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Mechanical Property and Microstructure of Gas Tungsten Arc Welded AZ91D Magnesium Plates

Author: GuoQiang
Tutor: YouGuoQiang；LongSiYuan
School: Chongqing University
Course: Materials Processing Engineering
Keywords: magnesium alloy Gas tungsten arc welding microstructure tensile strength pores
CLC: TG407
Type: Master's thesis
Year: 2011
Downloads: 121
Quote: 0
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Abstract


The purpose of this paper is to study the TIG technology for cast Mg alloys AZ91D,Die-casted plates of AZ91D magnesium alloy were double-sided welded by gas tungsten arc welding (GTAW),as-cast and as-extruded AZ91 magnesium alloys were also investigated for comparison. This paper in-depth study welding current have an effect on welding seam appearance,microstructure and mechanical properties, the porosity in the welded joints of die-casted magnesium was also discussed。①It was found that welding current have an great effect on welding seam appearance, the weld formation was bad while the current was small, with the welding current increased, the weld face get better. The weld face unfused when the welding current error is little②It was found that the welded joint was composed of a base material (BM), a wide heat-affected zone (HAZ) and a fusion zone (FZ) area. Compared with the grains both in the HAZ and BM, the grains in the HAZ were found to be grow larger, and the welded zone of contains finer equiaxed grains. The microstructure of the weld zones and base metal consist mainly ofα-Mg andβ-Mg17Al12.③With the back of the welding current increases, the heat affected zone and weld metal grain growth, heat-affected zone width increases. And weld in a network ofβ-Mg17Al12 reduced, while the increase of grainβ-Mg17Al12.④There were many pores in the welded joints of cast magnesium alloy, but the welded joints of wrought magnesium were different, Welded joints in the CAST larger pores can be observed, and in varying forms and gravity cast magnesium alloy welded joints was not observed in the stomata, indicating the state of the joint base metal production in the pores have a greater impact.⑤The mechanical properties of the welded joints was worse, the maximum tensile strength of magnesium alloy die-casting state is only 57% of the base metal, mainly because there were many holes in the welded joint, the tensile strength increased with increasing welding current.⑥The results show that the weld zones of all the specimens give the maximum hardness and the heat affected zone gives the minimal, while the hardness of the die casting give a value in between.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Welding, metal cutting and metal bonding > Welding general issues > Mechanical properties of welded joints and Intensity
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