RELATION BETWEEN THE 2ND ACOUSTIC-EMISSION PEAK AND THE SERRATED FLOWOF AGED ALZNMGCU ALLOY

The acoustic emission (AE) during plastic now of AlZnMgCu alloy aged u nder a wide range of temperature and time was investigated. For as-que nched and short time aged samples, there are strong burst-type AE sign als accompanied by serrated flow, its onset strain epsilon(c) delayed with prolonging aging time. For most aged samples, there is a continuo us second AE peak (AEII), the height of AEII in ringdown. count rate, N-II, is a function of aging time t, and the curve N-II-lg t has the s ame tendency as the curve of ultimate tensile strength sigma(B)-lg t f or the same aging temperature, with both maxima close to each other. F or well over-aged and annealed samples, the serrated now reap pears wi th small stress amplitude and AE bursts, which takes the place of the AEII gradually with prolonged aging time. The activation energies for N-II at the maximum, that of epsilon(c) of serration onset in short ti me aged and for well over-aged samples were calculated to be 1.4, 0.64 , and approximate to 2 eV, respectively. The origin of AE in aged AlZn MgCu alloy is discussed in connection with the interaction between pre cipitates and moving dislocations.