Study On Properties Of TiAl₃ Particle Reinforced Al Matrix Composites Fabricated By Combined Accumulative Roll-bonding

Particle reinforced aluminum matrix composites(PRAMCs)are widely used in aerospace and automobile industries due to their high specific strength and modules and good oxidation resistance.Achieving a high-volume fraction of reinforcing particles with meanwhile good dispersion is of key importance for the strengthening of PRAMCs.For TiAl₃/Al composites,formation of TiAl₃ particles is mainly through the reaction of added Tipowders and Al,for which the dispersion and final volume fraction of TiAl₃ are dependent on those of the initial Tiand the contradiction between them usually leads to degradation of strength of PRAMCs fabricated by traditional methods.In this paper,high strength Al matrix composites reinforced by TiAl₃ particles with high volume fraction were fabricated by combined accumulative roll-bonding with relatively low initial Ticontent.Microstructure and mechanical properties of the composites were analyzed by the means of optical microscopy(OM),scanning electron microscopy(SEM),hardness test and tensile test at room temperature.In addition,various strengthening mechanisms were discussed and the mechanical properties of as-fabricated composites were compared with those of other PRAMCs.Room-temperature accumulative roll-bonding(RT-ARB)up to 46 cycles was first applied to disperse Tinanopowders in Al matrix,then the TiAl₃/Al composites were successfully fabricated by high-temperature accumulative roll-bonding(HT-ARB)at600?with HT-ARB cycles of 4.Fine TiAl₃ particles with average size under 1?m were uniformly dispersed in ultrafine-grained Al matrix(about 500 nm).By adjusting the content of initial Tipowders,the final content of TiAl₃ particles can range from 7vol.%to 24 vol.%.The microhardness and tensile strength of the composites can reach122 Hv and 338 MPa,?4.4 and 4.9 times those of pure Al,respectively.To further enhance the volume fraction of TiAl₃ particles,accumulative roll-extruding(ARE)was applied at the HT-ARBed sample at 700?.As the ARE cycle increases,the content of TiAl₃ particles increases by selective extruding of Al matrix.The volume fraction of TiAl₃ particles can reach 49%after 12 cycles of ARE.Though TiAl₃ particles grow to?3?m,the grain size of Al matrix remains in ultrafine scale.The microhardness and tensile strength of the ARE composites can increase to 180 Hv and 455 MPa,?6.4 and 6.6 times those of pure Al,respectively.It is found that the high strength of the composites can be attributed to the grain size strengthening and the dislocation strengthening caused by the difference of coefficient of thermal expansion(CTE)between reinforcement(TiAl₃)and matrix(Al).On the other hand,when the volume fraction of TiAl₃ particle is high,geometrically necessary dislocation strengthening and load bearing effect play important roles.As compared with other PRAMCs,the present TiAl₃/Al composites still display a good balance between strength and ductility even at a very high reinforcement content.This paper provides a new way to fabricate high strength Al matrix composites reinforced by TiAl₃ particles with high volume fraction.