变形态Mg-Nd合金的组织转变和拉伸性能特征

研究不同变形条件对Mg-2.2Nd-0.5Zn-0.5Zr合金室温拉伸性能和组织的影响.经过不同条件的热挤压变形后,该合金的强度和延性都有不同程度的增加,屈强比从0.58提高到0.87左右.固定变形温度时,强度随变形速率增大而降低,延性反之.固定变形速率时,升高变形温度则强度降低,延性增加.弥散于晶界的Mg9Nd化合物细化了晶粒.变形态Mg-Nd合金的高温超塑拉伸研究发现,375℃是该合金的最佳超塑变形温度,应变速率在1×10-2s-1时,延伸率达到329%;当变形速率提高到2×10-2s-1时,该合金的延伸率仍可达到213%.分析不同真应变下的组织发现,在变形初期发生动态再结晶,晶粒得到破碎而变得细小,随着变形程度的增加,晶粒长大程度较小.在变形后的断口形貌中发现,Mg-Nd合金的超塑变形机制为晶界滑移控制下的孔洞连接协调机制.

Microstructural Evolution and Tensile Properties Features of Wrought Mg-Nd Alloy

Effects of various deformed conditions on microstructures and tensile properties of Mg-2.5Nd-0.5Zn-0.5Zr wt% (Mg-Nd) alloy were investigated. Mg-Nd alloy as-extruded exhibit higher strength and better ductility compared to that of as-T6 condition, while its ratio of yield strength to ultimate strength is enhanced from 0.58 to 0.87. With increasing of the extrusion strain rate, both yield strength and ultimate strength increase at the constant extrusion temperature. Nevertheless, the ductility obeys the opposite regulation. At the same extrusion strain rate, both yield strength and ultimate strength decrease with increasing of the extrusion temperature. Fine Mg9Nd compound particles precipitated in the grain boundaries refine the grains resulting in improving the mechanical properties of as-extruded Mg-Nd alloy. The alloy superplasticity behavior was also exploited in the tensile tests at high temperatures. The results depict that 375℃ is the optimal deformation temperature,while the elongation amounts to 329% at the strain rate of 1 × 10-2s-1. The fracture surface indicates that mechanism of the superplasticity of Mg-Nd alloy is controlled by the grain boundary sliding accommodated with cavities interlinked.