There are several types of horn plating that can be used in ultrasonic welding, including:

1. Hard chrome plating: This is the most common type of horn plating and is highly wear-resistant, making it suitable for high-volume production environments.
2. Nickel plating: Nickel plating is more corrosion-resistant than hard chrome plating, making it a good choice for welding materials that are highly reactive or corrosive.
3. Anodizing: Anodizing is an electrochemical process that creates a protective oxide layer on the surface of the horn, providing improved corrosion resistance and durability.
4. Electroless nickel plating: This is a type of nickel plating that doesn’t require an electrical current, making it a good choice for complex horn shapes that are difficult to plate using traditional methods.
5. Teflon coating: Teflon coating can be applied to the surface of the horn to provide improved release properties, making it easier to remove the welded parts from the horn.

The choice of horn plating will depend on several factors, including the type of materials being welded, the volume and frequency of use, and the desired durability and corrosion resistance of the horn.