A heat exchanger assembly for an internal combustion engine charge air cooler is formed from a plurality of aluminum modules, each provided with longitudinal through bores and opposite outer face portions with toothed heat exchange fins positioned in face-to-face relation. The assembly of tubular modules is interconnected with upper and lower aluminum header plates which receive the ends of the tubular modules and are secured thereto with fused joints made from the parent material of the modules and header plates. The openings in the header plates for the modules are flanged and have a thickness of at least about 0.090 inch and the wall thickness of the ends of the tubular modules also have a minimum thickness of about 0.90 inch such that the fused joints utilize substantially equal amounts of aluminum material from the modules and the header plate flanges.