Investigation of the effects on bonding quality for different type of mixer pin in friction stir welding

Welding is a process which is commonly used in Industry for joining metals by melting and causing permanent coalescence. Although primitive welting methods are easy and economic for fabrications and assembly applications it could not take an effective role in advanced technology due to causing deformation in material structure and phase changes. Moreover , avoiding these disadvantages of primitive welding have been leading many researches and experiments which shows friction stir welding patented in 1991,provides metals can be joined together as solid or semi-solid phase conditions without melting and any loss of mechanical properties. Also coalescence by friction stir welding is more long lasting and safety than primitive welding. The main point of having good quality of coalescence depends on used pin types and their properties. By this study, the pins used for friction stir welding are designed and manufactured. There are 20 different types of stir pin. Designs of screwed pins are structured on basically 5 different screw types (metric, trapeze, saw, square, and round) and 15 screwed pins are manufactured with 3 grooves and 4 grooves. The other 5 pins which are unscrewed are triangle, conical, square, with 3 grooves and with 4 grooves cylindrical stir pins. Aluminum planar parts and pins are fixed on fraise frame for the experiment. Pull of force, microstructure and microhardness test samples are prepared from the parts which are welded by friction stir welding and the pin is determined which has the best welding performance.