Principle for obtaining high joint quality in dissimilar friction welding of Ti-6Al-4V alloy and SUS316L stainless steel

Ti-6Al-4V alloy(Ti64) and SUS316 L stainless steel rods were dissimilarly friction welded. Especially focusing on the detailed observation of interface microstructural evolution during the friction welding(FW),the relationship between the processing conditions, weld interface microstructure, and mechanical properties of the obtained joints were systematically investigated to elucidate the principle for obtaining a high joint quality in the FW of Ti64 and SUS316L. A higher friction pressure produced a lower welding temperature in the FW, hence suppressing the thick intermetallic compound layer formation. However,hard and brittle Ti64/SUS316L mechanically mixed layers generally formed especially at the weld interface periphery due to the high temperature increasing rate, high rotation linear velocity and high outward flow velocity of the Ti64. These harmful layers tended to induce the cracks/voids formation at the weld interfaces hence deteriorating the joints’ mechanical properties. The rotation speed reduction and liquid COcooling during the entire processing decreased the temperature increasing rate, rotation linear velocity and outward flow velocity of the Ti64 at the weld interface periphery. Therefore, they suppressed the formation of the harmful mechanically mixed layers, facilitated the homogeneous and sound interface microstructure generation, and finally produced a high-quality dissimilar joint in the FW of Ti64 and SUS316L.