Papers by Author: Altino Loureiro

Abstract: Friction Stir Processing (FSP) is a relatively new post-processing technique. Fatigue strength of MIG fillet welds of aluminium alloys can be substantially improved using FSP. Beyond other properties intrinsically tied to fatigue life, especially attention should be paid to the effect of the final residual stress state. In this study the residual stress distribution in T-joints of two aluminium alloys was determined by Neutron and X-ray diffraction. FSP effect on the residual stress state and fatigue life was analysed.

Abstract: In this study friction stir welding of Al-Cu laminated composites were carried out by two different tool geometries. Welding procedure was carried out from both sides of Al and Cu. Analyzing cross section of welds showed that different contact conditions between shoulder and material, offers different material flow behavior which is dependent on the tool geometry. SEM analyses showed that mixing of materials in nugget region is more pronounced in the advancing side. Also XRD results indicated that welding from Cu side, leads to intermetallic formation in mixed regions.

Abstract: The samples studied in this paper were performed from carbon steel plates, cladded in one of the faces with stainless steel filler metals by submerged arc welding (SAW). After cladding work, the samples were submitted to post-weld heat treatments at different conditions and afterwards stainless steel coating surfaces were milled and mechanically polished, as in the industrial application. The residual stress analysis was performed by X-ray diffraction (XRD) and incremental hole-drilling methods (IHDM). The residual stresses profiles presented different in depth values in each sample, depending on the heat treatment conditions. The hole-drilling method was applied in several points of each stainless steel sample surface and the results presented similar evolution profiles. However compressive stresses increase with the increase of heat treatment temperature.

Abstract: Friction Stir Processing (FSP) is an innovative solid-state processing technology, which is being currently used to enhance locally the mechanical properties of conventional materials. In this work, 1 and 3 mm-thick copper-DHP plates were processed with the aim of simulating surface (SFSP) and bulk (VFSP) processing. The influence of the processing conditions on the microstructure and mechanical properties of the processed materials was analyzed. It was found that the tool geometry, which has a close relation with the plastic deformation and dynamic recrystallization kinetics inside the stirred volume, the processing parameters and the heat exchange conditions, which determine the extent of dynamic recrystallization and annealing phenomenon, are determinant in FSP.

Abstract: The influence of the heat treatment on the residual stress fields of weld cladded samples is discussed in this paper. The samples were elaborated from carbon steel plates, cladded in one of the faces with stainless steel filler metals by submerged arc welding. After the cladding process some of the samples were submitted to heat treatments with different parameters: one at 620° C for a holding time of 1 hour and the other at 540° C for a period of ten hours. The in‑depth residual stress profiles were determined by neutron diffraction. The results shown that the sample treated to 620 °C, presented the highest residual stress relaxation. The corresponding heat treatment has the industrial benefit to be shorter than the other heat treatment.

Abstract: The task of obtaining suitable welding parameters for the friction stir welding process is often a difficult one, due to the lack of published data and the fact that the exact mechanism by which the process operates has not yet been fully determined. Therefore, suitable welding parameters often need to be obtained by using extensive, time consuming and expensive experimental methods. The work detailed in this paper pertains to the use of the Taguchi method as a mean to reduce the disadvantages of these experimental methods, more specifically, their cost. The Taguchi method accomplishes this task by substantially reducing the number of welding trials that are needed to obtain suitable welding parameters. This reduction leads to the parameters being obtained more rapidly and at a substantially smaller cost. In this paper a procedure for applying the Taguchi method to the friction stir welding process is presented as well as its application to the welding of a specific component. The method was applied to the welding of 4mm thick AA5083-H111 plates in a butt joint configuration, which constitutes one of the most common industrial welding scenarios. The purpose of the experimental tests was to maximize the welding speed whilst ensuring an acceptable welding quality. The quality of the welds was determined through visual inspection and tensile and bending tests. The application of the Taguchi method allowed, with a relatively small number of experimental welds, to provide some insight into the manner by which the parameters should be altered in order to optimize the process.

Abstract: The aim of present research was to study the effect of the position of the tool relative to the support backing plate of the FSW machine on the formation of defects and on alterations of the microstructure and mechanical properties of friction stir welds in phosphorus-deoxidised copper (Cu-DHP) thin sheets of 1 mm thick. The welds were carried out using position control conditions; distances between the tool and the backing plate of 0.1 mm, 0.075 mm and 0.05 mm were used. The formation of defects like continuous voids along the weld is very influenced by the tool position, though the heat-input plays an important role in the process. Large grain refinement was observed in the nugget of the welds; the change of the relative tool position has little effect on this grain refinement. Substantial hardening was observed in the thermomechanically affected zone (TMAZ) of the welds. The welds exempt of defects, such as continuous voids, attained a little tensile strength overmatch condition.

Abstract: Friction Stir Welding (FSW) is a relatively young technology in the field of welding. Its process parameters and their influence on weld quality are currently the topic of intense research. Present work focuses on the influence of the tool plunging force on the mechanical properties, microstructure and surface finish of friction stir welds. Three welds have been produced using the same tool rotation and traverse speed and different tool dimensions and plunging forces. Visual inspection, optical and scanning electron microscopy were undertaken to assess surface and dimensional features as well as to study microstructure. Bend, hardness and tensile tests were carried out to characterise the weld strength. Taken into account the plunging force values of the conducted welds, a relationship between weld properties and calculated welding pressures was created. Favourable welding pressure values are recommended.

Abstract: The mechanical behaviour of homogeneous and inhomogeneous FSW aluminium tailored blanks is analysed in this paper. The heterogeneity in mechanical properties across the different weld zones is discussed based on hardness testing results. Tensile and formability test results are also shown and the mechanical behaviour of the welds is discussed in relation to the base materials. Despite the hardness tests have indicated very small differences in hardness, between the welds and the base materials, and the tensile test results also showed similarities in mechanical behaviour, the formability tests revealed additional difficulties in forming the welded sheets.

Abstract: The aim of this research is the development of activating fluxes to improve weld bead geometry and increase weld penetration depth in austenitic stainless steels. The effect on bead geometry of two home-made fluxes, composed of titanium and aluminium oxides, was studied, in combination with two shielding gases, respectively Argon and an Argon/Helium mixture. A significant increase in penetration was obtained in welds done with the Ti based activating flux across the whole range of welding currents for both shielding gases, which was not the case for welds performed with the Al based flux. A decrease in δ-ferrite content in the weld metal with increasing current was observed only in welds done with the Ti based flux.