Abstract
In the present work, attempts were made to join AA6061-T6 sheets by Friction Stir Welding (FSW) process. Al<sub>2</sub>O<sub>3</sub> nanoparticles were added into the aluminum matrix for refining the microstructure of the nugget zone (NZ) and to restrict the growth of granularly in the heat-affected zone (HAZ). In order to illustrate the influence of Al<sub>2</sub>O<sub>3</sub> nanoparticles on mechanical properties, namely ultimate tensile strength, micro-hardness distribution, and wear resistance of the welded joints, FSW was conducted with and without nanoparticles at a constant rotating velocity of 2000 rpm and transverse velocity of 70 mm/min. For characterization of microstructures, optical and scanning electron microscopes were employed. The findings revealed that Al<sub>2</sub>O<sub>3</sub> nanoparticles addition along the joint line resulted in remarkable refining of grains structure in the weld nugget zone. This was due to the pinning effect produced by nano-sized Al<sub>2</sub>O<sub>3</sub> particles which prevent the grain growth followed by recrystallization during FSW, leading to a remarkable reduction in grain size. Also, the sample with nanoparticles joined at rotating and transverse velocities of 2000 rpm and 70 mm/min showed higher tensile properties than the sample without nanoparticles. However, the employment of single FSW pass resulted in an unusual Al<sub>2</sub>O<sub>3</sub> nanoparticles distribution and void initiation at the interface between Al-matrix and Al<sub>2</sub>O<sub>3</sub> nanoparticles in the heat-affected zone resulted in the early fracture of welded joints during tensile loading. Moreover, Al<sub>2</sub>O<sub>3</sub> nanoparticles addition results in the reduction of frictional coefficient and increment in wear resistance due to fine small grains size and large distribution of hardness in NZ of friction stir welded specimens.
Highlights
Nowadays, weight reduction and less fuel consumption are the two most important demands in the marine, aerospace, and automobile industries
The results reveal that Al2O3 nanoparticles were uniformly distributed in nugget zone for single friction stir welding (FSW) pass and comprise of smaller grain size when compared with unreinforced welds
It was found that the AA6061-T6/Al2O3 nanocomposite can successfully be fabricated through FSW in a single FSW pass at optimal rotating and transverse velocities of 2000 rpm and 70 mm/min
Summary
Weight reduction and less fuel consumption are the two most important demands in the marine, aerospace, and automobile industries. The most serious concern in regards to joining of aluminum alloys, if conventional fusion welding process (CFWP) was adopted, is their weakening mechanism in the joint area. This was attributed to barriers which come across during (CFWP) of Al-metals, e.g., solidification cracking, porosity/gas interruption, and occurrence of intermetallic brittle phases, etc. No melting occurs in FSW in comparison to fusion welding. Because of this reason, this process resolves the issues regarding CFWP [6]. The amount of generated heat was strongly affected by processing conditions, which could be limited by rotational and traveling
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