Evolution of microstructures and mechanical properties of AZ31B magnesium alloy weldment with active oxide fluxes and GTAW process

Chun Ming Lin, Ju Jen Liu, Hsien Lung Tsai, Ching Min Cheng

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10 Citations (Scopus)

Abstract

In this study, the effect of active oxide fluxes with gas tungsten arc welding on the microstructure and mechanical properties of AZ31B magnesium alloy weldment was investigated. The gas tungsten arc welding process through a flux spray layer was applied to an AZ31B magnesium alloy sheet to produce a bead-on-plate specimen. Oxide (TiO 2, SiO 2, Fe 2O 3, Al 2O 3, and ZrO 2) powders were used as the activating fluxes. The macrographs and micrographs of the weld beads were examined using an optical microscope and a scanning electron microscope. The specimens with SiO 2 and Fe 2O 3 fluxes had high depth-to-width ratio welds, followed by those with TiO 2 and ZrO 2 fluxes and while that with Al 2O 3 flux had the low ratio weld. The use of 70A welding current for the specimens with different fluxes produced complete penetration, whereas the specimen without any flux required a 90 A welding current to produce complete penetration. The weld bead microstructure was affected by the activating fluxes, which created different thermal effects that changed the convection direction and promoted the formation of various precipitates in the fusion zone during solidification. Three types of precipitates were found in the fusion zones, that is, a long layer-shaped TiAlMg precipitate with TiO 2 flux, a spherical AlMgZn precipitate with Al 2O 3 flux, and an oval-shaped MgAlMn precipitate with all types of fluxes. The mechanical properties of AZ31B magnesium alloy were measured by tensile testing in the rolling direction. Fractures occurred in the fusion zone near the heat-affected zone interface of specimens welded with TiO 2 flux, revealing a brittle fracture with trans-granular cleavage facets and a large number of small, bright dimples at the center. Such brittle fractures also occurred in the fusion zone of specimens welded with Al 2O 3, ZrO 2, SiO 2, and Fe 2O 3 fluxes. Similarly, the specimens welded with Al 2O 3 exhibited a brittle fracture with trans-granular facets, whereas the other specimens revealed a brittle fracture with inter-granular cleavage facets.

Original languageEnglish
Pages (from-to)1013-1023
Number of pages11
JournalJournal of the Chinese Institute of Engineers, Transactions of the Chinese Institute of Engineers,Series A/Chung-kuo Kung Ch'eng Hsuch K'an
Volume34
Issue number8
DOIs
Publication statusPublished - 2011 Dec 1

Keywords

  • Active fluxes
  • Fracture
  • Magnesium alloy
  • Mechanical property

ASJC Scopus subject areas

  • Engineering(all)

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