Bonding method and bonding device for metal member

A bonding method for bonding a first bonding surface of a first metal member to a second bonding surface of a second metal member that is in contact with the first bonding surface by radiating a heat-bonding laser beam onto an irradiated surface of the first metal member to heat the first bonding surface, the bonding method comprising:

• an oxide-film forming step of radiating an oxide-film-forming laser beam at a first output onto the irradiated surface of the first metal member, and forming, on the irradiated surface, an oxide film having a film thickness that corresponds to the first output and an irradiation time of the oxide-film-forming laser beam;
• a first reflected-laser-beam detection step of detecting a second output that is an output of a first reflected laser beam generated from the oxide-film-forming laser beam upon being reflected by the irradiated surface;
• a first absorptance computing step of computing a first absorptance of the irradiated surface of the first metal member for the oxide-film-forming laser beam, based on the first output of the oxide-film-forming laser beam radiated at the oxide-film forming step and the second output of the first reflected laser beam detected at the first reflected-laser-beam detection step;
• a laser-beam switching step of switching the oxide-film-forming laser beam radiated onto the irradiated surface to the heat-bonding laser beam if it is determined that the first absorptance is equal to or higher than a predetermined absorptance;
• and
• a heat bonding step of, after the switching to the heat-bonding laser beam, radiating the heat-bonding laser beam at a third output onto the irradiated surface to heat the first bonding surface until a temperature of the first bonding surface reaches a predetermined bonding temperature, and bonding the first bonding surface to the second bonding surface.