Mechanical Evaluation of Dissimilar Metal Welds Made by VHP UAM for Energy Applications

Very High Power Ultrasonic Additive Manufacturing (VHP UAM) is an additive manufacturing process where layers of metallic foils are bonded, one by one, to create a near net shape part using an ultrasonic welding process.  The benefits of this process lie in its ability to fabricate 3-dimensional channels within a structure, embed objects and reduce the overall material and manufacturing costs of a similarly machined part.  The current research focuses on dissimilar joining of Al3003-H18 and Cu110 foils. The push-pin test was adopted to mechanically test the interface of welded layers.  Aluminum and copper dissimilar builds were created in 3 different geometric conditions.  These included “aluminum on top”, “copper on top” and “alternating Al/Cu”.  The same process parameters were used for each layer [34μm vibration amplitude, 35.5 mm/s travel speed, 5,560 N normal force, 14 layers and 20kHz frequency].  Alternating Al/Cu builds were also heat treated for 10 minutes at 350°C.  Heat treated samples had 39.5% higher maximum force than non-heat treated samples.  Future testing will be done of alternating Al/Cu builds with increased heat treatment times.  Push pin testing of stainless steel 316 and Inconel 600 will be conducted with similar configurations to the aluminum and copper dissimilar builds described previously.  Scanning Electron Microscopy has been used to analyze bonding on the fracture surface.  The analyses showed varying amounts of ductile fracture suggesting progressive metallurgical bond formation.