GH4169旋转摩擦焊飞边成形机理研究

In this work, continuous-drive rotary friction welding was conducted on GH4169 rods in diameter of Φ25 mm to investigate the flash formation mechanism. The welding parameters were set as burn-off length 5 mm, welding pressure 200 MPa and rotation speed ranged as 500-2 500 r/min. The high-speed camera was installed to monitor the burn-off rate; whereas the infrared camera to collect the surface temperature of the joint. The joints were cut for interface morphology and microstructure observation by OM, SEM and EBSD. On the other hand, the calculation on friction heat liberation was modeled and conducted in Matlab environment, which is correlated by the experiment of interim stops on welding process that were carried out to reveal the transient morphology of the joint. The results tell that, the joint shows the flash appearance as smooth, 'arcuate microcracked' and cracked consequently as the rotation speed is increased. The rotation speed was found a criterion at about 800 r/min, below which the joint presents smooth flash. When the rotation speed is around 800-1 500 r/min and over 1 500 r/min, 'arcuate microcracked' and cracked flash occur consequently. Smooth flash corresponds to slower growth speed of the flash with longer growth time, which provides the conditions for recrystallization and softening when the metal is extruded to form flash. Whereas, 'arcuate microcracked' and cracked flash correspond to faster speed and shorter time, where recrystallization has not been completed before work hardening and cracking during the flash formation. Moreover, different flash appearances correspond to different formation mechanisms. Smooth flash is the result of uniform flow and extrusion of plasticized metal, which is originated from the corona-bond initiating at middle to the edge (0.43R-R) of the interface and then extending. Whereas, 'arcuate microcracked' and cracked flash are formed under rapid forging process of interface metal at welding temperature due to the lack of plasticized metal, which initiates at inner side of the interface (0-0.43R) and then is closed without flow under the normal stress. Different flashes make neglectable effects on local strength distribution of the joint but the elongation sampled at periphery. The smooth, 'arcuate microcracked' and cracked flash correspond to 17%, 9% and 6% elongation sampled at periphery respectively, where the correspon-ding inhomogeneity of joint elongation increases from 8% to 50%, 66%.