Abstract
This paper aims to determine the role of in-nugget/residual Alclad in the friction stir spot welds of 1.6 mm thick Alclad AA2219 aluminum alloy via an assessment of microstructure, mechanical properties and fracture modes of welds. Alclad redistribution/dispersion within the stir zone of the alloy is varied by using different tool profiles (pinless and conical pin tools) and welding parameter combinations. The results reveal that a pinless tool facilitates the retention of Alclad within the weld's effective joint line/width while no substantial residual Alclad is observed in the effective bonded width of a conical pin weld. The increase in tool depth improves the weld strength of a pinless weld. The fracture morphology of a pinless weld is influenced by the in-nugget Alclad content. Interfacial fracture with midpoint defect, interfacial fracture and nugget pull-out are the fracture modes of pinless welds while a conical pin weld fails by circumferential nugget shear failure. A direct correlation exists between nugget rotation and lap shear failure load. Maximum lap shear failure loads of 4.0 kN and 2.1 kN are obtained in pinless and conical pin welds at the optimum welding parameter combinations of 1500 rpm – 0.8 mm – 8 s and 1400 rpm – 0.43 mm – 4 s, respectively.
Kurzfassung
Diese Arbeit zielt darauf ab, die Rolle von innenliegenden Nugget/Rest-Alclad in Rührreibpunktschweißungen von 1,6 mm dicker Alclad-AA2219-Aluminiumlegierung über die Bewertung der Mikrostruktur, der mechanischen Eigenschaften und der Brucharten von Schweißnähten zu bestimmen. Die Umverteilung/Dispergierung von Alclad innerhalb der Rührzone der Legierung wird durch Verwendung verschiedener Werkzeugprofile (stiftlose und konische Stiftwerkzeuge) und Schweißparameterkombinationen variiert. Die Ergebnisse zeigen, dass das stiftlose Werkzeug die Retention von Alclad innerhalb der effektiven Fugenlinie/-breite der Schweißnaht fördert, während kein wesentliches restliches Alclad in der effektiven gebundenen Breite der Schweißnaht mit konischem Stiftwerkzeug beobachtet wird. Die Vergrößerung der Werkzeugtiefe verbessert die Schweißnahtfestigkeit von stiftlos erzeugten Schweißnähten. Die Bruchmorphologie der stiftlos erzeugten Schweißnaht wird durch den Gehalt innenliegender Alclad-Nuggets beeinflusst. Grenzflächenbruch mit Mittelpunktdefekt, Grenzflächenbruch und Nuggetausreißen sind die Bruchmodi von stiftlosen Schweißnähten, während konische Stiftschweißung infolge umlaufender Nuggetscherung versagen. Es besteht eine direkte Korrelation zwischen der Drehung der Nuggets und der Zugscherbruchlast. Die maximale Zugscherbruchlast. von 4,0 kN und 2,1 kN werden für stiftlos und mit konischem Stiftwerkzeug erzeugten Schweißnähten bei den optimalen Schweißparameterkombinationen von 1500 U/min – 0,8 mm – 8 s und 1400 U/min – 0,43 mm – 4 s erreicht.
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