Precipitatie Transformation during Isochronal Aging in Al-Si-Mg(A356) Alloy

摘要

The Mg_2Si precipitates in A356 alloy have been characterized by high resolution transmission electron microscopy with the combined use of a computer-aided image processing system. We observed that G.P.zones, #beta#", #beta#', and B' phases aged at 155 deg C, 175 deg C, 195 deg C and 250 deg C, respectively. It was found that the orientation relationship between the precipitates and the matrix. The #beta#" phase has a monoclinic structure. The crystallographic orientation relationship is found as follows: (001)_(Al) // (010)_(#beta#"), (3-bar10)_(Al)//(001)_(#beta#"), (230)_(Al)//(100)_(#beta#") and #beta# approx= 105 deg. The #beta#' phase has two types of the crystal structure; the hexagonal structure with the lattice parameter a = 0.704 nm and the orthorhombic structure with lattice parameters a = 0.734 nm, b = 0.658 nm and c=0.405 nm. The B' phase has a hexagonal structure. The angle between the rod direction of B' phase and the (010) direction of the matrix is 10 deg.