Study On The Effect Of Cast Rolling Speed And Mn/Fe Ratio On The Evolution Of 6061 Aluminum Alloy Cast And Rolled Plate Tissue

6061 aluminum alloy has been widely used in automobile,shipbuilding and other machinery manufacturing industries due to its lightweight,high specific strength,and good formability and welding performance.Microalloying was one of the most efficient methods for improving aluminum alloy structural materials and comprehensive mechanical properties,has received considerable attention in recent years.Compared with the conventional forming method,the vertical twin-roll casting and rolling process was bound to become a preparation process with great potential due to its short process,high yield,high efficiency and energy saving.In this experiment,a thickness of 3.50 mm6061 aluminum cast and rolled plates were successfully prepared by NF6-300 vertical twin-roll strip casting machine.By controlling the casting and rolling speed,Mn/Fe mass ratio and heat treatment process,the microstructure evolution and mechanical properties of 6061 aluminum alloy cast and rolled plates were studied.The research showed that:(1)Casting rolling speed has an important influence on the formability,microstructure and mechanical properties of 6061 aluminum alloy plates.When the casting speed was 12 m/min or 15 m/min,the grain size was relatively small,and the second phase particles were relatively fine and evenly distributed between the grain boundaries When the casting speed was 21 m/min,the central segregation was more serious,and some α-Fe phase and Mg2 Si were locally aggregated,which has a great influence on the overall performance of the plate.When the casting speed was 15 m/min,the mechanical properties of 6061 cast and rolled plates were the best.The tensile strength,hardness and elongation were 187.92 MPa,72.33 HV0.1 and 16.87%,respectively.(2)The Mn/Fe mass ratio has a significant effect on the evolution of iron-rich phases and microstructures in 6061 cast and rolled plates.As the mass ratio of Mn/Fe in the 6061 cast and rolled sheet increases,the grain size of the structure gradually increases and tends to be constant.When the mass ratio of Mn/Fe reached 3.0,the paraxial grain size of the side columnar crystal and the core was relatively small,about53.40 μm and 33.63 μm,respectively.At the same time,the iron-rich phase in the edge structure was gradually changed from needle-like β-Al5 Fe Si phase to skeletal and granular α-Al12(Fe Mn)3Si phase;the heart was transformed from a needle-like β-Fe phase to a star-shaped Al6(Fe Mn)phase and finally to a dot-like α-Fe phase and amassive α-Al15(Fe Mn)3Si2 aggregate.When the mass ratio of Mn/Fe was 2.5,a large number of massive and petal-like α(Al)(Fe Mn)-Si phases begun to appear in the core.In addition,when the mass ratio of Mn/Fe was 2.0,the mechanical properties of cast and rolled plates were the best,and the tensile strength,hardness,elongation and electrical conductivity were 204.80 MPa,75.67 HV0.1,17.83% and 30.42% IACS,respectively.(3)When the Mn/Fe mass ratio was 2.0,the more feasible heat treatment system for casting and rolling 6061 sheet was 550℃/2 h solution treatment + 200℃/6 h artificial aging treatment.At this time,the tensile strength,hardness and elongation of the cast and rolled sheets were 317.64 MPa,126.85 HV0.1 and 13.50%,respectively.