A Study on the Optimization of Process Parameters and their Effects on the Mechanical Properties of the Magnetic Pulse Welded AA 6061 T6 Tubular Joints

Abstract

Judicious selection of materials for light weight structures require high strength-to-weight ratio and good corrosion resistance alloys. AA 6061 alloy with such properties has attracted the attention of researchers around the globe. Joining of Aluminum using conventional fusion welding methods has been a challenge owing to its properties like ductility, high thermal conductivity and high reflectivity. Magnetic Pulse Welding (MPW) is a modern day state of the art “cold welding” process or more precisely a “solid state welding” process that can produce clean and precise joints of Aluminium alloys. MPW uses electromagnetic forces to weld two similar or dissimilar materials through high-speed impact of the metals due to a controlled acceleration. In this investigation, an attempt is made to optimize the significant process parameters of MPW for obtaining maximum Tensile strength of the AA 6061 T6 tubular joints. The joint strength of MPW joints is highly dependent on the process parameters like Discharge Voltage, Standoff distance and Overlap length and hence these parameters are considered for analysis and optimization. Design of Experiment (DOE) statistical tool was adopted for the systematic conduct of the tests. Response Surface Methodology (RSM) was embraced to develop the empirical relationship. AA 6061 T6 MPW joints were produced in lap configuration using a 100kJ capacity B-Max made MPW equipment. The welded specimens were prepared for tensile testing using Wire cut EDM. A maximum tensile strength of 303 MPa was observed for the parameter values of Discharge Voltage 12kV, Stand-off Distance 1.75mm and Overlap length of 8mm. The maximum tensile strength obtained is 98.05% of the actual Tensile Strength of the base metal. The Tensile Strength predicted through RSM was 303.04 MPa which is almost equal to the experimental value. The Contour and three-dimensional surface plots showing the interaction effect of the influencing process parameters on the tensile strength were developed. It was found that the Discharge Voltage and Stand -off distance affect the strength of the joint largely as compared with the Overlap length. Microhardness survey was conducted across the base metal and the weld interface and the results revealed that the Vicker microhardness was 138 HV at the weld interface and it varied from 108 HV to 120HV at the base metals. Microstructural study showed well defined wavy weld interface which is a personification of typical MPW joint. The results of the proposed model were validated using confirmation tests.