1 Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (Ministry of Education), Shandong University, Jinan 250061, China 2 Shandong Al & Mg Melt Technology Company Limited, Jinan 250061, China
The microstructure and phase composition of Al-5Ti-1B, Al-4Ti-1C and Al-5Ti-0.8B-0.2C master alloys were investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS), and the effects of the three kinds of master alloys on the grain size and mechanical properties of 7050 alloy were investigated. The results show that the existence of Zr reduces the grain refining effects of Al-5Ti-1B and Al-4Ti-1C master alloys, but hardly influences the refinement of Al-5Ti-0.8B-0.2C master alloy. The reason is that Al-5Ti-0.8B-0.2C containing B-doped TiC can resist Zr-poisoning, and after adding 0.2% (mass fraction) Al-5Ti-0.8B-0.2C, the average grain size of 7050 alloy is reduced from about 200μm to (60±5) μm, the ultimate tensile strength increases from 405 MPa to 515 MPa, increasing by 27.2%, and the elongation rate increases from 2.1% to 4.1%. However, after adding 0.2% Al-5Ti-1B and Al-4Ti-1C master alloys, the grain size is larger and the distribution is uneven, exhibiting obvious "refinement poisoning" phenomenon.
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