1.What is the detection principle?
Propagation characteristics of sound waves in galvanized layer
Galvanized layer thickness: 20-100μm
Common probe frequency: 5-25MHz → Wavelength λ in steel ≈ 600-120μm (cannot distinguish thin layer details)
→ 50-100MHz high-frequency probe is required (λ reduced to 30-60μm) to improve resolution
2.What are the key technology breakthrough solutions?
Water immersion focus detection
Equipment configuration:
Probe: 50-100MHz high-frequency focus probe
Coupling: deionized water immersion
Motion control: XYZ three-axis scanning
Signal processing:
Time domain threshold filtering: Separate zinc layer echo from substrate echo
Wavelet noise reduction: Suppress grain scattering noise
Surface wave detection (fast scan)
Principle: Excite Rayleigh waves propagate along the surface of the coating, sensitive to depths twice the wavelength below the surface
Parameter optimization: Frequency: 10-15MHz
Incident angle: 28-32° (critical angle for Rayleigh waves in steel)
3.What is the industrial application process?
Step 1: Surface pretreatment
Laser cleaning to remove oil stains (to avoid coupling attenuation)
Surface roughness control: Ra < 3.2μm
Step 2: Reference block calibration
Use galvanized standard with artificial defects:
EDM wire cutting crack: width 10μm × depth 50μm
Micro drilling: Φ50μm × depth 30/60/90μm
Step 3: Detection Mode Selection
High-precision analysis in the laboratory: water immersion focusing + TFM
Online inspection of the production line: automatic surface wave scanning
Complex components (bolt holes): phased array sector scanning
4.What are the technical limitations and coping strategies?
Zinc nodule interference
Problem: Surface protrusions cause sound beam distortion
Solution: Use variable incident angle probe for adaptive adjustment
Coating thickness fluctuations
Problem: Thickness variation of ±15% triggers surface wave mode conversion
Solution: Real-time thickness compensation algorithm
High temperature galvanized parts inspection
Problem: Vaporization of coupling agent at >80°C
Solution: Electromagnetic ultrasonic non-contact inspection
5.How to balance accuracy and efficiency?
By using high-frequency probes to break through the diffraction limit, intelligent algorithms to remove interference signals, and three-dimensional imaging to locate defects, modern ultrasonic technology has achieved micron-level precise diagnosis of internal defects in the galvanized layer, providing core quality assurance for high-end manufacturing.