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首页> 外文期刊>Materials Science and Engineering. A, Structural Materials: Properties, Microstructure and Processing >The effect of chemical grain refinement and low superheat pouring on the structure of NRC castings of aluminium alloy Al-7Si-0.4Mg
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The effect of chemical grain refinement and low superheat pouring on the structure of NRC castings of aluminium alloy Al-7Si-0.4Mg

机译：化学晶粒细化和低过热度浇注对铝合金Al-7Si-0.4Mg NRC铸件组织的影响

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摘要

The effect of the addition of Al-5Ti-1B (wt.%) chemical grain refiners on the nuclei generation for a range of superheats during pouring in new rheocasting (NRC) of aluminium alloy Al-7Si-0.4Mg (wt.%) has been investigated. The contributions to the grain density by the grain refiner additions and impurity particles were quantified and it was found that the addition of grain refiner provides increasing number of nucleation sites as the superheat is decreased from 105 to 35 ℃. However, at superheats of 15 ℃, which are more typical of NRC, the grain density is similar in the alloy both with and without grain refiner additions. At this superheat, the equiaxed grain morphology is globular rather than dendritic and it is postulated that the grain size is dependant upon grain coarsening mechanisms rather than the number of heterogeneous nucleation events. In agreement with previous studies on semi-solid processing, it was found that the achievement of a fine globular grain structure led to a more homogeneous casting being produced. The mechanism of the macrosegregation observed in these castings is discussed and explained by the 'sponge effect'.
机译：Al-5Ti-1B（wt。％）化学晶粒细化剂的添加对铝合金Al-7Si-0.4Mg（wt。％）的新流变铸造（NRC）浇注过程中一系列过热的核生成的影响已被调查。量化了晶粒细化剂添加和杂质颗粒对晶粒密度的贡献，发现随着过热度从105降低到35℃，晶粒细化剂的添加提供了更多的成核位点。但是，在15℃的过热度下（这是NRC更为典型的），无论是否添加晶粒细化剂，合金中的晶粒密度都相似。在这种过热状态下，等轴晶粒形态为球状而不是树枝状，并且推测晶粒尺寸取决于晶粒粗化机理而不是异质成核事件的数量。与先前对半固态加工的研究相一致，发现细小球状晶粒结构的实现导致生产出更加均匀的铸件。在这些铸件中观察到的宏观偏析机理通过“海绵效应”进行了讨论和解释。

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