Effect Of Loading Direction On Dynamic Impact Properties And Microstructure Of 7B52 Laminated Aluminum Alloy

7B52 laminated aluminum alloy is composed of 7A62 aluminum alloy with high strength and 7A52 aluminum alloy with high toughness by rolling,and compounding with7A01 aluminum alloy in the middle.It is convenient casting and forming,easy to process and other advantages,it can be applied to military fields such as tank armor and amphibious combat vehicles.This article takes 7B52 laminated aluminum alloy as the research object,and uses Split hopkinson pressure bar(SHPB)to conduct dynamic loading experiments on7B52 laminated aluminum alloy in different directions,using microscopic detection methods such as metallographic microscope,scanning electron microscope and transmission electron microscope,the dynamic impact properties and microstructure of 7B52 laminated aluminum alloy under different loading directions have researched,and the conclusions are as follows:(1)When loading from the ND direction,on account of the differences between two sides,the stress would concentrate on the 7A52 layer alloy.Therefore,the 7A52 layer alloy will have serve deformation.At strain rate of 1500 s^-1,the 7A52 layer has better plasticity,and the 7A52 layer has a larger deformation than the 7A62 layer,as the strain rate increases to2300 s^-1,the alloy undergoes uneven local deformation,the 7A52 layer produces a large number of dislocations due to stress concentration,and the dislocations are entangled to form a cellular structure.When the strain rate further increases to 3000 s^-1,the deformation zone of the 7A52 layer changes to the transition zone.Cracks are formed when the strain rate increases above 3500 s^-1,the deformation zone of the 7A52 layer transforms into a transition zone,and finally cracks are formed,and shear fracture occurs.The fracture appears as a mixed fracture mechanism of ductile fracture and brittle fracture.(2)When loading from the RD direction,at low strain rate,the alloy is compressed because of the coordinated deformation of the two layers of metal.When the strain rate increases to 3000 s^-1,the stress is concentrated in the middle of the alloy,and the phenomenon of"upsetting"occurs inside the alloy.When the strain rate is further increased to 3500 s^-1,the two-layer metal coordinate deformation limit has reached,the 7A62 layer will produce a large number of dislocations due to the more concentrated stress under the same strain condition,the dislocations interact and aggregate to form multiple cellular structures.While the 7A52 layer is produced less dislocation,and these dislocations are entangled to form dislocation walls,at the same time,adiabatic shear bands are generated.When the strain rate continues to increase to 4000s^-1,both of the layer will undergo brittle fracture.(3)When loaded from the TD direction,under the low strain rates,the two layers of metal can be deformed in coordination,and the alloy structure is not changed significantly.when the strain rate increases to 3000 s^-1,the alloy has a"upsetting"phenomenon due to stress concentration.When the strain rate increases to 3500 s^-1,reaching the limit of the coordination of the two layers of metal,microcracks are generated in the 7A62 layer,and the deformation zone produced by the 7A52 layer.When the strain rate increases to 4000 s^-1,the7A62 layer is sheared fracture,the fracture surface shows a mixed fracture mechanism of ductile fracture and brittle fracture,and the 7A52 layer forms a transition zone.The impact resistance of loading from the TD direction is better than that in the RD direction,because the alloy stretches in the RD direction during rolling and compounding.The length is much larger than the TD direction,and the sample in the TD direction can absorb more energy during dynamic loading.(4)When loading dynamically from different directions,the energy absorption value is positively correlated with the strain rate.When loading from RD and TD direction the energy absorption always better than the value of loading from ND direction,the reason is that when loading from the RD and TD directions,the multi-layer alloy can be deformed in coordination,material energy absorption can reach the limit.While loading from ND direction,the main deformation occurs in 7A52 soft layer,the alloy fails because of concentrated deformation.