Characteristics of morphology and crystal structure of alpha-phase in two Al-Mn-Mg alloys

The characteristics of morphology and crystal structure of alpha-Al-12(Fe,M n)(3) Si phase in two Al-Mn-Mg alloys in as-cast and homogenized states hav e been studied. The results show that the morphology of primary alpha-parti cles is the same as that of primary beta-particles in as-cast ingots and 'A l-spots' is only the characteristic of alpha-phase transformed from beta-ph ase. alpha-precipitates are sterically irregular plates. The alpha-phase pr ecipitated from solid solution and transformed from beta-phase has an order ed body-centered cubic crystal structure. There is no obvious difference in the morphology of alpha-phase between two Al-Mn-Mg alloys. But in the allo y with high Si content there are more Mg2Si needles, which then cause the a lpha-precipitates in alignment along the direction [1 0 0] of Al matrix dur ing heating at lower temperature. (C) 2000 Published by Elsevier Science S. A. All rights reserved.