Dry Ice Cooling Effect on Friction Stir Welded AA6061 Alloy Using Brass Interlayer

This study investigated the impact of employing dry ice cooling and a brass interlayer on the metallurgical and mechanical behavior of AA6061 welded alloy. Friction stir welding (FSW) is commonly used to weld Al alloys as an alternative to the fusion welding process. Generally, FSW leads to the formation of recrystallized and refined grains in comparison to base metal. Despite the presence of grain refinement in the stir zone without an interlayer, the material experienced a reduction in strength due to thermal softening. The addition of a brass interlayer in between the welds during FSW produced strong metallurgical intermetallics. The production of strengthening metallurgical intermetallics enhanced weld mechanical properties with interlayer. However, strength recovery was not achieved in the heat-affected zone with normal cooling. Furthermore, premature failure was caused by the formation of brittle and hard intermetallics in the weld’s stir zone containing the interlayer. Therefore, dry ice cooling was employed to increase the hardness in the heat-affected zone and the overall strength of the weld. Dry ice cooling with the interlayer reduced heat-affected zone softening and enhanced hardness. Moreover, by employing dry ice cooling in conjunction with the interlayer, the formation of hard intermetallics was inhibited, and the volume of intermetallics was significantly reduced due to the rapid cooling rate. As a result, the overall strength of the weld joint was increased from 247 MPa with normal cooling to 268 MPa with dry ice cooling.