Aluminum Alloy Propeller Shaft and Friction Welding Process Thereof

A process of producing an aluminum alloy propeller shaft by friction welding, the aluminum alloy propeller shaft comprising a tube made of an aluminum alloy, and a pair of yoke members made of an aluminum alloy, each of the pair of yoke members comprising a cylindrical base portion butted against each of opposite end portions of the tube in an axial direction of the tube and bonded thereto, each of the pair of yoke members comprising a bifurcate-shaped tip end portion having a pair of bearing retaining holes aligned with each other in a radial direction of the base member, the process comprising:

• a friction step of fixing one of the tube and the pair of yoke members, and pressing a tip end surface of each of the end portions of the tube and an end surface of the base portion of each of the pair of yoke members which is butted against the tip end surface of each of the end portions of the tube with a predetermined pressure welding force in the axial direction of the tube, while rotating the other of the tube and the pair of yoke members;
• a position displacement detection step of detecting an amount of displacement of the tube and each of the pair of yoke members in the axial direction of the tube through an upset distance generated between the tube and each of the pair of yoke members in the friction step;
• a rotation stop step of outputting a rotation stop signal to stop rotation of the other of the tube and the pair of yoke members when the amount of displacement detected in the position displacement detection step has reached a predetermined value;
• and
• an upset step of outputting an upset pressure command signal to press the other of the tube and the pair of yoke members onto the one of the tube and the pair of yoke members with an upset pressure larger than the predetermined pressure welding force used in the friction step to the pair of yoke members during a period of time for which the rotation of the other of the tube and the pair of yoke members is completely stopped after the rotation stop signal is outputted.