Some investigations in friction stir welding of aluminium alloy 6082

Abstract

In many industrial applications steel is readily replaced by non ferrous alloys, in most cases aluminium alloys. Some of these materials combine good mechanical strength which is comparable with structural steel and low weight that allows a significant reduction in weight. But the joining of aluminium alloys by conventional welding processes can sometimes cause serious problems. The difficulties are often attributed to the solidification process and structure including loss of alloying elements and presence of segregation and porosities in the weld joint. Friction stir welding (FSW) offers an alternative through solid-state bonding, which eliminates all these problems of solidification associated with the conventional fusion welding processes. In this research work an attempt has been made to develop an empirical relationship between FSW variables and the mechanical properties (tensile strength, yield strength, percentage elongation, micro hardness and impact toughness) of friction stir welded aluminium alloy 6082-T651 joints. Response surface methodology was adopted for analyzing the problem in which several independent variables influence the response. Central composite rotatable design matrix was used to prescribe the required number of experimental conditions. A four-factors-five-level central composite design was used to determine the optimal factors of friction stir welding process for aluminium alloy. The central composite design (CCD) with a quadratic model was employed. Four independent variables namely - tool rotational speed (N), welding speed (S), axial force (F) and pin diameter (P) were selected. Each independent parameter was varied at five levels which were - 2,-1, 0, +1 and +2. First 16 experimental conditions were derived from full factorial experimental design matrix (24 = 16). All the variables at the intermediate (0) level constitute the centre points while the combinations of each process variable at either their lowest (-2) or highest (+2) with the other three variables of the intermediat