STUDIES ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF FRICTION STIR WELDED JOINTS OF Al ALLOYS

Abstract

Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. In particular, it can be used to join high-strength aerospace aluminium alloys like 2xxx (Al-Cu), 7xxx (Al-Zn) and other metallic alloys that are hard to weld by conventional fusion welding. FSW is considered to be the most significantly developing metal joining process over a decade. Now-a-days it can be used to join metals like Copper, Mild steel, Titanium, Stainless steels etc. In this investigation, an attempt has been made to understand the effect of friction stir welding on different grades of aluminium alloys like 2024-T6, 6082-T6 for similar metal joining. For dissimilar metal joining condition, 2024-T6 and 7039-0 are joined by friction stir welding. The effect of processing parameters on the mechanical and microstructural properties of aluminium alloys produced by friction stir welding was analyzed in this study. All the welds were produced in the rolling direction. In order to analyze the microstructural evolution of the weld joint, the weld cross-sections were observed by optical microscopy. Micro hardness (Hv), tensile and fatigue tests were carried out, which are used to evaluate the mechanical characteristics of the joints. The fracture surfaces were analyzed by using SEM. All the welds were produced by varying the welding speed from 19 mm/min to 120 mm/min. The optimum welding speed for 2024-T6 and 6082-T6 is 48 mm/min and for 7039-0 to 2024-T6 weld, optimum welding speed is 30 mm/min. The joint efficiency of 2024-T6 Al-alloy during tensile testing was found to be 87.09% and for 2024-T6 to 7039-0 Al-alloy weld, joint efficiency is 74.28%. For 6082-T6 Al-alloy weld, joint efficiency is 52.33% and the fatigue life of 6082- T6 Al-alloy FSW joint was found to be 454,347 cycles at stress amplitude of 72.5 N/mm2.