Physical Review B

Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

Joining steel with aluminum involving the fusion of one or both materials is possible by laser beam welding technique. This paper describes a method, called laser braze welding, which is a suitable process to realize this structure. The main problem with thermal joining of steel/aluminum assembly with processes such as TIG or MIG is the formation of fragile intermetallic phases, which are detrimental to the mechanical performances of such joints. Braze welding permits a localized fusion of the materials resulting in a limitation on the growth of fragile phases. This article presents the results of a statistical approach for an overlap assembly configuration using a filler wire composed of 85% Zn and 15% Al. Tensile tests carried on these assemblies demonstrate a good performance of the joints. The fracture mechanisms of the joints are analyzed by a detailed characterization of the seams.

Dissimilar material joining using laser (aluminum to steel using zinc-based filler wire)

Laser welding–brazing (LWB) technique with CW Nd:YAG laser was used for lap joining of zinc coated steel (DP600) with aluminum alloy (AA6016) using a filler wire composed of 85% Zn and 15% Al. LWB was performed with varying laser power, brazing speed, and wire feed speed. The microstructure and composition analyses of the brazed joints were examined using SEM and EDS while the mechanical properties were measured in the form of micro-hardness and tensile strength. The thickness of reaction layers formed along the steel–seam interface was in the range of 3–23 μm, and it varied with the brazing speed. The average micro-hardness value of this layer was 348 HV, compared to 150 HV in brazed seam and 230 HV in steel matrix. It has been found that joints produced with heat inputs between 60 and 110 J/mm exhibited higher mechanical resistance of about 220 MPa and the failures occurred away from the joints on aluminum side. The corresponding brazing speeds are between 0.5 and 0.8 m/min and the thickness of the layer produced ranged between 8 and 12 μm.

Study on laser welding-brazing of zinc coated steel to aluminum alloy with a zinc based filler

Joining mechanism of Ti/Al dissimilar alloys during laser welding-brazing process

The main problem in joining steel to aluminium by a thermal process (e.g. TIG, MIG) is the formation of brittle intermetallic phases, that causes the mechanical performance of the assembly to be poor. A laser beam, however, can localize the fusion and inhibit the formation of these phases. This article presents a feasibility study for steel/aluminium assemblies with filler wire of 88% Al and 12% Si. Analysis of the resultant joints may show the causes of fracture. An experimental design study is conducted, to see how the mechanical performance of such joints could be improved. This method establishes what the best operational limits are and shows how different operational conditions influence the various ways in which fractures occur.

Laser brazing of a steel/aluminium assembly with hot filler wire (88% Al, 12% Si)

One way of making car bodies lighter is to introduce some aluminium parts in place of steel. Steel and aluminium can be joined by laser braze welding. As in other types of thermal joining, inter-metallic phases may weaken the joint. In laser braze welding, these appear as a thin layer of brittle compounds at the steel/seam interface. Their formation is related to temperature. It has been shown that, if the layer is less than 10 μm thick, the joint is not compromised [Kreimeyer M., Sepold G. Laser steel joined aluminium-Hybrid structures, Proceedings of ICALEO'02, Jacksonville, USA; 2002]. Not only can temperature gradient be calculated by numerical simulation, but it is also possible to measure the surface temperature by thermography. We show here how thermography may be used to control temperature during laser braze welding.

Temperature control in laser brazing of a steel/aluminium assembly using thermographic measurements

Effects of the powder, laser parameters and surface conditions on the molten pool formation in the selective laser melting of IN718

The present study is dedicated to the numerical simulation of an industrial case of hybrid laser–MIG welding of high thickness duplex steel UR2507Cu with Y-shaped chamfer geometry. It consists in simulation of heat transfer phenomena using heat equivalent source approach and implementing in finite element software COMSOL Multiphysics. A numerical exploratory designs method is used to identify the heat sources parameters in order to obtain a minimal required difference between the numerical results and the experiment which are the shape of the welded zone and the temperature evolution in different locations. The obtained results were found in good correspondence with experiment, both for melted zone shape and thermal history.

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Alexandre Mathieu

Papers

Dissimilar material joining using laser (aluminum to steel using zinc-based filler wire)

Laser brazing of a steel/aluminium assembly with hot filler wire (88% Al, 12% Si)

Temperature control in laser brazing of a steel/aluminium assembly using thermographic measurements

Effects of the powder, laser parameters and surface conditions on the molten pool formation in the selective laser melting of IN718

The numerical simulation of heat transfer during a hybrid laser–MIG welding using equivalent heat source approach