半固态A380铝合金浆料凝固过程中显微组织的演变

Microstructure evolution of A380 aluminum alloy semi-solid slurry during solidification

采用石墨质蛇形通道制备半固态A380铝合金浆料,研究浆料凝固过程中显微组织的演变。结果表明:A380铝合金熔体在蛇形通道内发生一次凝固,在其通道内壁激冷作用和异质形核作用下形成大量的初生自由晶,半固态浆料的剩余液相在收集坩埚内发生二次凝固形成二次非枝晶组织。初生晶粒的游离模型表明一部分初生自由晶直接生长为球晶,其他部分则成长为枝晶,枝晶在"自搅拌"的作用下发生缩颈和熔断,通过"自旋转"在蛇形通道内得到初步球化和熟化。二次凝固形成的二次非枝晶在收集坩埚内得到初步球化和熟化。同时,初生晶粒在收集坩埚内得到进一步球化、熟化和均匀分布,最终制备得到球状晶粒均匀分布的半固态浆料。

The semi-solid slurry of A380 aluminum alloy was prepared by the graphite serpentine channel, and the microstructure evolution during the solidification was investigated. The result shows that the initial solidification occurs in the serpentine channel, a large number of primary free grains are generated in the alloy melt in the role of chilling and heterogeneous nucleation of the serpentine channel inner wall. The secondary non-dendrites are formed during the secondary solidification which occurs in the remaining alloy melt of the semisolid slurry in the collective crucible. The drifting mode of primary grains indicates that a part of primary free grains grow to the spherical grains directly, others develop to the dendrites, the “self-stirring” of the alloy melt make the dendrites neck and fuse, and the dendrites get initial spheroidization and ripening by the “self-rotating” in the serpentine channel. The secondary non-dendrites formed during the secondary solidification get the initial spheroidization and ripening in the collective crucible. Meanwhile, the primary grains get the further spheroidization, ripening and uniform distribution in the collective crucible. Finally, the semi-solid slurry with uniformly distributed spherical grains is obtained.