Effect of reduced or zero pin length and anvil insulation on friction stir spot welding thin gauge 6111 automotive sheet

Abstract

Friction stir spot welding (FSSW) is a relatively new process, which has not yet been fully optimised. The aim of the work presented was to investigate the influence of pin length and an insulating anvil on FSSW thin (0?9 mm) 6111-T4 aluminium automotive closure panels. A pinless, or 'zero pin length', tool was also tested. With a normal pin tool and a steel anvil the optimum pin length was found to be considerably shorter than conventionally used, being in the range 0?7-1 mm, as opposed to y1?4 mm. The insulated anvil increased the peak temperature in the bottom sheet by 45uC, but there was a 15% reduction in lap shear strength when used with a conventional pin tool. In the case of the pinless tool, successful welds were produced with comparable strengths to the highest values measured with the optimum conventional tool without a retained weld keyhole or top sheet thinning (hooking).

Modelling and visualisation of material flow in friction stir spot welding

“…Their chemical compositions are summarized in Table 1. Prangnell (2009) andBakavos et al (2011) provide details of the weld set-up and clamping arrangements. Rectangular samples of dimensions 100 × 25 mm were lap-welded in displacement control, with the weld located at the centre of a 25 mm overlap region (Fig.…”

“…The Manchester group in this project [Chen et al (2010), Bakavos and Prangnell (2009), Bakavos et al (2011)] have shown the feasibility of producing dissimilar aluminium to steel friction stir spot welds in thin automotive sheet (1mm thick). Welds between 6111-T4 aluminium sheets were produced successfully by Bakavos and Prangnell (2009) and Bakavos et al (2011), using optimised pinless tools, with a modest degree of profiling on the tool shoulder.…”

“…Welds between 6111-T4 aluminium sheets were produced successfully by Bakavos and Prangnell (2009) and Bakavos et al (2011), using optimised pinless tools, with a modest degree of profiling on the tool shoulder. Figure 1 shows the typical process geometry, with the three tools used in the current work.…”

The effect of a paint bake treatment on joint performance in friction stir spot welding AA6111-T4 sheet using a pinless tool

“…At the bottom position, some heterogeneous grain boundary (GB) precipitation can also be seen in both welds, but the volume fraction is minimal, particularly in the case of the 0.5 second weld. This precipitation is typical of the appearance of GB equilibrium phases seen on over-ageing in welding [14,15], but is very localised to the grain boundaries. However, in the hottest position immediately below the tool shoulder, within the top sheet, there was little evidence of additional precipitation, indicating that at this position the material exceeded the solvus temperatures of both the Q (Al 4 Cu 2 Mg 8 Si 7 at 440 °C) and β (Mg 2 Si at 540 °C) phase in the AA6111 alloy [14].…”

“…This precipitation is typical of the appearance of GB equilibrium phases seen on over-ageing in welding [14,15], but is very localised to the grain boundaries. However, in the hottest position immediately below the tool shoulder, within the top sheet, there was little evidence of additional precipitation, indicating that at this position the material exceeded the solvus temperatures of both the Q (Al 4 Cu 2 Mg 8 Si 7 at 440 °C) and β (Mg 2 Si at 540 °C) phase in the AA6111 alloy [14]. Thermocouple measurements recorded peak temperatures at the base of the weld of about 250 C and 350 C, for the 0.5 and 1 second welds, respectively.…”