Solution and aging behavior of Mg-Al alloy modified by Nd-Gd

Abstract

In order to investigate the effect of Nd, Gd composite modification and heat treatment process on the microstructure of Mg-8Al alloy, we analyzed the evolution behavior of Mg17Al12 closely related to mechanical properties of Mg alloys and rare earth phase. The microstructure of the specimens was characterized by metallographic microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), and the morphology and distribution of β-Mg17Al12 and Al2RE in Mg-8Al-1Nd-1Gd alloy during solution treatment at 420 ℃ and aging precipitation at 210 ℃ were observed. The experimental results show that the eutectic of Mg alloy after modification with Nd and Gd, β-Mg17Al12 transforms from a continuous network to a fine discontinuous island and Al2RE phase with good thermal stability is produced at the grain boundary. The phase decomposition process of eutectic β-Mg17Al12 in solution treatment is continuous network-discontinuous island-spherical particles. Finally, a supersaturated α-Mg solid solution is formed, while Al2RE phase do not change before and after heat treatment. Lamellar and acicular aging precipitation β-Mg17Al12 is distributed at the grain boundary and in the grain, respectively and the precipitated β-Mg17Al12 presents fine and dispersed distribution characteristics under the modification of Nd and Gd.

Keywords

• modified magnesium alloy
• solution and aging
• rare earth phase
• precipitate phase