Abstract
Behavior of microalloying elements in the early stage of phase decomposition of Al–Cu alloys has been extensively investigated using the electrical resistivity measurement, differential scanning calorimetry (DSC) and transmission electron microscopy. The microalloying element of Mg retards the initial phase decomposition and greatly accelerates the subsequent decomposition giving an increased resistivity maximum. The microalloying elements of Ag and Zn, on the other hand, have almost no effects on the decomposition of Al–Cu alloys. The combined additions of Mg and Ag markedly retard the phase decomposition in both the initial and subsequent stages. In order to elucidate the fundamental mechanisms of the microalloying effects in an atomic scale the Monte Carlo computer simulation was performed. In the simulation it was found that the element of Mg preferentially traps the quenched-in excess vacancies in the initial stage through so-called vacancy trapping mechanism. In the subsequent stage the characteristic complexes containing Cu, Mg and vacancies, i.e. Cu/Mg/vacancy complexes, are formed and they act as effective nucleation sites for GP zones.
