Effects of Quenched-in Excess Vacancies and Microalloying Elements on Phase Decomposition of Al-Cu Alloys

摘要

Effects of quenched-in excess vacancies and microalloying elements on the early stage phenomena of phase decomposition in Al-Cu alloys have been investigated. The microalloying element of Mg retards the initial phase decomposition and greatly accelerates the subsequent decomposition giving an increased electrical resistivity maximum. The microalloying elements of Si and Zn, on the other hand, have almost no effects on the decomposition of Al-Cu alloys. The combined addition of Mg and Si markedly retards the phase decomposition in the initial stage. In the simulation it was found that the element of Mg preferentially traps quenched-in excess vacancies in the initial stage through so-called vacancy trapping mechanism. In the subsequent stage 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. These clusters greatly affect the distribution of GP zones and the phase decomposition behavior.