Corrosion preventing layer forming method

A heat exchanger comprising:

• a plurality of radiator tubes for allowing coolant to flow therethrough;
• metallic radiator header tanks disposed at longitudinal ends of said plurality of tubes for communication with said tubes;
• a plurality of radiator tubes for allowing refrigerant to flow therethrough;
• and
• metallic radiator header tanks disposed at longitudinal ends of said plurality of radiator tubes for communication with said tubes;
• wherein
• said radiator header tanks are each constituted by a radiator tank main body extending in a direction normal to a longitudinal direction of said radiator tubes and constituted by a plurality of members, at least one of said plurality of members being formed through extrusion or drawing and radiator caps for closing the longitudinal ends of said tank main body;
• wherein
• said metallic radiator header tanks are each constituted by a radiator tank main body extending in a direction normal to a longitudinal direction of said radiator tubes and radiator caps for closing the longitudinal ends of said radiator tank main body;
• wherein
• both said tank main bodies are made integrally with each other through extrusion or drawing;
• and wherein
• said radiator tank main bodies and said radiator caps are joined to each other through heat brazing with a sacrificial material comprising a metal having a lower electric potential than that of said radiator tank main body being disposed in the interior of said radiator tank main body.