Effect of TiB2 on univariant eutectic growth in a directionally solidified Al-alloy

Abstract

During directional solidification of a near-eutectic Al–Mn–Si alloy the univariant eutectic is formed, following the reaction: L→α-Al + α(AlMnSi) + L′ and reveals a non-faceted α-Al/faceted α(AlMnSi) structure. The addition of titanium diboride (TiB₂) promotes the nucleation of intermetallic α(AlMnSi) silicide phase at solid/liquid interface as particles, which are pushed and periodically engulfed by the advancing planar interface. This type of growth, called symbiotic growth, leads to a layered microstructure. To study the influence of TiB₂ upon the morphology of α(AlMnSi) phase various amounts (from 0·05 up to 2·00 wt-%) of TiB₂ were added to alloys with identical composition. The results show that the behaviour and the influence of the inoculant is not trivial. Both the presence of titanium diboride at the solid/liquid interface and its inoculation effect determine the final morphology of the silicide phase.