Development of High Welding Speed in Friction Stir Welded 5182-H111, and the Resulting Influence on down Force

Abstract

In this manuscript the development of the process parameters to friction stir weld 5.15mm thick AA5182-H111 at a feed rate of 1500mm/min is discussed. Compared to a weld made at 200mm/min the weld-pitch had to be reduced from 2.0rev/mm to 0.3rev/mm and down force increased from 27kN to 59kN to create a weld with tensile-and yield strength exceeding that of the parent material, whilst elongation was only marginally reduced. The low weld pitch coupled with the high feed rate resulted in a reduction in the weld temperature and an increase in the process reaction forces. A lower down force was sufficient to consolidate the stir zone and result in ultimate tensile strength yield strength exceeding that of the parent material. However, elongation was reduced since the low weld pitch also reduced the effectiveness of the flutes on the pin to break up and disperse the oxide layer, rendering a pseudo bond along the ‘Lazy S’. This pseudo bond was eliminated through an increase in the down force.

Microstructural Changes and the Localised Mechanical and Crack Growth Properties in High and Low Speed FSW of 5182-H111 Alloy

“…In previous work, some of the present authors [1] have demonstrated successful FS welding in 5.15 mm thick plates of 5182-H111 alloy at a linear welding speed of 1.5 m/min. This was made possible by reducing the weld pitch from 2.0 mm/rev at linear welding speeds of 0.2 m/min, to 0.3 mm/rev at a linear welding speed of 1.5 m/min.…”

“…As noted above, Bernard et al [1] found increased tensile properties with the 1.5 m/min weld, proposing in a later publication [6] that this was achieved through the high levels of plastic strain. In a review paper by Heidarzadeh et al, [11] presented maps of strain, strain rate and temperature normalized to the melting temperature as a function of the position in the weld, based on results from other studies [12].…”

“…Interestingly, however, a 45% increase in yield strength (to 178 MPa) was observed in the high speed weld, compared with the parent plate value of 145 MPa [1]. In this context, Bernard et al [6] discussed the microstructural changes that occur in the 5182-H111 alloy during FS welding and showed that at the high welding speed of 1.5 m/min, the material directly ahead of the tool experienced dynamic recrystallization at lower temperatures than in low speed welding and proposed that this was due to the absence of sufficient time for significant heat transfer to occur ahead of the tool prior to it reaching any particular point in the weld run.…”

“…In the weld trials reported in reference [1], successful high integrity welds could be achieved at feed rates of 1.5 m/min and 0.2 m/min using a spindle speed of 500 rev/min. Using a single spindle speed facilitates comparison of the differences in microstructural development for these welds.…”

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Achieving high speed friction stir welding has proven to be challenging for 5xxx-series alloys, as they experience strain hardening during plastic deformation, which is inherent in the FSW process. An earlier publication has discussed the conditions under which welding speeds of up to 1.5 m/min can be achieved in 5182-H111 alloy [1]. The mechanical performance of high speed friction stir welds in 5182-H111 alloy is both surprisingly good and relatively unexplored.

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