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 Al2RE and the fine Al11Nd3 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 Al11Nd3 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 Al2(Nd + Gd) solid solution. The TEM bright-field image was taken along the B = [1¯1¯01]Mg zone axis with diffraction condition g = 101¯1¯ and Two-beam dark field image with diffraction condition g = 112¯0, which demonstrated the activation of and dislocations during creep deformation.

Keywords

• Mg–8Al–Gd–Nd alloys
• Inter-metallic compounds
• Creep resistance
• Dislocation substructure