A review of laser welding techniques for magnesium alloys

Gas tungsten arc (GTA) welds were performed on 4-mm thick plates, machined from as-cast magnesium AZ91D ingots. The microstructure and defect formation was investigated by optical and scanning electron microscopy. Mechanical properties were determined by standard tensile tests on small-scale specimens. A wide heat affected zone (HAZ) (>3 mm) was created adjacent to the fusion line that consisted of two regions: (1) a partially melted zone (PMZ), created near the fusion line; and (2) a wide region, which was heat affected without melting. It was found that, after resolidification, a continuous Al12Mg17 phase existed along the PMZ grain boundaries that markedly reduced the joint strength to below that of fully annealed Mg-AZ91D alloys. In contrast, specimens machined from welded metal exhibited improved strength and ductility that resulted from the microstructural refinement caused by the rapid cooling during resolidification of the fusion zone. When the creation of a large PMZ was prevented, as in electron beam welding, the joint strength was comparable to that of the base metal.

Mechanical properties and microstructure of gas tungsten arc welded magnesium AZ91D plates

Weld formation mechanism of fiber laser oscillating welding of austenitic stainless steel

Weldability of magnesium alloy to aluminum alloy in laser weld bonded (LWB) joints was investigated. Results showed that magnesium/aluminum could be easily joined by LWB under proper technological parameters. The weld was characterized by complex vortex flow at the bottom, and there existed intermetallic compound layer between weld pool and lower sheet metal, which was composed of the brittle phases of Al3Mg2 and Al12Mg17, resulting in the formation of weld cracking. Adhesive in the weld was heated up and then escaped in the form of gas, which would not affect the microstructures of weld. However, Adhesive near the weld was oxidized and carbonized, leading to the formation of a failure zone. But this failure zone had little influence on load bearing capability of the joints. Besides, it was also found that the penetration of LWB joints was greater than that of laser welded joints alone. In tensile shear test and T-peel test, LWB samples gave both the highest shear resistance and the highest peel resistance compared to laser welded samples and adhesive bonded samples.

Microstructure characteristics and mechanical properties of laser weld bonding of magnesium alloy to aluminum alloy

Five single oxide fluxes—MgO, CaO, TiO2, MnO2, and Cr2O3—were used to investigate the effect of active flux on the depth/width ratio in AZ31B magnesium alloy. The microstructure and mechanical property of the tungsten inert gas (TIG) welding seam were studied. The oxygen content in the weld seam and the arc images during the TIG welding process were analyzed. A series of emission spectroscopy of weld arc for TIG welding for magnesium with and without flux were developed. The results showed that for the five single oxide fluxes, all can increase the weld penetration effectively and grain size in the weld seam of alternating current tungsten inert gas (ACTIG) welding of the Mg alloy. The oxygen content of the welds made without flux is not very different from those produced with oxide fluxes not considering trapped oxide. However, welds that have the best penetration have a relatively higher oxygen content among those produced with flux. It was found that the arc images with the oxide fluxes were only the enlarged form of the arc images without flux; the arc constriction was not observed. The detection of arc spectroscopy showed that the metal elements in the oxides exist as the neutral atom or the first cation in the weld arc. This finding would influence the arc properties. When TIG simulation was carried out on a plate with flux applied only on one side, the arc image video showed an asymmetric arc, which deviated toward the flux free side. The thermal stability, the dissociation energy, and the electrical conductivity of oxide should be considered when studying the mechanism for increased TIG flux weld penetration.

Mechanism and Microstructure of Oxide Fluxes for Gas Tungsten Arc Welding of Magnesium Alloy

The importance of light weight magnesium alloys, especially for the automotive industry, has grown significantly during the last years. To fully benefit from the whole designing potential of this material, joining processes have to be developed. Laser beam welding turns out to be very suitable to join magnesium parts. The results of welding magnesium alloys AZ91HP and AM50HP with a 3 kW Nd:YAG laser and a 6 kW CO2 laser with an industrial robot and a gantry robot system are shown from a production point of view. The determination of the process window by analyzing the influence of laser type, power, welding velocity, and shielding gas, as well as the influence of the base material, leads to conclusions about process stability and production tolerances. Further investigations concerning fixturing techniques as well as seam preparation and joint geometry show effects on the process flexibility and the effort to realize high quality seams under production conditions. The investigated process parameters are e...

Welding of die-casted magnesium alloys for production

The importance of light weight magnesium alloys especially for the automotive industry is growing significantly, due to rising environmental requirements. Especially going along with ever more demanding safety standards which require the installation of heavy safety appliances, the use of light weight materials becomes more and more important. Magnesium is an extremely suitable material for die-casting. One goal of die-casting to reduce production costs is to avoid following process steps. Nevertheless joining processes have to be developed to fully benefit from the whole designing potential of this material. Laser beam welding turns out to be very suitable to join magnesium parts.Results welding the magnesium alloys AZ91HP and AM50HP with a 3 kW Nd:YAG-laser and a 6 kW CO2-laser with an industrial robot and a gantry robot system are shown from a production point of view. Especially the determination of the process window by analyzing the influence of laser type, power, welding velocity and shielding gas as well as the influence of the base material leads to conclusions about process stability and production tolerances. Further investigations concerning fixturing techniques as well as seam preparation and joint geometry show effects on the process flexibility and the effort to realize high quality seams under production conditions. The investigated process parameters are evaluated mainly in respect to their influence on the static strength of the welding seam.The importance of light weight magnesium alloys especially for the automotive industry is growing significantly, due to rising environmental requirements. Especially going along with ever more demanding safety standards which require the installation of heavy safety appliances, the use of light weight materials becomes more and more important. Magnesium is an extremely suitable material for die-casting. One goal of die-casting to reduce production costs is to avoid following process steps. Nevertheless joining processes have to be developed to fully benefit from the whole designing potential of this material. Laser beam welding turns out to be very suitable to join magnesium parts.Results welding the magnesium alloys AZ91HP and AM50HP with a 3 kW Nd:YAG-laser and a 6 kW CO2-laser with an industrial robot and a gantry robot system are shown from a production point of view. Especially the determination of the process window by analyzing the influence of laser type, power, welding velocity and shielding gas ...

C. Lehner

Papers

Welding of die-casted magnesium alloys for production

Welding of die-casted magnesium alloys on production machines