Flow Behavior And Microstructure Evolution Of 7A85 Aluminum Alloy During Hot Compression

7A85 aluminum alloy is a new kind of high strength aluminum alloy developed by our country.7A85 aluminum alloy has a low density,high specific strength,good hot-workability and weldability,better corrosion resistance and fracture toughness,so it is widely used in the field of aerospace engineering as main load-bearing structural components.In this paper,the flow stress behavior and the microstructure evolution of as-cast and as-extruded 7A85 aluminum alloy were studied by the hot compression tests,which were peformed on Gleeble-3500 thermal simulation machine at the temperature 300?,350?,400?,450? and strain rate 0.01s-1,0.1s-1,1s-1,10s-1.The constitutive equation of 7A85 aluminum alloy is obtained by linear regression.The optical microscopy and transmission electron microscopy were used to analysis the microstructure after hot compression.The main results obtained in this topic are as follows:(1)7A85 aluminum alloy has steady rheological characteristics and a trend to dynamic softening in isothermal compression process.The true stress rise to peak stresses rapidly in the initial deformation period,then the flow stresses decrease due to dynamic recovery and dynamic recrystallization,finally the flow stresses become steady.Peak flow stress and peak strain gradually decrease with the increasing deformation remperature and decreasing strain rate.The flow stress of as-extruded 7A85 aluminum alloy is higher due to fibre strengthening,GP zones and ?' strengthening.(2)The dependence of flow behavior on deformation temperature and strain rate can be described by Zener-Hollomon parameter.The hot deformation activation energy of as-cast and as-extruded 7A85 aluminum alloy respectively are 253.68 k J/mol and 229.656 k J/mol.(3)The main soften mechanism of 7A85 aluminum alloy during hot compression is dynamic recovery during lower compression temperature and higher strain rate. The main soften mechanism transformes into dynamic recrystallization with the increasing deformation remperature and decreasing strain rate. The main soften mechanism transformes from dynamic recovery to dynamic recrystallization as decreasing the value of parameter Z.(4)The shape and size of the grains,the density of dislocation,and the quantity and distribution of precipitated phase particles change with the different deformation conditions.With the decreasing of lnZ,the grains are elongated radially,the sub-grains grow up,the dislocation and the quantity of second phase particles decrease, recrystallized grains grow up.(5)The dynamic recrystallization is easier to take palce in the as-cast 7A85 aluminum alloy due to particle stimulated nucleation.There are more second phase particles in the as-extruded 7A85 aluminum alloy during compression,which inhibit dynamic recrystallization occurs.So the dynamic recrystallization is harder to take place in the as-extruded 7A85 aluminum alloy under the same deformation conditions.