Abstract
Precipitation phenomena and structural changes in Al-2.15mass%Li and Al-2.70mass%Li alloys were investigated respectively by hardness measurements, specific heat measurements and electron microscopy.Hardness increases slowly with aging time at room temperature and 323K, while increases remarkably at 373-473K in the both alloys. At 523K, no increase in hardness occurs in an Al-2.15mass%Li alloy, but rapid increase occurs initially in an Al-2.70mass%Li alloy. Various reactions of heat evolution and absorption were observed in the specific heat curves depending on aging temperatures and times. Furthermore, TEM observations suggest that the L12 ordered structure δ', which exists even in the as-quenched state, is completely coherent with the matrix initially and loses the coherency subsequently to become semi-coherent. The precipitation sequence in an Al-Li binary alloy was found to be as follows:α→Li cluster (GP(1))→Short range order(GP(2))→L12 orderedstructure(δ': coherent→semi-coherent)→Stable phase(δ)
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