| Magnesium alloy arouse researcher’s widespread concern and attention because of highspecific modulus and specific strength, high resistance to high temperature and impact, asmall thermal expansion coefficient, excellent vibration resistance, easy processing,recyclable and so on, which cause it important Green engineering material in the21stcentury. But magnesium alloy tend to burn and Oxidation in high temperature which make ithigh cost to produce goods with it. Semi-solid forming technology with nearly end near netforming characteristics can produce products with excellent mechanical properties which hasopened up broad prospects of magnesium alloy products development.The basic principle of semi-solid forming technology is follows: Near liquid line, Bystirring or heating the material to obtain semi-solid non-dendritic paste, then, using pressuremode, make the slurry coagulation to be products in the mold cavity. Using the principle ofsemi-solid forming method called rheological forming. However, preserve semi-solid slurrywhich already made through congealing it into ingot casting When you need to use theingot,cut it into the required size, heat it into semi-solid remelting. Using traditional methods(such as die casting, extrusion, forging, etc.)to take shape method is semi-solid Touch intofractal technology.The paper based on AZ91alloy as the research object, with rare earth samarium (Sm) asthe modifier, using chemical grain refinement to prepare semi-solid magnesium alloy billet.Systematically studied effect of the rare earth samarium on AZ91magnesium alloy grainrefining mechanism, comprehensive effect of pouring temperature and adding amount ofsamarium on grain refining effect. The study showed that1%wt of rare earth Sm to join andthe pouring temperature of750℃to cooperate to get the best effect on grain refining.In the process of semi-solid isothermal heat treatment, with the increase of isothermaltemperature, the increase in the number of the liquid phase of semi-solid organization；Withthe extension of isothermal time, the material change in the morphology of semi-solidorganization are dendrite melting mergers, separation of grain boundary melting, grain rose,the rose petals in the fusion fillet, nearly spherical grains, the grain growth.For the preparation of1.0%Sm-AZ91magnesium alloy in room temperaturecompression test, the results show that this kind of brittle material for magnesium alloys, thecompression rate of change has no effect on bearing capacity of AZ91magnesium alloy.Under the condition of different compression rate, almost the same size of the magnesiumalloy specimen occurs under the same load shear fracture of45degrees. In metal plastic deformation, on the basis of theoretical model, combining previous ofAZ91magnesium alloy thixotropic compression constitutive equation, the constitutiveequation was import the DEFORM software to uniaxial compression and AZ91magnesiumalloy semi-solid thixotropic extrusion forming numerical simulation, validation, into theconstitutive equation. It can better reflect the material in the mechanical behavior and the flowbehaviors of isothermal compression. The paper analyses the heating temperature of billet andprocess parameters on the material such as the compression rate of the distribution oftemperature field, equivalent stress and equivalent strain and the influence of the change. Theresult of the simulation results are very close to the compression test, both have good fit. Andaccording to the constitutive equation of precision can meet the requirements. The studyshows that the grain size of plastic deformation, mutual interface slippage between sphericalgrain flow in the liquid phase and solid phase organizations is magnesium alloy in semi-solidthixotropic compression deformation mechanism. The increase of deformation temperatureand strain rate decrease will cause the loss of material flow stress. |
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