| To clarify the precipitation behaviours of secondary phases in Al-Li-Cu-Mg-Zr alloy during ageing, the detailed measurement of hardness, specific heat and the observation of transmission electron micrography have been carried out. In the early stage of ageing, lath shape S´phase formed the corrugated composite sheets on the dislocation and T₁phase precipitated at the grain boundary and sub-boundary heterogeneously were observed, but δ´phase precipitated gomogeneously during quenching were grew uniformly with increasing ageing time. In both stage of peak and over ageing, the concomitance state of δ´, T₁, δ´ and α´composite phase were conformed and especially, fine T₁ and S`phases among those secondary phases played the key role on developement of secondary increasing in hardness. And the most of S´phase spaped fine rod-like type precipitated homogeneously in matrix and another type of S´phase precipitated on dislocation line is observed as lath-like corrugated composite sheet in matrix. It would be exactly confirmed that the precursor phase is formed at the range about 80∼110℃ and resolved in matrix at the range of about 110∼145℃ by thermal analysis of specific heat versus temperature curves. |
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