【作者】 陈海涛；

【导师】 邓文君；

【作者基本信息】 华南理工大学 ， 机械工程， 2020， 硕士

【摘要】 7系铝合金拥有高强度重量比、抗腐蚀性强以及导电率高等优异性能,它们往往成为大塑性变形法制备机械性能更高的超细晶材料的首选。然而高强度铝合金在室温下难以变形,加上室温变形所产生的变形热导致制备超细晶材料机械性能下降和表面形貌差等问题。由于低温能够提高超细晶铝合金的机械性能和成形性以及改善加工表面形貌加上它对环境产生零污染,故近年来低温大塑性变形法逐渐成为制备性能更优异的超细晶材料的趋势。常规正交切削作为一种大塑性变形法,其应变率高并且能够一步高效制备超细晶材料,在制备超细晶材料上有着得天独厚的优势。低温切削制备性能优异的超细晶材料有着光明的前景,研究低温切削机理对于低成本、环保制备性能更加优异的超细晶铝合金起到了重要的指导作用。本文采用有限元软件Deform 2D建立低温正交切削三维热力耦合模型,研究了低温切削和常温切削中加工参数对等效应力、等效应变率、等效应力以及切削温度的大小和在切削变形区分布的影响。同时对铝合金7075进行低温和常温切削实验,对制备超细晶材料的维氏硬度、切屑形貌、加工表面质量以及微观结构进行了表征。结果表明:(1)低温超细晶材料维氏硬度达到了167.46Hv,低温超细晶材料的硬度大于其对应参数下制备的常温超细晶材料的硬度。(2)常温下获得的超细晶材料在自由表面有许多裂纹,速度越高此现象越明显,而所有低温样品都拥有相对光滑的表面和连续的形状。低温切削下加工表面的形貌比常温切削下的更平整,并且低温切削下表面形貌受加工参数的影响比常温切削的更小。(3)低温能够有效地抑制动态回复,因此材料内部的微观组织变形更加剧烈,这大大提高了位错密度,从而进一步提高了超细晶材料的硬度。低温阻止固溶原子的析出提高了材料的成形性,因此低温切削铝合金下形成了连续平整的带材,加工表面的形貌也被改善了。更多还原

【Abstract】 7xxx series aluminum alloys have excellent properties such as high strength-to-weight ratio,strong corrosion resistance,and high electrical conductivity.They are often the first choice for the preparation of ultrafine crystal materials with higher mechanical properties by large plastic deformation.However,the high-strength aluminum alloy is difficult to deform at room temperature,and the deformation heat generated by the deformation at room temperature leads to problems such as reduced mechanical properties and poor surface morphology of the ultrafine-grained material.Because cryogenic temperature can improve the mechanical properties and formability of ultrafine-grained aluminum alloys and improve the surface morphology of the processing plus it won’t cause pollution to the environment,the cryogenic temperature large plastic deformation method has gradually become the preparation of ultrafine-grained materials with better performance trend.As a large plastic deformation method,conventional orthogonal cutting has a high strain rate and can efficiently prepare ultrafine-grained materials in one step.It has a unique advantage in preparing ultrafine-grained materials.Ultrafine-grained materials with excellent performance in cryogenic temperature cutting have bright prospects.Studying the mechanism of cryogenic temperature cutting has played an important role in guiding the preparation of ultrafine-grained aluminum alloys with better performance at low cost and environmental protection.This paper uses the finite element software Deform 2D to establish a three-dimensional thermo-mechanical coupling model for orthogonal cutting.The values of equivalent stress,equivalent strain rate,equivalent stress,cutting temperature,and their distribution in the cutting deformation zone of the machining parameters in cryogenic temperature cutting and room temperature cutting are studied.Cryogenic temperature cutting and room temperature cutting experiments were performed on aluminum alloy 7075,and the Vickers hardness,chip morphology,processed surface quality,and microstructure of the ultrafine-grained materials were characterized.The results show above:(1)the Vickers hardness of the cryogenic temperature ultrafine-grained material reaches 167.46 Hv,and the Vickers hardness of the cryogenic temperature ultrafine-grained material is greater than that of the room temperature ultrafine-grained material prepared under its corresponding parameters.(2)The ultrafine crystal materials obtained at room temperature have many cracks on the free surface.The higher the speed,the more obvious this phenomenon is.All cryogenic temperature samples have relatively smooth surfaces and continuous shapes.The morphology of the processed surface under cryogenic temperature cutting is smoother than that under room temperature cutting,and the surface morphology under cryogenic temperature cutting is less affected by processing parameters than under room temperature cutting.(3)Cryogenic temperature can effectively suppress dynamic recovery,so the microstructure deformation inside the material is more severe,which greatly increases the dislocation density,thereby further increasing the hardness of the ultrafine-grained material.The cryogenic temperature also prevents the precipitation of solid solution atoms and improves the formability of the material.Therefore,a continuous flat strip is formed under cryogenic temperature cutting of aluminum alloy,and the morphology of the processed surface is also improved.更多还原