A New Thermo-mechanical Treatment Of7050Aluminium Alloy

In this work, we systematically studied the effect to the microstructure andproperties of7050aluminum alloy with solution, large deformation cold rolling,annealing with high temperature in a short time, aging treatment process. Throughthe combination of deformation, annealing and aging, cooperative control of grainrefinement and precipitation behavior was achieved, and the overall property ofthe alloy was significantly improved. The microstructure evolution and secondphase precipitation of the alloy in thermo-mechanical treatment was studied bymeans of OM, EBSD and TEM. The effect of microstructure changes to themechanical properties was also researched through normal stretching. Thefollowing work showed that:The deformation texture of7050aluminum with80%cold rolling revertedafter aging treatment at120℃. The precipitated phases were spherical androd-shaped. With the aging time extending, the number and size of rod-shapedprecipitates both increased. Cold deformation promoted the precipitation andgrowth of precipitated phases. The strength of the alloy firstly decreased rapidly,and then increased, gradually decreased at last. The highest strength appeared at4h aging. Elongation increased rapidly at first, and then changed little. After4haging at120℃, the alloy with cold rolling was with tensile strength of681MPa,yield strength of645MPa, elongation of10.8%. The overall performance of thealloy was significantly improved with aging after cold rolling.Alloy was annealed for3-10min at380-420℃after cold rolling. The resultsshowed: When annealing below400℃with short time, the alloy partiallyrecrystallized. Recrystallization had obvious orientation; When annealing above400℃in short time, complete recrystallization of the alloy occured with fine anduniform grain size with an average size of28μm. As the annealing temperatureincreased, the size of precipitate decreased, the density increased first and thendecreased; Tensile strength and yield strength increased gradually. Elongationincreased rapidly first and then decreased.When short annealing below400℃, as the holding time extending,recrystallized fraction changed little. Size and density of precipitate increased. Theprecipitation process was not completed within10min; When short time annealingabove400℃, as the holding time extending, there was no significant coarsening ofgrains, but the size of precipitates increased, the density decreased and Ostwaldripening precipitates occurred. With the holding time extending, the strength of380℃annealed alloy increased and elongation decreased; When annealing at 410℃, the strength reduced, elongation firstly increased and then decreased.After solutionâ†'80%cold rollingâ†'410℃/5min annealingâ†'120℃/18haging treatment,7050aluminum was with tensile strength of573MPa, yieldstrength of492MPa, elongation of19.2%. While maintaining a close dissolvedstate with high plasticity, the alloy was with a strength over the solid solutionaging state alloy with the same aging process. Compared to commercial hot rollingplate7050, while maintaining the similar strength, elongation of the alloyincreased by4.2%, which significantly improved the overall performance of thealloy.