Effect Of Rare-Earth Modification On Microstructure Of Al-Si Eutectic Alloys

A413.0 aluminum alloy is an Al-12.6%Si-X eutectic alloy which contains 1.3 wt% of Fe, having excellent mechanical properties. However, its application is seriously restricted due to existence of the coarse α-Al dendrites, needle/plate of eutectic Si and β-Fe phases.The β-Fe phase is considered to be harmful in the aluminum alloys, so elimination of the phase becomes a very important research topic. So far, it still hasn’t been solved effectively.Therefore, this paper is devoted to improve the microstructure such as the coarse α-Al dendrites, needle/plate eutectic Si and β-Fe phases by adding Er and Ce-rich mixed rare earth(RE). In addition, the microstructure of A413.0 aluminum alloy is further improved by a T6 heat treatment process. Meanwhile, the effects of Er and Ce-rich mixed RE modification on the microstructure of A413.0 aluminum alloy were investigated using the microscope(OM), X-ray diffraction(XRD), scanning electron microscope(SEM) and energy dispersive spectrometer(EDS). The mechanism of the rare earth modifications was analyzed and the conclusions are as follows:The addition of 0.5 wt% Er has the best effect on A413.0 aluminum alloy.Experimental results show that addition of 0.5 wt% Er refined the primary α-Al grains and transformed eutectic Si from coarse needle/plate into fibrous/globular phase in its as-cast state. Moreover, it was seen that under low multiple(200X) the coarse lath-like β-Fe phases are almost completely eliminated. At the same time, it was seen that under higher multiple(500X) the small needle/plate β-Fe phases are refined in some extent. After the T6 heat treatment, the fibrous eutectic Si is modified into fine particle or shot rod structure,and uniformly distributed in the matrix. There is an obvious break-up trend for the β-Fe phases, and parts of them are modified into flocculent structure. The change of primaryα-Al grains was not obvious. However, the microstructure of A413.0 aluminum alloy gets worse when the content of Er is more than 0.5 wt%.The addition of 1.0 wt% Ce-rich mixed RE has a better effect on the A413.0 aluminum alloy. The addition of 1.0 wt% Ce-rich mixed RE refined the primary α-Al grains and transformed eutectic Si from coarse needle/plate into fibrous/globular phases in its as-cast state. Moreover, it was seen that under low multiples(200X) the coarse lath-like β-Fe phase was almost completely eliminated. However, it was seen that under higher multiples(500X) the change of morphology of the small needle/plate β-Fe phases is not obvious.After the T6 heat treatment, the fibrous eutectic Si is modified into fine particle or shot rodstructure, and uniformly distributed in the matrix. The changes of primary α-Al phase andβ-Fe phase are also not obvious. The microstructure of A413.0 aluminum alloy begins to worse when the content of Ce-rich mixed RE exceeds 1.0 wt%.So the Er modification has a better effect on the microstructure of A413.0 aluminum alloy than that of the Ce-rich RE modification.