Study On The Dynamic Microstructural Evolution Of The7150Aluminum Alloy During Hot Deformation

7150aluminum alloy has excellent performance, such as strength, exfoliationcorrosion resistance, stress corrosion cracking resistance property, fracture toughnessand fatigue strength. It is mainly used as the forging and extrusion part. Hotcompression tests of7150aluminum alloy were preformed on Gleeble-1500at thetemperature of300℃and450℃, the strain rate of10s-1and0.01s-1, to different straindegrees （0.2,0.4,0.6,0.8）, to study the relationship between flow stress and strain rate,temperature. The substructure and second phase changes were investigated usingmetallographic microscope （OM） and transmission electron microscope （TEM）. Thechange rule of hardness during hot deformation was studied by microhardness testing.The results are shown as following:（1） The true stress-true strain curves exhibited an initial rapid increase to a peakvalue, followed by a gradual decrease which showed a dynamic flow softening. Thesoftening mechanism at450℃was dynamic recrystallization, while dynamic recoveryat300℃.（2） With the increased strain, the grains were elongated perpendicularly to thecompression direction, coarse phases and brittle phases were fragmented. Whendeformed to strain of0.8, there were some equiaxed grains at the edge of grains at450℃, showing dynamic recrystallization process; the main soften mechanism wasdynamic recovery at300℃.（3） With the increased strain, dislocation density increased. Then themicrostructure evolved from dislocation tangles to cell structure and substructure, bymeans of sliding and climbing. When deformed to strain of0.8, the high-angleboundaries could be found at450℃. The rate of dislocation reaction was higherat450℃, speeding the changes of substructure.（4） At450℃and high strain rate, there were fewer approximate sphericalparticles precipitated during the holding time. During hot deformation, coarse rod-likephases （S（Al₂CuMg）, T（Al₂Mg₃Zn₃））, Al₃Zr dispersoids and micron-sized coarsephases could be observed, while η（MgZn₂） did not exist basically. The coarse phasesled to particle stimulated nucleation （PSN）. At300℃and low strain rate, particlesprecipitated during the holding time were refined and sphericized. The dynamic strainageing （DSA） caused a large number of η（MgZn₂） particles precipitated and coarsened. （5） The hardness value at450℃was higher than at300℃. At the sametemperature, the hardness value was slightly higher at higher strain rate. The hardnesswas almost not influenced by the strain.