joints was evaluated by both tensile shear test and cross tensile test. From the observation results on the microstructure of the weld interface, it was found that Fe/Al intermetallic compound with a few m thickness was formed at the interface. It was found that Zinc coated layer intrinsically has a role to protect the steel materials at a static condition, however, in the stirring condition of Al alloy, Zinc layer easily moved toward the outside of stirring zone and resultant fresh surface of the steel enables formation of the higher mechanical strength of the joint.

Abstract: The paper presents some aspects about the influence of the heat treatment’s parameters over the microhardness’s variation of a Bainitic S.G. Cast Iron at the end of an wear process. It was determinate the variation of the rapport () between the microhardness ( H) and the distance of the wear surface (l).

Abstract: Conventional welding methods, like resistance spot welding, are inefficient and difficult to apply to light alloys. Two alternative new solid state friction joining techniques, which have not yet been fully optimized, are high power Ultrasonic Spot and Friction Stir Spot Welding (USW & FSSW). Here we have compared the performance for these two processes for producing ‘keyhole-less’ welds in thin aluminium automotive closure panels. For friction stir spot welding this was achieved through using a novel ‘pinless’ tool to create a joint without a retained keyhole and reduce the weld cycle time. The properties of the welds that can be produced by each technique are compared, together with the stages of weld formation, and the relationship between welding conditions and joint performance.

Abstract: Friction stir spot welding (FSSW), developed based on principle of friction stir welding, has been paid attention as a new solid-state spot welding process. Since FSSW can produce high-quality weld in Al alloys more easily than resistance spot welding, this process has been already used for construction of Al components in the automotive industries. Despite the large industrial interests in FSSW, fundamental knowledge on welding phenomena of this process has not been fully understood. In this study, FSSW phenomena, such as the consolidation mechanism, the microstructural evolution and the material flow, were examined in Al alloy 6061. This study clarified that the elliptical zone found in the vicinity of the pin hole on the cross section was characterized by the initially lapped surface of two sheets. Moreover, the following material flow was proposed; capture of the upper material with the threads on the pin surface, spiral flow along the tool rotation, and then release at the tip of the pin.

Abstract: The formability of friction stir welded AZ31 magnesium alloy sheets was investigated by means of uniaxial tensile and hemispherical punch tests performed under different process conditions. The results of the tensile tests were analysed in terms of flow stress and ductility at different temperature and strain rate; the hemispherical punch tests, carried out at different temperatures, provided the limiting dome height. The formability of FSW-ed blanks was compared to the one exhibited by the base material in order to evaluate the quality of the welded joints.

Abstract: Friction Stir Welding (FSW) has been proven an excellent method for joining of non-ferrous alloys in several industrial areas. The introduction of industrial robots in FSW has extended the possibilities, now also including complex 3-dimesional structures to be joined. There is however issues regarding the robot system’s performance as well as how to really benefit from the extended flexibility features. This paper presents how the FSW robot system ROSIOTM is intended to be used to fully explore its potential usage in production and laboratory applications. This include presenting the system’s performance in a set of case studies, but also defining in which way this system may be a subject for increased productivity in FSW.

Abstract: Friction stir welding (FSW) is a complex thermo-mechanical process which produces wrought microstructure with microstructural gradients in grain size, grain orientation, dislocation density, and precipitate distribution. The type and degree of microstructural modification is a function of the particular alloy chosen, its initial temper, the tool design and corresponding weld process parameter window, and other variables like material thickness, size, fixturing, etc. Since the microstructural changes produced can dramatically affect resultant mechanical performance and corrosion response, a thorough understanding of the variables involved in those changes is needed. A design of experiments approach was used to study the effects of welding parameter selection on the microstructural changes wrought by FSW with two different sizes of the same FSW tool design. A combination of microhardness mapping and electrical conductivity testing was used to investigate potential differences. The importance of these factors and the means for characterizing them for developing standards and specifications are also discussed.

Abstract: Friction stir welding (FSW) has been generating interest in association with friction stir processing (FSP), a new technique that employs FSW tooling. In a recent study, this author investigated the excellent fluidity of aluminum alloy with FSP for creating metal matrix composites (MMCs) by the local dispersion of aluminum oxide particulate in aluminum alloy. In this study, two novel methods of property modifications, local reinforcement and local metallic foam of 6061 aluminum alloy by FSP, are proposed. Tungsten carbide (WC) particulate and SiC whisker reinforced aluminum alloy plate are produced for local reinforcement of 6061Al by FSP. FSP can also produce local aluminum composites containing titanium hydride (TiH2) particles. These results, which indicate the feasibility of producing local metallic foam by FSP, are discussed in terms of microstructure and mechanical properties.