Study On Microstructures And Grain Refining Effects Of Rapid Solidification Processed Al-5Ti-1B Master Alloys

Al-5Ti-1B master alloy is a type of grain refiner most common used in industry.The grain refining effect of the mater alloy is greatly affected by its microstructure.Therefore, study on the effect of the microstructure of Al-5Ti-1B master alloy on the influencing law of its grain refining effect is of very important theoretical and practical significance. In this study, the Al-5Ti-1B master alloy used in industry were rapid solidification processed by using arc melting method(AMM) and single roller spin quenching method(SRSQM), and the samples with different microstructures of the rapid solidification processed Al-5Ti-1B master alloy were obtained. And the microstructures of the samples were examined by employing optical microscope(OM), scanning electron microscope(SEM) and X-ray diffractometer(XRD), and the grain refining effect of the rapid solidification processed Al-5Ti-1B master alloy for pure aluminum was studied. The effects of the rapid solidification processed Al-5Ti-1B master alloy on the microstructures and mechanical properties of 7050 aluminum were also investigated. The main research contents and results are as follows.1. Al-5Ti-1B master alloy were rapid solidification processed by using AMM and SRSQM, and the microstructures of the rapid solidification processed and non-processed Al-5Ti-1B master alloy samples were examined. The results show that the rapid solidification process can significantly change the microstructure of the Al-5Ti-1B master alloy, and the faster the solidification rate, the more remarkable the microstructure change of the master alloy. In the non-processed Al-5Ti-1B master alloy, Ti Al3 phases are mostly presented as bulky plate strip and block, and their sizes are more than 100μm. Ti B2 particles mainly exist in grain boundaries in agglomeration state. In the AMM processed Al-5Ti-1B master alloy, Ti Al3 phases are mostly acicular and the sizes of them, which are about tens of microns, decrease significantly. The distribution of Ti B2 particles in the master alloy is relatively uniform. However, Ti Al3 phases cannot be observed from the microstructure of the sample of the SRSQM processed Al-5Ti-1B master alloy. Ti B2 particles are alsomore evenly dispersed in the matrix of the master alloy.2. The grain refining actions of the rapid solidification processed and non-processed Al-5Ti-1B master alloys for pure aluminum were contrastively studied.The results indicate that the rapid solidification processed and non-processed Al-5Ti-1B master alloys all can greatly refine the grains of pure aluminum. But when the addition contents of the master alloys to the pure aluminum melt are the same,two types of the rapid solidification processed Al-5Ti-1B master alloys have a better grain refining effect, and the optimum grain refining effect can be achieved when the addition content are of 0.5wt%. Therefore, the rapid solidification process can also reduce the addition content of Al-5Ti-1B master alloy to pure aluminum melt for obtaining a good grain refining effect.3. The fading behaviors of the grain refining effect of the rapid solidification processed and non-processed Al-5Ti-1B master alloys for pure aluminum were comparatively investigated. The results show that the grain refining effects of the rapid solidification processed and non-processed Al-5Ti-1B master alloys slightly fade only in the first 60 min of the melt holding time, and so they all have a very good ability of resisting the fading of grain refining effect. Nevertheless, the rapid solidification processed Al-5Ti-1B master alloys all have a better grain refining effect in all the melt holding time in this study.4. The effect of the rapid solidification processed Al-5Ti-1B master alloys on the microstructure and mechanical properties of 7050 aluminum alloy were studied.The results indicate that the grain refining abilities of the rapid solidification processed Al-5Ti-1B master alloys for 7050 aluminum alloy are somewhat enhanced compared with the non-processed master alloy. When the addition contents of the master alloys are the same, the grain sizes of the 7050 aluminum alloys with the addition of the rapid solidification processed Al-5Ti-1B master alloys decreased obviously, and the ratio of equiaxed grains in the microstructures of the alloys increased. Under the same test conditions, the Vickers hardness of the as-cast samples of the 7050 aluminum alloys grain-refined with the rapid solidification processed Al-5Ti-1B master alloys increase, and the tensile strength, yield strength and elongation of the as-extruded samples of the alloys are also somewhat improved.