Abstract
This work investigated the effect of friction stir welding (FSW) tool rotation rate and welding speed on the grain structure evolution in the nugget zone through the thickness of the 10 mm thick AA5083/AA5754 weldments. Three joints were produced at different combinations of FSW parameters. The grain structure and texture were investigated using electron backscattering diffraction (EBSD). In addition, both the hardness and tensile properties were investigated. It was found that the grain size varied through the thickness in the nugget (NG), which was reduced from the top to the base in all welds. Reducing the rotation rate from 600 rpm to 400 rpm at a constant welding speed of 60 mm/min reduced the average grain size from 33 µm to 25 µm at the top and from 19 µm to 12 µm at the base. On the other hand, the increase of the welding speed from 20 mm/min to 60 mm/min had no obvious effect on the average grain size. This implied that the rotation rate was more effective in grain size reduction than the welding speed. The texture was the mainly simple shear texture that required some rotations to obtain the ideal simple shear texture. The hardness distribution, mapped for the nugget zone, and the parent alloys indicated a diffused softened welding zone. The heating effect of the pressure and rotation of the pin shoulder and the heat input parameter (ω/v) on the hardness value of the nugget zone were dominating. Tensile stress-strain curves of the base alloys and that of the FSWed joints were evaluated and presented. Moreover, the true stress-true strain curves were determined and described by the empirical formula after Ludwik, and then the materials strengthening parameters were determined. The tensile specimens of the welded joint at a revolution speed of 400 rpm and travel speed of 60 mm/min possessed the highest strain hardening parameter (n = 0.494).
Highlights
Aluminum alloys have remained the prime selection in producing various components in many industries like aerospace, automotive, and shipbuilding because of their perfect strength to weight ratio [1,2,3,4,5]
AA5000-series alloys are characterized by a good strength-to-weight ratio and an appropriate corrosion resistance
They are difficult to join by conventional fusion welding techniques because of their dendritic structure, which seriously weakens the mechanical properties
Summary
AA5000-series alloys are characterized by a good strength-to-weight ratio and an appropriate corrosion resistance. They are difficult to join by conventional fusion welding techniques because of their dendritic structure, which seriously weakens the mechanical properties. Solid-state welding processes are appropriate joining for either similar or dissimilar aluminum alloys [6]. Resistance spot welding is considered one of the dominant solid-state welding processes in automotive constructions [7,8]. Friction stir welding (FSW) of the AA5000 series represents a promising technique to obtain defect-free and sound joints, either in similar [10] and dissimilar [11,12,13] welding combinations. FSW can be used effectively for the welding of different types of materials [14,15,16,17], and the same principle of FSW can be used for the development of metal matrix composites [18,19,20,21,22]
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