Wetting Contact Angle
The angle between the solid workpiece surface and the edge of the liquid solder droplet, which quantifies wettability.
Physical-Chemical Mechanism of Action
The contact angle of the solder describes the angle at which a droplet of liquid solder forms on the solid workpiece surface. This angle is a function of surface tension and the interfacial tension between solder and workpiece.
Metallurgical Relevance & Risks in Welding
A too-large contact angle (greater than 90°) means the solder has difficulty wetting the workpiece surface, making uniform wetting difficult. This can lead to incomplete fusion or porosity. A too-small contact angle (less than 90°) indicates good wettability, which is necessary for a sound weld.
Workshop Practice & Action Instructions
To ensure good wetting, the contact angle for most metals should be between 90° and 120°. This can be achieved by choosing the right solder and the correct welding temperature. If wetting issues arise, adjust the solder type or welding parameters.