In the laser treatment of a workpiece (9), e.g. for surface hardening, melting, alloying, cladding, welding or cutting, the adverse effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1). The two beams (1)(5) may be combined by a beam coupler (4) or may reach the workpiece (9) by separate optical paths (not shown). The shorter wavelength beam (1) improves the coupling efficiency of the higher- powered laser beam (5).

Laser Material Processing

Dissimilar friction welding of 6061-T6 aluminum and AISI 1018 steel: Properties and microstructural characterization

Dissimilar welding of carbon steel to 5754 aluminum alloy by nd:yag pulsed laser

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

Effects of Si additions on intermetallic compound layer of aluminum–steel TIG welding–brazing joint

The laser joining of a low carbon steel to a 6000 series aluminium alloy was realised in key-hole welding mode in a steel-on-aluminium overlap configuration and was investigated in a three-fold approach: (1) process optimisation, (2) material characterisation and (3) mechanical testing. No-defect welds, composed of a solid solution of aluminium in iron and richer aluminium “white solute bands” of FeAl phases were obtained when limiting steel penetration in aluminium to below 500 μm. Embrittlement of the joining zone was observed, mainly located on the weld–aluminium interfaces composed of Fe2Al5 and/or FeAl3 phases with thicknesses between 5 μm and 20 μm. Limiting penetration to below 500 μm allowed to restrict steel to aluminium dilution in order to confine the hardness of the welds. With such penetration depths, up to 250 N/mm in linear strength could be achieved, with failures located in the weld–aluminium interfaces. Increasing penetration depth led to a change in the assembly weak points (in the weld and on the steel–weld interfaces) and induced a severe decrease in strength.

Steel to aluminium key-hole laser welding

A new mean of assembling steel to aluminium was developed, following previous work by German workers [1] . In this new method, a laser-induced aluminium melt pool spreads and wets a solid steel, to generate, after solidification a sound and resistant interface layer. Joint properties were investigated, in terms of surface aspects, interface microstructures and mechanical resistances under tensile testing, for non-galvanized and galvanized DC04 steels. Thermal and diffusional finite element (FE) simulations were also carried out to calculate temperature history at interfaces, and reaction layer thickness. The 2–20 μm thick reaction layers formed all along the interface were found to be mostly composed of Fe 2 Al 5 intermetallic compound with a high hardness (1200 HV) and rather low ductility (presence of solidification cracks). The presence of a 10 μm thick Zn layer on the steel was shown to have a beneficial influence on the wetting characteristics of the joint, despite the formation of occluded pores in the melt pool due to Zn vaporisation. FE thermal modelling evidenced 760–1020 °C wetting temperatures at the interface between DC04 low carbon steel and 6016 aluminium sheets, with time maintains of the melt pool in the 0.2–0.5 s range, resulting in high-speed reaction kinetics. Using these temperature data, diffusion calculations were shown to provide a rather good prediction of intermetallic thicknesses. Tensile tests were considered on aluminium–steel lap joints and evidenced higher mechanical resistances (220 N/mm linear tensile strength) on galvanized steels, provided that fluxing of the steel surface was carried out prior to welding to avoid zinc vaporisation. Comparatively, non-galvanized assemblies exhibited much lower mechanical resistances (170 N/mm resulting in a 90 MPa interfacial shear strength). It was concluded that the laser-induced wetting technique is a rather effective way for generating Al-steel joints without filler material, and that it should be considered as a competitive technique versus solid assembly modes (friction stir welding …).

Generation of aluminium–steel joints with laser-induced reactive wetting

Galvanised steel to aluminium joining by laser and GTAW processes

The joining of DC04 steel to 6016-T4 Al alloy is achieved by laser braze welding using a 4047 (Al–12Si) filler wire and a brazing flux. The dissimilar joining is obtained both by welding the parent 6016 alloy to the 4047 filler wire, producing a continuous bonding without apparent macroscopic flaws, and by reactive wetting of the molten Al alloy on the solid steel, resulting in the formation of a thin layer of Fe–Al–Si intermetallic compounds at the steel/bead interface. The linear strength of the assemblies can be as high as 190 N mm−1, with a failure generally located in the reaction layer of the steel/bead interface. Last, the strength of the assemblies is shown to increase linearly with the reaction layer width.

Steel to aluminium braze welding by laser process with Al–12Si filler wire

https://hal.archives-ouvertes.fr/hal-00562399/document

G. Sierra

Papers

Steel to aluminium key-hole laser welding

Generation of aluminium–steel joints with laser-induced reactive wetting

Galvanised steel to aluminium joining by laser and GTAW processes

Steel to aluminium braze welding by laser process with Al–12Si filler wire

Study and prevention of cracking during weld-repair of heat-resistant cast steels