Fabrication of Multilayer Al/Al-B4C/Al composite by High Pressure Torsion (HPT) Process

Al based metal matrix composites (Al MMCs) are being considered as a group of new advanced composites due to their specific features such as light weight, high strength, high specific modulus, low coefficient of thermal expansion and good wear resistance. A modern type of these advanced composites, which is an interesting field of study for researchers, is multilayer composites. Because of the capability of multilayer composites to be engineered for getting specific characteristics from each layer, in recent years the researchers are focused on this type of composites.Severe plastic deformation (SPD) methods like accumulative roll bonding (ARB) and cold roll bonding (CRB), have been noticeably successful in fabricating multilayer structures. High Pressure Torsion (HPT) has also been introduced as a SPD technique with high potential for fabricating powder based composites, new alloying systems, ultra-fine grain materials (UFG) and also multilayer composites.In this study we’ve developed a new type of Al based multilayer composite consisting of two disks of bulk Al-1050 alloy as outer layers and Al/B4C composite powder as a middle layer between the disks. This complex structure was consolidated by HPT under the applied pressure of ≈2GPa for 1, 3 and 5 turns of high pressure torsion. Microstructural observations showed a cold diffusive bonding between the layers. SEM images indicated that in comparison with 1 and 3 turns of process, there is more homogenous distribution of B4C particles in Al matrix for the specimen endured 5 turns of HPT. Mechanical tests like tensile test and micro hardness was applied to evaluate mechanical properties of the fabricated specimens. Results showed a high tensile strength for the specimen processed under 5 turns of HPT. It has also been shown that, high contents of B4C resulted in weaker bonding strength between the layers in comparison with low contents.