Horns are made of different types of materials:
3) Hardened Steel 52-54 Rc.
Horns are usually manufactured from high strength aluminum alloys or titanium. Both metals have excellent acoustical property to transmit the ultrasonic energy with very little attenuation.
When part marking is a concern, a horn can be chrome plated. This smoother finish reduces wear marks during welding.
Horn material is often determined based on the application. Trinetics Group provides a free application analysis for any plastic welding project.