A plastic flow joining method for fixing cold bars with a hot plate, “indentation joining”, is proposed, and the optimum conditions of the proposed joining method for AA6061 aluminum bar and plate are examined by experiment and finite element simulation. In the developed plastic flow joining method, the cold bar is indented into the hot plate to pierce the plate without lubrication on a press. It is expected that the newly created surface of the hot plate will cause seizure and a high joining strength may be attained. After cooling of the plate, thermal shrinkage of the plate may assist to clamp the bar strongly. The attained shear bonding stress of the aluminum bar·plate is approximately 40% of the shear strength of the plate material. The bonding mechanism is discussed from the viewpoints of seizure of the plate and clamping force associated with the process. In the case of indentation temperature of 300 °C, about 80% of the bonding strength is due to seizure during indentation of the bar and about 20% of the bonding strength is due to clamping force after cooling of the plate.