Laser welding and brazing of dissimilar materials

doi:10.1533/9780857098771.2.255

Handbook of Laser Welding Technologies

Woodhead Publishing Series in Electronic and Optical Materials

2013, Pages 255-279

https://doi.org/10.1533/9780857098771.2.255 Get rights and content

Abstract:

Mixed-material joints between, for example, aluminium and steel or aluminium and CFRP are increasingly used in modern automotive, airplane or ship lightweight structures. The chapter addresses the present state-of-the-art and future perspectives for laser-based joining of such material combinations, focusing on both joining processes and joint properties.

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Cited by (14)

Electromagnetic field-assisted laser welding of NiTi to stainless steel: Towards a lightweight, high-strength joint with preserved properties
2023, Journal of Materials Processing Technology
In recent years, laser welding has attracted significant attention as a promising technology for joining smart alloys (e.g., NiTi) to structural materials (e.g., SS) thanks to its unique advantages such as exceptional control heat input and narrow fusion zone. However, obtaining a high strength weldment that also preserves the functional properties of the materials being joined together remains a key challenge in this field mainly due to the formation of brittle intermetallic components (IMCs) near and at the interfacial zone. This study investigates a novel technique for laser welding processing of NiTi/SS assisted by an external magnetic field. This technique, referred to as magnetic field supported, is hypothesized to suppress the formation of brittle intermetallics (e.g., TiFe and TiFe₂) during the laser welding of NiTi/SS, which, in turn, may improve the performance of the resultant joint. To test the hypothesis, comprehensive experimental assessment of the evolution of structural, mechanical and thermomechanical properties of NiTi/SS joints has been conducted. The findings demonstrate the full suppression of Ti-Fe-based IMCs in the joint area, accompanied by significant improvement in the strength (by 28 %) and ductility (by 137 %) of the MFSed joint when compared with conventional laser welding. Interestingly, negligible changes (∼0.6 °C) in the martensitic transformation temperatures have been obtained.
Role of ultra-fine intermetallic particles and martensite in strengthening of AISI 321/Cu/Ti laser welded joint
2022, Materials Characterization
Citation Excerpt :
The problem of welding of dissimilar materials has lately been fairly widely discussed in the scientific literature [1–5].
The study of the influence of phase transformations on residual stresses in heterophase materials is very important for predicting the service life of machines and constructions. Welded joints made of dissimilar materials are of particular interest. The chemical and phase compositions, microstructure, microhardness, strength, and fracture surface characterization of dissimilar AISI 321/Cu/Ti laser joints have been studied. Distinctive features of the laser welding conditions are the displacement of the focal spot to the steel/Cu interface and the deepening of the focus by 3 mm. The chosen mode of laser welding made it possible to obtain the following chemical composition of the melting zone (MZ): 55.3 wt% Cu, 32.2 wt% Fe, 8.5 wt% Cr, 4.0 wt% Ni, and 1.0 wt% Ti. After crystallization in MZ, two supersaturated solid solutions are formed: one based on copper and the other based on iron. During post-welding cooling, (Fe,Cr)₂Ti intermetallic particles sized 10 nm homogeneously precipitate in the Cu-based solid solution, and 10-nm TiCu₄ particles precipitate in the Fe-based solid solution. Fe-based regions become additionally hardened (to 540 HV 0.025) due to the formation of martensite crystals in the austenite matrix. Alloying of titanium with copper causes βTi stabilization at the interface Ti/MZ. During contact melting of titanium, Ti₂Cu intermetallic particles of three types emerged: from 2 to 5 μm eutectic, from 0.1 to 0.5 μm eutectoid, and those homogeneously precipitated in βTi during cooling, sized 10 nm. After quickly cooling, the compressive residual stresses formed in the welded joint. When specimens with welded joints were tensile tested, they fractured in the MZ according to a mixed type. Ductile fracture occurred in Cu- and Fe-based microconstituents by the MZ zone; brittle fracture occurred in the zone with (βTi + Ti₂Cu) structure near Ti. The ultimate tensile strength of the resulting welded joints is 470–515 MPa, and this significantly exceeds the available data.
Atomic scale characterization of a pure Al – galvanized steel spot magnetic pulse joint interface
2019, Materials Characterization
Citation Excerpt :
However joining aluminum with galvanized steel remains a challenge since these materials are characterized by different melting points, thermal conductivities, coefficients of thermal expansion, mechanical properties and flow laws [1–3]. In addition, the high chemical affinity between Al and Fe [4] may lead to the precipitation of brittle intermetallic compounds (IMCs) [1–2] at the joint interface. Diffusion is all the more favored that joining proceeds at the liquid state in the case of welding or brazing.
The bonding interface of pure Al – galvanized steel spot magnetic pulse welds was characterized at the atomic scale. The Al-Zn interface microstructure is worthy of attention as it contains a few micrometers thick biphased layer. This singular layer consists of an aggregate of grains with a 200 to 400 nm size containing islands of either Al or Zn solid solutions oversaturated in Zn or Al, respectively. Inside a grain, some mottled contrasts with a size in-between 5 and 10 nm correspond to fluctuant solute contents. Besides, some native oxides have been dissolved at the interface suggesting the incorporation of oxygen atoms in the biphased layer. Large and elongated (Al,Fe,Si) particles primitively contained in the base Al were also dissolved which gives rise to some round shaped Si particles in the biphased layer. All these microstructural features and changes are consistent with a ballistic origin. Due to both the absence of solidification defects and the rather planar morphology of the bonding interface, the process is expected to occur at the solid state.
Wetting and solidification characteristics of aluminium on zinc coated steel in laser welding and brazing
2016, Journal of Materials Processing Technology
Citation Excerpt :
Kreimeyer (2007) showed that for mechanical joint properties, that meet industrial requirements, wetting length is also a crucial factor. Moeller and Thomy (2013) showed that good quality seams of aluminium and steel can be easily accomplished using laser and laser-hybrid welding and brazing processes. When looking at the basic physical properties of liquids spreading on solid surfaces described by the relation of surface tensions according to Young’s formula, a wetting process between liquid aluminium and solid steel should be possible.
Bead-on-plate laser brazing and overlap laser welding of zinc-coated steel and aluminium is investigated. It is shown that the characteristic tendencies from recent single droplet model experiments in terms of solidification and wetting length can be applied to the case of bead-on-plate brazing but are different in case of overlap welding. Based on a straightforward model for estimating evaporative heat loss, it is shown that heat dissipation in case of bead‐on‐plate brazing and single droplet wetting might be significantly affected by evaporating zinc. A proper breakage of oxide layers seems to be mandatory to initiate spreading on zinc coated surfaces. The occurrence or lack of this necessary effect could be a potential reason for the diverging wetting behaviour observed for overlap welding compared to bead‐on‐plate brazing or single‐droplet wetting.
The role of zinc layer during wetting of aluminium on zinc-coated steel in laser brazing and welding
2014, Physics Procedia
The zinc layer of zinc-coated steel is known to be a crucial factor for the spreading of liquid aluminium on the coated surface. For industrial brazing and welding processes these zinc-coatings enable a fluxless joining between aluminium and steel in many cases. Yet, the reason for the beneficial effect of the zinc to the wetting process is not completely understood. Fundamental investigations on the wetting behaviour of single aluminium droplets on different zinc-coated steel surfaces have revealed a distinct difference between coated surfaces at room temperature and at elevated temperature regarding the influence of different coating thicknesses.
In this paper the case of continuous laser brazing and welding processes of aluminium and commercial galvanized zinc-coated steel sheets are presented. It is shown that in the case of bead-on-plate laser beam brazing, the coating thickness has a measureable effect on the resulting wetting angle and length but does not have a significant impact in case of overlap laser beam welding. This might be linked to different heat transfer conditions. The results also strongly indicate that proper initialbreakup of oxide layers is still required to accomplish good wetting on zinc-coated surfaces.
Numerical Simulation of Temperature Fields during Laser Welding–Brazing of Al/Ti Plates
2023, Materials

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