Study Of Solute Distribution Rule In Solidification Process To Magnesium Alloys

Distribution uniformity of solute elements, phase precipitation, solute segregation and grain size were influenced by solute distribution rule, study of solute distribution rule was very important significance to improve the comprehensive performance of cast magnesium alloys. Therefore, optimized solidification process, and getted the best comprehensive properties magnesium alloy castings of through the study of solute distribution rule in solidification process to magnesium alloys.Mg-Al alloys were investigated in this paper. The solute distribution rule and cast micstructure of alloys of different Al and Zn content is analysised by means of optical microscope, electrical resistivity measurements and DSC, etc. Following research results were obtained.According to the optical microstructure of the different quenching temperature, in solidification of earlyα-Mg grows by the means of the equiaxial crystal and slow growth. In the stable solidification stage, through the equiaxial crystal arm coarsening branch of growth and rapid growth way; In the stable solidification stage, the big grain absorbed other small grain, at the same time a lot of cellular crystal grew in surplus liquid.To Mg-Al and Mg-Al-Zn alloys, the solute distribution coefficient decreased with the increase of solid phase. This experimental solute distribution coefficient and balance solute distribution coefficient was close,when solid phase volume fraction was up to 50%. Meanwhile proved that augmentation amount of solute in the solid phase of front solidification was less than in liquid phase. With the addition of Al to the Mg-Al alloys, Al atoms in theα-Mg matrix solid solution volume increased gradually; but when the addition of Al was greater than 6%, the average Al atoms in theα-Mg matrix did not increase with the added volume; a large number of Al atomss precipitated at the grain boundaries or dendrite boundary. In Mg-6Al and Mg-9Al alloys, the content of Al atoms inα-Mg matrix was decreased, with a certain amount of Zn addition, so that more Al atomss precipitated in the grain boundaries or between dendrite.The solute distribution rule of the front of dendritic was compared with the Scheil model, Balance model and experimental values. For the initial solidification stage of Mg-Al alloys, when content of Al was 6%, experimental values was between the two model values, when content of Al was 6% and 9%, experimental values was higher than the two model values; For the Mg-Al-Zn alloys, experimental values were lower than the value of the two models. To the final solidification of the alloys, solute content of Al was close to Balance model values.To Mg-Al and Mg-Al-Zn alloys, too high or low segregation rate was not conducive to grain nucleation and grain growth inhibition, when segregation rate was higher than 41.72%, GRF bigger, finer grains; When segregation rate was lower than 41.72%, GRF larger more coarse grains.