Effects of Cooling Rate and Ti Content on the Solidification Characteristics of Al-Ti Alloys

In this paper, the solidification characteristics of Al-Ti alloys and the precipitation behavior of Al3Ti phases at different Ti contents and cooling rates were investigated by cooling curve thermal analysis. By heating the Al-xTi (x = 1, 2, 3) alloys melt to 1100 degrees C and cooling it under near-equilibrium solidification and non-equilibrium solidification conditions, the precipitation growth characteristics of the Al3Ti phase were analyzed under each solidification condition. The results demonstrated that the precipitation temperatures of the Al3Ti phase in Al-xTi (x = 1, 2, 3) alloys increased from 774.65 to 920.26 degrees C with the increase in Ti content from 1 to 3 wt.% under the condition of near-equilibrium solidification. Under the condition of non-equilibrium solidification, the volume fraction of the Al3Ti phase and the size of the Al3Ti phase formed by solidification at the mold temperature of 200 degrees C were larger than those at the mold temperature of room temperature. With the increase in Ti content, the volume fraction of the Al3Ti phase increased gradually, and the size of the Al3Ti phase increased first and then decreased, the yield strength and the tensile strength of the Al-xTi (x = 1, 2, 3) alloys increased, which reached the maximum values of 82.15 and 106.12 MPa at a Ti content of 3 wt.% under the condition of room-temperature mold casting. The morphology of the Al3Ti phase gradually changed from petal-like to block-like, needle-like, and finally to short needle-like. During the solidification process, Al-xTi (x = 1, 2, 3) alloys preferentially formed Al3Ti precipitated phases. As the heterogeneous nucleation core, the Al3Ti phase greatly promoted the nucleation of alpha-Al, resulting in a decrease in grain size, and the grain shape tended to be equiaxed.