Abstract: The HCP/BCC interphase boundaries between the Mg matrix and γ-Mg17Al12 precipitates for two kinds of precipitates produced in an aged AZ91 Mg-Al alloy were characterized using both conventional and high resolution TEM. It is found that the planar misfit across the (0002)α∥{330}γ habit plane of the first kind of precipitate is very low(<4%), thus forming a low (strain) energy interface, while that across the (011-0)α∥(3-30)γ habit plane of the second kind of precipitate is markedly high(15%), thus producing a high (strain) energy interface. The difference in precipitation density of various kinds of precipitate was interpretted in terms of the interfacial energy, and of the strain induced by the precipitation; and plausible ways of altering the relative densities of the precipitates so as to enhance the precipitation-strengthening effect of the alloy were proposed.
Structure of HCP/BCC interphase boundaries in AZ91 Mg-Al alloy
Abstract：
The HCP/BCC interphase boundaries between the Mg matrix and γ Mg 17 Al 12 precipitates for two kinds of precipitates produced in an aged AZ91 Mg Al alloy were characterized using both conventional and high resolution TEM. It is found that the planar misfit across the (0002) α ∥{330} γ habit plane of the first kind of precipitate is very low(<4%), thus forming a low (strain) energy interface, while that across the (0110) α ∥(330) γ habit plane of the second kind of precipitate is markedly high(15%), thus producing a high (strain) energy interface. The difference in precipitation density of various kinds of precipitate was interpretted in terms of the interfacial energy, and of the strain induced by the precipitation; and plausible ways of altering the relative densities of the precipitates so as to enhance the precipitation strengthening effect of the alloy were proposed.
Perpendicular to base plane (0001)α, i.e. parallel to[0001]α// [111]γ
Ⅲ
Short rod- shaped
Porter O.R.[6]:
(0001)α1°→(115?)γ
[011?0]α//[1?10]γ
(011?0)α//(1?10)γ
Parallel to [001]γ lying in habit plane, and 16° apart from [0001]α
图1γ-Mg17Al12析出相的形态
Fig. 1 Morphologies of γ-Mg17Al12 precipitates
(a)—Morphologies of three kinds of precipitates(Ⅰ,Ⅱ,Ⅲ)formed by aging at200℃for 48 h,and viewed along[1120]α;(b)—Morphologies of first(Ⅰ)and second(Ⅱ)precipitates produced by aging at
图2 第1类析出相在[1]α ∥[110]γ 位向下的高分辨电镜像
Fig. 2 HRTEM image of first precipitate (Ⅰ) viewed along
[0001]α ∥[110]γ
([0001]αlattice image is shown in bottom-left area,and thick Moire fringes produced due to overlapping matrix and precipitate are displayed in top-right area)
Fig. 3 HRTEM images of α/γ interphase boundaries of the first kind of precipitate (a)—(0001)α ∥(110)γ interface viewed along
[2?110]α//[11?1]γ; (b)—Interfaces formed among matrix(α) and two end-to-end butted particles (variants γ1, γ2) of the first precipitates, viewed along
[2?110]α, and Moire fringes formed within (γ1+ α) area due to crystal overlapping
Fig. 4 HRTEM image of
(011?0)α//(1?10)γinterface of the second kind of precipitate (viewed along
[2?110]α//[11????2]γand showing regular interfacial misfit dislocation array formed due to strain relaxation across interface)
