Pacific Northwest National Laboratory, Richland, Wash., announces that its engineers have developed and successfully tested a novel process called friction stir dovetailing that enables joining thick plates of aluminum and steel. Lab testing of joints made by friction stir dovetailing (FSD) show that, by combining metallurgical bonding with the dovetail configuration, not only is the joint strength superior, but also the material can stretch to over half a centimeter before the joint breaks — illustrating five times more ductility than aluminum and steel joined with other friction stir techniques.
In FSD, mechanical interlocks are formed at the aluminum-steel interface and are reinforced by metallurgical bonds in which intermetallic growth has been uniquely suppressed. Lap shear testing shows superior strength and extension at failure compared to friction stir approaches in which metallurgical bonding is the only joining mechanism. High-resolution microscopy reveals the presence of a 40 to 70-nm interlayer having a composition of 76.4 at.% Al, 18.4 at.% Fe, and 5.2 at.% Si, suggestive of limited FeAl3 intermetallic formation.
In woodworking, dovetails and glue are used to securely join pieces of wood together. FSD is a similar approach for metals. Aluminum plate is deformed by a specially designed tool into a steel dovetail groove to form a mechanical interlock. At the same time, the tool rubs along the bottom of the dovetail to form a thin metallurgical bond — an intermetallic compound — which “glues” the metals together within the dovetail.
“The combination of mechanical interlocking and metallurgical bonding formed during a single process is the innovation that produces joints of superior strength and ductility compared to joints created by other friction stir methods,” said PNNL engineer Scott Whalen, who leads the research.
The new process will be used to make lighter-weight military vehicles that are more agile and fuel efficient.
The April 15 issue of Scripta Materialia describes the process in detail and the testing of joints created using the new technique. The peer-reviewed journal covers original research on the relationship between the structure and properties of materials.
https://www.sciencedirect.com/science/article/pii/S1359646218300538?via%3Dihub
