**Abstract**

 Aluminum alloy is currently widely used for structural purposes because of its unique properties. In this research work, we weld aluminum alloy plates using FSW with different process variable parameters such as tool pin geometry, traverse speed, and tool rotating speed. Three types of FSW tool pin geometry (square pin, cylindrical straight pin and threaded straight cylindrical pin) and three different speeds (tool traverse speed and tool rotation speed) were selected. For analyzing the effect of process parameter, we carried out a tensile test to measure UTS along with elongation of the welded joint.

#### **1. Introduction**

 In 1991, friction stir welding (FSW) was discovered by Thomas [1] and this is very useful for welding non-ferrous materials (for example, aluminum and magnesium) and this process solved many problems related to traditional welding techniques.

All industries associated with fabrication are under pressure to produce stronger and lighter products from metals whilst having lower energy consumption, less contamination of harmful material to the environment, producing at a low cost and producing faster than before. FSW is a solid-state joining process that requires less energy. Its mechanical process is able to produce high strength welding between different materials (similar and dissimilar) and it offers a possibly lower-cost solution, therefore solving the above challenges.

#### **2. Literature survey**

 Hard and brittle stir zone (SZ) of welds obtained by polygonal pin geometry were compared to cylindrical pin geometry for equal shoulder bottom face [2]. The peak temperature during the welding process increased with an increase of tool speed and decreased with an increase in the welding speed for all shoulder diameters [3]. The welding process depends on heat generation and the heat is caused by friction between *Proceedings of the 4th International Conference on Innovations in Automation...* 

 the tool shoulder and the plate surface. High friction leads to high heat which lead to good welding (defect-free welding) using different variable welding process parameters [4]. Square pin tool geometry allows for better mechanical properties followed by hexagonal, octagonal pin tool profile [5]. Defects such as tunnel defect, cracks, pin holes, are due to unsuitable and inadequate flow of metal in the area [6]. The thermal cycle (hot to cold) is what increases the welding (mechanical) properties. Heat generation is strongly corelated to all post-weld mechanical properties [7]. Tensile strength (TS) of the dissimilar aluminum plates (AA6061-T651 plate) increases when heat input is lower and the good slurry from both the materials joined can be created at lower welding temperatures and higher tool rotating speeds [8]. Due to friction, heat generation occurred and plastic flow grain reordering occurred and the weld has been achieved [9]. When welding thermoplastic materials, it is found that the weld zone created using the threaded pin profile tool required less force. Square, triangular and grooved with square pin geometry created a defect-free weld with the same process variable parameter [10]. The overall response of mechanical properties is contingent on the ratio of the tool rotating speed to the tool travel speed [11]. Preheating of the plates is advantageous for refining the quality of the weld as well as an increase in the tool travel speed for material with a higher melting point such as steel [12].
