Researchers from the Oak Ridge National Laboratory (ORNL) have developed a laser process that could make joining carbon fiber composites and aluminum less expensive, with more robust joints as a result. The process promises cheaper lightweight, high-end components for use in cars and other multi-material high-end products.

During the improved bonding process, developed by a team led by ORNL researcher Adrian Sabau, lasers remove the surface layers of the materials instead of the traditional approach of preparing the surface of the materials by hand. ORNL says preparing materials by hand is labor-intensive and harmful to the environment. The researchers’ new laser process also improves the performance of the joints and provides a path toward high-volume use.

“Our technique is vastly superior to the conventional surface preparation methods,” Sabau said. “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.”

As ORNL explains, the surface treatment of aluminum and carbon fiber polymer composites 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, adding that 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.

Test results show that with the new laser technique, “single-lap shear joint specimens showed strength, maximum load and displacement at maximum load were increased by 15 percent, 16 percent and 100 percent, respectively, over those measured for the baseline joints.”

Also, joints made with laser-structured surfaces can absorb approximately 200 percent more energy than the conventionally prepared baseline joints, researchers reported. Sabau says those results have implications for crash safety and potential use in armor for people and vehicles. Tim Skszek of Magna International, a partner in the project, agrees.

“The results are most encouraging, enabling the automated processing of a multi-material carbon fiber aluminum joint,” Skszek said. “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.”