Microstructural evolution and properties of laser spot-welded Zr[sbnd]Al[sbnd]Co[sbnd]Ta bulk metallic glass under various initial welding temperatures

To enhance weldability, this study used a Nd:YAG laser (which produces a faster thermal cycle) in combination with a liquid cooling device (LCD) to spot weld (Zr ₅₃ Al ₁₇ Co ₂₉ ) ₉₉ Ta ₁ BMG. Here, an LCD was employed to provide a variety of initial welding temperatures (IWTs), with progressively lower IWTs from room temperature (RT) to -5 °C. After the welding process, the microstructure evolution (including parent material (PM), heat affected zone (HAZ), and weld fusion zone (WFZ)), glass forming ability (GFA), and mechanical property (microhardness) of the laser-welded samples were investigated. The results showed that two types of crystallines were observed in the HAZ after RT welding. The GFA indicators of the welded samples and microhardness in the HAZ were affected significantly. When the IWT decreased to 0 °C, the crystalline phase in the HAZ and WFZ were barely noticeable which resulted in a softer HAZ; the GFA indicator of the welded sample was not substantially different than that of the PM.