Papers by Author: Francesco Bellucci

Abstract: The durability of metal structures depends most upon the corrosion behaviour of its materials as well as the on the electrochemical behaviour of joints and the technology employed to construct the joints itself. This work describes the effect of Laser Beam Welding (LBW) technology on the electrochemical and corrosion behaviour of parent materials and bead of several aluminium alloy joints. Investigation was carried out by using dc electrochemical techniques (open circuit potential monitoring, OCP, and anodic polarization) on selected micro areas of parent materials and bead by means of a suitable electrochemical microcell. With regards to the corrosion behaviour of heat affected zone (HAZ), no data has been presented due to the small area of HAZ when compared to the microcapillary area adopted in this study. Alloys investigated in this work are the AA 2139 and AA 6156 as skin in the form of rolled sheets, and AA 2139 and PA 765 as stringer, in form of extruded parts. In addition, the AA 4047 has been used as filler material in form of wire. Results obtained in this investigation indicated that no major corrosion concerns arise from the LBW of both laminated AA 2139 skin with extruded AA 2139 stringer and laminated AA 6156 skin with extruded AA 2139 stringer. In the former case, the bead exhibits corrosion potential nobler than that exhibited by the skin and stringer of circa 100 mV for the AA 6156 skin with extruded AA 2139 joint. This result is attributed to the presence of Si in the bead due to the process parameters adopted for such a weld. Quite similar corrosion behaviour was observed for the skin, stringer and bead in the latter case. Attention must be paid when laminated AA 2139 skin with extruded PA 765 stringer, and laminated AA 6156 skin with extruded PA 765 stringer are joined by LBW. In this case low potential and high surface activity were observed on the stringer and bead and attributed to the excess of Zn in the PA 765 alloy.

Abstract: Laser beam welding of light alloys has always represented a big challenge for both designers and technologists due to the large number of process parameters to take into account and the variable responses of the different materials to be welded. In this paper the results of experimental research on laser beam welds of innovative heat treatable aluminum alloys is reported. The well known T geometry (a stringer welded to a skin) has been considered. Two different skins have been analyzed: AA 2139 and AA 6156, both in form of rolled sheets. Two different stringer have been analyzed: AA 2139 and PA 765, both in form of extruded parts. AA 4047 has been used as filler wire. In the first part of the paper, all the steps leading to the realization of sound welds will be described. The criteria used in order to assess the soundness of a weld was the absence of defects, such as cracks or large pores, verified by means of NDE. In the second part of study, both micro structural analysis and mechanical characterization of welds will be described and discussed. Conclusions will demonstrate the importance of the influence of chemical composition of the parts, above all stringer. The performance of the best welds, however, were very close to those of parent materials.

Abstract: The current research has assessed the correlation between welding parameters and corrosion behaviour for friction stir welded 6056 aluminium alloy. Different thermal treatments and welding parameters were considered. For the welding parameters studied in this project, the data strongly indicate that sensitivity to corrosion is linked to the welding parameters employed. Substantial differences were found for the higher and lower speed welding parameters, with the lower speed parameters appearantly resulting in less corrosion resistance. The most widespread form of corrosion observed was pitting; however, intergranular corrosion (IGC) was also seen. While the T78 thermal treatment appears to decrease the corrosion resistance of the parent alloy, the weld region tends to improve, with the nugget being cathodic.