Friction Stir Welding of Al-B 4 C Composite Fabricated by Accumulative Roll Bonding: Evaluation of Microstructure and Mechanical Behavior Alireza Moradi Faradonbeh, Morteza Shamanian, Hossein Edris, Moslem Paidar, and Yahya Bozkurt (Submitted July 16, 2017; in revised form October 27, 2017) In this investigation, friction stir welding (FSW) of Al-B 4 C composite fabricated by 10 cycles accumulative roll bonding was conducted. In order to investigate the influences of pin geometry on microstructure and mechanical properties, four different pin geometries (cylindrical, square, triangular and hexagonal) were selected. It was found that FSW parameters had a major effect on the fragmentation and distribution of reinforcement particles in stir zone. When the tool travel speed was increased, the distribution of B 4 C particles was become gradually uniform in the aluminum matrix. The effect of tool rotational speed on the peak temperature was determined to be greater than the tool travel speed. The attained data of tensile properties and microhardness tests showed that the tool travel speed had bilateral effect on the tensile strength. The maximum tensile joint efficiency was obtained as 238% for FSWed of Al-2%B 4 C composite to annealed base Al sheet. Keywords accumulative roll bonding, friction stir welding, peak temperature, pin geometry, tensile strength, tool rotational speed 1. Introduction Metal matrix composites (MMCs) are considered in some critical applications such as aerospace and automotive indus- tries due to their good mechanical, thermal and tribological properties. Among these materials, aluminum matrix compos- ites (AMCs) are very attractive because of their low density, high specific strength, high specific stiffness and high wear resistance. In addition, the utilization of AMCs in cars and other vehicles can reduce the fuel consumption and exhaust gas release due to their high strength to weight ratio (Ref 1, 2). Accumulative roll bonding (ARB) is a unique solid-state process, which can be used to produce particle-reinforced metal matrix composites. During ARB, two or more sheets of metals are roll-bonded to a reduction of 50% after appropriate annealing and surface treatments. This produced roll-bonded sheet is cut into the same sheets, and then the ARB process is repeated for required times (Ref 3). In addition to the application of the ARB for MMCs, the fact that ARB causes severe plastic deformation in metals has made it as a promising candidate for production of ultrafine-grained metal matrix composite (Ref 4). According to these good properties of the ARBed materials, there will be an increasing demand to weld them for different applications. Fortunately, FSW has been proved by some researchers to be a promising process to weld the different ARBed materials. FSW was originally developed for joining low melting temperature materials, such as difficult-to-fusion weld Al alloys, in early 1990s by the Welding Institute. This relatively new joining technique is widely considered to be one of the most significant welding techniques to emerge in the last 30 years (Ref 5). In addition, it is a green technology because of its energy efficiency, environment friendliness and adapt- ability (Ref 6). During FSW, a rotational tool travels along the welding line and severe plastic deformation in conjunction with frictional heating results in a solid-state joint. It is a novel welding procedure that has proved its great potential in welding materials, which are conventionally difficult to join (Ref 7). Some research groups have investigated the FSW of the ARBed materials in recent years (Ref 8-12). Topic et al. (Ref 9) studied the effect of FSW on the microstructure and mechanical properties of the ARBed commercial-purity aluminum AA1050 and aluminum alloy AA6016. They revealed that the ultrafine- grained materials showed softening in the SZ of the joints, although the hardness of this area was similar to the conven- tionally grained aluminum sheets. Sato et al. (Ref 10) applied FSW to join an ARBed Al alloy 1100. They showed that FSW reproduced fine grains inside the SZ due to dynamic recrys- tallization, and hence it successfully prevented the softening in the ARBed alloy. Hosseini et al. (Ref 11) compared the effect of FSW media, i.e., air and underwater, on the microstructure and mechanical properties of the ARBed Al alloys. They observed that the hardness and tensile properties of the joints welded at underwater media and ARBed alloy showed more similarity compared to the joints welded in air. This was due to the formation of the finer grains and subgrains in the underwater condition. Although there have been some investigations on the effect of FSW of ARBed alloys such as indicated in Ref (9-11), the studies on the AMCs reinforced with B 4 C particles are very Alireza Moradi Faradonbeh, Morteza Shamanian, and Hossein Edris, Department of Materials Engineering, Isfahan University of Technology, Isfahan 8415683111, Iran; Moslem Paidar, Department of Materials Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran; and Yahya Bozkurt, Department of Metallurgy and Materials Engineering, Faculty of Technology, Marmara University, Goztepe Campus, 34722 Istanbul, Turkey. Contact e-mail: m.paidar@srbiau.ac.ir. JMEPEG ÓASM International https://doi.org/10.1007/s11665-018-3131-2 1059-9495/$19.00 Journal of Materials Engineering and Performance