Study On Vertical Roll-casting Process And Microstructure And Properties Of 6022 Aluminum Alloy Slab

As one of the main materials of automobile plates,6022 aluminum alloy is mainly produced by semi-continuous casting and rolling process.The preparation of 6022 aluminum alloy slab by vertical roll-casting process can shorten the production process and achieve energy saving,emission and cost reduction.However,the technology of preparing aluminum alloy strips by vertical rollcasting is still not mature,and many bottlenecks need to be further studied.In this paper,6022 aluminum alloy was used as the research object.Based on a large number of vertical twin-roll casting experiments,the vertical roll-casting process was improved.The effects of casting speed and melt temperature treatment on the micro-structure and properties of roll-casting slab were studied.The results are as follows:(1)The influence of casting speed on the vertical roll-casting process was studied.It was found that the phenomenon of twin-roll casting in the slow casting was related to the shape of the liquid dead zone in the molten pool,and roll-casting process was determined.The casting speed range is 2?15m·min-1.(2)The surface of the slab prepared by casting speed of 2?1Om·min-1 is reverse segregated,and the core of the slab prepared by 15m·min-1exists macro-segregated.The elements of Mg,Si and Fe will be enriched at the grain boundary.The second phase is ?-Al+Mg2Si binary eutectic phase,?-Al+Mg2Si+Si ternary eutectic phase and AlFeSi phase.The mechanical properties of the sheet obtained by rolling and T4P heat treatment is related to the amount of deformation and second phase.(3)The effect of melt superheat treatment on the structure of roll-casting slab was studied.The edge of the superheat roll-casting slab is columnar crystal,and the core is equiaxed dendrite.The heat treatment of the melt reduces the average spacing of dendrites in the core of the cast slab,second phase is dispersed,macro-segregation is improved.The effects of casting temperature and casting speed on the micro-structure of superheat roll-casting slab were studied.when the melt casting temperature was raised from 800? to 1100?,It was found that the primary dendrite extension length of the slab surface layer increased,and the dendrite spacing of the core was reduced.Primary dendrite spacing reduced from 6.7?m to 5.0?m.With the casting speed increased,melt flow becomes disordered and the surface layer has cracks.(4)The effect of near-liquidus treatment on the micro-structure and properties of roll-casting slab was studied.The structure of near-liquidus rollcasting slab is equiaxed,and the grain size is larger than which of conventional cast slab.Compared with near-liquidus roll-casting sheet,the T4P state plasticity is obviously improved,but the strength is decreased.When the casting speed is increased from 5m·min-1 to 15m·min-1,the surface of the slab is de-segregated.The elongation of the T4P sheet is reduced from 24.4%to 18.3%,but the tensile strength is increased from 175.8MPa to 193.1MPa.The yield strength increased from 93.8MPa to 108.3MPa.After homogenization treatment,the T4P state mechanical properties were improved,and the effect of rapid roll-casting sheet was more obvious.The tensile strength increased from 193.1MPa to 241.6MPa,and the yield strength increased from 108.3MPa to 129.0MPa,the elongation increased from 1 8.3%to 2 1.7%.