Browsing by Author "Sousa, V. F. C."
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- A comparative study of heat-treatment effects on high-strength ductile cast irons weldmentsPublication . Silva, Francisco José Gomes da; Sousa, V. F. C.; Pereira, A. B.; Fecheira, J. S.Ductile cast irons have known significant developments, closely following the evolution in mechanical strength recorded in other metal alloys. In fact, the chemical composition and treatments that ductile cast irons can currently be subjected to, give them mechanical strength far superior to the ductile cast irons that existed three decades ago, with rupture stresses in the order of 500 MPa and even higher. These properties combined with the fact that it is easy to manufacture parts with an almost final shape, makes these alloys highly sought after in some types of industry, such as the automotive industry. Due to the high content of carbon and other alloy elements with identical effects, welding is not a process that is seen as viable for the manufacture of parts in this type of alloys. However, the same is no longer the case in terms of repair, where welding can play a key role. Through a comparative study, this work intends to show that there is no single way to improve the mechanical properties in the welding of this type of alloys, and that each alloy should be properly studied in order to obtain the best results. In this case, the heat treatments applied to ductile cast iron with an ultimate tensile strength of 450 MPa and 700 MPa from the same manufacturer are compared, making it clear that to achieve the best results in terms of mechanical resistance, it is necessary to follow different routes, that is, choose to preheating or post-heating treatments, depending on the microstructure of the alloy used. Thus, the results obtained intend to show the mechanisms in which treatment is actually acting on the alloy, promoting greater efficiency of the joint and having been achieved interesting results at this level.
- Recent developments on friction stir welding of aluminium alloys: a comprehensive reviewPublication . Silva, Francisco José Gomes da; Pereira, A. B.; Fecheira, J. S.; Sousa, V. F. C.Friction stir welding is a relatively new joining technology, that has been succefuly applied in the connection of large and complex structures, with considerable progress being made throughout time. The development of this new solid-state welding technique has opened up new possibilities for joining similar and dissimilar materials, allowing the obtention of extremely interesting mechanical properties. This welding technique becomes even more interesting when applied to materials that are traditionally considered difficult to weld by conventional fusion methods. As it is well known, despite the fact that aluminum alloys have a low melting point, these are difficult to weld due, mainly, to their high thermal conductivity, requiring relatively high amounts of energy, wich can interfere with the low melting temperature of the alloys. Thus, numerous studies have been carried out around the Friction Stir Welding (FSW) process in various different alloys, however, given the intensive use of aluminum alloys in the most diverse sectors, these have deserved special attention by the researchers. In this chapter, the welding of different aluminum alloys with different process parameters and their influence on mechanical property of the joints are analyzed. This review intends to describe, in a structured way, the most recent developments around FSW of aluminium alloys, with special attention given to the microstructure and mechanical properties of the joints obtained by this process, as well as the parameters able to achieve the best joint properties.