Refining performance and recession of Al–TiO2–C–La2O3 refiners

Al–TiO2–C–La2O3 refiners were synthesized by the in-situ exothermic dispersion method using TiO2, C, Al and La2O3 powders as raw materials. Scanning electron microscopy equipped with energy dispersive X-ray spectrometry and X-ray diffraction were used to investigate the microstructures of the Al–TiO2–C–La2O3 refiners. Commercial pure aluminum was refined by the Al–TiO2–C–La2O3 refiners, aimed at investigating refining performance and the resistance to recession. The results show that the Al–TiO2– C–La2O3 refiner with 0.2% La2O3 is composed of α-Al, blocky Al3Ti, dispersive Al2O3 and TiC, which has a better refining effect on commercial pure aluminum than the Al– TiO2–C refiner. The average grain size refined by the above refiner is about 80 μm and it performs better and has a longer refining effect. The grain structure refined by Al–TiO2– C–La2O3 becomes finer within 5 min and remains the same after 120 min, while refined by the Al–TiO2–C refiner the equivalent times are 10 min and 30 min respectively.

The influence of gadolinium on Al–Ti–C master alloy and its refining effect on AZ31 magnesium alloy

Grain refinement has a significant influence on the improvement of mechanical properties of magnesium alloys. In this study, a series of Al–Ti–C-xGd (x = 0, 1, 2, 3) master alloys as grain refiners were prepared by self-propagating high-temperature synthesis. The synthesis mechanism of the Al–Ti–C-xGd master alloy was analyzed. The effects of Al–Ti–C-xGd master alloys on the grain refinement and mechanical properties of AZ31 (Mg-3Al-1Zn-0.4Mn) magnesium alloys were investigated. The results show that the microstructure of the Al–Ti–C-xGd alloy contains α-Al, TiAl3, TiC and the core–shell structure TiAl3/Ti2Al20Gd. The refining effect of the prepared Al–Ti–C–Gd master alloy is obviously better than that of Al–Ti–C master alloy. The grain size of AZ31 magnesium alloy was reduced from 323 μm to 72 μm when adding 1 wt.% Al–Ti–C-2Gd master alloy. In the same condition, the ultimate tensile strength and elongation of as-cast alloy were increased from 130 MPa, 7.9% to 207 MPa, 16.6% respectively.

Influence of some Chemical Elements on SDAS of A357 Alloy

A solidification model of coarsening coefficient for the criterion of secondary dendrite arm spacing has been established in this paper. When the model is applied to aluminum cast alloy, it is found that the model is in good agreement with the experiment results. Experiments and analysis show that addition of some chemical elements is conducive to the refinement of the secondary dendrite arm spacing under the same solidification condition. Different chemical elements have different refining effects, and Zr and Ti have better refining effect on A357 aluminum cast alloy than Cu.

Effects of Gd on the microstructure and mechanical properties of Mg–Li dual-phase alloys

Gadolinium (Gd) (up to 10 wt.%) was added to Mg-7Li dual-phase alloys, and the Gd-containing alloys were heat-treated for 3 h at 698 -748 K. The microstructure and mechanical properties of the as-cast and heat-treated alloys were then examined. The results indicated that the addition of Gd introduced the Mg3Gd phase into the duplex Mg-7Li alloy, containing a-Mg and b-Li phases. Gd also refined the grains, and the addition of 8 wt.% Gd resulted in the highest grain refining effect. The Gd atoms in the a-Mg phase, as well as precipitates in b-Li matrixes and at the surface of the a-Mg phase, strengthened the alloys. The highest strength alloy was obtained after the addition of 6 wt.% Gd, with tensile and compressive yield strengths of 143- 147 MPa, about twice as those of the Mg-7Li alloy. Heat treatment, which was found to be optimum at 723 K for 3 h, can decrease both the amount of precipitate and the hardness of the alloy, but not the amount of the Mg3Gd phase.