Contact Angle Hysteresis
Contact angle hysteresis is the difference between the advancing angle when wetting and the receding angle when dewetting of a solder on a surface. It indicates the microstructural roughness and chemical inhomogeneity of the material.
Physicochemical Mechanism of Action
Contact angle hysteresis happens because the solder's attraction to the surface differs during wetting and dewetting. On rough or chemically uneven surfaces, the receding angle differs from the advancing angle, which is called hysteresis.
Metallurgical Relevance & Welding Risks
High contact angle hysteresis can cause more surface cracking and weaker weld joints. It increases surface stress and can lead to hot cracks or zinc buildup, especially at high temperatures.
Workshop Practice & Procedures
To keep contact angle hysteresis low, you should:
• Use a solder with low surface tension.
• Clean and smooth the workpiece surface beforehand.
• Pick a suitable solder for chemically uneven materials.
• Control the temperature to keep surface stress to a minimum.