搅拌摩擦沉积增材7075-T6铝合金组织及性能

Microstructure and Properties of Additive Friction Stir Deposited 7075-T6 Aluminum Alloy

摘要:

本研究基于压力控制的固相摩擦挤压增材设备，进行了AA7075-T6搅拌摩擦沉积增材（additive friction stir deposition，AFSD）工艺试验，探讨移动速度对沉积层微观组织及力学性能的影响。研究表明：在主轴转速300 r/min与横向移动速度分别为100和150 mm/min的工艺参数下成功获得成形良好及无缺陷的AA7075-T6沉积试样。沉积区为完全致密细小等轴晶组织，其平均晶粒尺寸与原始母材36.33±1.99 μm的晶粒组织相比显著细化。由于强烈的热-力耦合摩擦挤压作用使得沉积区再结晶比例超过80%，沉积区硬度及拉伸性能具有不均匀分布特征。随着移动速度从100 mm/min增加到150 mm/min，沉积区顶部硬度从120 HV提高到141 HV，分别达到母材硬度的69.8%和82.1%；对应沿TD方向抗拉强度从416.5 MPa提高到477.5 MPa，平均伸长率从6.25%上升到9.25%；但沉积区底部抗拉强度从397.0 MPa增加到414.0 MPa，平均伸长率从11.5%上升到12.25%。沉积区最高抗拉强度和伸长率分别可达到母材的78.2%和80.6%，沉积试样断裂模式均具有韧断特征。这说明提高移动速度有利于AFSD沉积区强度及塑性的改善。

Abstract:

Based on the pressure-controlled solid-state friction extrusion additive equipment, additive friction stir deposition (AFSD) process tests of AA7075-T6 were carried out to explore the effect of travel speed on the microstructure and mechanical properties of the deposited layer. The results show that well-formed and defect-free AA7075-T6 deposited specimens were fabricated at a spindle rotational speed of 300 r/min and travel speeds of 100 and 150 mm/min. The deposited area exhibits a fully dense and fine equiaxed grain microstructure. The average grain size is significantly reduced compared with that of the original feed rod (36.33±1.99 μm). Due to strong thermal-force coupling friction and extrusion, the recrystallization area fraction of the deposited area is more than 80%, while the hardness and tensile properties exhibit uniform distribution. As the travel speed increases from 100 mm/min to 150 mm/min, the hardness of the top of deposited layers increases from 120 HV to 141 HV, corresponding to 69.8% and 82.1% of that of the feed rod, respectively. The corresponding tensile strength along transverse direction increases from 416.5 MPa to 477.5 MPa, and the average elongation improves from 6.25% to 9.25%. However, the tensile strength of bottom deposited layers increases from 397.0 MPa to 414.0 MPa, and the average elongation increases from 11.5% to 12.25%. The largest tensile strength and elongation of deposited layers can reach 78.1% and 80.6% of those of the feed rod, respectively. The fracture mode of the deposited specimens is characterized by ductile fracture. This indicates that the increase in travel speed is favorable to the improvement of strength and plasticity of the AFSD-treated layers.