【作者】 张勇；

【导师】 李丽； 常青；

【作者基本信息】 山东理工大学 ， 工程硕士（专业学位）， 2021， 硕士

【摘要】 金属零部件的失效往往源于磨损、腐蚀和划伤等表面损伤,因此,实现对零部件表面损伤的修复对资源的节约和经济的可持续发展具有重要意义。铜合金因其具有导热性好、高温易氧化以及对激光吸收率低的特性,使其零部件的修复存在很大的局限性。电火花沉积技术（Electro-spark deposition,ESD）由于具有对母材热输入小、成形层与基体呈冶金结合并且便携易操作的特点,常被用于零部件的表面修复。本课题首先采用ESD进行铜合金表面成形层的制备,研究了主要工艺参数对成形层及其性能的影响规律,并对成形层的表面和截面形貌以及微观组织进行了表征和分析。然后,通过超声滚压（Ultrasonic surface rolling,USR）对成形层进行强化处理,使其耐磨性超过基体水平。分析了USR对成形层的强化效果及强化机理,探究了工艺参数对USR强化效果的影响规律。主要研究内容及结论如下:（1）选取QAl9-4铝青铜为研究对象,研究了ESD工艺参数（沉积功率、沉积电压、比沉积时间和放电频率）对不同指标（沉积效率、致密度和表面显微硬度）的影响规律,并对成形层的微观组织进行了表征和分析。工艺参数对不同指标的影响呈不同甚至相反的趋势,工程应用中应根据对不同指标的要求进行优选。成形层晶粒为垂直于基体表面生长的柱状晶,各元素分布均匀,物相为Cu₃Al基金属化合物。（2）使用USR进一步提高成形层的性能,评估了USR对成形层的强化效果,并分析了其强化机理。USR使电火花沉积成形层表面粗糙度降低,晶粒细化,孔隙缺陷愈合,显微硬度和表面纳米硬度提高,抗静力蠕变性能增强,残余拉应力被消除并引入了残余压应力。成形层表面性能的提高主要源于USR使材料发生了剧烈的塑性变形。USR使成形层内部位错增殖并堆积,在晶粒内部形成新的晶界,从而使成形层晶粒细化。位错强化和晶界强化效应使成形层耐磨性提高,平均摩擦系数和磨损量减小,使USR处理后成形层耐磨性优于基体。ESD与USR复合能够实现QAl9-4铝青铜的有效修复。（3）通过单因素试验探究了USR工艺参数（静压力,滚压次数、滚压速度和进给量）对成形层表面性能（显微硬度、残余应力和粗糙度）的影响规律。工艺参数通过影响材料塑性变形程度、晶粒细化程度以及超声滚压处理的均匀性进而影响成形层的表面性能。静压力的增大、滚压次数的增多以及滚压速度和进给量的减小都会提高材料的塑性变形程度,从而使成形层的表面性能提高,但过于剧烈的塑性变形会造成成形层的破坏,反而会降低成形层的性能。更多还原

【Abstract】 The failure of metal parts often results from surface damage such as wear,corrosion and scratch.Therefore,the repair of surface damage of metal parts is of great significance to the saving of resources and the sustainable development of economy.Copper alloy has great limitations in the repair of its parts because of its good thermal conductivity,easy oxidation at high temperature and low laser absorption.Electro-spark deposition technology（ESD）was often used to repair the surface of parts,because of the characteristics of small heat input to the base metal,metallurgical bonding between the forming layer and the substrate,and easy to operate.In this work,firstly,ESD was used to prepare the surface forming layer of copper alloy.The effects of main process parameters on the forming layer and its properties were studied,and the surface,cross-section morphology and microstructure of the forming layer were characterized and analyzed.Then,the ultrasonic rolling（Ultrasonic surface rolling,USR）was used to strengthen the forming layer,so that the wear resistance of the forming layer exceeded the substrate.The strengthening effect and mechanism of USR on the forming layer were analyzed,and the influence of process parameters on the strengthening effect of USR was explored.The main research contents and conclusions are as follows:（1）QAl9-4 aluminum bronze was selected as the research object.The effects of ESD process parameters（deposition voltage,deposition capacitance,specific deposition time and discharge frequency）on different indexes（deposition efficiency,density and surface micro-hardness）were studied,and the microstructure of the forming layer was characterized and analyzed.The influence of process parameters on different indexes is different or even opposite,so it should be optimized according to the requirements of different indexes in engineering application.The grains of the forming layer are columnar crystals growing perpendicular to the surface of the substrate.the elements are uniformly distributed,and the phases are Cu₃Al-based metal compounds.（2）USR was used to further improved the performance of the forming layer.The strengthening effect of USR on the forming layer was evaluated and its strengthening mechanism was analyzed.USR can reduce the surface roughness,refine the grains,heal the pore defects,improve the micro-hardness and surface nano-hardness,enhance the resistance to static creep,eliminate the residual tensile stress and introduce the residual compressive stress.The severe plastic deformation caused by USR is the main reason for the improvement of the surface properties of the forming layer.USR makes dislocations multiply and accumulate,resulting in the formation of new grain boundaries in the grains,which refines the grains in the forming layer.The effect of dislocation strengthening and grain boundary strengthening can improve the wear resistance of the formed layer,which shows that the average friction coefficient and wear amount was reduced,resulting in the wear resistance of the formed layer better than that of the substrate after USR treatment.QAl9-4 aluminum bronze could be repaired by the hybrid process of ESD and USR.（3）The effects of USR process parameters（static pressure,rolling times,rolling speed and feed）on the surface properties（micro-hardness,residual stress and roughness）of the formed layer were investigated by single factor test.The process parameters affect the surface property of the forming layer by affecting the plastic deformation degree of material,the degree of grains refinement and the uniformity of USR.The increase of static pressure,the increase of rolling times and the decrease of rolling speed and feed quantity will increase the degree of plastic deformation of the material,so as to improve the surface performance of the forming layer.However,too severe plastic deformation will cause the destruction of the forming layer,which will reduce the performance of the forming layer.更多还原