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

TL;DR

This paper studies how laser welding affects the properties of a specific bulk metallic glass alloy, focusing on microstructure and corrosion resistance.

Contribution

The study reveals how initial welding temperatures influence phase formation and corrosion resistance in laser-welded Zr-Al-Co-Nb bulk metallic glass.

Findings

Lower initial welding temperatures reduce the volume and density of Zr(AlxCo1−x)2 phases in the heat-affected zone.

Welds at 0 °C initial temperature showed no pitting corrosion in the heat-affected zone after 120 h in HCl.

Pitting corrosion in the heat-affected zone increased with higher initial welding temperatures.

Abstract

In this study, the Nd:YAG laser process was employed with preselected welding parameters and varying initial welding temperatures (including room temperature, 10 °C, and 0 °C) for spot welding of (Zr53Al17Co29)Nb1 bulk metallic glass. Following welding, the microstructure—including the parent material, heat-affected zone (HAZ), and weld fusion zone (WFZ)—as well as the microhardness, thermal properties, and corrosion resistance of the welds, were systematically investigated. Owing to the low glass-forming ability of the alloy, a small amount of Zr6CoAl2 phase was observed within the amorphous matrix at the center of the bulk metallic glass cast plate. After the laser welding, sub-micron or nanoscale Zr(AlxCo1−x)2 phases have formed in the HAZ of all welded samples, which significantly influenced the microhardness, thermal properties, and corrosion resistance in this region. As the initial welding temperature decreased, both the volume fraction and the density of the Zr(AlxCo1−x)2 phase were reduced. Notably, for the weld performed at the lowest initial temperature of 0 °C, small crystalline phases were detected only at approximately 70 μm below the surface of the HAZ. To clarify the effect of IWTs on corrosion resistance, welded samples were immersed in 6 M HCl at 35 °C for 72–120 h. Surface morphologies after corrosion were examined by SEM in the PM, HAZ, and WFZ. No evident pitting was detected after 72 h of immersion. After 120 h, pitting corrosion was observed on the HAZ surfaces of welds subjected to RT and 10 °C IWTs, whereas no obvious pitting was found at an IWT of 0 °C. The pit size and density in the HAZ increased with increasing IWT. In contrast, no pitting was observed in the WFZ under any IWT condition.

Figures