The effect of the third-element addition on the fatigue properties of mechanically alloyed Al-Ti alloys

AI-Ti-X (X=B, V, Zr, Ce) alloys were prepared by mechanical alloying and their fatigue properties were examined at room temperature, 300 degrees C and 400 degrees C. MA Al-Ti alloys showed fatigue strengths competitive with those of conventional precipitation hardened Al alloys (Al 7075, Al 2024) and the addition of third elements further improved the fatigue strength of MA alloys. As the temperature was increased to 300 degrees C and 400 degrees C, a decrease in fatigue strength was observed but the general trend in fatigue properties was the same as that at room temperature. The fatigue strength of AI-TI-X alloys, except for the Ce-added alloy, was enhanced compared with AI-Ti alloy because the third element addition reduced the lattice mismatch between Al and AI,Ti effectively and thus maintained the fine particle size of dispersoids. AI-Ti-X alloy showed the smallest precipitate size and the best room and high temperature fatigue strengths. The fatigue ratio of MA Al-Ti alloys was about 0.4 and improved slightly with temperature. The fracture mode of MA Al-Ti alloys was thought to be intergranular failures, in some cases involving also the interface between the matrix and the dispersoids. (C) 1999 Elsevier Science S.A. All rights reserved.