Study On The Microstructure Of 3003 Aluminum Alloy Sheet By Vertical Roll-casting

3003 aluminum alloy,one of the most common 3XXX aluminum alloys,has good corrosion resistance,weldability and mechanical properties and thus is widely used in batteries,air conditioners,packaging and other industries.During vertical twin roll casting(VTRC)of 3003 alloy,serious center macrosegregation would form in the sheet as a result of the stronger cooling rate near sheet surface than that at sheet center,which is further caused by the strong cooling capacity of the rolls.After homogenization annealing and cold rolling,the recrystallized structure is not uniform along sheet thickness.Therefore,it is necessary to reduce the segregation of VTRC 3003 sheet by changing the casting process.Moreover,different cold rolling and annealing processes should be used and investigated to obtain a uniform fine recrystallized structure.In this paper,the effects of casting speed and refiner Al-Ti-B on the microstructure and Mn segregation of VTRC 3003 sheet were studied.The effects of different homogenization annealing and cold rolling on the recrystallization micro structure of the sheet were also studied.The following conclusions were obtained:(1)Casting speed has a significant effect on the microstructure of VTRC 3003 sheet.With the increase of the speed,columnar grains in the sheet are refined and the size of central segregation zone decreases.When casting speed is 25 m/min,the center segregation zone is the smallest.(2)Microstructure of VTRC 3003 sheet is mostly columnar and the grains at the center are very coarse.The columnar crystallization is weakened and dendritic arms are refined after adding Al-Ti-B refiner.The coarse grains at sheet center are also refined.(3)The dendrite segregation is reduced to some extent under homogenization treatment.Phases precipitate from the supersaturated solid solution and gather and grow during the treatment.However,the center segregation can not be completely eliminated during the treatment.(4)The homogenization microstructure of VTRC 3003 sheet indicates that the two-stage homogenization is better than the single-stage homogenization.The precipitated phases are finer and smaller and uniformly distributed after 580℃×15h+500℃×7h treatment.(5)The recrystallized structure in cold rolled VTRC 3003 sheet suffered a single-stage homogenization of 580℃×15h before cold rolling is coarse and narrow.The recrystallized structure is fine and uniform in the 85%reduction cold rolled VTRC sheet that suffered a 580℃×15h+500℃×7h homogenization before cold rolling.Al-Ti-B refiner is added during casting of the latter sheet.