| Industrial pure aluminum(≥99.99%), Al-10 Zr and Al-10 Ti master alloys were used as experimental materials in this paper, and the experimental alloys containing different content of Ti, Zr elements were prepared by cast metallurgy. The effect of Ti, Zr separate and combined addition on the microstructure and mechanical properties of alloys was investigated by mechanical property test, metallographic microscope(OM), field emission scanning electron microscope(FSEM), energy spectrum(EDS),X-ray diffraction(XRD) and transmission electron microscopy(TEM) observing and analysing, such as observing the composition, morphology, size and distribution of the nucleation particles. While the anti-fading properties of grain refinement and the antirecrystallisation properties of the alloys with Ti, Zr separate and combined micro-alloying were also investigated and compared in order to fully reveal the existing forms and function mechanism of Ti, Zr elements in the alloy. The research results are as follows:Although Ti, Zr separate and combined micro-alloying can both produce good grain refinement effect, the effect of combined micro-alloying is more excellent than that of Ti, Zr separate addition, because the three kind of nucleation particles Al3 Zr, Al3 Ti and Al3(Ti,Zr) exist simultaneously and effectively promote the grain refinement. The number of nucleation particles will increase gradually with the increase of Ti, Zr combined content, the refinement degree of grain size and mechanical properties of the alloy also get further increased. When combined content of Ti and Zr are respectively 0.5% and 0.3%, the alloy has the finest grain size and the most excellent mechanical properties, the average grain size of the alloy is only 62μm, the strength, hardness and elongation of the alloy are respectively increased to 94.4MPa, 49.32 HV and 43.9%. However, when the combined content of Ti and Zr respectively increase to 0.3% and 0.5%, the grain refinement effect and mechanical properties of the alloy are both decreased, which is due to the high content and uneven distribution of Zr element causing the roughening and segregation of Al3 Zr particles and largely reducing the number of nucleation particles Al3 Zr and Al3(Ti,Zr).Ti and Zr combined micro-alloying has good anti-fading properties of grain refinement. When Ti and Zr combined addition, a large number of primary composite particles, with small size, high dispersion and high melting point, Al3(Ti,Zr) formed. These particles can not only act as effectively heterogeneous nucleation to promote grains refinement, but effectively hinder the grain growth at high temperature for a long time. Therefore,when 0.15%Zr and 0.15%Ti combined added to the melt at 730 holding 110 min, the alloy remains a good grain refinement effect.℃Ti and Zr combined micro-alloying has a strong inhibitory effect on recrystallization of the alloy. During the homogenizing annealing and forging heating of the alloy with Ti, Zr composite addition, the dispersed precipitation of a large number of secondary Al3 Zr and Al3(Ti, Zr) particles with high melting point have strongly pinning effect on dislocations and subgrain boundaries, and effectively prevent recrystallization and enhance the recrystallization temperature of the alloy to a higher temperature. Therefore, the recrystallization of Al-0.15Zr-0.15 Ti can be effectively inhibited until the annealing temperature exceeds 400℃. |
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