Crystal system of rod-shaped precipitates in an Al-1.0mass%Mg 2Si-0.4mass%Si alloy

Abstract

The crystal system of a rod-shaped precipitate (metastable phase) in an Al-Mg{sub 2}Si pseudo-binary alloy had been presumed to have a face centered cubic or hexagonal unit cell. Recently, the crystal system of the precipitate was confirmed to be a H.C.P. unit cell through the high resolution transmission electron microscopy (HRTEM) and electron diffraction. The crystal system of the metastable phase in the Al-Mg{sub 2}Si alloy containing excess silicon is not yet precisely determined, although the crystal structure is assumed to be the same as the metastable phase formed in an Al-Mg{sub 2}Si pseudo-binary alloy. In this study, the crystal system of the metastable phase in an Al-1.0mass% Mg{sub 2}Si alloy containing 0.4mass% silicon in excess was investigated using transmission electron microscopy (TEM). A new phase with a hexagonal lattice was found in the present alloy. Both the lattice parameter and the orientation relationship with the matrix are different from those of the metastable phase formed in a pseudo-binary Al-Mg{sub 2}Si alloy.