الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 161 |  |  |
| | | from | 161 | | |
Abstract
Friction stir spot welding (FSSW) is a local solid state joining technology. In this work, FSSW is applied to weld similar lap joins of two different aluminum alloys (AA5052 with 2 mm sheet thickness and AA1050 with 1.5 mm sheet thickness). The effect of rotation speeds of 500, 1000 and 1500 RPM at different dwell times of 1, 2 and 3 sec on the microstructures and mechanical properties (hardness and tensile/sheer) are examined. Both Al alloys are also jointed using riveting process for comparison. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to evaluate the microstructures of the welded joints. Fracture surfaces after tensile/shear testing for the welded joints were examined for AA5052 Al alloy. The grain size of the as received Al alloys and the welded joints was determined using electron backscatter diffraction (EBSD) advanced technique. The obtained results showed that FSSW succeeded at the suggested welding parameters spot weld two different Al alloys in chemical composition and thickness with higher joint efficiency than the rivet. FSSW for both AA5052 and AA1050 Al alloys at all welding conditions give better mechanical properties in terms of tensile/shear load than that obtained by riveting process. For AA5052 Al alloy, the highest tensile/shear load was reached 5.6 KN at FSSW condition of 500 RPM and 2 sec, and the FSSW joint strength of AA5052 Al alloy is nearly equivalent to rivet joint strength with 6 nails. Whereas, it’s maximum value reaches 6.5 KN at FSSW condition of 500 RPM and 1 sec for AA1050 Al alloy, and the FSSW joint strength of AA1050 Al alloy is nearly equivalent to rivet joint strength with 7 nails. EBSD study for both FSSW AA5052 and AA1050 Al alloys showed that FSSW has resulted in fine grain structure inside the weld region compared to the base materials. The hardness maps showed an increase in the hardness values over the base alloys in the stir zone which can be attributed to the grain refining in that region. Finally: the present work provides some useful insights into the use of FSSW for joining Al alloys in lap configuration in petroleum industry instead of riveting.