Study On O-DECAP And Its Effect On Microstructure And Mechanical Properties Of Al-Zn-Mg-Cu Alloy

The double equal channel angular pressing?DECAP?is derived from the classical large plastic deformation method,equal channel angular pressing?ECAP?.This subject applies the closed floating die technology in DECAP,and develops a occlusive double equal channel angular pressing process?O-DECAP?.Using the finite element simulation software Deform-3D,the characteristics and advantages and disadvantages of the three processes are compared,and the deformation process of each process is analyzed in detail by the physical mesh method and the simulated grid.The shear deformation area of ECAP process is about 70%,the shear deformation area of O-DECAP process is 40%,and the elongation deformation area accounts for28%.The results of the study on the uniformity of the sample show that there are 4kinds of deformation areas in DECAP.The distribution of strain in multi pass extrusion is not only related to the rotation mode of the sample,but also on the placement direction of the sample.On the 3 and the 4 time,the uniformity of samples prepared by the way of"I+E"placement is the best.In view of the problem of specimen cracking during extrusion,it is found that extrusion temperature is the main influencing factor.Increasing the corner fillet is not conducive to reducing the cracking tendency.As a lightweight and high-strength structural material,Al-Zn-Mg-Cu alloy is widely applied.The large plastic deformation process?SPD?can remarkably refine the grain and improve the morphology and distribution of the alloy phase.In recent years,many scholars have carried out a great deal of research on the aluminum alloy through the SPD process.In this paper,the die of O-DECAP process was designed.The extrusion experiment on the A path of cast X3 aluminum alloy was carried out at350 C.Through the mechanical properties test,optical microstructure observation and X-ray diffraction analysis,the influence of O-DECAP technology on the microstructure and properties of the cast X3 aluminum alloy was investigated.Finally,the samples after large plastic deformation were treated by solid solution and aging.It was verified that the material properties could be further improved by heat treatment after large plastic deformation.The results of optical microstructure observation show that the grain size can be greatly reduce by the O-DECAP process.The grain size is reduce to 10?m from the initial 98?m after deformation,and the second phase particles are more dispersed.The XRD test results show that the dislocation density of the cast X3 alloy is2.458?10¹³m^-2 and the crystallite size is 74.8nm.With the increase of the extrusion pass,the dislocation density increases first and decreases,and the maximum value is reached after the two pass extrusion;the microcrystal size decreases first and slightly increases,and the second pass is the smallest?30.3nm?.The mechanical performance test showed that the the degree of increase of strength in 4 deformation zones after different times of extrusion is different,and the area with large strain increases more.The increase of metal strength relative to the initial state in the shear deformation zone after 1,2 and 4 passes is 25%,73.9%and 83.6%,respectively.After one pass extrusion,the initial sample is treated by solid solution and aging,the tensile strength is up to 771MPa,which is 187.7%higher than that of the initial sample.The large plastic deformation+heat treatment process has a great advantage over only heat treatment or only large plastic deformation process in improving the strength of X3aluminum alloy.