Research On Casting And Thermo-mechanical Treatment Of2024Aluminum Alloy

Al-Cu-Mg aluminum alloys have excellent properties such as low density, highspecific modulus, high strength to weight ratio and mechanical working properties,which have the widespread application value and prospect in aerospace, defense andother areas.In order to improve the performance of Al-Cu-Mg aluminum alloys, the2024aluminum alloy was prepared by vacuum induction melting and copperwater-cooled mould casting in this thesis. Compared with the conventional casting,vacuum induction melting casting can improve the quality of the melt, purify the meltsand eliminate blowhole defect. Copper water-cooled mould casting can refine grainsize and increase the number of equiaxial crystal. The mean grain size decreases from125μm to28μm. The microstructure of alloy was improved to some great extent.The effects of vacuum induction melting and copper water-cooled mould castingparameters on the microstructure and properties of2024alloys were studied. Theresults reveal that the grain size, secondary dendrite arm spacing and dendrite inprimary (Al) were significantly refined with the cooling rate increasing. The meltstiring in crucible was strengthened when increasing the power consumption and themicrostructure of alloy was improved when casting temperature increased to810℃.The mean grain size was28μm. After the thermomechanical treatment, the dislocationsin alloy increased and uniformly distributed. There were substructures andprecipitation in fine grains, so the mechanical property of alloy was improved.The effects of thermo-mechanical treatment parameters on the microstructure andproperties of the alloys prepared by vacuum induction melting and copperwater-cooled mould casting and conventional casting were studied. The results revealthat100℃/6h presaged treatment could prepare more nucleation cores for the peakaged treatment and avoid the heterogeneous precipitation of S phase. The alloycould obtain better work hardening and precipitation strengthening when the warmrolled process was190℃/30%. The precipitation were small and homogeneous, andmore micro-substructure remained when the sheets were peak aged at150℃.Theultimate tensile strength of conventional casting alloys after thermo-mechanicaltreatment increased from450MPa to535MPa. Also compared with the T81thermaltreatment, the tensile strength, highest yield strength and elongation of vacuuminduction melting and copper water-cooled mould casting of alloys after thermo-mechanical treatment reached to603MPa,581MPa and12%, respectively. Thealloys had better corrosion resistance and good mechanical property under hightemperature. The optimal thermomechanical treatment of2024aluminum alloyprepared by vacuum induction melting and copper water-cooled mould casting was hotrolling at400-430℃, solution treatment at490℃/30min, pre-aging treatment at100℃/6h, warm deformation in190℃to30%and final ageing at150℃/5h.