GB/T 40792-2021 in English

Analysis of the core content of the standard

This standard specifies the weight loss detection method of sintered NdFeB permanent magnets in the harsh environment of 120℃/100%RH/0.2MPa, and evaluates the corrosion resistance by quantifying the corrosion loss of the material. The key control points of the test include:

Specimen preparation specifications

Standard requirements for specimen processing must meet the following:

• Preferred size: 12×12×8mm square or φ13×8mm cylinder
• Magnetic orientation requirements: 8mm direction is the easy magnetization direction
• Surface treatment: nitric acid solution rinsing (accumulated ≥105s) + three-level ultrasonic cleaning

Key parameters of the test device

The device shown in Figure 1 of the standard must meet the following requirements:

1. The pressure vessel material must be corrosion-resistant (high borosilicate glass is recommended)
2. The temperature gradient in the central test area must be ≤4℃
3. The sample spacing must be ≥10mm and the distance from the box wall must be ≥50mm

Key points of data processing

Weight loss calculation formula:
WL=1000×(m0-m1)/S
Special attention should be paid to the determination of the magnetic orientation area S:

• Conventional samples: only calculate the surface perpendicular to the easy magnetization direction
• Abnormal corrosion: use the total exposed surface area instead
• Special magnetic orientation: must be clearly stated in the report

Standard implementation suggestions

1. Quality control: It is recommended to add XRD to detect the surface phase composition of the sample to eliminate false weight loss caused by improper pretreatment
2. Equipment selection: Prioritize test equipment with automatic water replenishment system to ensure long-term test stability of more than 168h
3. Data application: Combine SEM to observe the corrosion morphology and establish a correlation model between weight loss rate and actual service life