The potential benefit of functionally integrated components made of steel and aluminum has sparked global research in methods to weld these two dissimilar staple metals for many years. The ability to leverage steel and aluminum alloys in mixed metallic components could dramatically reduce the weight of automobiles and planes without sacrificing mechanical strength, and offers consumer and medical device manufacturers unique alternatives to solve thermal, and electric property challenges in compact spaces. Additional benefits include formability, corrosion resistance, and the generally lower costs of mixed metals. The development of versatile alloys have therefore served many applications, but welding them together perfectly and repeatedly continues to be an evasive process. In this blog we’ll be talking about how advanced fiber laser technologies and techniques have been demonstrated to provide the most success. But to understand the benefits of the fiber laser, one can first gain insight from the pitfalls of more traditional laser welding methods.
The low miscibility of aluminum alloys and steel is a well-known phenomenon caused by very large differences in their thermophysical, electrical, and chemical properties, mainly, the melting temperature difference between aluminum at 660 °C and steel at 1538 °C. The density of aluminum is also a third of that of steel, which means it will become liquid that much faster. In addition to “floating” on the steel, liquid aluminum absorbs more laser energy than when in its solid state and results in laser-induced plasma. This often leads to porosity, hot cracks, and the formation of brittle Fe-Al intermetallic compounds. These intermetallic compounds greatly reduce the weld strength and reliability, and are often hard to predict with most welding processes.
Some success has been found with ultrasonic welding, friction welding, explosion welding, and resistance welding of aluminum alloys and steel. But these welding processes are only suitable for very specific weld joint types, and limit their use. Cold Metal Transfer (CMT), vacuum brazing, and furnace brazing has also been studied, but the mechanical strength of the weld joints is typically low. Higher mechanical strength aluminum-steel weld joints has been demonstrated with TIG, MIG, electronic beam, and laser welding.
Fiber laser welding offers:
- offers highly accurate control of the heat input
- enables automation and higher throughput
- Presents low distortion, complex weld joints and shapes
- Has a small heat-affected zone (HAZ)
- Allows for high energy density welding (on advanced machines)
Moreover, the enhanced control and capabilities of laser welding technologies and processes can be developed to reduce the development of Fe-Al intermetallics, increasing the weld joint strength compared to other methods. Laser welding can also reduce the segregation tendency and provide enhanced microstructure formation within the weld zone.
The precision control of modern fiber laser technologies, however, have been used, and are being evaluated for their ability to weld these two metals that have been separated for so long. Unlike other welding technologies, these laser welding technologies are able to be pulsed, the pulses can be shaped, and hence, the temperature of the weld joint can be precisely controlled at the molten joint. Specifically, the small focus diameter of fiber laser technology offers enhanced power density, a smaller heat-affected zone, lower cycle time, and lower heat input, which can lead to a lower volume of intermetallics and even controlled intermetallic development.
Additionally, the flexibility of these laser platforms also enable automated, repeatable, and reliable implementations of welding techniques that have been demonstrated to reduce porosity and sputtering that limits other laser welding techniques. Moreover, deeper control of intermetallic mixing regions has also been demonstrated with recent techniques, such as with wobble-head technology, that are able to produce strong dissimilar metal welds.
As these techniques, and future developments, become more widespread, innovations in many applications, including RF, medical, and battery technology may be enabled. Also, reduced weight and complexity of automobile, aircraft, and naval ship platforms can be achieved, ultimately reducing the fuel use and environmentally damaging emissions.
The potential benefit of functionally graded components of steel and aluminum alloys has sparked global research in methods to weld these two dissimilar staple metals and reduce the cost and time of manufacture by avoiding complex fixturing