深冷挤出切削制备超细晶7075铝合金的组织、性能及时效行为研究

Research on Microstructure,Mechanical Properties and Ageing Behaviors of Ultra-fine Grained 7075 Aluminum Alloy Fabricated by Cryogenic Temperature Extrusion Machining

传统的大变形工艺制备超细晶材料时不可避免地会产生大量的热,削弱材料的力学性能。深冷挤出切削(CT-EM)作为一种新型的超细晶材料制备工艺,可消除切削热,抑制动态回复,达到提升材料强度与可加工性的目的。本工作以7075铝合金为研究对象,对比分析了常温挤出切削(RT-EM)与CT-EM超细晶切屑的微观组织、物相演变、力学性能以及时效行为。结果表明:切屑的晶粒尺寸被极大程度地细化,CT-EM切屑的平均晶粒尺寸更小,位错密度更大,硬度和强度更高。经时效处理后,切屑组织内出现了大量弥散析出相,RT-EM与CT-EM切屑的屈服强度分别进一步提升至455 MPa和507 MPa,细晶强化、位错强化及析出相强化共同发挥作用;深冷处理可增强组织内二次相的析出动力,CT-EM切屑更快地达到峰值硬度,且其延伸率有小幅提升,拉伸断口内出现更多的韧窝。

Traditional severe plastic method inevitably produces large amounts of heat,which weakens the mechanical properties of materials.Cryogenic temperature extrusion machining(CT-EM),as a new ultra-fine grained materials fabrication process,can eliminate cutting heat,suppress dynamic recovery,and improve materials strength and machinability.In this study,the microstructure,phase evolution,mechanical properties and aging behavior of ultra-fine grain 7075 aluminum alloy chips fabricated by RT-EM and CT-EM were analyzed.The results show that the average grain size of CT-EM chips is highly refined,the dislocation density is higher,and the hardness and strength are further improved.After aging treatment,a large number of dispersed precipitates appeared in the chip,the yield strength of RT-EM and CT-EM chips increased to 455 MPa and 507 MPa respectively.The grain strengthening,dislocation strengthening and precipitate strengthening work together.Cryogenic temperature treatment can enhance the precipitate kinetics of secondary phase in the microstructure,so that the CT-EM chips reach peak hardness faster.Additionally,the elongation of peak aged CT-EM sample is slightly improved,and more dimples are present in the tensile fracture.