Microstructure Evolution Law Of Deep Cooling Magnesium Alloy Under Magnetic Field Condition

Magnesium alloy was difficult to be formed due to it has a low plasticity, which lead to it far from other metal materials in practical application. It can made metal take regular movement that the force produced by electromagnetic stirring method. In this way, it can reduce the dendritic crystal and increase the equiaxed zone ratio. Therefore, in the process of magnesium alloy solidification, it could be improved that the magnesium alloy’s micro structure and plasticity by electromagnetic stirring technique, which has very vital significant to promote the application of magnesium alloy.AZ91 magnesium alloy was selected as the research object in this paper. It was studied that the influence of electromagnetic stirring on the AZ91 magnesium alloy’s micro structure and plasticity when the stirring frequency is different. Besides, the changes of magnesium alloy’s microstructure and plasticity are also was studied after it had solid solution treatment and cryogenic treatment.These magnesium alloy were prepared under natural solidification,120A-6Hz and 120A-8Hz electromagnetic stirring conditions. Their microstructure were observed, and elongation were tested, some conclusions can be attained as follows:These alloy’s elongation were improved significantly under the condition of electromagnetic stirring. When the stirring frequency was 120A-8Hz, the AZ91 magnesium alloy’s elongation reached to 5.5%. The grain was refined more obviously with the increasing of electromagnetic stirring frequency. The a-Mg primary phase’s morphology was transformed from gross dendrites to rose and honeycomb shape crystals, while the β-Mg17Al12 phase morphology was more easy to damage and dispersed compared with its morphology under natural solidification condition.After the three group alloy had solid solution treatment, they were founded that the elongation would rises with the growth of the solid solution time. Under 120A-8Hz electromagnetic stirring, when the cast AZ91 had solid solution treatment for 24h, the elongation reaches to its maximum value, it was 12.7%. When increasing the solid solution time, the β-Mg17Al12 phase was dissolved more completely, but there was some a-Mg crystal grain growing among the matrix.After the solid solution treatment, the three group AZ91 magnesium alloy had been implemented by cryogenic treatment immediately. When observing their microstructure and elongation, they were founded that the cryogenic treatment can further cement the solid solution degree. When the electromagnetic stirring frequency was 120A-8Hz, the AZ91 magnesium alloy had been implemented by solid solution treatment and the cryogenic treatment for 24h. It reached the maximum value,it was 13.3%. After the solid solution treatment, the cryogenic treatment should be implemented immediately, so that the β-Mg17Al12 phase in the grain boundary could be dissolved completely into the a-Mg matrix.