INTERNAL FRICTION ASSOCIATED WITH THE RE-SOLUTION AND PRECIPITATION OF THE θ - PHASE ALONG THE GRAIN BOUNDARIES AND IN THE MATRIX OF ALUMINIUM-COPPER ALLOYS

Abstract
Low frequency internal friction and elastic modulus measurements were made with aluminium containing 0.015 to 1.2 wt % Cu. (1) When Cu content is than that of the grain boundary peak observed in pure aluminium. (2) When copper content reaches 0.5 wt %, P₁ appears in measurements with descending temperatures. Eowever, this peak is lowered considerably when measured with ascending temperatures and another peak P₂ appears around 360°C and is independent of frequency out varies with copper content, the way of changing temperatures, and ageing temperature and time. The elastic modulus dreps abruptly corresponding with the appearance of P₂. (3) When copper content reaches 1.2 wt %, a peak P₃ appears around 290°C when measured with descending temperatures. The behavior of P₃ is similar to that of P₂, except the elastic modulus rises insted of dropping corresponding with the appearance of P₃. Experiments with specimens containing only a few bamboo boundaries and X-ray analysis show that the appearance of P₂ and P₃ is originaled respectively from the resolution and the precipitation of θ-phase along the grain boundaries. Experimente with Al-4 wt % that P'₂ (430°C) and P'₃ (410 °C) peaks associated with the re-solution and precipitation of θ-phase inside the grains proper appear together with peaks P₂ and P₃.