Abstract
This study presents the effect of the welding parameters variation on the results of forces, temperature, residual stresses and Vickers micro hardness of dissimilar butt joints of AA2024-T3 and AA7475-T761 welded by friction stir welding (FSW). The tool rotational speed, feed rate and tool tilt angle were investigated using the Design of Experiments method. The obtained results of penetration force, temperature in the weld zone compared with the microscopic analysis of the microstructure showed that it is necessary a minimum amount of force and heat input to obtain a defect free weld zone. It was also notable that, friction stir welding has a wide stability range of its most significant parameters - rotational speed and feed rate - which grantee this minimum condition. Micro hardness’ profiles showed the effect of the grain size refinement towards the thermo-mechanically affected zone as well as, the effect of recrystallization inside the nugget. Residual stresses’ profiles showed a tensile stress peak at the shoulder contact area due the pressure with the base material on thermo-mechanically affected zone and the stress relief effect caused by high temperatures in the nugget resulting in a decrease in residual stress value. The most significant variables for residual stress results were rotational speed of the tool and welding feed rate, once their interaction rule the heat input in the weld zone.
Highlights
Friction Stir Welding (FSW) is a solid-state welding process developed by The Welding Institute (TWI) in 1991 in the United Kingdom, which has been extensively studied due to its applicability
The good performance of the process is observed by the optical microscopy of Figure 5 where it is possible to observe the refinement of the grains towards the TMAZ, which is composed of grains much finer than the heat affected zone (HAZ), as well as through Figure 6, obtained by scanning electron microscopy (SEM)
It demonstrates the good mixture and absence of defects in the case of a medium value of rotational speed (1450 rpm) and low value of feed rate (40 mm / min), which enables sufficient heat input in the region of the nugget resulting in the good mixture and material flow
Summary
Friction Stir Welding (FSW) is a solid-state welding process developed by The Welding Institute (TWI) in 1991 in the United Kingdom, which has been extensively studied due to its applicability. It is used especially in low melting point alloys such as Al, Mg and Cu1-3 and heat treatable Aluminum alloys, such as the 2XXX and 7XXX series, as welding them by conventional techniques generates loss of mechanical properties, as well as formation of solidification cracks, brittle fracture and oxide formation due to the high temperatures reached in conventional welding processes[4]. The feed rate of the tool and the relative rotational movement between the tool and the base material allow the plasticized material to consolidate, guaranteeing the execution of the weld[8]
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