Properties of Laser-Welded Zr-Al-Co-Nb Bulk Metallic Glass

Area of Science:

• Materials Science
• Metallurgy
• Corrosion Engineering

Background:

• Bulk metallic glasses (BMGs) offer unique properties but their weldability and performance in harsh environments require investigation.
• Nd:YAG laser spot welding is a potential method for joining BMGs, but its effect on microstructure and properties needs characterization.
• The (Zr53Al17Co29)Nb1 BMG exhibits low glass-forming ability, potentially leading to phase precipitation during thermal processing.

Purpose of the Study:

• To investigate the effect of varying initial welding temperatures (IWTs) on the microstructure, microhardness, thermal properties, and corrosion resistance of laser-welded (Zr53Al17Co29)Nb1 BMG.
• To understand the formation and influence of Zr(AlxCo1-x)2 phases in the heat-affected zone (HAZ) after welding.
• To evaluate the corrosion behavior of welded BMGs in a 6 M HCl environment.

Main Methods:

• Nd:YAG laser spot welding of (Zr53Al17Co29)Nb1 BMG at room temperature, 10 °C, and 0 °C.
• Microstructural analysis (parent material, HAZ, weld fusion zone - WFZ) using SEM.
• Microhardness testing, thermal property assessment, and electrochemical corrosion testing (immersion in 6 M HCl).

Main Results:

• Sub-micron/nanoscale Zr(AlxCo1-x)2 phases formed in the HAZ of all welded samples, with reduced volume fraction and density at lower IWTs.
• Welding at 0 °C resulted in minimal crystalline phase formation in the HAZ, primarily below the surface.
• Corrosion testing in 6 M HCl showed pitting on HAZ surfaces at RT and 10 °C IWTs after 120 h, but no significant pitting at 0 °C IWT. WFZ exhibited no pitting under any condition.

Conclusions:

• Lowering the initial welding temperature during laser spot welding effectively suppresses the formation of deleterious Zr(AlxCo1-x)2 phases in the HAZ of (Zr53Al17Co29)Nb1 BMG.
• Reduced phase precipitation at lower IWTs significantly enhances the corrosion resistance of the HAZ in acidic environments.
• The weld fusion zone (WFZ) demonstrates superior corrosion resistance compared to the HAZ, irrespective of the initial welding temperature.