Effects of Mn addition on aging behavior in Al-1%Mg₂Si-0.4%Si alloys

Aging phenomena of Al-1%Mg₂Si-0.4%Si alloys containing Mn up to 0.8% were studied by means of electrical resistivity measurement, transmission electron microscopy and tensile test. With an increase of Mncontents, the aging rate once decreases and then increases at 150 and 200°C aging. At the peak aging condition at 200°C, mean spacing of precipitates once decreases and then increases with increasing Mn content. In the 0.8% Mn additional alloy aged at 250°C, the aging rate decreases as compared with that of Mn free alloy. This alloy shows absolutly low age-hardenability because extremely coarse precipitates distribute randomly in the matrix. The interface between insoluble particles and matrix act as sinks for excess vacancies, so the heterogeneous nucleation of precipitates and a decrease of aging rate occur due to reduce the excess vacancies in the matrix.