الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 128 |  |  |
| | | from | 128 | | |
Abstract
In the present study AA1050 plates of 8 mm thickness were processed via bobbin-tool friction stir processing technique at a constant rotation speed of 600 rpm and different travel speeds ranging from 50 to 300 mm/min using three-pin geometries of triangle, square, and cylindrical. The temperatures of the processed zone, the advancing side, and the retreating side were measured; the machine torque during processing was also recorded. The processed materials were evaluated in terms of surface roughness, macrostructure, tensile properties, and hardness measurements. The fracture surfaces of the tensile fractured specimens were investigated using SEM. The results indicated that the pin geometry and processing speed significantly affect the generated heat input and the morphology of the processed zone. The peak temperature in the center of the processed zone decreases with increasing the travel speed from 50 to 300 mm/min at all applied pin geometries. The maximum temperature of " ~ "400 _C was reached using the cylindrical pin geometry. The machine torque increases
with increasing the travel speed at all applied pin geometries, and the highest torque value of 73 N.m is recorded using the square pin geometry at 300 mm/min travel speed. The top surface roughness of the processed area using the cylindrical pin is lower than that given by the other pin geometries. Under all applied conditions, the hardness of the processed area increases with increasing
travel speed, and the cylindrical pin shows a higher hardness than the other pin geometries with 19% enhancement over the BM. The AA1050 processed using a cylindrical pin at 200 mm/min travel speed and a rotation speed of 600 rpm produces a sound processing zone with the highest ultimate tensile strength of 79 MPa.
The bobbin tool friction stir processing (BT-FSP) with a cylindrical pin was utilized to produce bulk processed AA1050 and AA1050/6.5 vol% silica fume (SF) composite at a rotation speed of 600 rpm using two travel speeds of 100 and 200 mm/min. The BT-FSP xix
temperature was measured for both processed materials. Phase composition, relative density, macrostructure, hardness, ultimate tensile strength, and compressive strength were examined for the AA1050 base material, processed AA1050 and AA1050/SF composite. The results showed that the temperature of BT-FSP was increased with SF addition. The addition of fine SF resulted in a small crystallite size compared to the AA1050 BM and the processed AA1050. Moreover, the SF addition to the AA1050 matrix improved mechanical properties in terms of hardness, ultimate tensile strength, and compressive strength compared to AA1050 BM and processed AA1050. The bulk AA1050/6.5 vol% nano SF composite produced at 600 rpm and 200 mm/min showed remarkable enhancements in properties compared to AA1050 parent material; i.e. 50% in hardness, 11% in compressive strength, and 40% in ultimate tensile strength.