*3.3. E*ff*ect of Plate Positioning in Dissimilar Al*/*Cu Lap Joints*

To compare the soundness of lap joints with respect to the position of the plates, initial experiments were performed keeping 2219 Al plate onto the Cu plate (1.65 mm). The joining was done using the WC tool and a range of welding speed as listed in Table 8. Successful joining in this stacking configuration was realized for the welding speed ranging from 23.5 mm/min to 37.5 mm/min (Figure 8 and Table 8). On the other hand, the entire range of joints remained unsuccessful when the Cu plate was stacked onto the Al plate (Table 9). In fact, the authors observed melting of the Al plate during welding as

evidenced in Figure 11a,b. This observation points out that the Cu plate being very conductive radiated heat into the Al plate, and the heat was sufficient to cause melting of Al.


**Table 8.** Experiments for fabricating 2219Al-Cu lap joint using WC square-pin tool (TD: 22 s).


**Table 9.** Experiments for fabricating Cu -2219Al lap joint using WC square-pin (TD: 20 s).

(**c**) (**d**)

**Figure 11.** Dissimilar Cu-2219 Al lap joints fabricated by WC square-tool.

To reduce excessive heat generation, the rotational speed was decreased in steps from 1500 rpm to 600 rpm (Table 9). However, success could not be realized as the defects like cracks and holes occurred as observable from Figure 11c,d.
