ZA27合金自孕育流變壓鑄顯微組織及凝固行為ZA27合金自孕育流變壓鑄顯微組織及凝固行為Microstructure and solidification behavior of ZA27 prepared by self-inoculation rheological die casting 采用自孕育法制備ZA27半固態漿料，研究流變壓鑄成形過程中的顯微組織及凝固行為。結果表明：ZA27半固態漿料在480 ℃等溫保溫3 min，能夠制備出細小、圓整、分布均勻的初生α(Al)晶粒，平均晶粒尺寸52.32 μm。漿料在成形過程中發生液相偏析，在受力較大部位，二次顆粒長成“蠕蟲狀”。剩余液相在鑄件不同部位的凝固方式不同，但都沒有粗大的樹枝晶存在。在冷卻速率較小的部位，二次凝固方式主要為依附初生晶粒生長，在共晶組織中有包晶β相析出。在冷卻速率較大部位主要為形核凝固，二次晶粒數目多，共晶組織細小。二次晶粒既能夠以富Zn的α(Al)相形核，也可以直接以β相形核生長。Cu富集在共晶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 of β phase. Cu element is enriched in the eutectic η phase.
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