Effects Of Al-5Ti-0.25C-2RE On The Microstructures Of A356 And 3003 Alloys

A356 and 3003, respectively, the most widely used of the two alloys in the foundry aluminum alloy and wrought aluminum alloy. However, the coarse grains and block secondary phase in the alloy can decrease the mechanical properties, and restrict the using field of the alloys. In this paper, Al-5Ti-0.25C-2RE master alloy is used to refine and modify A356 and 3003 aluminum alloys. The effects of Al-5Ti-0.25C-2RE on A356 and 3003 alloys were analyzed by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and other methods. The refining parameters and mechanisms were also studied and discussed in this paper.The results show that A356 with 0.5wt% of Al-5Ti-0.25C-2RE has weak refining effect. Grain size decreases with the increase of the master alloy addition level, when the addition amount of Al-5Ti-0.25C-2RE reaches 3wt%, the macro-grains of A356 were refined from 1230μm to 230μm. Though little Al-5Ti-0.25C-2RE has a poor refining effect on the grain size of A356, it can effectively refine the dendritic structure and reduce the secondary dendrite arm spacing (SDAS). When add 3wt% of Al-5Ti-0.25C-2RE to melt of A356, the SDAS can get an 18.86% reduction. Al-5Ti-0.25C-2RE can effectively modify the needle/plate like eutectic silicon and iron-rich impurity phase to short rod/granular like. Al-5Ti-0.25C-2RE can get a better refining effect in A356 when compared with Al-5Ti-0.25C.The macro-grains of 3003 were refined from 1729μm to 192μm with 0.5wt% Al-5Ti-0.25C-2RE master alloy. Increasing the addition amount of Al-5Ti-0.25C-2RE, there is no more apparent improvement on the grain refinement. After adding the Al-5Ti-0.25C-2RE to the melt of 3003, when the holding time reaches 1min, grains were refined to 296μm; when the holding time reaches 15min, grains were refined to 156μm; when the holding time reaches 120min, the refining effect shows certain of fading trend. Al-5Ti-0.25C-2RE can modify the needle like eutectic phase to granular like. Al-5Ti-0.25C-2RE master alloy can effectively eliminate the segregation of Mn in 3003 alloy, and promote the spheroidizaiton of the eutectic phase. Al-5Ti-0.25C-2RE can get a better refining effect in 3003 alloy when compared with Al-5Ti-0.25C. In the preparing and refining process, RE can promote the activity of TiC particles; change the morphology of TiAl3; react with the melt and generate TiAl20Ce, and then release Ti atoms and RE atoms to the melt. In this way, RE ensures the rapidly available and long time efficiency of Al-5Ti-0.25C-2RE master alloy. In the refining process, trace elements can affect the refining effect greatly. 1.0-1.5% of Mn in 3003 can promote the refining effect of Al-5Ti-0.25C-2RE. The high level of Si in A356 can hinder the refining effect of Al-5Ti-0.25C-2RE by reacting with the melt and producing Al-Ti-Si phase.