Eutectic modification by ternary compound cluster formation in Al-Si alloys.

ABSTRACT: Al-alloys with Si as the main alloying element constitute the vast majority of Al castings used commercially today. The eutectic Si microstructure in these alloys can be modified from plate-like to coral-like by the addition of a small amount of a third element to improve ductility and toughness. In this investigation the effects of Eu and Yb are studied and their influence on the microstructure is compared to further understand this modification. The two elements impact the alloy differently, where Eu modifies Si into a coral-like structure while Yb does not. Atom probe tomography shows that Eu is present within the Si phase in the form of ternary compound Al₂Si₂Eu clusters, while Yb is absent in the Si phase. This indicates that the presence of ternary compound clusters within Si is a necessary condition for the formation of a coral-like structure. A crystallographic orientation relationship between Si and the Al₂Si₂Eu phase was found, where the following plane normals are parallel: 011_Si//0001_Al2Si2Eu, 111_Si//6[Formula: see text]10_Al2Si2Eu and 011_Si//6[Formula: see text]10_Al2Si2Eu. No crystallographic relationship was found between Si and Al₂Si₂Yb. The heterogeneous formation of coherent Al₂Si₂Eu clusters inside the Si-phase is suggested to trigger the modification of the microstructure.

SUBMITTER: Barrirero J 

PROVIDER: S-EPMC6445082 | biostudies-literature | 2019 Apr

REPOSITORIES: biostudies-literature