Precipitation phenomena and mechanical properties in an Al-Li-Cu-Mg-Zr alloy were investigated by hardness measurements, tensile test, specific heat measurements and electron microscopy.
Hardness increased gradually but monotonously with aging time at room temperature and 323K, and increased remarkably at 373-473K. The rate of age hardening in this alloy was extremely larger than that for an Al-Li binary alloy. Various reactions of heat evolution and absorption were observed in the specific heat curves and were suggested to originate from the structural changes such as the precursory structure of δ', δ',
T1 and S' phases. The δ' phase contributed most to the increase in the mechanical strength.
Typical serrations were observed in the stress-strain curves for the under-aged specimens, while no serrations for the over-aged ones. Fracture surface structures revealed the morphology of a grain boundary fracture, and were more rugged for the specimens with higher strength.
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