Effect of copper addition and heat treatment on segregation behaviour of Al–7Mg–Cu alloys

Abstract

Electron probe microanalysis showed that Al–7Mg–Cu alloys possess serious segregation tendencies. The addition of copper promoted the segregation of magnesium and led to the formation of non-equilibrium eutectic. With an increase in the copper content of the alloys, the severity of the solute segregation increased. Homogenisation reduced the solute segregation significantly. During homogenisation, the non-equilibrium eutectic compound Al_xCu_yMg_z gradually dissolved. Its dissolution behaviour depended on its copper content. Precipitates of Al_xCu_yMg_z with a comparatively low level of copper dissolved, while those with a high level of copper were less soluble and became divided into small blocks. The higher the copper content of the alloys, the larger and the greater in number the remaining Al_xCu_yMg_z particles. In the undissolved Al_xCu_yMg_z, the concentration of copper increased and that of magnesium decreased. Two step homogenisation reduced the solute segregation and dissolved the non-equilibrium eutectic further.

MST/3194