2:45pm - 3:00pm
Vapor plume behavior during a standalone laser pulse on the dissimilar aluminum/titanium interface: high-speed imaging with 810 nm band-pass filter
Université de Bourgogne Franche-Comté, France
The understanding of plume behavior in dissimilar laser welding is little studied and can bring an insight to the concurrent vaporization process and keyhole dynamics. The present study is dedicated to the high-speed imaging and post-mortem characterization of a standalone Yb:YAG laser pulse on aluminum A5754/titanium interface with different offsets to the joint line. Plume morphology, dimensions, orientation and propagation velocities were characterized basing on the videos performed with a 810 nm band-pass filter. The main observed feature of the plume was its pronounced initial inclination towards aluminum side, accentuated by the beam offset on aluminum and reduced by the offset on titanium, followed by a progressive redressing resulting in a close-to-vertical jet. This behavior was attributed to the domination of the vapor jet from titanium side over that of aluminum side during the evolution of keyhole curvature. SEM observations of the melt were found in agreement with this statement.
3:00pm - 3:15pm
New strategies for joining of aluminum alloys to steel by means of laser
1CINTECX, University of Vigo, LaserON Research Group, Vigo, SPAIN; 2Department of Mechanical and Materials Engineering, University of Turku, Turku, FINLAND; 3Materials Engineering, Applied Mechanics and Construction Dpt., University of Vigo, EEI, Vigo, SPAIN
Joining steel and aluminum, is still a challenging task. This is due to significant differences in their fusion, expansion coefficients, thermal conductivity, and the practically zero solubility of Fe in Al. This low solubility leads to formation of intermetallic compounds (IMCs) on the interface between aluminum and steel.
IMCs are necessary to effectively join aluminum and steel, but the intermetallic layer can seriously deteriorate the mechanical properties of the joint.The growth of the IMC layer is the consequence of a diffusion process and, therefore, it is dependent on the welding thermal cycle. In this context, laser welding stands out relative to other welding processes by providing high energy densities and processing, with a moderate heat input.
This paper presents recent developments on the laser joining of aluminum alloys to steel. Succesfull examples of this type of dissimilar welding will be shown, comparing the mechanical performance of the final joint parts.
3:15pm - 3:30pm
Joining dissimliar materials: a new approach based on laser beam welding and melt displacement by electromagnetic forces
In order to reduce weight of vehicles, the interest in multi-material-design has been growing within the last few years. For vehicles the combination of steel and aluminium alloys offers the most promising compromise between weight, strength and formability. Thermal joining of these dissimilar materials is still a challenge to overcome. A possible approach is a new joining technology, whereby a combination of laser beam welding and contactless induced electromagnetic forces are used to displace the generated melt of one joining partner into a notch of the other. This paper presents the working principle and shows numerical analyses to improve the understanding of this joining process. The simulations help to calculate the thermal development of the joining partners, which is important for the formation of intermetallic phases. Furthermore, the calculation of the time required for a complete displacement is possible. The numerical results are validated by experimental results.
3:30pm - 3:45pm
Temperature measurement for heat conduction laser joining of metals to polymers
University of Luxembourg, Luxembourg
Laser joining of metals to polymers offers several advantages to produce hybrid assemblies of metals and polymers. One of the most important ones is the exceptional control over the heat input which defines the temperature at the interface of the materials. For the current study, the materials are joined in an overlap configuration with the heat conduction laser joining technique. To enlarge the joining area, beam trajectory was implemented with a continuous-wave fiber laser. The temperature was recorded simultaneously at different areas between the materials with K type thermocouples to identify the behavior of polymer at different temperatures. The results show that due to excessive heat input, polyamide degrades and leaves porosities near the interface of metal/polymer. The optimum condition considering mechanical properties of the welded samples and the absence of the porosities is achievable in a narrow process window between the melting range and the degradation of the polyamide.
3:45pm - 4:00pm
Metallurgy of dissimilar laser beam welded lap joints of supra-ductile and ultra-high strength steels
Fraunhofer Institute for Laser Technology, Steinbachstrasse 15, 52014 Aachen, Germany
Results of research on laser beam welding of a high manganese X30MnCrN16-14 (1.4678) to a press hardened X46Cr13 (1.4304), a dual phase steel (1.0944), and a press-hardened manganese boron steel (1.5528) in lap joint configuration will be reported. A pre-assessment of the local mechanical properties by micro hardness measurements revealed their uneven distribution over the weld zone. Based on metallographic inspection the underlying microstructures were revealed. By EDS analyses the local alloy constitutions were determined and assed by of COHMS diagrams. It was confirmed that in the combination with the high manganese steel the formation of ferritic phases, ferrite is largely suppressed to the favour of austenite and α’ and ε martensite. These findings were in part confirmed by nano indentation. The results allow an insight into the properties linked to melt transport, but indicate some further research.