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Metal matrix composites (MMCs) are known for their enhanced properties like stiffness, strength and wear resistance. Aluminium alloys reinforced with ceramic particles were found to exhibit isotropic behaviour and offer the advantage of being processed by conventional secondary routes (Torralba et al., 2003). Fusion welding methods were found to create grain growth and unnecessary metallurgical modifications. The undesirable matrix-reinforcement reactions at elevated temperatures lead to joints of poor quality. Furthermore, the fusion zone was susceptible to hot cracking, leading to degradation in strength. An expanded application of these MMCs is not possible without proper solution to the problems concerned with their joining. The solution to problems encountered in fusion welding could lie in a solid state joining technique like friction welding (FW) which involves temperature well below the melting point of parent metal. In FW, coalescence is produced by the heat flux generated due to the rubbing action between two surfaces of parent material.
Continuous drive friction welding employs rotation of one part against a static part to produce sufficient thermal flux at the interface. An additional pressure (axial pressure) is applied to facilitate plastic flow of material at interface to form the joint. Ferritic stainless steel (AISI430) was normally difficult to weld but could be joined successfully by friction welding. The joints were found to possess good tensile strength comparable with that of parent material. However the tensile failures were observed mainly in the weld interface region (Sathiya et al., 2007). AISI 1040 specimens were joined successfully by continuous drive FW and the strength of joints were found out using tension test (Akata and Sahin, 2003). Inertia radial FW could be used to join H90 Brass with D60 Steel rods as large as 157 mm in diameter (Luo et al., 2012). The microhardness observed in weld zone was higher than that of the parent (Celik and Ersozlu, 2009). The friction welded joints between aluminium alloy and 2124Al/SiCp composite were also investigated to study the effects of reinforcements on the strength of dissimilar joints (Ceschini et al., 2010). The AISI 1030 steel could also be joined with SiC reinforced aluminium alloy using continuous drive FW. Build-up of alloying elements observed at the interface of bonds between aluminium and stainless steel was detected as an important reason for the poor strength of bonds. However selection of optimal parameters could avoid such poor bonds (Ç̧elik and Gunes, 2012). FW was found to produce good joints with AA7075-T6 alloy and the welding parameters like friction pressure, speed and burn-off length were identified as the noteworthy parameters affecting the bond strength. A substantial amount of difference in flash was observed in all the joints (Khalid Rafi et al., 2010).
The variation in welding parameters like rotational speed, upset pressure and burn off length were found to affect the mechanical properties of joints and its microstructure in case of friction welded dissimilar joints. The properties of these joints were found to be influenced significantly by frictional pressure (Ananthapadmanaban et al., 2009). The interaction between frictional pressure and speed was found to affect the interface temperature and hence the quality characteristics of joint. Similar effects were observed during the dissimilar metal joints formed between austenitic and ferritic stainless steels (Sahin, 2010). Selection of proper welding parameters was essential to form good bonds with dissimilar materials, however post weld heat treatment becomes essential to relieve the effects of strain hardening (Hazman et al., 2010). The friction welded bonds were observed to fail mainly in the thermo mechanically affected zone during tension test (Deya et al., 2009). Rotational speed was found to be significant in determining the properties of bonds between alumina-6061 and aluminum samples and the extent of deformation was observed to be more on aluminium alloy than on the alumina part (Meshram et al., 2007). However upset pressure was identified as an important parameter affecting the properties of bonds between 6061-T6 aluminium and AISI 1018 steel (Rotundo et al., 2010).