Joints between aluminum and,galvanized steel pose a challenge for current manufacturing technologies. A hybrid joining method, which combines a pulsed and a continuous laser beam in a single process, has been identified as a potential solution for this challenge. The feasibility of this approach is verified by joining different base material alloys using zinc- and aluminum-based consumables. It is shown that the double beam method can be applied to different joint geometries by joining both double-flanged joints and lap joints. An analysis of the joint microstructure using metallographic cross-sections and transmission electron microscopy shows that intermetallic compounds can be limited to non-critical amounts. Tensile tests show that joint strengths in excess of 150 MPa can be achieved for both types of joint geometries. When shear loads are applied, the use of aluminum-based consumables leads to superior strength. (C) 2015 Elsevier B.V. All rights reserved.

Multi-material structures pose an attractive option for overcoming some of the central challenges in lightweight design. An exceptionally high potential for creating cost-effective lightweight solutions is attributed to the combination of steel and aluminum. However, these materials are also particularly difficult to join due to their tendency to form intermetallic compounds (IMCs). The growth of these compounds is facilitated by high temperatures and long process times. Due to their high brittleness, IMCs can severely weaken a joint. Thus, it is only possible to create durable steel-aluminum joints when the formation of IMCs can be limited to a non-critical level.To meet this goal, a new joining method has been designed. The method is based on the combination of a continuous wave (pw) and a pulsed laser (pw) source. Laser beams from both sources are superimposed in a common process zone. This makes it possible to apply the advantages of laser brazing to mixed-metal joints without requiring the use of chemical fluxes. The double beam technology was first tested in bead-on-plate experiments using different filler wire materials. Based on the results of these tests, a process for joining steel and aluminum in a double-flanged configuration is now being developed. The double flanged seams are joined using zinc- or aluminum-based filler wires. Microsections of selected seams show that it is possible to achieve good base material wetting while limiting the growth of IMCs to acceptable measures. In addition, the results of tensile tests show that high joint strengths can be achieved.

Laser brazing is a joining technology which is typically employed in areas with particularly high quality requirements, e.g. to create zero gap roof joints in automotive production. These seams have to be leak proof and are situated in an area of the car body which is in direct view of the customer. Hence, seam defects and imperfections are inacceptable and require extensive rework whenever they occur. Resulting high rework costs can be avoided by investigating the causes of these imperfections in order to prevent their formation. One type of imperfection which may occur during the laser brazing of galvanised steel are dark deposits on the seam surface. This paper examines the mechanisms leading to the formation of this type of imperfection. Results on the properties of surface deposits are presented along with conclusions regarding the systematic reasons behind their formation. Finally, strategies for preventing the occurrence of surface deposits are recommended.

Laser brazing has become firmly established as a joining process in the automotive industry. While this process offers many advantages, brazed seams also have to meet particularly high quality requirements. The challenge of creating a suitable online quality control system is magnified by the increasing use of aluminum in automotive engineering. This paper introduces recent works on the development of a system for controlling both aluminum and steel brazing processes. It also discusses some of the challenges connected to this task and discloses some of the results derived from the corresponding process analysis.

Laser brazing of zinc coated steel is a widely established manufacturing process in the automotive sector, where high quality requirements must be fulfilled. The strength, impermeablitiy and surface appearance of the joint are particularly important for judging its quality. The development of an on-line quality control system is highly desired by the industry. This paper presents recent works on the development of such a system, which consists of two cameras operating in different spectral ranges. For the evaluation of the system, seam imperfections are created artificially during experiments. Finally image processing algorithms for monitoring process parameters based the captured images are presented.