表面机械研磨处理对热轧态Mg-Gd-Y合金微观组织和力学性能的影响

Effect of surface mechanical attrition treatment on the microstructure and mechanical properties of a hot-rolled Mg-Gd-Y alloy

摘要:

镁合金由于塑性变形能力较差,采用传统热轧工艺得到的晶粒组织往往较为粗大,导致力学性能不佳。本文采用表面机械研磨处理(SMAT)在热轧态Mg-Gd-Y合金中获得梯度组织,以提高合金的强韧性并揭示相关机理。热轧态合金在峰时效之后,强度显著上升但塑性急剧下降,这是因为沉淀相容易在粗晶内引起应力集中,诱发解理开裂、造成脆性断裂。SMAT试样在峰时效之后,强度相当、而塑性增加,显示了较好的强韧性。这是因为表面细晶层由于均匀变形能力较好导致延性断裂,阻碍了试样内部粗晶层解理开裂对试样截面的贯穿,从而抑制了早期开裂,使塑性得以提升。

Abstract:

_{: Due to the poor deformability of Mg alloys, the microstructure obtained by the conventional hot-rolling processes generally contained coarse grains. This could lead to inferior mechanical properties. To enhance the toughness, surface mechanical attrition treatment (SMAT) was utilized in this work to produce gradient structure in a hot-rolled (HR) Mg-Gd-Y alloy. The underlying mechanisms for toughening were disclosed. After peak-ageing (PA), the strength of the HR alloy increased obviously while the ductility decreased sharply. This was because the precipitates blocked dislocations and generated stress concentration, resulting in cleavage fracture as a brittle rupture. The HR-SMAT-PA sample showed comparable strength with the HR-PA sample, while the ductility was enhanced, exhibiting better toughness. The ultrafine grains in the near-surface layer led to uniform deformation and ductile fracture. Thus, the cleavage fracture in the deep layer could not go through the entire cross-section of the sample. As a result, the premature failure was inhibited and the ductility was increased}.