Which Automotive Sintered NdFeB Magnets Meet High-Temperature and Anti-Demagnetization Requirements?

What Core Performance Indicators Define High-Temperature Anti-Demagnetization Capability?

Automotive sintered NdFeB magnets face severe temperature challenges, with operating temperatures in some motors reaching up to 200℃. To resist thermal demagnetization, two key indicators are indispensable: ultra-high coercivity and stable remanence. Coercivity determines the magnet's ability to withstand external demagnetizing forces, while remanence directly affects its magnetic energy output. Research shows that when the ambient temperature exceeds the magnet's maximum operating threshold, domain wall movement intensifies, leading to unstable magnetization states. Thus, magnets for automotive applications must maintain sufficient coercivity at high temperatures to inhibit domain wall displacement and ensure consistent magnetic performance.

Which Technical Paths Achieve High Coercivity Without Sacrificing Performance?

Traditional methods of improving coercivity involve adding large amounts of heavy rare earth elements such as Dysprosium (Dy) and Terbium (Tb), as their alloy phases with iron and boron exhibit much higher anisotropic fields than Nd₂Fe₁₄B. However, this approach causes significant reductions in remanence and magnetic energy product while increasing material costs. The emerging grain boundary diffusion technology has become a breakthrough solution. By depositing Dy/Tb on the magnet surface and heating it to 800℃~1000℃, these elements diffuse along grain boundaries to form a heavy rare earth-enriched shell around the main phase grains. A study demonstrated that this method only increased Dy content by 0.33 wt.% but boosted coercivity by 3.94 kOe, with remanence dropping merely 1.1%, effectively balancing anti-demagnetization capability and magnetic efficiency.

How Are High-Temperature Grades Classified for Automotive Applications?

National standards for sintered NdFeB magnets (GB/T 13560-2017) categorize materials into seven coercivity grades, with three high-temperature grades dominating automotive applications. The SH grade (1350-1590 kA/m coercivity) supports a maximum operating temperature of 150℃, suitable for general high-performance automotive motors. The EH grade (1990-2380 kA/m) can withstand 200℃, meeting the needs of high-temperature environments in specialized vehicle systems. The top-tier TH grade (2380-2780 kA/m) offers extreme anti-demagnetization resistance for critical components requiring stable performance under extreme conditions. This classification system provides clear guidance for matching magnets to specific automotive application scenarios.

What Structural Characteristics Ensure High-Temperature Stability?

The intrinsic thermal stability of sintered NdFeB magnets originates from their unique Nd₂Fe₁₄B tetragonal crystal structure, which inherently inhibits domain wall movement at elevated temperatures. Grain boundary diffusion technology further enhances this stability by creating a concentration gradient of heavy rare earth elements. Electron probe microanalysis (EPMA) reveals that Dy elements concentrate significantly in intergranular phases after diffusion, increasing the anisotropic field by 6.01 kOe—this is the primary mechanism for coercivity enhancement. Additionally, advanced powder metallurgy processes and post-diffusion tempering (550℃~650℃) optimize crystal integrity, reducing internal defects that could trigger demagnetization under thermal stress.

Why Are These Magnets Indispensable for Modern Automotive Development?

Sintered NdFeB magnets are critical to the performance of electric and hybrid vehicles, providing the high energy density and torque required for efficient motor operation. Their high coercivity and temperature stability ensure reliable power output in engine compartments and other high-temperature zones. As automotive electrification advances, demands for smaller, lighter, and more efficient motors continue to grow—properties that high-temperature anti-demagnetization sintered NdFeB magnets uniquely deliver. With energy product reaching up to 52 MGOe, these magnets enable miniaturization of automotive components while maintaining performance, supporting the industry's pursuit of energy efficiency and emission reduction.