Study On Compression Behavior And Rolling Of Semi-solid7050Aluminum Alloy

Semi-solid forming Metal technology (SSM) is different from the traditional liquidforming and solid plastic deformation. Compared with conventional casting process, theforming temperature of SSM is lower and the die life can be extended. Compared with theconventional solid plastic forming, SSM forming has less deformation resistance,forming complex parts. In this work,7050aluminum alloy was prepared by Strain InducedMelt Activated method (SIMA). The compression deformation behaviors and microstructurecharacteristics of semi-solid7050aluminum alloy were studied by the Gleeble-3500thermo-simulation machine. Moreover, semi-solid7050aluminum alloy through hot rolling、spray rolling、thixo-rolling were also studied. The main results are as follows:The results show that the semi-solid7050alloy can be prepared by SIMA with a largeextrusion ratio for pre-deformation. The optimum parameters are as follows: the extrusionratio is about11.11with the isothermal temperature of590℃and the holding time of about20min. Pre-deformation temperature, isothermal temperature and holding time are the mainfactors for semi-solid7050alloy through SIMA method. During the formation of anon-dendrites structure in7050aluminum alloy, the recovery and recrystallization of grainsoccur at the heating stage. On the other hand, the low melting point phase segregating alongthe grain boundary can lead to the separation and breakup of recrystallized grains. During thetemperature-keeping stage, the separated and broken grains gradually spheroidize under theatomic diffusion and surface tension. The grain consolidation and growth follow Ostwardripening law.The flow stress behavior of semi-solid7050aluminum alloy during hot compressiondeformation was studied by thermal simulation test at the deformation temperatures of420-465℃, strain rates of0.001-0.1s1on Gleeble-3500thermal-mechanical simulator.The maximum amount of compression was0.69.The results show that when the strain rate isconstant, the flow stress decreases with increasing deforming temperature, when thedeformation temperature is constant and the flow stress increases with increasing strain rate. This alloy has positive strain rate sensitivity. The flow stress and strain rates follow therelationship of hyperbolic sine. The hyperbolic sine logarithmic of the flow stress and thecountdown of thermodynamic temperature follow the linear relationship. The Z parameterscan describe the flow stress according to this relation. The material constants at highdeformation temperatures were calculated. The deformation activation energy is151.997KJ/mol. The flow stress constitutive equation during hot compression is obtainedthrough regression analysis method. The microstructures after hot compression deformationare obviously uneven.The results of hot rolling texts show that with increasing rolling temperature the strengthfirst increases and then decreases. There is no great change in the elongation. For hot rollingat470℃, the mechanical properties are the best, the tensile strength increases with increasingrolling reduction while the plastic decreases. After solution treatment and aging, themechanical properties improve significantly. The tensile strength is up to546.0MPa,increasing12.8%.The results of spray rolling tests show that with increasing rolling temperature thestrength changes with the same trend as in the hot rolling. The plasticity is very bad and theelongation is about3.0%. The mechanism of tensile fracture is cleavage fracture. Aftersolution treatment and aging, the plasticity improved. The elongation increases to more than8.0%. There are different sizes of dimples in the tensile fracture surface and the fracturemechanism is dimple fracture.The results of thixo-rolling tests show that there is no difference in the strength betweenthixo-rolling and hot rolling. The elongation is about10.0%. After solution treatment andaging, the mechanical properties are also improved. But it is lower than that after hot rolling.The mechanism of tensile fracture is dimple fracture before and after heat treatment.