ON THE MECHANISM OF THE LOW TEMPERATURE INTERNAL FRICTION PEAKS IN COLD-WORKED Al - 0,5 wt% Cu AND Al - 4 wt% Cu ALLOYS

A detailed analysis of the low-frequency internal-friction peak observed in cold-worked Al-0.5 wt% (0.21 at%) Cu around 214 K (f= 2Hz) showed that it consists of two closely-situated internal-friction peaks : a relaxation peak (R-peak) and a "phase transformation peak" (P-peak). A.model of dragging by dislocations is suggested for the R-peak in which the copper atom-vacancy pairs are the mobile pinning agents. Experiments on Al-4 wt% (1.6 at%) Cu showed that the frequency-independent P-peak observed around 224 K cannot be attributed to the presence of G.P. [1] zone. This peak may be associated with some clustering stage of the Cu atoms in aluminum just before the formation of the G.P.[1] zone and may be correlated to an ordering phenomenon