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- Efect of Tool Rotational Speed on Microstructure and Mechanical Properties of Friction Stir Welded Al–16Si–4Cu–10SiC Composite/ Al–4Cu–Mg Alloy JointsPublication . Aval, Hamed Jamshidi; Galvão, IvanThis study investigates the effects of different rotational speeds on the friction stir welding process of two distinct materials: an Al-16Si-4Cu-10SiC composite and an Al-4Cu-Mg alloy. The research primarily concentrates on the microstructure, mechanical properties, and corrosion resistance of the welded materials. The findings reveal that surface grooves and tunnel defects emerge at heat inputs of 1296 and 3024 J/mm, respectively. When the rotation speed decreases from 1200 to 800 rpm, the Zener parameter increases from 12.45 x 1013 to 14.78 x 1014, and the average grain size after recrystallization reduces from 3.7 +/- 0.3 to 2.1 +/- 0.4 mu m. The welding process results in the formation of theta-Al2Cu and S-Al2CuMg precipitates in the stir zones of the Al-16Si-4Cu-10SiC composite and Al-4Cu-Mg alloy, respectively. A reduction in rotational speed from 1200 to 800 rpm leads to hardness, ultimate tensile strength, and corrosion resistance values of 149.8 +/- 10.1 HV, 401.4 +/- 8.1 MPa, and 0.39 mm/year, respectively.
- Influence of softening mechanisms on base materials plastic behaviour and defects formation in friction stir lap weldingPublication . S, SREE; Galvão, Ivan; Leitao, Carlos; Rodrigues, DulceThe AA6082-T6 and AA5754-H22 aluminium alloys were selected as the base materials to fabricate similar and dissimilar friction stir lap welds. Three lap configurations, AA6082/AA5754, AA5754/AA6082 and AA6082/AA6082, were produced using three pin profiles and tested to analyse the role of the plastic behaviours of the base materials on the welding conditions. The macrostructural characterisation was carried out to understand the material flow response and hook defect formation. The mechanical characterisation of the joints was done by microhardness and lap tensile shear testing. The finite element analysis and phase simulation were conducted to predict the phase dissolution temperatures and the softening kinetics. The welding torque and axial forces registered were analysed to quantify differences in the alloy’s flowability during welding. The analysis of the welding machine outputs enabled to conclude that higher axial forces were registered when the AA5754 alloy was placed at the top of the dissimilar lap joint, showing that the non-heat-treatable alloy has lower flowability than the heat-treatable alloy. These results were associated with the flow-softening of the AA6082 alloy in plastic deformation at high temperatures. The coupled experimental and numerical analysis revealed that the plastic behaviour of the base materials strongly influenced the material flow and, in this way, the hook defect formation and the shear tensile properties of the welds.
- Explosive welding of aluminium to stainless steel using carbon steel and niobium interlayersPublication . Carvalho, Gustavo; Galvão, Ivan; Mendes, R.; Leal, R. M.; Loureiro, AltinoThis work aimed to study aluminium to stainless steel explosive welds produced using two different interlayers: carbon steel and niobium. The use of each interlayer was analysed and compared microstructurally and mechanically using many characterisation techniques. The final joints using both interlayers presented favourable interfacial microstructure: waves on both interfaces. However, the joint using the carbon steel interlayer showed the best mechanical properties compared to the joints using the niobium interlayer. All interfaces found on both welds were wavy. However, depending on the metallic alloy combination, the shape of the wave is completely different. The results suggest that the shape of the waves is influenced by the shock impedance mismatch of the materials being welded. The impedance mismatch parameter (IMP) developed for explosive welding in this work proved to be a compelling method to order metallic combinations in a single axis to estimate the tendency to form typical or curled waves. Typical symmetrical waves tend to develop less quantity of IMCs than curled waves. However, the mechanical tests performed did not detect differences that could have been caused by this difference.
- Failure mode analysis of a 1.9 turbo diesel engine crankshaftPublication . Mateus, J.; Anes, Vitor; Galvão, Ivan; Reis, LuisThis paper reports a failure mode analysis of a 1900 cm(3) turbo diesel engine of a well-known commercial brand. The engine is a supercharged diesel engine with turbocharger, producing a maximum power of 81 kW; it was produced in 1999 and collapsed at 120,000 km without warning. A fracture occurred at the crankpin n degrees 1 of the crankshaft in the region of web-fillet. Crankshafts are mechanical power transmission components with complex geometries and experience multiaxial stress states in main journals and crankpins. The objective of this work is to determine the root cause that led to the crankshaft collapse. A fractographic, metallographic, and numeric analysis were performed to understand the crankshaft failure mode and its mechanical mechanisms. Results show that the crankshaft failure resulted from a fatigue process governed by normal stresses raised by two possible processes, namely, a notch in the crack initiation spot, or the crankshaft misalignment.
- Joining of fibre-reinforced thermoplastic polymer composites by friction stir welding—A reviewPublication . Pereira, Miguel A.R.; Galvão, Ivan; Costa, José D.; Amaro, A. M.; Leal, RuiThe objective of the current work is to show the potential of the friction stir welding (FSW) and its variants to join fibre-reinforced thermoplastic polymer (FRTP) composites. To accomplish that, the FSW technique and two other important variants, the friction stir spot welding (FSSW) and the refill friction stir spot welding (RFSSW), are presented and explained in a brief but complete way. Since the joining of FRTP composites by FSSW has not yet been demonstrated, the literature review will be focused on the FSW and RFSSW techniques. In each review, the welding conditions and parameters studied by the different authors are presented and discussed, as well as the most important conclusions taken from them. About FSW, it can be concluded that the rotational speed and the welding speed have great influence on heat generation, mixture quality, and fibre fragmentation degree, while the tilt angle only has residual influence on the process. The reduction of internal and external defects can be achieved by adjusting axial force and plunge depth. Threaded or grooved conical pins achieved better results than other geometries. Stationary shoulder tools showed better performance than conventional tools. Regarding the RFSSW, it has not yet been possible to deepen conclusions about most of the welding parameters, but its feasibility is demonstrated.
- Formation of intermetallic structures at the interface of steel-to-aluminium explosive weldsPublication . Carvalho, Gustavo; Galvão, Ivan; Mendes, R.; Leal, Rui; Loureiro, A.The formation of intermetallic structures at the interface of carbon steel to 6082 aluminium alloy explosive welds and their influence on the weldability of these two materials were studied. The morphology, the microstructure, the chemical and phase compositions of the welds were characterised by several types of microscopy techniques. The interface characterisation proved that explosive mixtures with a lower detonation velocity were revealed as being more suitable for achieving consistent welds since jet entrapment was prevented and continuous molten layers were not formed at the weld interface. It was also found that the physical properties of the intermetallic phases generated at the weld interface have a strong influence on the weldability of steel-to-aluminium explosive welds. Specifically, it was shown that the formation of aluminium-rich intermetallic phases at the weld interface increases the solidification time of the interfacial molten material, decreasing the weldability of these two materials. The formation of these intermetallic compounds should be avoided by reducing the interaction between the flyer and the baseplate as well as by avoiding excessive molten layers.
- Friction stir welding and explosive welding of aluminum/copper: process analysisPublication . Carvalho, G. H. S. F. L.; Galvão, Ivan; Mendes, R.; Leal, Rui; Loureiro, AltinoThe 6082 aluminum alloy was welded to copper-DHP by friction stir welding and explosive welding. The effect of each welding process on the microstructural evolution, the intermetallic phases distribution, and the mechanical behavior of both types of welds was analyzed and compared. The microstructural changes proved to be much more expressive in friction stir welding due to the larger area under plastic deformation, the stirring and mixing of the alloys, the longer time under high temperature, and the longer interaction times between the base materials during welding. As explosive welding process is much faster, it avoids extensive microstructural changes and significant interaction of the materials, reducing the intermetallic volumes and their distribution along the interface. The friction stir welds presented Cu-rich intermetallics while the explosive welds presented Al-rich intermetallics. For alloys that can easily form brittle intermetallic phases, excessive interaction during the welding process leads to a very poor mechanical behavior of the joints.
- Microstructural characterization and corrosion-resistance behavior of friction stir-welded A390/10 wt% SiC composites-AA2024 Al alloy jointsPublication . Aval, Hamed Jamshidi; Galvão, IvanThis study examined the effect of traverse speed on the mechanical properties, corrosion-resistance behavior, and microstructure of friction stir-welded A390/10 wt% SiC composites AA2024 Al alloy joints. The laminar flow of both materials was found to diminish in the stir zone (SZ) when the traverse speed of the tool increased from 40 to 80 mm/min, lowering their mixing rate. Large aspect ratio Si particles are broken by the tool pin-induced applied plastic strain, which turns them into refined equiaxed particles. Their aspect ratio remains unchanged in the SZ, despite their decreasing size. SiC and Si particles progressively come into view when moving from the AA2024 alloy’s SZ to the composite workpieces. These changes happen abruptly as traverse speed increases due to the lack of an interfacial layer structure. The advancing side (AS)’s SZ grain size drops from 4.2 ± 0.3 μm to 1.2 ± 0.2 μm as the traverse speed drops from 80 to 40 mm/min. Increased traverse speed from 40 to 80 mm/min will result in a 5.8% decrease in elongation percentage (EP) and 8.4%, 36%, and 10.3% increases in the ultimate tensile strength (UTS), corrosion resistance, and yield strength, respectively.
- Characterization of friction stir welded Al-4Cu-Mg alloy / Al-16Si-4Cu-10SiC composite jointPublication . Aval, Hamed Jamshidi; Galvão, IvanThis study investigated the tool’s rotational speed effect during dissimilar friction stir welding of A390–10 wt.% SiC composite-AA2024 aluminum alloy on microstructure, mechanical properties, and corrosion resistance. The results show that the tunnel defect is created on the advancing side at low rotational speeds of 400 and 600 rpm due to insufficient material flow and a high rotational speed of 1200 rpm due to turbulent material flow in the stir zone. Finely equiaxed recrystallized grains are formed in the stir zone under a high plastic strain rate and particle-stimulated nucleation mechanism. The minimum hardness occurs in the TMAZ of the AA2024 aluminum alloy side, and by increasing the rotational speed from 800 to 1000 rpm, the average hardness in the stir zone decreases from 146.06±8.67 to 137.86±3.98 HV0.1. Also, by increasing the rotational speed from 800 to 1000 rpm, the stir zone’s yield strength and ultimate tensile strength decrease by 4.9 and 5.2%, respectively. With the increased rotational speed from 800 to 1000 rpm, corrosion current increases from 0.0213 to 0.0225 mA.cm_2 and corrosion resistance decreases by 17 %. After friction stir welding with a rotational speed of 800 rpm and traverse speed of 20 mm/min, the corrosion resistance of the joint increases and decreases compared to the composite base metal and AA2024 aluminum alloy base metal, respectively.
- Influence of the structure and phase composition of the bond interface on aluminium-copper lap welds strengthPublication . Andrade, David; Galvão, Ivan; Verdera, David; Leitao, Carlos; Rodrigues, DulceThe structure and phase composition of the bond interface of aluminium-copper lap welds produced by friction stir welding and tool-assisted friction welding were analysed. Microstructural analysis proved that no through-interface material flow took place in tool-assisted friction welding and that aluminium-copper joining resulted from the formation of a thin and continuous intermetallic layer at the lap interface. For the welds produced by friction stir welding, evidences of through-interface material flow were found, promoting mechanical interlocking of both base materials, at the lap interface, and formation of discontinuous intermetallic layers. Mechanical testing showed that the tool-assisted friction welds, with excellent surface finishing, had low strength, contrary to the friction stir welds, which displayed excellent bond strength. The comparison of the mechanical and microstructural results, for both weld types, pointed to the ineffectiveness of the continuous intermetallic layer in providing high strength bonding.
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