Mechanical Properties of Al-Cu Alloy Layered Structure Made by Ultrasonic Consolidation Process

Ultrasonic consolidation (UC) process is an innovative solid-state manufacturing technology that combines computer control contour milling and ultrasonic welding of metal foils to produce a solid freeform part. However, the overall mechanical properties of layered structure made by UC process have rarely been reported.

In this work, the mechanical properties of Al-Cu alloy layered structure made by UC process were investigated by tensile tests, fatigue tests and fracture toughness tests, at room temperature. These tests were conducted based on ASTM standards for specimens along different directions and after different heat treatments (T4 and T62). Additionally, the fractography of the specimens were characterized by scanning electron microscope (SEM) technique. Mechanical properties of layered specimens were assessed by comparison to the base Al-Cu alloy material under the same test condition.

Due to the defects formed in the area of the interfaces of specimen, the foil specimens showed lower tensile strength and shorter fatigue life than base material. However, the fracture toughness of foil specimens was higher, possibly due to the energy required for delamination of foils during the tests. In addition, the different failure modes of foil specimens and base metal specimens were proposed based on the observations by SEM. The foil specimen had multi-site crack initiation stemming from defects at foil interfaces. Crack initiations of base metal were from the high stress regions at surfaces or sub-surfaces. Probably due to the lower ductility of T62 specimens, their crack growth rate was faster, leading to a little shorter fatigue life and also lower fracture toughness than T4 specimens.