in the microstructure from the edge area of the middle position, the fine particular-like primary α-Al in the microstructure resulted from the secondary arms broken off from dendritic crystal, as shown in Fig. 2b. The microstructure on the edge area, near the bottom, still consisted of particle-like and rosette-like α-Al, as shown in Fig. 2c. In addition, no dendritic-like crystals
which did not fully change into rosette-like primary α-Al or dendritic-like crystals were observed in the microstructure. Along the radial direction of the same height in the
ingot, the microstructure in the top did not change, and basically consisted of particle-like or globular-like primary α-Al and rosette-like primary α-Al, as shown in Fig. 1a and Fig. 2a. Few changes to the morphol- ogy of microstructure along the radical direction in the mid position were noticed from the particle-like or globular-like primary α-Al in the central area and the transition area changing to the microstructure mixed with particle-like or globular-like primary α-Al in the edge area, as shown in Fig. 1b and 2b. Some changes to the morphology of microstructure occurred along the radial direction in the bottom, from the particle- like or globular-like primary α-Al in the central area transforming to microstructure mixed with particle- like or globular-like primary α-Al and rosette-like primary α-Al, up to the microstructure mixed with particle-like and rosette-like primary α-AL in the edge area, as shown in Fig.1c and 2c. Fig. 3 shows the microstructure morphology of a semi-solid A356 alloy prepared by LSPSEMS with the same processing parameters. The obvious changes for the micro- structure morphology occurred along the radial direction, presenting three typical structural areas. The morphology of primary α-Al in the central area of ingot was particle-like or globular-like, and the grain size of the primary α-Al was finer but coarser than that of the primary α-Al prepared by the com- pound process, as shown in Fig. 3a. The primary α-Al morphology was changed from the particle-like or globular-like to the rosette-like in the transition area of the ingot. A few coarse dendritic-like crystals which
图2为复合工艺制备的半固态A356合金铸锭不 同部位边缘的组织形貌。由图可见，边缘的组织形 貌较心部的组织和过渡区域的组织稍有变化，但不 明显。该部位的组织随着铸锭高度由上而下，发生 了一些变化。上部的边缘组织是由颗粒状的初生相 和极少量蔷薇状的初生相构成，如图2a所示；而中 部边缘的组织中，蔷薇状初生相稍有增加，组织中 细小的颗粒状α相应是树枝晶上脱落下来的二次臂 所致，见图2b所示；靠近铸锭底部，其边缘的组织 仍由颗粒状初生相和蔷薇状初生相组成，见图2c所 示。另外，在组织中未观察到未完全转变成蔷薇状 初生相的树枝状晶，或树枝状晶。
对于铸锭中同一高度沿径向的组织形貌的分布来 看，上部的组织形貌沿径向基本上无变化，其组织 是由颗粒状或球状的初生α相构成，见图1a和2a所 示。中部的组织形貌沿径向的变化也很小，由心部 和过渡区域的颗粒状或球状的初生α相向着边缘部 位的以颗粒状或球状的初生α相为主，伴有少量蔷 薇状初生相的混合组织转变，见图1b和2b所示。 底部的组织形貌沿径向尚有一些变化，由心部的颗 粒状或球状的初生α相向过渡区域的以颗粒状或球 状的初生α相为主，伴有少量蔷薇状初生相的混合 组织转变，直至边缘部位的颗粒状初生相和蔷薇状 初生相组成的混合组织，见图1c和2c所示。 图3是研究中按照相同的工艺参数，利用低过热度 浇注和弱电磁搅拌技术制备半固态A356合金浆料 的对比实验结果。由图3可见，采用低过热度浇注 和弱电磁搅拌技术制备的半固态A356合金浆料， 其铸锭组织的形貌沿径向有明显的变化，呈现典型 的三个组织区域。铸锭心部的初生α相呈颗粒状或 球状，尺寸较细小，但是比新工艺所获得的初生α 相的尺寸略大一些，见图3a；而在过渡区域，初生
Fig. 3. Shown is the morphology of micro- structure along radial direction in an A356 semi-solid slurry pre- pared by LSPSEMS along the central area (a), transition area (b) and edge (c).
图3 低过热度浇注 和弱电磁搅拌制备 的A356半固态浆 料铸锭沿其径向的 组织
a b c 44 |
FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION May 2013
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