Optimization of Process Parameters for Friction Stir Welding of AA6061 and AA7075 Using Response Surface Method Under Different Fluidic Conditions

Abstract

In past twenty-eight years, after the invention of Friction Stir Welding (FSW) by The Welding Institute in 1991, attractiveness of research about this green technology process is escalating day by day in many industries, fields and academics. Joining of non-ferrous alloys, aluminum alloys in particular, is the main domain of research in FSW. Being a solid state process it offers many advantages over fusion welding processes. Joining heat treatable aluminum alloys of different grades/series is a research oriented task due to variation in physical, chemical and thermal properties of these alloys. Dissimilar friction stir welding of AA6061-T6 and AA7075- T6 has been carried out already and influence of various process parameter has been discussed in literature. The heat generated during friction stir welding results in coarsening and decomposing of strengthening precipitates in these alloys which in turn deteriorate the mechanical properties of welded joints. Under water FSW is adopted for the purpose of reducing temperature peaks and cooling time by many researchers. As compared to under water/submerged friction stir welding, welding with the flowing/ splashing coolant is more practical option in industry. Use of flowing/splashing coolant fluid for joining of AA6061 and AA7075 has not been reported. Therefore, in this research the friction stir welding of AA6061 and AA7075 under different fluidic conditions is studied along with rotational speed and traverse speed. Response surface method is used to correlate input parameters to the output parameters. Mechanical testing and microstructure is studied after experimentation. It is found that use of flowing water as well as mixture of oil and water improved the mechanical properties of welded joint. Joint welded at rotational speed of 1185rpm and travel speed of 25mm/min with coolant fluid B achieved ultimate tensile strength of 267 MPa while joint welded at rotational speed of 1750rpm and travel speed of 50mm/min with coolant fluid C.