A Study On Solidification Microstructure Of Al-Fe Binary Alloy

The thick needle plate-like Al3Fe phases in the ordinary cast Al-Fe alloy are found in the matrix and greatly reduce the strength of the alloy, which restricts the application of Al-Fe alloy as a new type of lightweight heat resistant alloy. In order to study the changing rule and the mechanism of solidification microstructures in the Al-Fe ordinary cast alloy, a lot of jobs have been done in this thesis which could support the refinement of the microstructures. In this work we obtained the solidification structures of eutectic and hypereutectic Al-Fe alloy through slow cooling in crucible, and we obtained the solidification structures of eutectic and hypereutectic Al-Fe alloy through iron mould casting. We also obtained the cooling curves during solidification. The effects produced by Fe contents and the pouring temperature on the solidification structures of Al-Fe binary alloy are studied in a systematic way in various microstructure testing methods. The main results are as follows.(1) Equilibrium solidification occurs to the Al-Fe alloy during slow cooling in crucible, which cooling rate is0.5-1℃, and obtained needle-like and plate-like Al3Fe phase. Non-equilibrium solidification occurs to the Al-Fe alloy during metal mould casting, which cooling rate is about100℃/s, and obtained small Fe rich phase. It indicates that cooling rate can refine Fe phase.(2) There exists primary a-Al dendrite at the edge of Al-Fe alloy ingot on the cooling condition of metal mould which is made of cast-iron. Meanwhile with the Fe content increasing the range of the a-Al dendrite decreases and completely disappears when the Fe content reaches5%. In the center of ingot, Al-2Fe alloy is hypoeutectic, which is consist of a-Al and Al-A16Fe; Al-3Fe alloy is consist of Al-Al6Fe eutectic, Al-4Fe alloy has clusters that containing Al3Fe phase, in addition to Al-A16Fe eutectic. There has more clusters in Al-5Fe alloy, and the clusters connected together with each other.(3) Al-A16Fe eutectic reaction occurs in Al-3Fe alloy under the cooling condition of iron mold casting, the eutectic temperature is643℃, the supercooling is12℃. Al-A13Fe eutectic reaction occurs in Al-5Fe alloy, the eutectic temperature is650℃, the supercooling is5℃. It indicates the greater the degree of supercooling, the more favorable of Al-A16Fe eutectic reaction. (4) There is Al-A16Fe eutectic in Al-3Fe alloy when pouring at810℃and840℃in the center, basically has no A13Fe phase. But when pouring at780℃clusters containing Al3Fe phase appears. There has the similar phenomenon in Al-5Fe alloy. There has more clusters when pouring at810℃compared with pouring at840℃and870℃, and clusters connected with each other. It indicates that when the pouring temperature is too low, it is not favorable of Al-Al6Fe eutectic reaction.