Study On Post-rolling Cooling Rate,Microstructure And Properties Of Twin-roll Casting 6061 Aluminum Alloy

The 6XXX series aluminum alloy（the Al-Mg-Si alloy）is a heat treatable reinforced aluminum alloy in which Mg and Si can form main strengthening phase Mg₂Si.After heat treatment strengthening,6XXX series aluminum alloy can have medium and high strength,good plasticity,strong corrosion resistance and excellent weldability,and is widely used in free forging,rolling,stamping and other process operations.At present,Al-Mg-Si aluminum alloy has been widely used in aerospace,automobile manufacturing,electronic home appliances and other fields.The twin-roll strip casting and rolling（TRC）process can effectively shorten the production process and make the cast-rolled strip product more compact and have high strength and hardness.Due to the cooling effect of the rolls on the aluminum alloy during the casting and rolling process,the surface of the cast slab is cooled faster,and the core temperature of the slab is still relatively high.Therefore,coarse and equiaxed crystals appear in the grain structure at the center of the cast slab along the thickness direction,and the overall grain size is uneven.In this paper,6061 cast aluminum alloy was studied as the research object.The effects of cooling rate,reduction treatment and heat treatment on the microstructure and properties of aluminum alloy were studied.Optical microscopy（OM）,X-ray diffractometry（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,microhardness tester and universal stretching machine were used to observe the microstructure.of the double-roll casting6061 aluminum alloy slab.And mechanical properties such as hardness,strength and elongation of the material were obtained.The experimental results show that the 6061 aluminum alloy produced by the twin-roll casting process is cooled at different cooling rates.With the increase of cooling rate,the smaller the grain size inside the 6061 aluminum alloy rolled and rolled sheet,the more the number of precipitated phases,the morphology of the precipitated phase will change,and the second phase Mg₂Si and iron-rich phase will appear more easily.The morphology of the second phase Mg₂Si is changed from a black discontinuous particle shape under slow cooling conditions to a needle shape under rapid cooling conditions.The form of the iron-rich phase changes from a granular shape to a bright white rod shape,even a thick slat shape as the cooling rate increases.The hardness,maximum tensile strength and elongation of aluminum alloy cast-rolled sheets will increase with the increase of cooling rate,and the hardness value under water-cooling conditions is up to 95 HV.According to the experimental results,the overall performance of the cast-rolled sheet under the air-cooling condition with an average cooling rate of 3℃/s is the best.The yield strength at this time is 64.37 MPa,the tensile strength is 177.79 MPa,and the elongation is 15%.The pressing treatment can significantly reduce the equiaxed crystalline as-cast structure of the slab core,but does not affect the internal phase of the precipitate.The crystal grains and the precipitated phase are elongated in the rolling direction,and the grain refining effect is remarkable,and the phase is analyzed to be crushed to form a discontinuous dot shape.The yield strength,tensile strength and elongation of 6061aluminum alloy rolled and rolled sheets have been improved.The heat treatment helps to evenly distribute the internal elements of the aluminum alloy,effectively improving the strength and hardness of the aluminum alloy.The hardness value under water cooling condition is up to 108 HV,but at the same time,the elongation of aluminum alloy is decreased,and the influence of different cooling rate conditions on the hardness of aluminum alloy cast slab is reduced,and the hardness difference between different cooling rates is reduced.