Abstract
In this study, butt welding of commercial AZ31 magnesium alloy sheets has been investigated by using the tungsten inert gas welding process with alternating and pulsed current. Magnesium alloy welding, although well developed and understood, can present some problems, such as porosity, hot cracking, oxide formation, etc. Samples of the welded parts have been examined by optic microscopy and mechanic tests. Results showed that porosities and homogeneous micro size oxides were rarely found. Orientation of the weld microstructure in direction of the heat transfer were also rarely observed and equiaxed grain morphology was the dominant grain structure as in the base metals. In addition, fusion zone and HAZ of the welded samples have generally shown twins. This seems to be a very dominant grain type particularly in pulsed samples. Hot cracking was not observed in any samples. Results of mechanical tests showed that pulsed current seems to generate more favorable higher mechanical properties of weld joints than alternating current for magnesium alloys.
Kurzfassung
In dieser Studie wurde das Stumpfschweißen von Blechen aus der kommerziellen Magnesiumlegierung AZ31 mit dem Wolfram-Inertgas-Schweißverfahren mit Wechsel- und Impulsstrom untersucht. Das Schweißen von Magnesiumlegierungen, obwohl gut entwickelt und verstanden, könnte hinsichtlich Porosität, Heißrissbildung, Oxidbildung usw. problematisch sein. Schweißproben wurden lichtmikroskopisch und anhand mechanischer Tests untersucht. Ergebnisse zeigten, dass Porositäten und homogene Feinstoxide selten auftraten. Orientierungen des Schweißgefüges in Richtung der Wärmeübertragung wurde auch nur selten beobachtet. Äquiaxiale Kornmorphologie dominierte, ebenso wie im Grundwerkstoff. Darüber hinaus finden sich in der Schmelzzone und WEZ der geschweißten Proben generell Zwillinge. Dies scheint ein sehr dominanter Korntyp besonders in gepulsten Proben zu sein. Heißrissbildung wurde an keiner Probe beobachtet. Mechanische Tests zeigten für Magnesiumlegierungen, dass mit gepulsten Strömen scheinbar bessere mechanische Eigenschaften der Schweißverbindung erzielt werden als mit Wechselstrom.
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