Influence of friction stir welding conditions on joinability of V-alloy/SUS316L dissimilar joint

As one of the joining method to join between V-alloy and austenitic stainless steel SUS316L without melting of V and Fe to realize the self-cooled liquid-lithium blanket of fusion reactor, friction stir welding (FSW) is selected and the effect of FSW conditions on joinability of this dissimilar joint was examined. The sound dissimilar joint can be fabricated under the condition that V-alloy is set on the advancing side and the FSW tool is plunged into the SUS316L. Although the surface appearances of joint indicate that the case of the largest total heat input is the best condition, the results of cross-sectional microstructures and tensile tests suggests that the amount of adhesion to FSW tool seems to increase due to the higher temperature during FSW and the stir condition would be deteriorated. In addition, it is found that the higher rotational and traveling speeds might cause an insufficiency of the plastic flow and then crack or kissing bond would be generated. Moreover, it is revealed that one of the most preferable methods to prevent the adhesion of the mixture of base materials to the tool during processing is the selection of an appropriate coating on FSW tool.