| In this paper,1060 pure aluminum plates,7050 aluminum alloy plates and1060/7050 composite plates were fabricated by accumulative extrusion bonding(AEB).The effects of different AEB passes on the microstructures and mechanical properties of1060,7050 aluminum alloy plates and 1060/7050 composite plates were studied.At the same time,the microstructural evolution and properties of 7050 aluminum alloy plate and 1060/7050 composite plates after different ageing treatment were also studied.The mechanical properties of 7050 aluminum alloy plate and 1060/7050 composite plates were further increased by the improved cross accumulative extrusion bonding(CAEB)and water cooling outside the die.The results showed that the ultra-fine grained pure aluminum sheet with 10~6 layers was successfully prepared by 6-pass AEB process.With the increase of accumulative strain,the grain size of the plate was refined continuously.After 3 passes,the average grain size was about 0.51μm.After 6-pass AEB,the average grain size of the sheet was refined from the initial 108μm to 0.44μm.The main texture components of pure aluminum sheet processed by AEB were Copper{112}<111>and S{123}<634>.The number of large angle grain boundaries increased with the increase of AEB passes,and after 6-pass AEB,the volume fraction reached the maximum value,which was approximately 71.5%.In addition,the mechanical properties of pure aluminum sheet changed significantly,in which the strength of the sheet was positively correlated with the number of passes.When the number of passes was more than 3,the strength of the sheet tended to be stable.After five-pass AEB,the yield strength and tensile strength reached the peak values of 183 MPa and 195 MPa,respectively,and the elongation remained above 16%.The remarkable increase in the strength of the sheet after AEB is mainly attributed to two mechanisms:fine-grained strengthening and dislocation strengthening.Compared with the traditional ARB,when the accumulative strain is approximately the same,the AEB process has more advantages in refining the grain size and improving the mechanical properties of 1060 pure aluminum sheet.7050 aluminum alloy plates with different layers were prepared by three-pass AEB process.After different AEB passes,the interface bonding of 7050 aluminum alloy plate was good.After aging at 120 ℃ for 24 h,the second phases with different size,morphology and quantity were precipitated randomly on the surface of the matrix.The existence of these precipitates greatly improved the mechanical properties of 7050plates.In order to further optimize the properties of the plate,7050 aluminum alloy plates were prepared by cross cumulative extrusion(CAEB)+external water cooling.After aging treatment,the yield strength and ultimate tensile strength of 7050 aluminum alloy plates prepared by two-pass CAEB+water cooling were 477 MPa and 562 MPa,respectively.Compared with 7050 aluminum alloy after solid solution treatment,the yield strength and ultimate tensile strength of the plate were increased by 92.3%and39%,while the elongation decreased significantly.The change of mechanical properties is mainly related to dislocation strengthening and aging strengthening.In addition,the tensile fracture morphology revealed that the fracture mode was ductile brittle fracture.After two-pass AEB,a good metallurgical bond was formed between the layers of1060/7050 aluminum alloy multilayer composite plates without delamination.The mechanical properties of the composite plates were further improved after aging at 120℃ for 24 hours.Tensile fracture morphology showed that 1060 layers were a typical ductile fracture mode,while 7050 layers were a brittle fracture mode.After two-pass CAEB+external water-cooling,the interfaces of 1060/7050 multilayer composite plates appeared wave-like,bowl-like and W-like,which can improve the mechanical occlusion between the interfaces.The composite plates prepared by two-pass CAEB+water-cooling after aging at 120 ℃ for 24 hours had good strength and toughness. |
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