Preliminary Study Of Devices And Technology Of Electrostimulated Rolling Of Mg

Poor ductility is a bottleneck of processing and application of magnesium, cast aluminum alloys and other brittle alloys,so ductility enhancement becomes a key to research and application of hard and brittle materials.It is difficult to have a continuous multiprocessing of the workpiece after traditional plastic deforming process especially the cold-working process of metal,because of the internal dislocation formation and movement which leads to a work hardening and causes hardness and brittleness in materials.As to refractory, hardworking and brittle metals and alloys, in order to overcome the deficiencies of the traditional plastic processing, the paper will explore preliminarily a new plastic processing technology electrostimulated rolling(ER).Firstly, the paper conducts a through study to the technology requirement of ER, has developed small equipment for ER, and applied for a relevant patent (application number:200910117549.8).Secondly, the paper presents the corresponding experimental program, carrying out the electric-pulsed rolling experiments to AZ91D plate under different processing conditions.And then makes a tensile strength,elongation and other mechanical properties testing to the original sample and samples which carry out ER treatment under electric pulse.Observe the microstructure changes between the original sample,samples under ER treatment and those under cold-rolling condition with metallographic microscope.Then conduct a comparative analysis of mechanical properties and microstructure to the samples under traditional rolling and ER.The results show that:1. The ER technology can process poor-ductility alloys. AZ91D magnesium alloy has been proved to be rolling under the treatment of electropusing. After repeated experiments the optimum parameters of ER processing for AZ91D magnesium plate can be obtained:pulse frequency of 50Hz, pulse voltage of 72V, pulse current of 550A, rolling speed of 25r·min-1.2. The maximum deformation of sample under cumulative passes ER processing gradually increases with the current increasing, but reaches a certain peak value and then decreases. Due to the electric plastic effect, the maximum deformation after ER can reach to 59.5%.3. The mechanical properties such as the tensile strength of AZ91D magnesium can be remarkably improved under the optimum parameters of ER processing. But there is still a phenomenon of work hardening.4. AZ91D magnesium alloy microstructure has significantly changed after ER. There was fibrous tissue, some dendrites were interrupted, and grains are obviously refined. The grain deformation of center area of deformation region is more significant than the edge. There were more fine grains in the center area.In addition, the ER to 3A21 aluminum is carried out and the results were compared with those of AZ91.Finally, an exploratory study about ER mechanism is carried out according to the electroplastic deformation theory and other relevant theories, found that the pulse current can greatly increase the the plastic indicator of the processing metal, the thermal effect of electroplastic effect(EPE) can decrease the recrystallization temperature at the onset of rolling, accelerate its recovery and recrystallization process, increases the nucleation rate of recrystallization. So t the properties of metal can recover rapidly. Doing this we can effectively reduce the number of intermediate annealing or even avoid the process, strengthen the production process, greatly increase productivity.