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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 aluminum alloys and other metallic alloys that are difficult to be welded using fusion welding processes. Main friction stir welding advantage is the low welding temperature eliminating many problems concerned with fusion welding processes. Friction stir welding process has recently become a subject of wide study. There are currently no large databases of weld properties and, in fact, no specifications on how to make or test friction stir welds exist.This study deals with advancing scientific understanding of this solid state welding process and its metallurgical consequences. The focus is concerned with its different parameters including backing plate, spindle speed, welding speed as well as tool geometry that includes tool shoulder (diameter and profile) and tool pin profile (cylindrical, taper, threaded and non threaded). The effect of these parameters on structure and properties of welded joints has been clarified. Quality of friction stir welded joints is evaluated using different nondestructive and destructive testes. Nondestructive testes included visual test of all joints and radiographic test of visually accepted joints. Destructive tests included macroscopic investigation, microstructure analysis, hardness measurements and tensile tests.The results obtained in this investigation showed that using backing plate has resulted in a significant influence on welded joints. Regarding tool geometry, using filet shoulder and threaded screw pin has resulted in a better weld quality. This is related to higher heat generation that can facilitate the flow of the plastic material in this case in comparison with straight shoulder and non threaded pin. On the other hand, the screw thread on the pin exerts an extra downward force that is beneficial to increase the flow of the plastic material. Also it is found that using threaded taper pin has further improvement to the weld quality.Results have shown also that the combination of both welding speed and spindle speed should be optimized to obtain high quality of welded joints.Based on the results of non-destructive and destructive tests of friction stir welded joints, accepted welded joints can be produced using any of the following conditions:• 1000 rpm spindle speed, 35.5 mm/min welding speed and threaded taper pin 5/3 mm, L=4.87 mm [tool no.5]• 1000 rpm spindle speed, 35.5 mm/min welding speed and non threaded taper pin 5/3 mm, L=4.87 mm [tool no.6].• 1000 rpm spindle speed, 35.5 mm/min welding speed and cylindrical threaded pin M 5 x 4.87 mm [tool no.4].However results of mechanical tests indicated that welded joints with highest mechanical properties were obtained using 1000 rpm, 35.5 mm/min using threaded taper pin 5/3 mm, L= 4.87 mm [tool no.5]. Tensile strength and hardness of this welded joint is high as 97 % of base metal properties. This is due to homogeneous microstructure of welded nugget that contains finer grain structure. It can be deduced that friction stir welding process maintains the mechanical properties of welded joints in comparison with fusion welding processes.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 aluminum alloys and other metallic alloys that are difficult to be welded using fusion welding processes. Main friction stir welding advantage is the low welding temperature eliminating many problems concerned with fusion welding processes. Friction stir welding process has recently become a subject of wide study. There are currently no large databases of weld properties and, in fact, no specifications on how to make or test friction stir welds exist.
This study deals with advancing scientific understanding of this solid state welding process and its metallurgical consequences. The focus is concerned with its different parameters including backing plate, spindle speed, welding speed as well as tool geometry that includes tool shoulder (diameter and profile) and tool pin profile (cylindrical, taper, threaded and non threaded). The effect of these parameters on structure and properties of welded joints has been clarified. Quality of friction stir welded joints is evaluated using different nondestructive and destructive testes. Nondestructive testes included visual test of all joints and radiographic test of visually accepted joints. Destructive tests included macroscopic investigation, microstructure analysis, hardness measurements and tensile tests.The results obtained in this investigation showed that using backing plate has resulted in a significant influence on welded joints. Regarding tool geometry, using filet shoulder and threaded screw pin has resulted in a better weld quality. This is related to higher heat generation that can facilitate the flow of the plastic material in this case in comparison with straight shoulder and non threaded pin. On the other hand, the screw thread on the pin exerts an extra downward force that is beneficial to increase the flow of the plastic material. Also it is found that using threaded taper pin has further improvement to the weld quality.Results have shown also that the combination of both welding speed and spindle speed should be optimized to obtain high quality of welded joints.Based on the results of non-destructive and destructive tests of friction stir welded joints, accepted welded joints can be produced using any of the following conditions:• 1000 rpm spindle speed, 35.5 mm/min welding speed and threaded taper pin 5/3 mm, L=4.87 mm [tool no.5].• 1000 rpm spindle speed, 35.5 mm/min welding speed and non threaded taper pin 5/3 mm, L=4.87 mm [tool no.6].• 1000 rpm spindle speed, 35.5 mm/min welding speed and cylindrical threaded pin M 5 x 4.87 mm [tool no.9.However results of mechanical tests indicated that welded joints with highest mechanical properties were obtained using 1000 rpm, 35.5 mm/min using threaded taper pin 5/3 mm, L= 4.87 mm [tool no.5]. Tensile strength and hardness of this welded joint is high as 97 % of base metal properties. This is due to homogeneous microstructure of welded nugget that contains finer grain structure. It can be deduced that friction stir welding process maintains the mechanical properties of welded joints in comparison with fusion welding