Springer Online Journal Archives 1860-2000
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Abstract For gravity castings made from Zn-12% Al alloys wide variations of impact strength have been observed that could not be explained in terms of casting soundness. Previous unpublished research isolated trace impurities of silicon as the cause of a large increase in eutectic grain size and subsequent decrease in impact strength. In the present study the effect of silicon on the as-cast eutectic grain size and impact strength of Zn-12Al is confirmed. Thermal analysis and interface equilibration experiments indicate that silicon impedes nucleation of the eutecticβ phase. Finding that the presence of silicon lowers the primaryα′/eutectic liquid interfacial energy, it is concluded that silicon, rejected by the pro-eutecticα′phase during primary solidification, poisons the interface causing the difficulty with the nucleation of eutecticβ on the primaryα′ surface leading to the increase in eutectic grain size.
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