The Influence Of Warm Rolling And Heat Treatment On Microstructure And Mechanical Properties Of 6061 Aluminium Alloy Cast-rolled Sheet

In recent years,6000 series aluminium alloy has become a research hotspot at home and abroad because of its excellent comprehensive properties such as strength,toughness and corrosion resistance.As the representative of 6000 series aluminium alloy,6061 alloy has the advantages of good hot extrusion formability,moderate strength and good weldability,and has been widely used in automobile,high iron,aerospace and other fields.Casting rolling is a short process,low investment,low energy consumption and high efficiency production process,but there are serious segregation and second phase coarseness problems in 6061 aluminum alloy sheet produced by casting rolling,which greatly reduces the mechanical properties of the sheet.In order to reduce the tendency of segregation,refine the grain size,improve the morphology and distribution of precipitates,and improve the overall properties of sheet metal,a warm rolling process is used in this study.The warm rolling can not only avoid the oxidation caused by hot rolling,but also avoid the working hardening caused by cold rolling.In addition,the heat treatment process can further eliminate some defects caused by rolling and rolling,and then improve the comprehensive performance.By means of OM,SEM,XRD,tensile test and hardness test,the effects of warm rolling temperatures at 320?,345?,370?,390?and 20%,35%,50%,65%and80%reduction on the microstructures and mechanical properties of 6061 aluminium alloy were studied,and the warm rolled sheets were heat treated.The results showed that:?1?In the warm rolling process,when the cumulative reduction reached 50%,the as-cast structure of 6061 aluminium alloy Cast-rolled sheet was transformed into rolling structure.The second phase in the alloy gradually changes from mesh and sheet shape to line shape along the rolling direction with the increase of rolling passes,and finally to fine granular shape.?2?The Cast-rolled 6061 alloy mainly contains heat-resistant phase Al_0.7Fe₃Si_0.3,Al₉Fe_0.84Mn_2.16Si and a small amount of strengthening phase Mg₂Si.After warm rolling,new precipitated phase Al_0.5Fe₃Si_0.5 was formed.The heat-resistant phases Al_0.7Fe₃Si_0.3,Al_0.5Fe₃Si_0.5 and Al₉Fe_0.84Mn_2.16Si are mainly contained in the Cast-rolled sheet after heat treatment.A new precipitated phase AlMn_0.75Fe_2.25 was formed after heat treatment after warm rolling,and Mg₂Si phase had no obvious peak in XRD.?3?The hardness of 6061 aluminium alloy Cast-rolled sheet increases linearly with the increase of reduction,and the maximum slope of hardness curve is 2.4.When the temperature of warm rolling is 370?.The hardness value is 84.28 HV,the tensile strength,yield strength and elongation are 209.34 MPa,79.09 MPa and 20.11%respectively,at 80%of the cumulative reduction.?4?The DSC curve of hot rolled 6061 aluminium alloy Cast-rolled sheet?560?,2 h?after solution is the same as that of 6061 aluminium alloy precipitation peak,which consists of four exothermic peaks.There was no obvious peak of Mg₂Si in XRD after secondary ageing?180?,8 h?+?210?,2 h?.?5?After heat treatment,the hardness of 6061 aluminium alloy Cast-rolled sheet increases linearly with the increase of reduction,and the maximum slope of hardness curve is 4.9 when the temperature of warm rolling is 370?.When the accumulative reduction is 80%,the hardness of the sheet reaches the maximum,which can reach130.8 HV.The tensile strength,yield strength and elongation are 318.76 MPa,88.48MPa and 20.53%respectively.