Modern cars are like construction kits made from different metals. To make vehicles both safe and fuel-efficient, engineers have long used hybrid body structures: a rigid steel safety cage around the passenger compartment to protect occupants, combined with lightweight aluminium panels (doors, hoods and fenders) to reduce the vehicle’s overall weight.
However, this is where a major engineering challenge arises. When a lightweight aluminium door must be attached to a strong steel pillar, or a steel longitudinal beam welded to an aluminium subframe, the two metals do not bond easily. Conventional welding causes them to form an extremely hard but brittle layer at the interface, known as intermetallic compounds. Imagine a layer of cement between two pieces of rubber: it may look secure, but when a car hits a pothole or vibrates under engine operation, the joint can crack and the component can break away.
Scientists from 海角社区, working with their colleagues from China, have found an innovative solution. Instead of simply melting the metals using electric current, they decided to subject them to intense vibrations at the same time. Their new spot-welding technology incorporates ultrasonic waves with a power output of approximately 1200 W. These are sound vibrations similar to those used in ultrasonic dental cleaning, but much more powerful. During welding, ultrasonic waves travel through the heated metal, producing a remarkable effect: the crystals inside the weld become smaller and more uniform, with their size is reduced by almost five times. The brittle intermetallic layers that previously weakened the structure become twice as thin. The vibrations also help dislodge gas bubbles from the metal, resulting in a highly compact, defect-resistant weld.
The test results are impressive: joint strength doubles, while component service life increases by almost two times (a factor of 1.9). As a result, components can withstand continuous vibration for years without developing cracks.
This breakthrough paves the way for a new generation of products and structures.
Electric vehicles: lighter bodies will allow cars to travel significantly farther on a single charge.
Aircraft: lighter airliners will be able to carry more passengers or cargo while saving tons of aviation fuel.
Construction: bridges and high-rise buildings could benefit from dissimilar-metal joints that provide connections stronger than monolithic concrete.
The findings have been published in the Engineering Fracture Mechanics leading scientific journal: