Underwater Friction Stir Welding of AA5754 Aluminum Alloy in Saltwater Environment: A Preliminary Study

Abstract The Underwater Friction Stir Welding (UFSW) environment was proven to improve mechanical properties of the Friction Stir Welded (FSW) joints. However, carefully selected set of parameters is necessary to succeed. This study presents preliminary results of the research on water salinity level effect on the properties of the AA5754 aluminum alloy joints. For this purpose, the Plackett-Burman design was used. The design of experiment consists of ten attempts with process parameters as variables: welding speed, rotational speed, tool tilt angle and water salinity level. The following tests were proceeded: visual tests, tensile strength tests and fractography analysis. Thus, the response variable was ultimate tensile strength (UTS). Surface defects were found in joints performed with low heat input (i.e. low rotational speed, high welding speed). The highest UTS values – 100% of base metal were obtained for the joint made with process parameters: welding speed - 37.5 mm/min, rotational speed - 1235 rpm, tool tilt angle - 2°, water salinity level - 10%. The fractography of the joint revealed precipitates formation and very small dimples. All of the investigated welding parameters were found to be statistically significant. However, the tool tilt angle was of drastically highest significance. The order of the other process parameters was as following: welding speed, rotational speed and water salinity level.