Study on the weld formation, microstructure and mechanical properties of AZ31B Mg alloy in AC/DC mixed gas tungsten arc welding process

Abstract

In this work, a new welding electrical signal waveform of the AC/DC mixed waveform is purposed to improve the welding quality of magnesium alloy TIG. The method is named as AC/DC mixed tungsten inert gas arc (MIX-TIG) welding. The AZ31B Mg alloy welded joints were obtained by AC-TIG and MIX-TIG. Through investigation of the weld formation, microstructure and mechanical properties of welded joints, the results showed that when the welding current of 90A∼110 A, the completely penetration of welded joints could be obtained. There was no obvious difference for the geometrical parameters of the weld cross-section between the AC-TIG and MIX-TIG. The microstrcuture of fusion zone consisted of α-Mg matric and β-Mg17Al12 phase. At the same welding conditions, the average grain size and β phase number in the MIX-TIG were less than that of the AC-TIG. The microhardness of the AC-TIG fusion zone was slightly larger than that of the MIX-TIG owing to the increase of β phase number. The strain of the AC-TIG welded joint was reduced by approximately 24% compared with that of the MIX-TIG welded joint.

Keywords

• AC/DC mixed TIG
• Magnesium alloy
• Weld formation
• Microstructure
• Mechanical properties