Electron-beam welding behavior in Mg-Al-based alloys

Abstract

The electron-beam welding (EBW) behaviors of pure Mg and the AZ31, AZ61, and AZ91 Mg alloys are examined in this study, in terms of fusion-zone characteristics, grain structures, texture evolution, and joint efficiency. With increasing A1 content, the Mg-based materials were found to be more easily fusion welded. The AZ91 alloy could be welded using a beam power of 2200 W and a weld speed of 16 mm/s, resulting in a weld depth of 29 mm with a fusion-zone aspect ratio of 8.2. The grains inside the fusion zone were nearly equiaxed in shape and ϳ10 m in size, due to the rapid cooling rate. Extended partial melting zones were observed in alloys with high solute contents, such as AZ61 and AZ91. The postweld tensile strength of the Mg alloys could recover back to ϳ80 to 110 pct of the original strength. The texture in the fusion zone was traced by X-ray diffraction (XRD) and electron-backscattered diffraction (EBSD). The grain orientations inside the rapidly solidified electron-beam-welded fusion zones are still rather diversely distributed. The a 1 -, a 2 -, and a 3 -axes of some grains tend to align at 90 or 30 deg with respect to welding direction, and the c-axis tends to align along the plate normal direction. The influence from surface tension on the weld top-surface appearance and weld depth was not pronounced for the current four Mg materials. Instead, differences in the solidus temperatures and thermal conductivity should be the primary factors.

Texture characterisation of hexagonal metals: Magnesium AZ91 alloy, welded by laser processing

“…It appears that the development of this texture affects the distribution of stresses with a relaxation of the stresses at the surface and a maximum in the under layer [43]. We explain these modifications by the fact that the level of plastic flow, related to local stresses, is dependent on grain orientation [28,44,45,46].…”

Welding of Thin Light Alloys Sheets by CO2 Laser Beam: Magnesium Alloys

“…It appears that the development of this texture affects the distribution of stresses with a relaxation of the stresses at the surface and a maximum in the under layer. We explain these modifications by the fact that the level of plastic flow, related to local stresses, is dependent on grain orientation (Su et al, 2002;Agnew & Duygulu, 2005;Wu et al, 2007).…”

Characterization of AZ31B magnesium alloy joints welded with a Nd:YAG laser

“…19 In Mg alloys, both <1010>-type and a-type axes <1120> directions of the hcp-crystal lattice are close-packed crystallographic directions, which are the preferred growth orientations during a solidification process. 20,21 Furthermore, the crystal growth within the fusion zone is also significantly influenced by the heat-conduction direction (the thermal gradient) during the solidification process and the maximum value of the thermal gradient is perpendicular to the fusion boundary. 12 Therefore, the grains whose close-packed orientation is parallel to the direction of the maximum thermal gradient, grow more rapidly and restrict other, less favorably oriented grains.…”

“…These findings are in good agreement with the results observed in Figures 3 and 5a. Su et al 21 studied the electron-beam-welding (EBW) behavior of Mg-Al-based alloys and found that no apparent columnar grains were formed, while many fine equiaxed grains were observed in the Mg-alloy welding bead. Similarly, they also attributed the absence of co- …”