Research on Effect of Process Parameter on Micro Hardness of Friction Stir Welded Aluminium Alloy [A6061] Joints (original) (raw)

Friction stir welding (FSW) process is a promising solid-state joining process with the potential to join low-melting point material, particularly, aluminium alloy. The most attractive reason for joining aluminium alloy with this process is the avoidance of the solidification defects formed by conventional fusion welding processes. In this research article, an attempt has been made to develop an empirical relationship between FSW variables and Micro Hardness. A factorial design was used by considering three factor and eight trials, which enables to quantify the direct and interactive effect of three numeric factors, that is, tool rotational speed, welding speed, and shoulder diameter on the Micro Hardness. The developed relationship is useful for prediction of Micro Hardness in friction stir welded AA6061 aluminium alloy joints at 95% confidence level. It will also be helpful for selection of process variable to obtain the desired strength of the joint. Furthermore, the optimized capabilities in design-expert software were used to numerically optimize the input parameters. I. INTRODUCTION In many industrial applications steel is readily replaced by non-ferrous alloy, in most cases aluminium alloys. Some of these materials combine mechanical strength comparable with structural steel and low weight, allowing for a significant reduction of weight. But the joining of aluminium alloys can sometimes cause a serious problem by the conventional welding process. The difficulty is often attributed to the solidification process and structure including loss of alloying elements and presence of segregation and porosities. 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. The dependence on friction and plastic work for the heat source precludes significant melting in the work piece, avoiding many of the difficulties arising from a change in states, such as changes in gas solubility and volumetric changes, which often plague fusion welding processes. Further, the reduced welding temperature makes possible dramatically lower distortion and residual stresses, enabling improved fatigue performance and new construction techniques and making possible the welding of very thin and thick materials. FSW has also been shown to eliminate or dramatically reduce the formation of hazardous fumes and reduces energy consumption during welding, reducing the environmental impact of the joining process. Further, FSW can be used in any orientation without regard to the influence of gravitational effects on the process. These distinctions from conventional arc welding processes make FSW a valuable manufacturing process with undeniable technical, economic, and environmental benefits. The process and the terminology are schematically explained in Fig: 1.1. The welding process parameters such as tool rotational speed, welding speed, and pin diameter play a major role in deciding the weld quality. In general, the solid-state nature of the FSW process, combined with its unusual tool and asymmetric nature, results in a highly characteristic microstructure. The microstructure can be broken up into the following zones as explained in Fig: 1.2.