Study On The Accumulative Roll-bonding Processing And High-temperature Plastic Deformation Properties Of The In-situ Nano ZrB₂/6X82Al Composites

In the present study, the accumulative roll-bonding(ARB) at 300 o C was employed toachieve the uniform distribution of the nano reinforcements and improve the mechanical properties of the in situ nano Zr B2/6X82 Al composites, fabricated by direct melt reaction in6X82Al-K2 Zr F6-KBF4 system with electromagnetic stirring. The microstructure and phase composition of the composite, as well as the morphology, size and distribution of the in situ particles are investigated by OM, SEM, EDS, TEM and XRD. The tensile properties of the composites under different conditions are investigated by tensile testing. And, the strengthening mechanism during the ARB processing is established. The high-temperature plastic deformation characteristic of the composites has also been investigated by high-temperature tensile testing. At the same time, the composites’ high-temperature deformation mechanisms were also studied.When the K2 Zr F6 and KBF4 power were mixed with mass ratio about 52:48, the reaction temperature remained 1123 K for 30 min, magnetic stirring and purification of melts were necessary, the composites fabricated successfully. The microstructure characterization of the cast composites shows that the in situ synthesized Zr B2 nanoparticles in the composites exhibit a hexagonal or square morphologies with average size of 30-100 nm, and lots of the nanoparticles agglomerate in local area of the matrix. And, the addition of Zr B2 nanoparticles plays an important role in the grain refinement of the composites.The microstructure characterization of the composites during ARB processing indicated that the uniformity of the Zr B2 nanoparticles as well as the precipitation improved, with the increasing of the ARB cycles. Simultaneously, the grain of the composites is much finer with the increasing of the ARB cycles. Especially, after nine cycles of ARB processing, the composites exhibit a homogenous ultra-fine grained structure with average grain size of 380 nm. And the SAR composites exhibit a finer grain structure compared with the SRA composites, due to the existence of more precipitated phases during ARB processing.The tensile testing results show that both the tensile strength and ductility of the composites increased with increasing cycles of ARB processing, due to the uniformity improvement of the nano reinforcements and the grain refinement of the matrix as well as the elimination of thedefect. For example, the 3wt.% SAR composites possess strength of 310 MPa and elongation of 15.8% with nine cycles of ARB processing, about 138.5% and 66.3 % higher than the cast6X82 Al alloy.High-temperature tensile tests shows that accumulative roll processing makes an enormous impact on the high temperature plastic deformation properties of the composites. Composite after accumulative roll stills remain a certain strength at a high temperature.when the mass fraction of3 wt.%, after nine cycles of ARB processing, the composites get the best high-temperature’plastic deformation properties, the maximum temperature elongation was about 140%. With increasing both deformation temperature and strain rate, composite elongation decreased firstly and then increased, whether low strain rate or high deformation temperature contributes to the decrease of the high-temperature plastic characteristic of the composites. And the best high temperature plastic deformation parameters is: deformation temperature 600 K, strain rate of 5×10-3s-1.The strength of grain internal is over than that of the grain boundary during the high-temperature plastic deformation. The grain boundary happened to slide and deflect under external force in that situation,simultaneously,the slippage of the dislocation and dynamic recovery and recrystallization also plays an important role in the plastic deformation. The grain refinement of the composites is the key factor about the high-temperature plastic deformation properties. However, the strength of roll-bonded interface dramatically decreases under high temperature, then the nondeformable nano Zr B2 in the off single-layer composites easily cause humorous stress concentration, that’s the reason why no further enhancement of the high-temperature plastic deformation characteristic is observed.