表面机械研磨处理Mg-Gd-Y合金不同应变层的时效硬化行为和机理

Age hardening behaviors and mechanisms of gradient-structured Mg-Gd-Y alloy processed by surface mechanical attrition treatment

摘要:

采用表面机械研磨处理(SMAT)在Mg-Gd-Y合金中获得了梯度组织结构,通过维氏硬度计和透射电子显微镜对试样中不同应变层的时效硬化行为和机理进行了研究。SMAT后合金梯度组织可以分为三层：剧烈应变层、中等应变层和无影响层。在225°C时效,不同应变层的时效硬化行为表现出明显差异。出现峰时效的时间由剧烈应变层、中等应变层到无影响层依次延长；而峰时效时的硬度增量则依次降低。这与不同应变层中沉淀相的形态、分布以及与位错等缺陷的相互作用有关。剧烈应变层显示了最短的峰时效时间和最高的峰时效硬度,说明SMAT表面纳米化对促进Mg-Gd-Y合金的时效硬化有显著效果。

Abstract:

Surface mechanical attrition treatment (SMAT) was conducted on a Mg-Gd-Y alloy to obtain a gradient structure. Vickers micro-hardness tests and transmission electron microscopy were employed to study the age hardening behavior and the mechanisms. The gradient structure in the SMATed alloy can be classified into three layers: the severely deformed layer, the moderately deformed layer and the undeformed layer. The different layers exhibited distinct age hardening behaviors when aged at 225°C. The aging times for peak hardness increased in the order of the severely deformed layer, the moderately deformed layer and the undeformed layer; however, the hardness increments at the peak aging times decreased in the same order. This was attributed to the different distributions of the precipitates and their variable interactions with dislocations in the different layers. The severely deformed layer exhibited the shortest aging time and the highest value for peak hardness, which indicated that the surface nanocrystallization had remarkable effect on promoting age hardening for the Mg-Gd-Y alloy.