Microstructure and Mechanical properties of CMT welded AA6063-T6/B4C/ES metal matrix composite using ER5356 filler wire

Abstract

Aluminium alloy 6063-T6 is a popular choice among different industrial sectors as it portrays various desirable properties like moderate strength, improved corrosion resistance, better weldability and formability etc. These advantages make AA6063-T6 a common choice for matrix in a metal matrix composite. Mostly conventional fusion welding methods like Metal Inert Gas (MIG) and Tungsten Inert Gas (TIG) seem preferable options for welding aluminium and its alloys but it remains a challenge to use them to weld aluminium metal matrix composite. A modified version of MIG i.e. CMT welding, can be explored to overcome the challenges. In this study, an aluminium metal matrix composite has been fabricated with AA6063-T6 as matrix and two reinforcements −one organic, i.e., Eggshell (ES) and one inorganic, i.e., Boron Carbide (B4C), using the conventional stir casting method. CMT welding has been performed on plates cut out from the composites. Microstructure, hardness, tensile strength and residual stress of weld joint of composite have been observed. From micrographs, it is observed that a finer grain has been formed at the Fusion Zone (FZ) in comparison to the Heat Affected Zone (HAZ) and Parent Material (PM). XRD analysis at the fusion line has identified several intermetallic stoichiometric compounds (Al12Mg17, Mg2Si, CaMgSi, CaO, B2O3) and reinforcement B4C and CaCO3 within the matrix volume. The FZ exhibits higher hardness than the HAZ and the PM. Further, the tensile strength of the FZ exceeds that of the unwelded composite due to the presence of metastable strengthening phases of Mg2Si in the FZ, along with reinforcement (B4C and ES) particles. Residual stress analysis reveals tensile stress in the FZ and more compressive stress in the HAZ than in the PM.