Research On Microstructure And Mechanical Property Of Aluminum Alloy Sheets Under Different Deformation Conditions

6000 series aluminum alloy can be used as heat treatment strengthening type aluminum alloy,because of its good comprehensive mechanical properties,high strength,good formability,good corrosion resistance,good weldability and easy coloring paint surface,high quality,and has become the focus of research on materials of the scientific research units.It will be widely used in the transportation industry to realize the lightweight of vehicles.At present,6000 series aluminum alloy has been adopted as the structural material on the outer panel of car body,such as car top cover,back luggage cover,engine cover plate and door.In this paper,6014 and 6016 aluminum alloy sheet are adopted in the study.Research on high temperature rheological behavior of the 6016 aluminum alloy through the one-way isothermal thermal tensile test.Deformation at temperature of 400 ?,450?,500?and 550?,and the strain rate is set to 0.01s-1,0.1s-1,1s-1and 10s-1.We studied the influence of deformation conditions on the true stress-true strain curve.The constitutive equation of high temperature rheological behavior was established by the true stress-true strain curve.We analyzed the relationship between the microstructure and the deformation conditions and integrated the processing map at same time.The forming performance of 6014 aluminum alloy sheet was studied.The cupping test,drawing test and bulge test of 6014 aluminum alloy was made of room temperature and thermo-forming temperature.The thermo-forming temperature contains 100 ?,200 ?and 300?.According to the punch velocity,the deformation rate was on the range of5mm/min~30mm/min.And we also studied the microstructures after deformation,and analyzed the influence of deformation condition on microstructure.The research results of this subject have the following points:(1)6016 aluminum alloy has steady-state rheological and dynamic softening characteristics during thermal tensile deformation.With the increase of deformation temperature,the influence of temperature on the plasticity of the material increases deeply.The constitutive equation of the flow stress of the alloy was solved by using the true stress-true strain curve to full.And error analysis of the constitutive equation was given to make sure it has good application value.The critical conditions of dynamic recrystallization for the aluminum alloy were proposed in this paper.And the relationship between the critical strain of dynamic recrystallization and the Z parameterwas established.(2)Formability test of 6014 aluminum alloy sheet shows that it is the turning point for cupping performance and deepening performance which the thermo-forming temperature has reached near the 300 ?.The forming performance is relatively poor under the 300 ?.By analyzing the results of FLD test,the calculation model about major strain and minor strain in FLC curve of 6014 aluminum alloy was fitted.However,it shows that the FLC curve of the rolling direction is more or less the same as the vertical rolling direction in the experimental results.And the FLC curve of vertical rolling direction is slightly lower than the rolling direction in calculation model.(3)The microstructures of the two kinds of aluminum alloys under different deformation conditions were observed.It was found that the main dynamic softening mechanism is dynamic recovery at 400 ? and 450 ? for 6016 aluminum alloy.Dynamic re-crystallization occurs in the alloy at 500? and 550?.Increasing the strain rate,which result in a non-homogeneous dynamic recrystallization microstructure.Increasing the deformation temperature would cause the coarsening of the recrystallized microstructure.At the same time,the dynamic recrystallization grains are elongated in the direction of stretching.For the thermo-forming temperature below 200 ?,the microstructure of 6014 aluminum alloy after cup and deep deformation got a practically similar microstructure with corresponding cold deformation.At 300 ?,the grain elongation was relatively serious,which is consistent with the mechanical test results.(4)A synthetic analysis about microstructure of the two kinds of 6000 series after deformation at cold,warm and thermal.It shows that the difference is little in microstructures under cold deformation and corresponding original microstructures.Under the condition of warm deformation,the deformation degree of grain increase with the temperature of the deformation increase.And as the mechanism of recovery is moderate,the grain boundary remains flat.Finally,the difference is clear in microstructure after thermal deformation and corresponding original microstructures.At this moment,dynamic restoration mechanism is notable.There are crystal surface of the multilateral phenomenon when dynamic recovery is the main softening mechanism.When dynamic recrystallization occurs,the dynamic recrystallized structure is determined by the deformation temperature and the strain rate.