【作者】 王飞；

【导师】 朱新德； 于永江；

【作者基本信息】 山东大学 ， 材料与化工（专业学位）， 2025， 硕士

【摘要】 钕铁硼永磁材料因其超高磁能积和强剩磁特性,广泛应用于新能源汽车、风力发电、5G通信等领域。然而,其高温矫顽力低、重稀土依赖性强及耐蚀性差等问题,严重限制了其应用范围。传统晶界扩散受限于扩散深度,难以满足厚磁体的性能需求,而电镀、磷化等表面处理虽能提升耐蚀性,却面临成本高、工序复杂、环境污染等问题。为此,本研究在晶粒细化、扩散源设计与表面防护三个关键环节进行针对性优化,系统研究磁体性能提升的关键机理,主要研究内容与结果如下:(1)通过调控筛分参数,制备了 4.78μm、4.28μm、3.50μm三种晶粒尺寸的烧结NdFeB磁体,并进行Tb扩散,系统研究晶粒细化对磁体扩散过程和性能的影响。实验发现,细晶磁体(3.50μm)扩散后,矫顽力达27.06kOe,显著高于粗晶扩散样品,形成了更均匀的(Nd,Tb)2Fe14B核壳结构,抑制反磁化畴形核,削弱磁耦合效应,同时优化富Nd相分布,使剩磁仅下降1.82%。因其晶界密度高,增加扩散通道的同时引入高能缺陷,提供额外驱动力,使Tb可以扩散至300μm深处。扩散后磁体显微硬度、电阻率也呈现有规律增加。然而,细晶扩散磁体由于晶界比例高,存在局部扩散不均及结构缺陷的问题,导致耐蚀性劣化,腐蚀电流密度升至4.21×10-4A/cm2。(2)为解决晶界扩散深度受限与重稀土利用率不足的难题,设计了 Tb,Tb60Nd5Al30Ga5及Tb65Pr10Nd5Al5Cu10Ga5扩散源体系,进而揭示扩散源组分对磁体性能的调控机制。实验发现,三种扩散源扩散后磁体矫顽力均达到27.5kOe,提升约49%。Tb扩散样品中,出现了扩散过饱和区与反核壳结构,阻碍Tb纵深扩散,损害磁性能。Tb60Nd5Al30Ga5扩散样品中大量Al、Tb进入到主相当中,形成的宽晶界、厚壳层结构使磁体各项性能降低,其腐蚀电流密度达3.74×10-4A/cm2。而Tb65Pr10Nd5Al5Cu10Ga5扩散样品综合性能最佳,其剩磁达13.39kGs,最大磁能积为43.93MGOe,均达到峰值。此外,其显微硬度最高,为779.98HV。耐蚀性在扩散样品中最优,腐蚀电流密度为1.09×10-4A/cm2。这是由于多元合金的高熵特性能够避免Tb过度进入主相,Pr对剩磁损失起到补偿作用,同时与Al、Cu、Ga优化晶界润湿性,促进Tb纵深扩散,形成了理想的晶界结构。(3)为了突破磁体耐蚀性差的局限性,通过多气氛热处理筛选后,发现氧气热处理可显著提升表面防护能力。其盐雾耐蚀时间延长至15min,磁通不可逆损失仅0.24%。进一步优化其处理时间发现,120min时氧化膜厚度达11μm,湿热耐蚀时间提升至320min,显著高于其它处理组,腐蚀电流密度降至9.58×10-5A/cm2。但处理时间达180min时会导致膜层微裂纹,耐蚀性下降。磷化样品耐蚀性略优,但磁通不可逆损失大,环保性不足,而氧化工艺在磁体表面形成了致密Fe3O4与Nd2O3复合膜层,实现了耐蚀性、磁性能与工艺稳定性的全面提升。更多还原

【Abstract】 NdFeB permanent magnetic materials,characterized by their ultra-high magnetic energy product and strong residual magnetism,have been widely applied in new energy vehicles,wind power generation,5G communications,and other fields.However,these materials suffer from issues such as low coercivity at high temperatures,heavy reliance on rare earth elements,and poor corrosion resistance,which severely restrict their application scope.Traditional grain boundary diffusion technology is limited by diffusion depth and struggles to meet the performance requirements of thick magnets.Surface treatments like electroplating and phosphating can enhance corrosion resistance but face challenges such as high costs,complex processes,and environmental pollution.Therefore,this study conducted targeted optimizations in three key areas:grain refinement,diffusion source design,and surface protection,systematically investigating the mechanisms that improve magnet performance.The main research contents and results are summarized as follows:1.By controlling screening parameters,three sintered NdFeB magnets with grain sizes of 4.78μm,4.28μm,and 3.50μm were prepared and subjected to Tb diffusion.The influence of grain refinement on the diffusion process and magnet performance was systematically studied.Experimental findings revealed that after diffusion,the coercivity of the fine-grained magnet(3.50μm)reached 27.06kOe,significantly higher than that of the coarse-grained diffusion sample.A more uniform(Nd,Tb)2Fe14B core-shell structure was formed,inhibiting the nucleation of anti-magnetization domains and reducing magnetic coupling effects.Simultaneously,the distribution of the Nd-rich phase was optimized,resulting in only a 1.82%decrease in residual magnetism.This outcome stems from the high grain boundary density of the fine-grained magnet,which increases diffusion channels and introduces high-energy defects,providing additional driving force for Tb to diffuse to a depth of 300μm.After diffusion,the microhardness and resistivity of the magnet increased regularly.However,due to the high proportion of grain boundaries,the fine-grained diffusion magnet exhibited local diffusion inhomogeneity and structural defects,leading to poor corrosion resistance with the corrosion current density rising to 4.21 × 10-4A/cm2.2.To address the limitations of shallow grain boundary diffusion and insufficient utilization of heavy rare earths,diffusion source systems of Tb,Tb60Nd5Al30Ga5,and Tb65Pr10Nd5Al5Cu10Ga5 were designed,revealing the regulation mechanism of diffusion source components on magnet performance.Experimental results showed that the coercivity of the magnets diffused with the three sources all reached 27.5kOe,representing an approximate 49%increase.In the Tb diffusion sample,a diffusion supersaturation zone and inverse core-shell structure emerged,hindering deep Tb diffusion and impairing magnetic performance.In the Tb60Nd5Al30Ga5 diffusion sample,significant amounts of Al and Tb entered the main phase,forming a wide grain boundary and thick shell layer structure,which reduced magnet performance with a corrosion current density of 3.74 × 10-4A/cm2.Conversely,the Tb65Pr10Nd5Al5Cu10Ga5 diffusion sample demonstrated the best comprehensive performance,achieving a residual magnetism of 13.39kGs and a maximum magnetic energy product of 43.93MGOe,both reaching peak values.Additionally,its microhardness was the highest at 779.98HV,and it exhibited the best corrosion resistance among the diffusion samples,with a corrosion current density of 1.09×10-4A/cm2.This is attributed to the high-entropy characteristic of the multi-component alloy,which prevents excessive Tb entry into the main phase,Pr compensating for residual magnetism loss,and optimizing grain boundary wettability with Al,Cu,and Ga,promoting deep Tb diffusion and forming an ideal grain boundary structure.3.To overcome the limitation of poor corrosion resistance in magnets,multi-atmosphere heat treatment was conducted,revealing that oxygen heat treatment significantly enhances surface protection.The salt spray corrosion resistance time was extended to 15 minutes,with an irreversible magnetic flux loss of only 0.24%.Further optimization of processing time indicated that at 120 minutes,the oxide film thickness reached 11μm,and the wet heat corrosion resistance time increased to 320 minutes,markedly higher than other treatment groups,with the corrosion current density decreasing to 9.58×10-5A/cm2.However,a processing time of 180 minutes resulted in micro-cracks in the film layer,reducing corrosion resistance.Phosphated samples exhibited slightly better corrosion resistance but suffered from significant irreversible magnetic flux loss and insufficient environmental friendliness.In contrast,the oxidation process formed a dense composite film layer of Fe3O4 and Nd2O3 on the magnet surface,achieving a comprehensive enhancement in corrosion resistance,magnetic properties,and process stability.更多还原