STUDIES OF DISSIMILAR ALUMINIUM ALLOY IN FRICTION STIR WELDING

Abstract

Welding processes have evolved as one of the joining processes with enormous potential. Different welding processes have been invented during their evolution. The increasing use of aluminum has become the basis of the need for a welding process to

overcome the limitations of the fusion welding techniques. The invention of a Solid- state welding technique-Friction Stir Welding (FSW) has eliminated the drawbacks of

fusion welding associated with the solidification process. In the present research work, an empirical model has been established between tool rotational speed, tool traverse speed, tilt angle and square pin size, and mechanical properties (ultimate tensile strength, yield strength, percentage elongation and impact strength) of friction stir welded dissimilar non-heat-treatable AA 5083-O and heat treatable AA 6082-T651. Statistics based Response surface methodology (RSM) was used to perform the experiments, analyze the results and optimize the parameters. Rotatable Central composite design (CCD) was used to generate the design matrix to perform the welding. Four factors each having five levels were used to generate the matrix. Total thirty-one experiments without blocking were performed on a dedicated friction stir welding machine. The levels of the tool rotation speed and traverse speed were decided from extensive trial runs performed on a customized friction stir welding machine. The square pin size and tilt angle levels were decided after the literature review.

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The experiment runs were performed randomly to eliminate inherent error in experimentation. The dissimilar base plates were welded, standard samples were machined, mechanical properties were measured and empirical relationships were established. Adequacy of the empirical relationship was ensured by Analysis of variance (ANOVA). The significance of various parameters was found and non-significant factors were omitted from the empirical model to generate reduced models. The optimized values of the input parameters were obtained to maximize each response. Multi-objective optimization was used to find the optimized values of input parameters to obtain maximum values of all responses simultaneously. Microhardness values were measured and found that on the retreating side its value minima points were found between heat affected zone and thermo mechanical affected zone. Residual stresses of friction stir welded plates were measured and analyzed using the cos (α) method. X-Ray Diffraction (XRD) analysis was performed to check the crystallinity of the joints and base material. The scanning electron microscopy (SEM) analysis of the nugget zone of welded plates was performed. Optical microscopy of various microscopic zones was also analyzed.