The Mircostructures And Thermal Deformtion Behavior Of Al/Mg/Al Clad Sheets

Magnesium alloy has been widely used in mechanical,electronic and aerospace fields due to its low density,high specific strength and good damping performance.However,its poor corrosion resistance is one of the main reasons limiting its application.By covering the 5052 aluminum alloy layer on both sides of the AZ31 magnesium alloy sheet,the Al/Mg/Al clad sheet was fabricated with both the advantages of light weight of magnesium alloy and good corrosion resistance of aluminum alloy.To get practical application for this kind of clad sheet,it is necessary to form various structural parts through stamping deformation.Therefore,it is of theoretical and practical value to study its microstructures and mechanical properties,especially stamping performance.The microstructures of the Al/Mg/Al clad sheets were observed by optical microscopy?OM?,scanning electron microscopy?SEM?,and transmission electron microscopy?TEM?,the phases were identified by X-ray neutron diffracion?XRD?,and the textures were analyzed by electron backscatter diffraction?EBSD?.The mechanical properties at warm temperatures were tested by universal tensile testing machine and the forming properties were tested by buldging and deep drawing.The mechanical properties,stamping properties,microstructures and plastic deformation mechanism of the Al/Mg/Al clad sheet were explored,the evolution of its microstructures during the process of rolling,thermo-plastic deformation and forming was investigated,and its constitutive model and the forming limit diagram were established.Three kinds of Al/Mg/Al clad sheets were rolled with single-pass reductions of 33%?denoted as 33R?and 48%?48R?and four-pass total reduction of 71%?71R?at 400 ? and annealed at different temperatures.Microstructure analysis showed that there were no pores and cracks at Mg/Al interface in various clad sheets.No new precipitation phases were observed at the interlaminar interface of 48 R as-rolled and its annealed sample at 200 ?;while Al₃Mg₂ and Mg₁₇Al₁₂ phases were generated and continuously distributed along the interlaminar interface after annealed at 300 ? for 1 h.The same precipitated phases were also generated and discontinuously distributed at the interlaminar interface of 71 R as-rolled and these phases grew up after annealed above 220 ?.The results of uniaxial tensile tests at room temperature indicated that the clad sheets have good comprehensive mechanical properties after annealing at 200 ? for 1 h because of complete recrystallization of AZ31 with the refined grains and weakened textures.However,the mechanical properties of the clad sheets decreased when the annealing temperature was too high,mainly due to the formation and growth of reaction diffusion layer.The thermal deformation behavior of Al/Mg/Al clad sheets was studied by means of warm uniaxial tensile tests?bulging and deep drawing.Warm uniaxial tensile tests suggested that the clad sheet was a kind of positive strain rate sensitive material,and the relationship between the deformation conditions can be expressed as???,where the average of the stress factor ? is 0.0083 MPa-1,the average of the stress index n 4.1037,and the average value of strain activation energy Q 97.9939 kJ·mol-1.The forming limit diagram obtained from bulging showed the best bulging capacity exhibited at 230 ?,and the corresponding limit bulging height is 36.5 mm.Differential temperature drawing showed the clad sheet had the best drawability at 200 ?,and the limit drawing ratio was up to 3.1.Microstructures analysis of the Al/Mg/Al clad sheets showed that Al/Al₃Mg₂?Al₃Mg₂/Mg₁₇Al₁₂ and Mg₁₇Al₁₂/Mg in the annealed clad sheet were coherent phase interfaces: ???,misfit degree was 0.7%;??? and???,misfit degree 0.64%;???,misfit degree 2.7%.The AZ31 component sheet exhibited the basal texture while the 5052 component sheet the cubic texture.During the process of bulging,the position and number of the cracks of reaction diffusion layer are affected both by the forming temperature and the stress-strain state.For the best bulging sample,most of the grains in AZ31 were elongated along the rolling direction?RD?and a small part of the grains underwent continuous dynamic recrystallization,increasing the intensity of the basal texture.In the 5052 component sheet,the cubic texture component accounted the largest proportion,followed by S texture.During the deep drawing process,the most serious cracks in reaction diffusion layer occurred at the corner of the cylindrical part.The basal texture intensity of AZ31 at bottom,corner and wall of the best cylindrical part decreased in turn,the c-axis of the grains gradually shifted from rolling direction?RD?to transverse diraciton?TD?,and dynamic recrystallization extented,accompanied by the activation of basal and non-basal slips.When the deep forming force is parallel to RD,the schimid factors of ???????slips of AZ31 in cylindrical part were higher and??? ????were lower than that of AZ31 in annealed clad sheet.When the deep forming force is parallel to TD,the results were opposite.At cylindrical part corner,5052 presented the largest recrystallization extent with random orientation.The proportion of Cube and Goss texture components was more than that of the Brass texture component,which indicated that some Brass oriented grains were oriented to the adjacent Goss orientation during deep drawing process.At bottom and wall,5052 was dominated by the deformation texture.