Thick metal plate large-area butt joint braze welding method

A thick metal plate large-area butt joint braze welding method is implemented through the following the steps that the connecting portions of a braze welding surface of a metal plate and an upper surface of a metal plate are respectively provided with a rectangular notch through machining, and thus a U-shaped groove is formed when the two metal plates are in butt joint; foil type braze welding flux is arranged between the braze welding surfaces of the two metal plates, the two metal plates and the foil type braze welding flux are tightly combined through a clamp, and the braze welding flux is arranged in the U-shaped groove in advance; the welding seam of the two clamped metal plates is arranged between an upper electrode plate and a lower electrode plate of a resistance welding machine, contact electrodes cover the whole braze welding seam, and the braze welding seam is perpendicular to the contact surface of the contact electrodes; the upper electrode plate and the lower electrode plate of the resistance we