Tensile properties and microstructure of surface tension transfer (STT) arc welded AA 6061-T6 aluminum alloy joints

Abstract

The wide usage of 6xxx series aluminium alloys in automobile sector is mainly because of the exceptionally good weldability characteristics and better corrosion resistance. Surface tension transfer (STT) arc welding is one of the variants of gas metal arc welding (GMAW) that has potential features such as low heat input and arc stability with an innovative wire feed system. STT is a modified short-circuiting metal transfer technique that regulates the metal transfer rate using a high-frequency inverter power supply This process is widely used in automobile industry due to its higher welding speed and capability to weld thin sheets without defects like spatter, distortion and burn through. This article reports the welding of thin aluminium 6061 sheets by STT arc welding process and presents the tensile properties of the welded joints. The features of the microstructure are characterized by optical microscopy. The fracture surfaces are being examined by scanning electron microscopy. During the tensile test, the welded joint failed at 12 mm from weld zone. It is evident that failure is generated by softening in (heat affected zone) HAZ region due to the production of β′or β precipitates which are softer and incoherent in nature. The tensile properties of STT welded aluminium alloy joints yielded a better joint efficiency of 71.08 % due to the presence of higher hardness in the welded region. The hardness results signify that the HAZ noted low hardness which is called as softened zone, where the transformation of precipitates or coarsening of grains takes place.