Vehicle lightweighting isn’t an ideal, it’s an imperative. Alongside ever-improving safety equipment, the batteries and complex powertrains that push cars more miles per gallon are making cars heavier. Which, ironically, makes it harder to achieve increasing fuel economy targets. There are plenty of lightweight materials to throw at car architectures, but beyond the expense is the issue of combining them – different metals commonly don’t like to stick together, or bond inefficiently without arduous, expensive preparations unsuitable to a mass-market production line. Researchers at the Oak Ridge National Laboratory (ORNL) have found a laser-powered laboratory solution to better bonds between aluminum and carbon fiber, one of the most ideal, yet onerous, lightweighting pairings.
Aluminum fresh off the press is coated in oils and impurities, while carbon fiber is typically covered in chemical agents used to release the composite from its mold. Because sturdy joins happen at the molecular level it’s not enough to merely wash the aluminum and composite before bonding them, it takes manual labor, grit blasting, and toxic solvents to prepare each surface. It’s a process that can only be justified for expensive vehicles.
Instead of using abrasives, the ORNL scientists, working with 3M and automotive supplier Magna International, used a laser to peel away the top layers of material from the metal and the composite. With the aluminum contaminants removed and the top resin CF layer burned away to expose individual fibers, the adhesive makes a better bond due to both increased purity and having more surface area to bond with. Research into applying lasers this way has been going on for years.
When the researchers tested a bonded single-shear lap joint in aluminum and carbon fiber using their laser method, they found the joint 15 percent stronger than when using traditional preparation methods, in addition to being able to support 16 percent more maximum load and withstand double the displacement at maximum load. The joint could also absorb 200 percent more energy, making it an even better option for safety applications, and even vehicle armor. Best of all, the preparation process enables “the automated processing of a multi-material carbon fiber-aluminum joint” for less time and money than it takes right now.
Yet a lab is not a production line, so after the ORNL team presents its findings at a conference for The Society for the Advancement of Materials and Process Engineering this month, they’ll spend more time with Magna and 3M trying to scale the method up to industrial capability. But ORNL has experience in this, having worked with Honda to figure out a new way to bond aluminum and steel for the Honda Accord.
