Joining method of dissimilar metal plates and dissimilar metal joined body

A method of joining dissimilar metal plates of an aluminum alloy plate and a plated steel plate by means of adhesion of an adhesive and spot welding,

• the method comprising:
• a lapping step of lapping the aluminum alloy plate and the plated steel plate via the adhesive;
• a pre-pressuring step of clamping the aluminum alloy plate and the plated steel plate between the pair of electrodes and applying pressure therebetween;
• a pre-heating step of clamping both of the metal plates that have been lapped in the lapping step between a pair of electrodes for spot welding and applying pressure thereto, and applying a current between the pair of electrodes;
• a cooling step of pressurizing, after the pre-heating step, where both of the metal plates are pressed between the pair of electrodes at a pressing force which is higher than that at the start of the pre-heating step in a state where conduction between the electrodes is stopped, and continuing this pressurization over a predetermined cooling time;
• and
• a welding step of pressurizing, after the cooling step, where both of the metal plates are pressed between the pair of electrodes at a pressing force which is higher than that at the start of the pre-heating step, and both of the metal plates are welded by applying a current which is higher than the conduction current value in the pre-heating step between the pair of electrodes,
• wherein the pressing force of the electrodes is set to a first pressing force during a predetermined period from the start of the pre-heating step, the pressing force is increased to a second pressing force that is greater than the first pressing force in the middle of or at the end of the pre-heating step, and the pressurization is continued with the second pressing force until the completion of the cooling step and the welding step;
• and
• wherein the pressing force in the pre-pressurization step is set to be greater than the first pressing force.