The Simulation And Experimental Research On Rotary Degassing Process For AZ91Magnesium Alloy

Because of the low density, high specific strength, high specific stiffness, and goodelectromagnetic shielding, heat dissipation and damping performance, magnesium alloys havebeen proved to be a promising structural material and widely used in aerospace, transportation,and many other fields. However, in the process of smelting alloys there are still someproblems such as inclusions and gas and the comprehensive performance of castings would beseverely weakened. The low purity has become the bottleneck of the development ofmagnesium alloy. In this paper, we used HFC-134a mixture gas as the protective gas of AZ91magnesium alloy and systematically researched purification effects of different refiningprocesses—rotary degassing、C2Cl6metamorphic refining and the combination of them.At the beginning of this research, the purification mechanism and the influence factors ofrotary degassing were outlined. The spinning rotor which was partly designed by ourself wasadopted and CO2-NaOH solution system was used to carry on the water simulationexperiment which simulate the process of refining of magnesium melt. The orthogonalexperiment method was adopted and the handling time of different combination of rotatingspeed, gas flow and the location was analyzed. By the variance analysis method, we obtainedthe significantly factor and the best order of purification process parameters under thisexperimental condition. We studied the influence of rotating speed and gas flow on depth ofthe vortex and the effect of different rotation mode on the processing time, finally obtainedbetter purifying effect of rotary degassing process.We applied the computer simulation analysis software—Fluent and researched theinfluence of different combination of rotating speed and gas flow on the distribution of Ar gasin magnesium alloy melt analyzing the mechanism of each factor. The simulation resultsshowed that only when the gas flow reached a certain value, could Ar be diffused in the alloymelt apparently, and would the rotating speed affect the distribution of Ar. The two parameters should interact together to achieve good Ar distribution in the melt.Under the protection of HFC-134a mixture gas, we adopted rotary degassing as therefining process during melting AZ91magnesium alloy and carried on the orthogonalexperiment. The influence of the three main factors: gas flow, rotating speed and the locationon mechanical properties and microstructure of the samples were investigated, and theconsequence showed that rotary degassing purification technology significantly improved themechanical properties of castings and the primary and secondary sequence is gas flow>rotating speed> the location. The optimum process parameters are gas flow of200L/h,rotating speed of475r/min and the location of40mm. Quantitative detection of inclusions forcastings had been done and we found the percentage of inclusions in the unrefined castingwas1.573%and after rotary degassing process the percentage was reduced to0.5%.The composite purification technology which is the combination of C2Cl6purificationand rotary degassing process was used to purify the melt. Compared with the castingunrefined, the tensile strength and the elongation were increased to161MPa and3.14%from95MPa and1.64%respectively. What is more, the microstructure had been improvedsignificantly.