📖 ABSTRACT/OVERVIEW
The joining of dissimilar aluminium alloy grades is a recurring challenge in automotive component fabrication, where lightweight structural assemblies increasingly demand the combination of high-strength heat-treatable alloys with more formable and corrosion-resistant grades that are incompatible with conventional fusion welding. This study models and optimises the process parameters of friction stir welding of dissimilar AA6061-T6 and AA5083-H111 aluminium alloy joints, with reference to the material combinations commonly used in vehicle body frame and suspension component fabrication at assembly plants in the Lagos-Ogun industrial corridor. A central composite design experiment was developed, varying tool rotation speed, welding speed, and tool shoulder diameter at three levels each, and a total of 20 weld specimens were produced and characterised. Response surface methodology was applied to develop second-order polynomial regression models for ultimate tensile strength, hardness at the nugget zone, and percentage elongation as functions of the process parameters. Analysis of variance confirmed the significance and adequacy of the developed models. Multi-objective optimisation using the desirability function approach identified the optimal parameter combination as a rotation speed of 1,050 rpm, welding speed of 80 mm per minute, and shoulder diameter of 18 mm, yielding a predicted joint efficiency of 88 percent relative to the weaker base material. Microstructural analysis using optical microscopy and scanning electron microscopy confirmed the development of a refined grain structure in the thermomechanically affected zone under optimised conditions. Keywords: friction stir welding, dissimilar aluminium alloys, response surface methodology, optimisation, automotive fabrication.
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