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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.
- 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.
- 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.
- Impact welding of materialsPublication . Galvão, Ivan; Loureiro, Altino; Mendes, RicardoRecent industrial criteria, focused on obtaining increasingly efficient structures, require the production of multimaterial components. However, the manufacturing requirements of these components are not met by conventional welding techniques. Alternative solid-state technologies, such as friction or impact-based processes, must be considered. Impact welding processes have the advantage of presenting a very short cycle time, which minimises the interaction of the materials under high temperature. This fact strongly contributes to reducing the formation of brittle intermetallic compounds (IMCs), i.e., one of the main concerns of welding dissimilar materials. Moreover, as the influence of the welding process is confined to a very narrow band around the materials interface, similar and dissimilar welds with high-strength bonding and a minimal heat-affected zone can be produced. The impact welding family encompasses different welding processes, such as explosion welding, magnetic pulse welding, vaporising foil actuator welding, and laser impact welding. Although these processes share the main operating principle, consisting of a high-velocity collision between a flyer and a target, they differ in the way the flyer is accelerated. These processes also present very different length scales, providing the impact welding family with a broad applicability range. The technical interest of impact welding is driving the ongoing development of many scientific studies, which are essential to optimise the current manufacturing processes by developing new welding strategies and solutions. The present special issue presents a sample of the cutting-edge research that is being conducted on the multidisciplinary field of impact welding.
- Microstructure and corrosion behavior of A390-10 wt% SiC composite-AA2024-T6 aluminum alloy dissimilar joint: Effect of post-weld heat treatmentPublication . Aval, Hamed Jamshidi; Galvão, IvanThe weldability of aluminum matrix composites to other materials, such as aluminum alloys, is an essential point in expanding the use of these materials. This study investigated the effect of rotational speed and post-weld heat treatment on the microstructure, mechanical properties, and corrosion behavior of A390-10 wt% SiC composite/ AA2024-T6 aluminum alloy dissimilar joint. Friction stir welding is performed using a square frustum pyramid pin tool with a rotational speed of 400–1200 rpm and a traverse speed of 40 mm/min. Results found that a surface groove formed on the weld crown at a rotational speed lower than 800 rpm due to insufficient material flow. Also, the tunnel defect formed on the advancing side at a rotational speed higher than 1000 rpm due to the turbulent flow of material. By increasing rotational speed from 800 to 1200 rpm, the average grain size of the advancing and retreating sides increased by 41.1 and 46.3 %, respectively. Compared to AA2024-T6 and A390-10 wt% SiC composite base metals, the average hardness of the stir zone of the joint fabricated by the rotational speed of 800 rpm increased by 8.4 and 38.2 %, respectively. By increasing the rotation speed from 800 to 1000 rpm, the yield strength and ultimate tensile strength decreased by 6.8 and 6.5 %, respectively. By decreasing rotational speed from 1000 to 800 rpm, the elongation and corrosion resistance decreased by 5.4 % and 34.7 %, respectively. After post-weld heat treatment, the hardness, yield strength, ultimate tensile strength, and corrosion resistance increase 15.9, 12.7, 7.8, and 28.9 %, respectively.
- Evaluation of tool rotational speed effect in Al-16Si-4Cu-10SiC composite/Al-4Cu-Mg alloy jointPublication . Jamshidi Aval, Hamed; Galvão, IvanThis study investigated the influence of the rotational speed of the tool with a cylindrical threaded pin on the microstructure, mechanical properties and corrosion resistance of the Al-16Si-4Cu-10SiC composite/Al-4Cu-Mg alloy joint. The results show tunnel defects are formed on the advancing side in the heat input less than 121 J/mm and more than 342 J/mm. With the increase of rotational speed from 800 to 1000 rpm, the silicon particle size and the aspect ratio have decreased and increased from 5.6 ±1.2 to 3.5±1.4 µm and 0.6 to 0.8, respectively. By decreasing rotational speed from 1000 to 800 rpm, the maximum hardness (152.3 ±0.6 HV0.1), yield strength (383±6 MPa), ultimate tensile strength (469±9 MPa) and corrosion rate (1.03 mm/year) were achieved.
- Recent developments in non-conventional welding of materialsPublication . Leal, Rui; Galvão, IvanWelding is one of the technological fields with the greatest impact in many industries, such as automotive, aerospace, energy production, electronics, the health sector, etc. Welding technologies are currently used to join the most diverse materials, from metallic alloys to polymers, composites, or even biological tissues. Despite the relevance and wide application of traditional welding technologies, these processes do not meet the demanding requirements of some industries. This has driven strong research efforts in non-conventional welding processes, such as laser welding, ultrasonic welding, impact welding, friction stir welding (FSW), diffusion welding, and many other welding technologies. Important studies have been recently developed all over the world on the application of these processes to the joining of cutting-edge materials and material combinations, enabling the production of joints with improved properties. Thus, this Special Issue presents a sample of the most recent developments in the non-conventional welding of materials, which will drive the design of future industrial solutions with increased efficiency and sustainability.