Abstract
A phenomenon that the density of β'-precipitates is not always unifbrm through the section of rolled sheet, . that is, the precipitates are often denser near the sheet surface was investigated in Al-Mg alloys containing 5 to 10%Mg. The rolled sheets were solution treated at 400°to 500°C and aged at 200°C for prolonged times. The phenomenon is partly related to the internal oxidation during soaking before rolling, because the oxides formed finely and densely near the surface act as nucleation sites for β'; and partly to the increased concentration in the effective quenched-in vacancies, being a function of solution treatment temperature and quenching rate. The β'-precipitation and age hadenability are enhanced by the appearance of the above phenomenon, leading to the ununiformity of aged sheets.
