| In this study, Al-2.5Li-1.3Cu-0.7Mg-(0.12Zr, 0.05Ti-O.O1B) alloy was produced, and the effect of heat treatment on the mechanical properties and microstructures was investigated. The ingot structure of Ti-B added alloys is regular and the average grain size is smaller than that of Zr added alloy. After homogenization treatment, the grain size of Ti-B added alloy become even finer than that of Zr refiner. The hardness and ultimate tensile strength of super-saturated solid solution heat-treated at 520℃ for 30min was, 90Hv and 275㎫ at only Zr additional alloy, respectively, 110Hv and 340㎫ at only Ti-B, and 114Hv and 360㎫ at Zr and Ti-B. The strength of the alloy containing Ti-B was much higher than that of the alloy containing Zr, but recrystallization during heat treatment caused the hardness and tensile strength of three alloys similar. The maximum hardness and U.T.S. of three alloys at 190℃ heat treament were, respectively, 140∼144Hv and 438∼456㎫ at 8 hour. And after the time, hardness and U.T.S. were down, but the slope of the alloy containing Zr was gentler than that of not. This was the reason that precipitated Al₃Zr phase retrained growth of δ`(Al₃Li) phase. Elongation graph reversed in comparison with strength, and showed 4.5∼5% at 8 hour. The results of TEM observation showed principal hardening phase δ`, and Al₃Zr phase, the complex phase were observed. In conclusion, the ingot structure of Ti-B additional alloys was regular and fine, and Zr addition was effective to restrain abrupt decrease of mechanical properties during heat treatment. |
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