RESISTIVITY STUDY OF AGING IN AL-LI-CU ALLOYS

Precipitation in Al-Li-Cu ternary alloys has been investigated mainly by a resistivity study. The precipitation sequence in this alloy is as follows: supersaturated solid solution->delta'->T-1. The resistivity decreases at first and then decreases again passing through a peak. Th is anomalous behaviour has been interpreted using transmission electro n microscopy and it is suggested that the resistivity decreases accomp anying the precipitation of delta' (Al3Li), while it increases with pr ecipitation of the T-1 (Al2CuLi) phase and then decreases through a ma ximum. The time taken to arrive at the maximum in resistivity is compa rable with the time to peak hardness, which suggests that the increase in resistivity may be attributed to the strain field around T-1 preci pitates. Contrast experiments by transmission electron microscopy show the strain field due to the T-1, which disappears on prolonged aging.