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双螺旋搅拌工艺制备了AZ91D合金半固态浆料,获得金属半固态加工要求的细小、等轴分布均匀的非枝晶组织。研究了熔体温度、搅拌速度和剪切时间对该组织的影响规律。结果表明:采用合适的搅拌工艺,可获得金属半固态加工要求的细小、等轴分布均匀的非枝晶组织。即降低降体温度、搅拌速度及适当剪切时间有利于细小球形晶粒的形成。加大搅拌速度及合理搅拌时间可以细化晶粒,主要是由于是高剪切作用下熔体获得一个非常均匀温度场,从而增加有效形核的缘故。
AZ91D alloy semi-solid slurry was prepared by double-helix stirring process to obtain the fine and equiaxed uniform non-dendritic microstructure required for semi-solid metal processing. The effects of melt temperature, stirring speed and shear time on the microstructure were studied. The results show that the non-dendritic microstructure with fine and equiaxed distribution required by semi-solid metal processing can be obtained by proper stirring process. That is, lowering the temperature of the falling body, the stirring speed and the proper shearing time are favorable for the formation of fine spherical grains. Increasing the mixing speed and mixing time can refine the grain, mainly due to the fact that the melt obtains a very uniform temperature field under high shear, thus increasing the effective nucleation.