Effect Of Growth Rates And Alloying Elements On The Solidification Process Of Al-Fe Alloy

Al-Fe alloy is a new type of light heat resistant alloy.Thick needle-like and needle plate-like Al₃Fe compounds in cast Al-Fe alloy are found in the matrix,they greatly reduce the strength of the alloy and restricts the applications of the alloy.The refinement of the microstructure is one of the most effective means of improving the alloy properties. However,many solidification problems of Al-Fe alloy are not well understood.Therefore, the refinement of the microstructure is difficult.In order to understand certain solidification problems,In this paper unidirectional solidification technique was used to study the eutectic Al-Fe alloy,hypereutectic Al-5%Fe,Al-5%Fe-2%Cr and Al-5%Fe-3%RE alloy under different growth rates,and the mechanisms of alloys were also investigated on the base of the experimental results.When temperature gradient is fixed at 75℃/cm,it is found from the experimental results that with an increase in growth rates,the morphology of eutectic Al₃Fe changes from plate-like,to needle plate-like and finally to needle-like,and at the same time the size of eutectic phase becomes fine and the lamellar space of the eutectic phase become smaller. When the growth rates is 61.73μm/s,the preferred crystal face of the growth ofα-Al phase is(111) and(220) at the stable section,however the preferred crystal face of the growth ofα-Al phase changes to(200) while growth rates is 103.41μm/s.The increase of growth rates causes the degree of supercooling of solid-liquid interface to increase,thus causes the macromorphology of solid-liquid interface of eutectic Al-Fe alloy transforming from plane-like to alveolar-like.As to hypereutectic Al-5%Fe alloy,It is found from the experimental results that with an increase of growth rates,the morphology of primary Al₃Fe changes from thick plate-like to thick slice-like,to thin slice-like,and finally to branched slice-like,and at the same time the lamellar space of the primary phase becomes smaller.The numerous primary Al₃Fe phases cause eutectic Al₃Fe andα-Al phase to divorce growth,the morphology of eutectic Al₃Fe phase in the hypereutectic Al-Fe alloys changes from slice-like to needle-like with the increase of growth rates.At the same growth rates,after the Cr added,the morphology of primary Al₃Fe changes from thick plate-like,thick slice-like,thin slice-like,and branched slice-like to lump-like,slice-like and circular caky-like,and primary Al₃Fe plase becomes fine because Cr distributes mainly inside Al₃Fe compound,They suppress the preferential growth of Al₃Fe compound by means of atom occupation space.When RE is added,on one hand it can purify the melt,which restricts the aggregation and growth of primary Al₃Fe phase;on the other hand,it is,as the surface acticity element,easy to fill in surface flaw of the growing primary Al₃Fe phase, which leads to the primary Al₃Fe phase refinement.At the same time,the morphology of eutectic Al₃Fe changes from plate-like,to needle-rod-like,in accordance with macroscope the needle-rod-like eutectic Al₃Fe phase form the network.