Influence And Refining Mechanism Of Grain Refiners On Hypereutectic Al-Fe Alloy

By changing the addition and holding time, the influences of different grain refiners (including Al-Ti-B, Al-Ti-C, Al-Ti-C-B), trace element Sc, and combination of alloying elements with electric current treatment on the microstructure and mechanical property of hypereutectic Al-Fe alloy were investigated in this thesis. The mechanisms of these grain refiners on hypereutectic Al-Fe alloy were also discussed based on the experimental results.When 1ï¼…Al-Ti-B was added in the hypereutectic Al-5%Fe alloy, and the holding time of alloy melt was kept 90 min, the refining effect on the alloy was better. The primary Al₃Fe phase changed from the extremely thick plate-like to fine particle-like and flower-like, furthermore, the size of the primary Al₃Fe phase was reduced obviously.While 1ï¼…Al-Ti-C-B was added in the hypereutectic Al-5ï¼…Fe alloy, and the holding time of alloy melt was kept 90 min, the better refining effect was observed. The primary Al₃Fe phase majorly appeared fine flower-like, and some particle-like primary Al₃Fe phase was dispersed around it. The tensile strength of the alloy was raised to 131.0MPa from 121.4MPa, and was improved 7.9ï¼….Further, Al-5Ti-0.25C was added in the hypereutectic Al-5ï¼…Fe alloy. When the addition was 1ï¼…and the holding time was kept 30min for the alloy melt, the best refining effect was achieved. The primary Al₃Fe phase changed from the extremely thick plate-like to fine needle-like, flower-like and particle-like. The tensile strength of the alloy was 144.2MPa, and was raised 18.8ï¼….In addition, trace element Sc was added in the hypereutectic Al-5ï¼…Fe alloy. When 0.4ï¼… Sc was added with the holding time of melt being 30 min, the best refining effect was acquired. The primary Al₃Fe phase was changed to fine needle-like, particle-like and flower-like. And the tensile strength of the alloy approached 186.2MPa, and was raised 53.4ï¼…. The addition of Sc element can not only cause the constitutional undercooling at the interface of solidification interface, but also reduce the misfit degree and interfacial energy between the primary Al₃Fe phase and the matrix. Thus, the primary Al₃Fe phase was greatly refined.Electric current treatment of 59A/dm² was acted on the hypereutectic Al-5ï¼…Fe alloy containing 0.4ï¼…Sc. It was found that the size of primary Al₃Fe phase was reduced obviously, the particle-like primary Al₃Fe phase looked much more finer, the short needle-like primary Al₃Fe phase was reduced, and the morphology of the alloy was apparently improved. Electric current treatment of 59A/dm² was exerted on the hypereutectic Al-5%Fe alloy with addition of 1%Al-5Ti-0.25C. It was observed that the size of primary Al₃Fe phase was further reduced, and appeared to be fine needle-like and particle-like.