时效处理对搅拌摩擦沉积增材稀土镁合金组织及性能的影响

Effect of Aging Treatment on Microstructure and Properties of Rare Earth Magnesium Alloy Fabricated by Additive Friction Stir Deposition

摘要:

采用压力控制的固相摩擦挤压增材设备进行Mg-Gd-Y-Zr(GW83K)稀土镁合金搅拌摩擦沉积增材(additive friction stir deposition，AFSD)工艺试验，探讨时效处理对沉积层微观组织及力学性能的影响。研究表明:在工艺参数250 rpm/min主轴转速及100 mm/min横移速度下获得无宏观缺陷及完全致密的GW83K稀土镁合金沉积试样，与原始棒料比较沉积区具有显著混晶组织特征，沉积层前进侧局部粗晶区平均晶粒尺寸为17.37±7.29 μm，但中部及后退侧大部分区域平均晶粒尺寸显著细化为5.66±2.58 μm和4.36±2.32 ?m。沉积态试样在215℃下时效30小时后，获得均匀细小晶粒组织，硬度由85.8 HV提升至109.5 HV，其屈服强度(YS)和抗拉强度(UTS)最高可达329.5±11.7 MPa、384.25±7.5 MPa，延伸率保持为8.125±0.25%，拉伸试样具有韧-脆混合断裂特征。研究证实时效处理在保留沉积层细小晶粒的基础上，析出细小β"强化相，显著改善了AFSD制备的GW83K稀土镁合金的强塑性协同性能。

Abstract:

In this study, additive friction stir deposition (AFSD) experiments of Mg-Gd-Y-Zr (GW83K) rare earth magnesium alloy were carried out using a pressure-controlled solid-phase friction extrusion additive manufacturing equipment. The effects of aging treatment on the microstructure and mechanical properties of the deposited layer were systematically investigated. The results indicate that fully dense GW83K rare earth magnesium alloy deposited specimens without macroscopic defects are obtained under the process parameters of a spindle speed of 250 rpm and a traverse speed of 100 mm/min. Compared with the original bar stock, the deposited zone presents an obvious mixed grain structure. The average grain size of the local coarse-grained region on the advancing side of the deposited layer is 17.37±7.29 μm, whereas the average grain size in most regions of the middle part and the retreating side is significantly refined to 5.66±2.58 μm and 4.36±2.32 ?m. After aging treatment at 215 ℃ for 30 h, the as-deposited specimens possess a uniform and fine grain structure. The hardness increases from 85.8 HV to 109.5 HV; the yield strength (YS) and ultimate tensile strength (UTS) reach up to 329.5±11.7 MPa and 384.25±7.5 MPa, respectively, with an elongation of 8.125±0.25%. The tensile fracture surfaces of the specimens exhibit a ductile-brittle mixed fracture characteristic. This study verifies that aging treatment precipitates fine β" strengthening phases on the basis of retaining the fine grains of the deposited layer, which significantly improves the strength-ductility synergy of the GW83K rare earth magnesium alloy fabricated by AFSD.