Effects of Er addition on the crystallization characteristic and microstructure of Al-2wt%Fe cast alloy

Abstract

Effects of Er addition on the crystallization characteristic and microstructure of Al-2wt%Fe cast alloy have been investigated using cooling curve thermal analysis, optical microscopy, X-ray diffraction, SEM and TEM. Results showed that the Er addition has important effect on the crystallization characteristic of studied alloys. Thermal analysis indicated that at studied cooling rate of 1.3 °C/s, the Al-2wt%Fe cast alloy consists L→Al+Al3Fe eutectic transformation, while the alloy composes of L→Al+Al3Fe and L→Al+Al3Er eutectic transformation simultaneously with Er addition. The nucleation temperature of Al+Al3Fe eutectic increased first and then decreased with the increase of Er addition, the crystallization time of (Al+Al3Fe) eutectic decreased with the increase of Er addition. When Er addition is 0.3 wt%, the nucleation temperature has reached a peak of 650.95 °C. The addition of Er has a role of refinement on eutectic phase of Al-2wt%Fe alloy. As a favorable heterogeneous nucleation nucleus of eutectic α-Al, the primary Al3Er particle reduces the required undercooling and increases the nucleation rate. The average length of Al3Fe of 0.3 wt% Er reaches a minimum value of 37.69 μm, which is reduced by nearly half compared with that of Er free alloy. When Er content is 0.5 wt%, a small number of hollow square or diamond shaped Al3Er particles grown up to about 2 μm which can not be used as site of heterogeneous nucleation. With the content of Er from 0.1 wt% to 0.5 wt%, the growth temperature of (Al+Al3Er) eutectic increased from 626.46 °C to 635.41 °C. The supersaturated Er segregated at the α-Al/Al3Fe phase interface after solidification, and the orthorhombic Al10Fe2Er was found adhered to Al3Fe.