Effects of Gd/Nd ratio on the microstructures and tensile creep behavior of Mg–8Al–Gd–Nd alloys crept at 423K

Abstract

The specific Nd/Gd mass ratios were designed for optimizing the microstructure of the Mg–8Al–Nd–Gd alloys, and the strengthening mechanism of Al-Gd-Nd phase in the creep process was revealed. The Mg–8Al-1.0Gd-1.0Nd (T6) at Gd/Nd ratio of 1:1 exhibited excellent tensile creep resistance at 423 K/60 MPa, owing to the diffusely distributed Al 2 RE and the fine Al 11 Nd 3 particles, which hindered the motion of dislocations and grain boundary sliding. The stead-state creep rate and creep strain of the alloy were 1.03 × 10 −8 s −1 and 0.312%, respectively, which were superior to that of AZ91 alloy. It could be verified that Gd showed little aging precipitation strengthening effect, while it made the typical rod-like Al 11 Nd 3 evolved into dot-like phase. A TEM thin foil was extracted by focused ion beam (FIB), and the result showed that Nd occupied the Gd sites to form Al 2 (Nd + Gd) solid solution. The TEM bright-field image was taken along the B = [ 1 ¯ 1 ¯ 01 ] Mg zone axis with diffraction condition g = 10 1 ¯ 1 ¯ and Two-beam dark field image with diffraction condition g = 11 2 ¯ 0 , which demonstrated the activation of <a> and <a+c> dislocations during creep deformation.