Researchers led by a team from Oak Ridge National Laboratory (ORNL) have developed a new laser process that could make joining carbon fiber composites and aluminum for lightweight cars and other multi-material high-end products less expensive—as well as making the joints more robust.
The process would replace the practice of preparing the surface of the materials by hand using abrasive pads, grit blasting and environmentally harmful solvents. Using a laser to remove layers of material from surfaces prior to bonding improves the performance of the joints and provides a path toward automation for high-volume use.
Our technique is vastly superior to the conventional surface preparation methods. Combined with the potentially dramatic reduction in the cost of carbon fiber polymer composites, this represents an important step toward increasing the use of this lightweight high-strength material in automobiles, which could reduce the weight of cars and trucks by 750 pounds.—Adrian Sabau
The surface treatment of aluminum and carbon fiber polymer composite is a critical step in the adhesive joining process, which directly affects the quality of bonded joints. Aluminum surfaces typically contain oils and other contaminants from production rolling operations while carbon fiber surfaces often contain mold releases.
These surface contaminants affect surface energies and the quality of adhesion, so it is critical that they are removed, said Sabau. The laser also penetrates into the top resin layer, leaving individual carbon fibers exposed for direct bonding to the adhesive and increasing the surface area for better adhesion.In testing, single-lap shear joint specimens showed strength, maximum load and displacement at maximum load increased by 15%, 16% and 100%, respectively, over those measured for the baseline joints. Also, joints made with laser-structured surfaces can absorb approximately 200% more energy than the conventionally prepared baseline joints, researchers reported.Sabau noted that the process also doubles the energy absorption in the joints, which has implications for crash safety and potential use in armor for people and vehicles.
The results are most encouraging, enabling the automated processing of a multi-material carbon fiber-aluminum joint. With this work, we were able to focus on addressing the gaps in technology and commercial use, and we look forward to applying these findings to products.
Sabau will present the team’s findings at The Society for the Advancement of Materials and Process Engineering conference 23-26 May in Long Beach, California. Other members of the research team are Claus Daniel, Dave Warren, Donald Erdman III, Jian Chen and John Henry of ORNL and Mary Caruso Dailey of 3M Co., St. Paul, Minnesota. This work is funded by DOE’s Vehicle Technologies Office.