In a method for fabricating a heat exchanger, a metal body includes a bore and inlet and outlet connectors fitted to the body at respective inlet and outlet ends of the bore. The connectors each include an inner surface in which annular grooves are formed. A tube is inserted in the bore such that inlet and outlet ends of the tube are respectively located in the inlet and outlet connectors. A mandrel is operated to expand at least a portion of the tube into contact with the body, and to expand the inlet and outlet tube ends into contact with the grooves of the inlet and outlet connectors, respectively. The heat exchanger provides improved thermal exchange efficiency between the tube and the body, and fluid-tight connections between the tube and the inlet and outlet connectors.