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 ∼10 µm 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 ∼80 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 α 1-, α 2-, and α 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.