Michael Kreimeyer

Joining of dissimilar materials

The combination of dissimilar materials is a challenging goal for the development of parts with locally optimized properties. The main goal of these developments are weight reduction, optimization of properties or the tailoring of the properties for specific applications in combination with an efficient joining technology. However, using conventional high temperature joining technologies, the formation of intermetallic phases within the joining zone is a nearly unavoidable phenomenon when joining dissimilar material combinations. These phases cause a lack of the mechanical stability in the joining zone. By using an optimized laser joining technology for thin sheet materials this problem could be overcome. The localized energy input of the laser beam and a controlled heat distribution leads to minimized interaction of the joint materials. To overcome process instabilities a special working head technic was developed. At present, Fe-Al and Ti-Al material combinations are successfully joined by this process. Metallurgical and mechanical properties of a number of selected dissimilar material joints will be presented and applications discussed.

Development of a combined joining-forming process for aluminum-steel joints

A modified process for joining dissimilar material combinations like steel with aluminum is invented by the Bremer Institut fur angewandte Strahltechnik (BIAS). Within this process the low melting aluminum is heated up to the melting point and a wetting of the steel surface occurs. Simultaneously, a mechanical force is applied to realize a press-forming in such a way that an overlap is formed to a butt joint. Thereby, joints with minimized intermetallic phases should be realized, providing further improved mechanical properties compared to dissimilar material joint prepared by other technologies. Beside the description of the joining technology, this paper focuses on the metallographical characterization and first mechanical properties of the joints using this technology.A modified process for joining dissimilar material combinations like steel with aluminum is invented by the Bremer Institut fur angewandte Strahltechnik (BIAS). Within this process the low melting aluminum is heated up to the melting point and a wetting of the steel surface occurs. Simultaneously, a mechanical force is applied to realize a press-forming in such a way that an overlap is formed to a butt joint. Thereby, joints with minimized intermetallic phases should be realized, providing further improved mechanical properties compared to dissimilar material joint prepared by other technologies. Beside the description of the joining technology, this paper focuses on the metallographical characterization and first mechanical properties of the joints using this technology.

Gap tolerant joining of aluminum with steel sheets using the hybrid technique

Laser joining of dissimilar materials is one of the core competences of BIAS and is from interest focusing new design concepts for weight savings in different fields in automotive and aeronautic industry. Beside the development of joining techniques for thin aluminum-steel sheets, the joining of thicker material is of interest. Therefore specific processes have to be developed which allow dissimilar joints with small intermetallic phases. By using a hybrid process (Nd:YAG-Laser+MIG), a gap tolerant joining of aluminum-steel joints with a thickness of 3–4 mm, in butt-joint configuration is possible. Furthermore, the developed process allows a flux free joining of these dissimilar material combinations. For the characterization of the joining zone microstructural examinations have been carried out by optical and electron microscopy as well as electron backscattered diffraction analyses. Additionally, results from mechanical examinations like tensile and fatigue tests will be reported.Laser joining of dissimilar materials is one of the core competences of BIAS and is from interest focusing new design concepts for weight savings in different fields in automotive and aeronautic industry. Beside the development of joining techniques for thin aluminum-steel sheets, the joining of thicker material is of interest. Therefore specific processes have to be developed which allow dissimilar joints with small intermetallic phases. By using a hybrid process (Nd:YAG-Laser+MIG), a gap tolerant joining of aluminum-steel joints with a thickness of 3–4 mm, in butt-joint configuration is possible. Furthermore, the developed process allows a flux free joining of these dissimilar material combinations. For the characterization of the joining zone microstructural examinations have been carried out by optical and electron microscopy as well as electron backscattered diffraction analyses. Additionally, results from mechanical examinations like tensile and fatigue tests will be reported.

Laser‐MIG‐Hybridfügen von Aluminium‐Stahl Leichtbaustrukturen

Im Fahrzeugbau wird derzeit der Einsatz von hybriden Strukturelementen aus artungleichen Werkstoffen intensiv diskutiert. Ziel ist es dabei, Gewichtsreduktionen zu erreichen und gleichzeitig die mechanischen Eigenschaften zu erhalten oder zu verbessern. Das Fugen von Aluminium- mit Stahl-Legierungen ist dabei besonders interessant fur den Fahrzeugbau, aber auch fur den Schiffbau.

Development of a new joining technology for hybrid metal aircraft structures

With the introduction of the laser beam welding of skin-stringer-joints into the aircraft industry, Airbus set a new standard for the processing of metallic materials. New design principles and joining processes for high performance materials enhance the overall performance of the integral metallic fuselage. Improved exploitation of material properties is driving the development of ‘tailored’ hybrid components. The newly developed laser beam joining process of aluminium and titanium offers the chance to create low weight and corrosion resistant hybrid structures like seat tracks.With the introduction of the laser beam welding of skin-stringer-joints into the aircraft industry, Airbus set a new standard for the processing of metallic materials. New design principles and joining processes for high performance materials enhance the overall performance of the integral metallic fuselage. Improved exploitation of material properties is driving the development of ‘tailored’ hybrid components. The newly developed laser beam joining process of aluminium and titanium offers the chance to create low weight and corrosion resistant hybrid structures like seat tracks.

Processing of laser joined aluminum-steel tailored blanks in overlap and butt joint configuration

The formability is an essential requirement for future applications of laser joined aluminum - steel tailored blanks in the automotive industry e.g. for the deep drawing of floor panels. A laser joining process for aluminum-zinc-coated steel tailored blanks was developed and improved in recent years at BIAS. Generally, tailored blanks can be joined in butt and overlap configuration. However, the formation of intermetallic phases during the thermal joining of dissimilar materials has a significant influence on the mechanical properties of the joint and therefore also on the formability of the tailored blanks. The phase formation results in a deterioration of the mechanical properties of the joint. With locally restricted energy input and high joining speeds by application of the laser technology, the thickness of such phases can be minimized in both butt and overlap joining techniques below 2 µm. For the characterization of the seam morphology, optical and electron microscopy have been carried out in addition to the mechanical and formability characterization. Thereby fracture stresses of 166 N/mm2 at butt joints and 180 N/mm2 at overlap joints in combination with a promising forming behavior have been achieved.Within this paper both butt and overlap techniques will be presented. This includes the process technologies, the problems of the intermetallic phase formation and the resulting formability of the tailored blanks.The formability is an essential requirement for future applications of laser joined aluminum - steel tailored blanks in the automotive industry e.g. for the deep drawing of floor panels. A laser joining process for aluminum-zinc-coated steel tailored blanks was developed and improved in recent years at BIAS. Generally, tailored blanks can be joined in butt and overlap configuration. However, the formation of intermetallic phases during the thermal joining of dissimilar materials has a significant influence on the mechanical properties of the joint and therefore also on the formability of the tailored blanks. The phase formation results in a deterioration of the mechanical properties of the joint. With locally restricted energy input and high joining speeds by application of the laser technology, the thickness of such phases can be minimized in both butt and overlap joining techniques below 2 µm. For the cha...

Laser joining of aluminum to titanium with focus on aeronautical applications

For aeronautical applications, hybrid structures made of titanium and aluminum alloys offer advantages in comparison to conventional designs. Due to the demands of the aircraft industry for new material combinations based on commercially available and qualified materials, laser processes for joining aluminum to titanium in different configurations are developed.By utilizing laser technique instead of conventional thermal joining processes, joining of aluminum-titanium Tailored Blanks and structures with desirable properties can be achieved. In such dissimilar material joints, the properties are generally dominated by the intermetallic phase layer, which is formed during thermal joining of aluminum with titanium. By minimization of the overall energy input due to high joining speed and geometrically restricted energy input, the intermetallic phase formation can be limited to a minimum size, resulting in good tensile strength and promising forming behavior.Within this paper, an overview about laser joining of aluminum to titanium in different joint configurations will be presented, including FEM-simulation, characterization of the seam morphology and the mechanical properties.For aeronautical applications, hybrid structures made of titanium and aluminum alloys offer advantages in comparison to conventional designs. Due to the demands of the aircraft industry for new material combinations based on commercially available and qualified materials, laser processes for joining aluminum to titanium in different configurations are developed.By utilizing laser technique instead of conventional thermal joining processes, joining of aluminum-titanium Tailored Blanks and structures with desirable properties can be achieved. In such dissimilar material joints, the properties are generally dominated by the intermetallic phase layer, which is formed during thermal joining of aluminum with titanium. By minimization of the overall energy input due to high joining speed and geometrically restricted energy input, the intermetallic phase formation can be limited to a minimum size, resulting in good tensile strength and promising forming behavior.Within this paper, an overview about laser joining ...

Laser-MIG-Hybridfügen von Aluminium-Stahl Leichtbaustrukturen: Neues Fügeverfahren verspricht Effizienzgewinn

Im Fahrzeugbau wird derzeit der Einsatz von hybriden Strukturelementen aus artungleichen Werkstoffen intensiv diskutiert. Ziel ist es dabei, Gewichtsreduktionen zu erreichen und gleichzeitig die mechanischen Eigenschaften zu erhalten oder zu verbessern. Das Fugen von Aluminium- mit Stahl-Legierungen ist dabei besonders interessant fur den Fahrzeugbau, aber auch fur den Schiffbau.