2524-T3 Joints Formed via Ultrasonic Additive Manufacturing

The aircraft industry is interested in joining aluminum skins without large stress concentrations from fasteners or heat affect zone (HAZ) from welding. Ultrasonic (US) joining is a low heat joining process that does not create large stress concentrations or HAZ. The goal of this project is to create flush joints between metal sheets without loss of the certified material properties. This presentation details the efforts made using US joining to fabricate a double-sided v-channel structure and presents resultant properties achieved. The alloy used to fabricate the structure was 2524-T3 aluminum.

The US joining process was performed by layering multiple thin foils to a substrate one at a time. The process translates ultrasonic vibration through foil, while under compression, to the lap joint interface. The process occurs to such a degree that it plastically deforms the material at the interface leading to gapless joints between the foils. The resulting single object has a refined grain structure at the interfaces. A specialized horn was used for the v-channel structure.

A limitation to ultrasonic joining is the ability to join thick sections. The magnitude of energy required to project through the thickness of the material in contact with the horn to the degree of inducing dynamic recrystallization is large. The thicker the material, the more energy is required. To reduce the thickness required to create a 0.100” thick sheet metal joint, the edges of the sheet metal were scarfed into a v-channel on both sides. Material properties were tested for both uniaxial tension and fatigue – low K_t. Testing was performed to ASTM E8 and ASTM E466. Both baseline and US scarf joints were tested and compared for strength and microstructural properties.