A modified strain-induced melt activation（SIMA）process consisting of homogenization,equal-channel angular pressing（ECAP）and subsequent heating to the semisolid temperatures was introduced to prepare the 7075 alumi...A modified strain-induced melt activation（SIMA）process consisting of homogenization,equal-channel angular pressing（ECAP）and subsequent heating to the semisolid temperatures was introduced to prepare the 7075 aluminum alloy with superior thixotropic behaviors.The effects of both the homogenization and the number of ECAP passes,as well as the isothermal temperatures on the microstructural evolution,were investigated.The results indicate that ideal microstructure wherein fine and globular solid grains surrounded by uniform liquid films can be achieved through ECAP deformation-recrystallization mechanism.Increasing the number of ECAP passes accelerates the recrystallization of strained grains,thus reducing the average grain size and improving the grain sphericity.Moreover,higher holding temperatures and prolonged soaking time can improve the growth of the solid grains.Two main coarsening mechanisms,viz.coalescence and Ostwald ripening,contribute to the growth of the solid grains simultaneously and independently.The tensile strength of the 7075 alloys after four-pass ECAP-based SIMA and T6 heat treatment is relatively lower than the as-received billet,while the elongation of SIMA processed samples is much higher than that of as-received ones.Increasing the number of ECAP passes improves the tensile strength for alloys with and without T6 treatment due to the fine grain strengthening mechanism.展开更多
基金supported financially by the National Natural Science Foundation of China(Nos.51174028 and 51541406)
文摘A modified strain-induced melt activation（SIMA）process consisting of homogenization,equal-channel angular pressing（ECAP）and subsequent heating to the semisolid temperatures was introduced to prepare the 7075 aluminum alloy with superior thixotropic behaviors.The effects of both the homogenization and the number of ECAP passes,as well as the isothermal temperatures on the microstructural evolution,were investigated.The results indicate that ideal microstructure wherein fine and globular solid grains surrounded by uniform liquid films can be achieved through ECAP deformation-recrystallization mechanism.Increasing the number of ECAP passes accelerates the recrystallization of strained grains,thus reducing the average grain size and improving the grain sphericity.Moreover,higher holding temperatures and prolonged soaking time can improve the growth of the solid grains.Two main coarsening mechanisms,viz.coalescence and Ostwald ripening,contribute to the growth of the solid grains simultaneously and independently.The tensile strength of the 7075 alloys after four-pass ECAP-based SIMA and T6 heat treatment is relatively lower than the as-received billet,while the elongation of SIMA processed samples is much higher than that of as-received ones.Increasing the number of ECAP passes improves the tensile strength for alloys with and without T6 treatment due to the fine grain strengthening mechanism.
