Nanoparticles Addition Effect during Friction Stir Welding Of Al-Mmcs

Singh T

Published on: 2021-09-15


In recent years, automotive, marine, transportation, and aerospace sectors have demand for optimization of product design for lighter and high-performance materials. The need for weight reduction in such industries is to improve the fuel economy, increasing the capacity of payload, and meet the standards according to the policies of greenhouse gas emissions. The most effective way to achieve the goal of weight reduction without affecting the design performance is to use more advanced light materials. A large diversification of engineering light materials including aluminum, magnesium, and titanium alloys are available in the market. Considering its high strength to weight ratio and corrosive resistance, aluminum alloys are used widely for applications in the aerospace, transport, ship-building, and marine industries.


Nanoparticles; Communication satellites


From the last decade, the development of Metal-Matrix Composites (MMCs) as advanced material opens numerous ways and possibilities to produce lighter-weight structural components or parts [1,2]. Due to their high strength-to-weight ratio, high stiffness, high thermal conductivity, and high wear and corrosive resistance, the MMCs were adopted as a new alternative material to high strength aluminum alloys in aerospace structures, aero engines, and automobiles. The most common applications of MMCs are tubing on space shuttle orbiter fuselage, roller coasters braking systems, communication satellites, and door panels for automobile vehicles [3,4]. The major hurdle in the joining of MMCs is the size of MMCs welded parts and the degradation of mechanical properties when the fusion welding process is employed. This is due to the occurrence of chemical reactions between particles and molten metal matrix, decomposition of ceramic particles that leads to the formation of intermetallic undesirable brittle phases. Also, the non-uniform distribution of added particles in the base matrix limits the join ability of MMCs those results in insufficient welds strength [4]. Based on this, there is always a continuous push provided by the industries to use lighter material in MMCs that requires advanced joining techniques as Friction Stir Welding (FSW) (or solid-state welding technique) [3]. This process was patented and proven via experiments in The Welding Institute (TWI) in the UK in December 1991. FSW involves friction, adiabatic heat inputs, and plastic deformation which are the combination of extrusion-forging-shearing and solid-state diffusion. In this process, the non-consumable rotating tool plunges into the workpiece interface and moves along the joint line. Due to this action, the material gets soft (in the deformed plasticized state) which is further forged from forth to the front of the tool and induced joint in the solid-state condition without melting the workpiece to be joined [5-8]. Initially, FSW process was developed for joining aluminum alloys and was first employed by NASA to join space shuttle external tanks that are super light in weight [6]. Now, with the outgrowing development in FSW, it makes a suitable process to join AA2xxx, AA6xxx, and AA7xxx alloys those expected as impossible to join (non-weldable) using the fusion welding process [9,10]. Also, due to FSW's versatile nature, it is regarded as a viable process to join Metal-Matrix Reinforced Welds (MMRWs) for various high strength Al-alloys (AA2xxx, AA6xxx, and AA7xxx) [11-13]. Likewise, the dissimilar MMRWs with different metal combinations were also produced using FSW without much concern of compatibility in base materials compositions. This leads to the breakthrough factor in the conventional fusion welding process that helps to avoid the defects in the weld zones. Therefore, today's scenario demands to carry forward the current attention of the FSW process towards the fabrication and joining of welds using nanoparticles. Based on the existing research to join such materials using different welding processes, efficient and durable welds with less porosity, crack nucleation, weld distortion, and particle dissolution during the process can be produced when the FSW process is employed [14,1,2]. Moreover, the FSW process was also used to join structural and design parts of Falcon IX rockets, Delta IV, Altas V, and Orion crew exploration vehicles [3]. Aluminum alloys based FSW welds using nanoparticles are expanded as a new class of MMCs due to their low cost, high modulus, high wear resistance, high thermal conductivity, high stiffness, and high strength to weight ratio. This results in numerous benefits for different advanced applications in the aerospace, automobile, and transportation industries [15,16], But the issues related to the weldability of these materials when the fusion welding process is employed are the prime obstacles in developing interest in the aerospace industries. However, the narrow process window is the major hurdle during welding of such materials using FSW compared to Al-alloy which is due to the presence of particles incorporated into the base matrix. With the major development in the FSW process to join reinforced aluminum welds, the challenges remain with the appreciable progress in the current years [17-19]. The information related to the tensile properties, fractography, and wear behavior of aluminum-based nanoparticles reinforced FSW welds is minimal in the existing literature. This is attributed to the complex mechanical and microstructural behavioral phenomenon that occurred during the FSW process [19,20]. Moreover, the different process welding parameters (like tool rotational speed, traverse speed, tool geometry, and the power/load applied) combinations significantly affect the final joint properties.


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