Study On Retransformation Strengthen Of The Deformation Close Grain Of The AZ31 Magnesium Alloy

In allusion to the poor plasticity and low intensity at room temperature of AZ31 Mg alloy, this paper studied the progress of once deformation and twice deformation and how the temperature, deforming rate, and deforming amount influence the rheological stress and room temperature intensity after deformation. Moreover, all of these are tested in products which provided theoretic gist for Mg alloy deforming strengthening.First, rheological property of AZ31 at different temperature and deforming rate is studied appling Gleeble-1500 thermal-mechanical simulator. The emphasis is on how deforming temperature, deforming rate, and deforming amount influencing deformation resistance of material, from which the law is found. The mathematic model of deformation resistance of this material is set up according to regressive method, which provided basic gist for choosing technological parameter of isothermal extrusion formation.On this basis, variation law of AZ31 tensile strength at room temperature was studied after the once deformation and twice deformation. The result indicated that the deformation effect of the once deformation is conspicuous at 210℃, the reason of which is gaining thin crystal grain, while the twice deformation can raise AZ31 strength. While the deformation temperature is 240 ℃, the deformation degree reach 1.79, the strength is highest which is 390 Mpa, and complex strengthening effect is the most conspicuous, which is 157Mpa higher than the strength after sinking strain and 220 Mpa higher than homogenizing annealing of casting blank, elongation also has greater improvement than as-cast ingot. There is no essential difference of deformation mechanism between once deformation and twice deformation. So all of them can be explained using the same microstructure. But twice deformation has sinking strain as the preconditioning which eliminated casting defect, and can be manipulated at lower temperature and higher deformation velocity. If the technology is controlled properly, the twice deformation has advantage in enhancing mechanical behavior. Forming mode should be choosen according to concreted case.Finally the result is tested by experiment. In allusion to shape characteristic radiator frame loaded by helicopter and the twice deformation characteristic of AZ31,we constituted forming processing routes: bar saw cutting——flat blank making——preformation——clearance by acid——reshaping, choosing and optimizing technology parameter. We choose blacklead + animal oil/vegetable oil as extruding lubricant. The experiment results indicated that the constituted process and the die designed are reasonable and feasible, and the mechanical property, microscopic structure and size accuracy of the forming accessory are all satisfactory, which provided theory and practical gist for plastic forming of large flat bar accessories.