| Compared with conventional single metal materials,laminated metal composites consist of various constituent metals can achieve excellent impact toughness,fracture toughness and corrosion resistance in addition to synthesize advantage performance of constituent layers.As one of the severe plastic deformation processes,accumulative roll bonding(ARB)provides a new idea for the design and fabrication of dissimilar laminated metal composites because it can achieve large plastic deformation without changing of the volume of the material.For the multilayered composites obtained by ARB,interfacial structure and morphology are closely related to the plastic deformation process and the properties of constituent metals.Ultrafine-grained structure can be produced in laminated metal composite by severe plastic deformation,but the strain hardening caused by large deformation will lead to a characteristic of high strength and low ductile,which resulted in the industrial application was limited.AA1100 and AA7075 aluminum alloys with obvious mechanical difference were selected as constituent metals in present article,and mechanical properties and microstructural evolution of Al alloy laminated metal composites were pertinently investigated according to the technological process of ARB.The evolution of microstructure and interfacial structure of 1100/7075 Al alloy laminated metal composites was characterized using optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),electron backscattered diffraction(EBSD)and X-ray diffraction(XRD).The effects of rolling process,deformation path and thermo-mechanical treatment process on the mechanical properties,interface structure and morphology of the laminated composites were systematically studied.The interface regulation of Al alloy laminated metal composites was proposed,and the comprehensive mechanical properties of Al alloy laminated metal composites were optimized.The main conclusions in present research are as follows:(1)The plastic instabilities near interface of Al alloy laminated metal composites can be effectively controlled as a result of repeated intermediate annealing during high temperature ARB process,resulting in the achieving of straight interface morphology.With the increasing of reduction in cold rolling,the interfaces between constituent layers changed from straight and continuous to wavy shape,and obvious necking was developed in hard layers.After 75% reduction,the complete fractures were observed at 7075 hard layers.The results obtained by finite element analysis and experimental observation proved that the plastic instabilities(e.g.necking and fracture)were derived from shearing regions with preferential local deformation introduced by the difference in flow properties between the constituent metals.It is evident that the elongation of 1100/7075 Al alloy laminated metal composites was increased as the increasing of deformation degree,and the increasing of tensile strength was also detected before 75% reduction,which is attributed to the occurrence of strain hardening behavior.However,when the reduction is75%,the hard layers were difficult to support the load sufficiently and resist deformation due to the occurrence of fracture in 7075 layers,resulting in the decreasing of strength of laminated metal composite.(2)The plastic instabilities occurred in 7075 layer were effectively inhibited and the mechanical properties of the laminated metal composite were improved through the changing of strain path.The formation of straight and continuous interfaces is due to the difference in flow properties between the constituent layers was decreased after cross rolling.The experimental and simulation results show that,the mechanical properties of laminated metal composite with continuous and straight interface structure was better than those with wavy interface structure.It is found that the strain path change during cross rolling results in the typical rolling texture is shifted from the ideal Brass(110)<112>along the ?-fiber to the near ND-rotated Brass(011)<755> component,weakening the mechanical isotropy of the 1100/7075 Al alloy laminated metal composite.(3)Al alloy laminated metal composites with various grain size distributions were successfully constructed by different strain paths and annealing treatments.The results show that the mechanical properties of the laminated metal composite after heat treatment was higher than that predicted by the mixture rule in the Al alloy laminated metal composites,indicating that an extra strengthening effect was present in the laminated metal composites.Under the condition of cross rolling and annealing at 300 ? for 60 min,the high strain gradient at the interface can achieve a good match between the strength and plasticity of the laminated metal composite,and the optimal mechanical properties were achieved.In the process of tensile deformation,the strain incompatibility caused by the multi-scale interface structure led to the distribution of a high density of geometrically necessary dislocations(GNDs)near the interface of the soft layer.The back stress strengthening and high strain hardening rate were introduced into the laminated metal composites to improve the strength and plasticity of the Al alloy laminated metal composite.(4)The mechanical properties of 1100/7075 Al alloy laminated metal composite were effectively improved by various thermo-mechanical treatments.Cold rolling had a significant improvement on mechanical properties of Al alloy laminated metal composite after aging treatment before aging,resulting from the high density dislocations,increased microstrain and refined grains.After aging treatment,the optimal combination of strength and ductility was achieved in ST+CRP+aging(solution treat,cold rolling and aging),in which the high density of ?? phases and dislocations contributed to the enhancing of strength,while the increasing of ductility was attributed to the improvement of strain hardening rate caused by dislocation accumulation.With the decreasing of rolling temperature,an increase in anisotropy behavior of 1100/7075 Al alloy laminated metal composite was significant,which was attributed to the formation of considerable rolling texture components and enhanced texture intensity after cold deformation.(5)1100/7075 Al laminated metal composites with different laminar parameters but straight and continuous interface were successfully fabricated,and the effect of thickness ratio and layer number on bending fracture behavior and toughening mechanism was investigated in detail.The bending toughness was enhanced with the increasing of thickness in 1100 layer,which was attributed to the crack growth resistance was limited by the thickness of crack bridging ligament during plastic deformation.With the increasing of layer number,a slight improvement of bending strength was observed,but toughness was decreased obviously.Combined with the evolution of the elastic deformation and plastic deformation stage and crack generation and propagation stage,it is proved that the effect of layer thickness on toughness still existed at laminated metal composite after the layer number increasing,and the phenomenon of crack deflection or delamination at the interface caused by the change of interfacial bonding strength played an important role in the toughening behavior of laminated metal composite. |
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