【作者】 李泽宇；

【导师】 高明；

【作者基本信息】 华中科技大学 ， 光学工程， 2022， 硕士

【摘要】 电弧增材制造（WAAM）具有沉积效率高、制造成本低,适合成形大尺寸复杂金属构件的优点,是零件修复与再制造的关键方法之一,但是现有铝合金WAAM研究主要聚焦于室内条件。实际上,基于电弧燃烧物理过程的WAAM对气流和风向非常敏感,在当前缺乏铝合金自保护药芯焊丝的情况下,现有工艺无法满足野外恶劣环境下零件修复与再制造的应用需求。为此,本文模拟野外环境开展了有风环境下的4043铝合金丝粉同步WAAM工艺和机理研究。主要研究结果如下:系统研究了丝粉位置、送粉量、电弧电流等参数对丝粉同步WAAM单层单道沉积形貌特征的影响规律,发现适当粉末添加能够有效增强电弧稳定性,改善熔池润湿铺展性,将沉积熔宽和熔深分别增加11%和23%。基于送粉效率和成形质量综合分析发现,丝粉间距是该工艺的关键影响因素,其优化范围为4～6 mm。探讨了有风环境下Mg、Ti O₂、Na F等多种粉末及其配比对丝粉同步WAAM单层单道工艺特性的影响规律,基于工艺稳定性提升原理得到了最优粉末配比为90%Mg+5%Ti O₂+5%Na F（重量比）。在此优化配比下,丝粉同步WAAM的抗风能力可以提升至3.5 m/s,是常规WAAM的3.5倍。粉末添加提升WAAM抗风能力的核心机理在于:Mg粉促进电弧电离,提高其稳定性,Ti O₂和Na F有助于降低熔体粘度,提升熔体润湿铺展性,并形成保护熔池的表面焊渣层。研究了有风环境下丝粉同步WAAM薄壁墙零件的成形特征、显微组织和拉伸性能,发现丝粉同步WAAM工艺能够在3.5 m/s风速下稳定成形,突破常规WAAM在超过1 m/s风速无法成形的技术瓶颈。在此基础上引入激光清洗去除沉积层表面附着氧化物,能够将内部气孔率由31.2%降低为10.3%,同时将零件抗拉强度和延伸率分别提升至166 MPa和3.7%,达到室内常规WAAM的98.2%和31%。分析认为丝粉同步WAAM试样能够通过形成Mg₂Si颗粒增强相来弥补较高气孔率对力学性能不利影响,从而获得接近室内环境的拉伸性能。更多还原

【Abstract】 Due to the advantages of high deposition efficiency and low manufacturing cost,wire arc additive manufacturing（WAAM）is suitable for forming of large-sized complex metal components,and considered as one of the key methods for parts repair and remanufacturing.However,the existing WAAM studies on aluminum alloys focuses on indoor conditions because the WAAM based on arc burning is very sensitive to airflow and wind direction.Due to the absence of self-shielded flux-cored wire,the existing WAAM on aluminum alloys cannot meet the application requirements of parts repair and remanufacturing under the harsh outdoor conditions.Therefore,in the current study,the process and mechanism of synchronous wire-powder WAAM of 4043 aluminum alloy under a windy environment were studied by simulating the field environment.The main findings are as follows:The effects of main parameters including wire-powder position,powder feeding amount,and arc current on the single-layer and single-pass forming quality of synchronous wire-powder WAAM were analyzed.It is found that a proper powder addition enhances the arc stability and improves the wetting and spreading of the molten pool.The width and penetration depth of the WAAM deposited layer are increased by 11%and 23%by adding powder.Based on the comprehensive analysis of powder feeding efficiency and forming quality,it is found that the wire-powder distance is the most critical factor that affecting the process,and its optimization range is obtained as 4～6 mm.The effects of powder composition including Mg,Ti O₂,Na F,etc.,and their ratios on the process characteristics of the single-layer and single-pass forming by synchronous wire-powder WAAM under a windy environment was discussed.Based on the principle of process stability improvement,the optimal powder composition ratio was obtained as 90%Mg+5%Ti O₂+5%Na F（wt.%）.Based on the optimized powder composition,the wind resistance ability of synchronous wire-powder WAAM can be improved to 3.5 m/s,which is 3.5 times higher than conventional WAAM.The reason to improve the wind resistance ability of WAAM by adding powder is that Mg promotes arc ionization and improves its stability,while Ti O₂ and Na F benefit to reduce the viscosity of liquid metal and improve its wetting and spreadability,and form a protective slag layer on the surface of molten pool.The forming characteristic,microstructure,and tensile properties of the thin wall parts obtained by synchronous wire-powder WAAM under a windy environment were studied.It was found that the synchronous wire-powder WAAM is capable of stable forming at a wind speed of 3.5 m/s,which solves the problem that conventional WAAM is hard to form at a wind speed of more than 1 m/s.Then,laser cleaning was proposed to remove the oxides attached to the surface of the deposited layer,which reduces the porosity from 31.2%to10.3%.Moreover,the tensile strength and elongation of the parts are increased to 166 MPa and 3.7%respectively,reaching 98.2%and 31%of the indoor conventional WAAM.The synchronous wire-powder WAAM compensates for the adverse effect of higher porosity on mechanical properties by forming Mg₂Si particle reinforcement phase,so as to obtain the tensile properties close to the indoor conventional WAAM.更多还原