Study On The Precipitation Behavior And Mechanical Properties Of Cryorolled 6069 Al Alloy

Compared with the traditional steel materials,aluminum alloy has advantages of low density,high strength,good corrosion resistance and recyclable.It is widely used in all fields of life and production.In order to meet the requirements of sustainable development,realize energy conservation and emission reduction,Al-Mg-Si-Cu alloys are becoming more and more widely used in transportation field.However,the low strength of Al-MgSi-Cu alloy limits its application fields.Therefore,how to improve the strength of Al-MgSi-Cu alloy while maintaining its plasticity has become a common concern in academia and industry.This project adopted a combination treatment of cryorolling and aging treatment to prepare 6069 aluminum alloy with high strength and plasticity.In this experiment,universal hardness tester,transmission electron microscope(TEM),scanning electron microscope(SEM),differential scanning calorimeter(DSC)and other testing equipments were used to invest the effects of rolling temperature,rolling reduction ratios,pre-aging treatment process and post-aging treatment on the precipitation behavior,microstructure and properties of the alloy during aging deformation process for preparing high strength and high plasticity 6069 aluminum alloy.The main contents and results are as follows:(1)Samples after solution treatment were rolled at room temperature and cryogenic temperature.The microstructure of the sample after cryorolling was finer and the yield strength,tensile strength and elongation were higher than which of room temperature rolling.No matter cryorolling or room temperature rolling,the failure model of tensile samples was ductile dimple fracture.The size of dimples of cryorolling samples was bigger than room temperature rolling samples.In the subsequent aging process,the cryorolled treatment had an effect on the precipitation sequence of 6069 Al alloy and promoting the separating out of ?" phase and L phase,at the same time,reducing its activation energy about 23 kJ/mol.(2)Altering the reduction rate of 6069 Al alloy by cryorolling and adopting the low temperature aging process,it was found that,the tensile strength and yield strength of the alloy increased,while the elongation decreased with the rolling reduction increasing.After post aging treatment,the mechanical properties of all samples increased.At the same time,the precipitation temperature of the ?" phase and the L phase moved to the low temperature region and the DSC precipitation peak area decreased.(3)The solid solution samples were pre-aged at 180? for 10 min and 8 h respectively before cryorolling.Compared with non-pre-aging samples,the results show that the tensile strength and yield strength of 6069 Al alloy increased,while the elongation decreased after cryorolling.Pre-aging can significantly reduce the precipitation activation energy of ?" phase and L phase.(4)The samples of 6069 Al alloy after cryorolling were aged at 100?,130?,160 ? for 2?20 h.When the aging temperature was 100?,the yield strength and tensile strength of aluminum alloy tended to increase slowly with the aging time,while the elongation decreased;when the aging temperature was 130?,the yield strength and tensile strength of the alloy increased firstly and reached the peak after 12 h and then decreased,while the elongation decreased firstly and then increased;when the aging temperature was 160?,the yield strength and tensile strength showed a downward trend,while the elongation decreased firstly and then increased.