采用自孕育法制备ZA27半固态浆料,研究流变压铸成形过程中的显微组织及凝固行为.结果表明:ZA27半固态浆料在480℃等温保温3 min,能够制备出细小、圆整、分布均匀的初生α(Al)晶粒,平均晶粒尺寸52.32 μm.浆料在成形过程中发生液相偏析,在受力较大部位,二次颗粒长成“蠕虫状”.剩余液相在铸件不同部位的凝固方式不同,但都没有粗大的树枝晶存在.在冷却速率较小的部位,二次凝固方式主要为依附初生晶粒生长,在共晶组织中有包晶β相析出.在冷却速率较大部位主要为形核凝固,二次晶粒数目多,共晶组织细小.二次晶粒既能够以富Zn的α(Al)相形核,也可以直接以β相形核生长.Cu富集在共品η相中.
The semi-solid slurry of ZA27 casting alloy was prepared by self-inoculation method.And then,the microstructure and solidification behavior during rheo-diecasting forming process were studied.The results show that the semi-solid slurry of ZA27 alloy with the morphology of fine,round and uniform distribution of primary α(Al) grains can be prepared when the slurry is isothermally holded at 480 ℃ for 3 min,the average size of primary grain is 52.32 μm.Segregation of liquid phase would be occured during the forming process of semi-solid slurry,the secondary solidified grains grow into "vermicular" in the area of the high stress.Remaining liquid has different solidification ways in the different parts of castings,but without coarse dendrites.In the positions of low cooling rate,the peritectic phase (β) can be generated in eutectic microstructure,where the attachment growth is the mainly way for secondary solidification.On the contrary,in the position of high cooling rate,the mainly way is nucleation solidification with a lot of secondary crystal nucleus and the fine eutectic microstructure.The grains of secondary solidification can either nucleate by α(Al),or grow directly by the nucleus ofβ phase.Cu element is enriched in the eutectic ηphase.
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