| As a face-centered cubic structural material,Copper and its alloys have excellent electrical and thermal conductivity,corrosion resistance and ductility.They are one of the most popular raw materials in electrical industry and electronic components manufacturing.However,the application and development of Copper and its alloys are limited due to their poor hardness and strength properties.Magnesium and its alloys are close-packed hexagonal structural materials with higher specific strength and better thermal shock absorption properties,However,it is difficult for magnesium and its alloys to deform at room temperature due to the existence of basal texture during deformation.At present,the plastic deformation theory of magnesium alloy is not perfect and mature,and the development of plastic processing technology is relatively slow,which limits the development of Magnesium alloy.Therefore,it is necessary to carry out in-depth systematic research on the plastic deformation methods of copper alloys and magnesium alloys,so as to explore a process that can effectively improve the comprehensive properties of materials.The mechanical properties of metal materials are closely related to microstructure(grain size distribution and grain orientation),and the different deformation conditions and recrystallization conditions have important influence on the evolution of the microstructure.Thus,we systematically investigated the microstructure and texture evolutions of Cu-Ag、pure Cu and AZ31 Mg alloy during different deformation process and different annealing conditions using optical microscopic(OM),X-ray diffraction(XRD)and electron backscatter diffraction(EBSD)analysis.The effect of cryogenic rolling on the microstructure,texture and recrystallization of Cu-Ag alloy was systematically studied.In addition,the effect of loading stress on the behavior of annealing behaviors of Cu-Ag alloy after large plastic deformation was studied.Besides,the multi-directional compression experiments were carried out on pure Cu samples,the microstructure and texture characteristics of the material after deformation and recrystallization are analyzed.Meanwhile,the effects of multi-directional compression on microstructure,texture and mechanical properties of AZ31 magnesium alloy were studied and study the effect of multi-directional compression on the recrystallized structure and mechanical properties of AZ31 magnesium alloy,too.The main conclusion can be reached as below:1.Compared with the materials rolled at room temperature,it can be found that both the tensile strength and yield strength of the materials after cryogenic rolling were increased due to the suppression of dynamic recovery during rolling.The appearance of Brass and S texture which replaced the Copper texture in the samples during cryogenic rolling,and the recrystallization in the cryogenic temperature rolled samples can be started at a lower temperature than that in the room temperature rolled sheet at the same reduction of 90%,because that during CT-rolling,the dynamic recovery was suppressed and corresponding a higher driving force for recrystallization than that in RT-rolling can be provided.2.The experimental results of 95%cold-rolled Cu-Ag alloy annealed under applied stress show that the annealing with lower stress(10MPa)inhibits the recrystallization behavior of the material,but promotes the formation of recrystallized Cube texture.In addition,the larger loading stress(50MPa)has more obvious inhibition effect on the nucleation of new grains during recrystallization,but it accelerates the growth of grains.The main reason is that the larger applied stress is already greater than the critical resolved shear stress required by the dislocation slip movement,so new defects appear during the loading and annealing process.The driving force of high grain growth.3.The "necklace" structure was observed in the optical microstructure test results of as-cast pure Cu after multi-directional compression at room temperature,indicating that dynamic recrystallization occurred during compression.The multi-directional compressed sample exhibits a very symmetrical texture is composed of three components each of which is Goss{011}<100>、CubeTD {011}<011>and CubeND {001}<110>.However,the Cube texture did not appear after complete recrystallization in the multi-directional compression samples.This is due to the three deformation textures of the multi-directional compressed samples that make the grains preferential nucleation and growth of other orientations,thus limiting the nucleation and growth of the Cube oriented grain.4.There is a phenomenon of detwinning behavior in magnesium alloy during multi-directional compression at room temperature.With the increase of the multi-directional compression passes,the(0002)peak value of XRD diffraction first increased and then decreased,which indicates that multi-directional compression can weaken the {0002} texture of the AZ31 Mg alloy.AZ31 Mg alloy after 10 passes multi-directional compression annealed for 30 min has completely recrystallized,the 4 passes sample was completed at 40 min.However,the samples annealed at 120 minutes after unidirectional compression were still in the mixed state of original coarse grains and fine new grains.At the same time,the multi-directional compressed 10 pass samples have the smallest grain size and more uniform after recrystallization.5.As a result of multidirectional compression at room temperature,a large number of high-density twin boundaries are produced in the grains of AZ31 magnesium alloy,which hinder the dislocation slip,so the sample has obvious work hardening phenomenon.In addition,multi-directional compression of grain refinement results in the maximum accumulated deformation of AZ31 magnesium alloy at room temperature up to 40%.Compression test results after full recrystallization show that the mechanical properties of 10-pass specimens under multi-directional compression are obviously better than those under unidirectional compression.The tensile strength and compression rate are increased by 26%and 69%,respectively.However,the yield strength of the specimens is not significantly improved due to the weakening of the basal texture. |
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