Research on the Fluxless Brazing of Aluminum Air Cooled Oil Cooler

Abstract

Controlled atmosphere brazing of aluminum air cooled oil cooler without flux was investigated. The materials of the middle plates and the mounting plates used in the research are fluxless brazing alloy with five layers. The materials of the other parts are conventional 3003 single layer aluminum alloy. After assembling, the oil cooler is put into the CAB brazing furnace, without appended any flux on it. After brazing, the surface of the oil cooler is dark, and the brazing fillets between the middle plates can hardly be seen from the outside of the oil cooler by naked eyes. The metallographic analysis of the sections of the oil cooler shows that the fillets of the brazing seams near the outside of the oil cooler are very small, but the fillets of the brazing seams of the interior are very big. This phenomenon shows that the molten brazing filler flows from the outside of the oil cooler to the inside during brazing. The SEM and EDS analysis results shows that a thin flux layer is covered on the surface of the middle plates of the outside of the oil cooler. The existence of the flux layer effects the oxide removing ability of the fluxless brazing materials. Consequently, the wetting and spreading abilities of the brazing filler on the surface of the aluminum alloy after melting are influenced.