CHEMICAL FILM FROM KF SOLUTION TO ALUMINUM FOR FLUXLESS BRAZING

摘要

PURPOSE: Disclosed is a surface capable of brazing without using flux by subjecting the surface of an Al material to thermal degreasing or alkali aq. soln. degreasing, thereafter bringing it to contact with a KF aq. soln, of a specified concn. at a specified temperature for a specified time and then forming a chemical film composed of K3AlF6 and KAlF4. CONSTITUTION: The surface of Al or an Al alloy is subjected to high temperature degreasing or degreasing with an alkali aq. soln. to almost perfectly remove oils and fats. The Al surface subjected to the treatment is brought into contact with a KF aq. soln. of 2.0 to 2.5 wt.% for at least 5 sec at 32 to 100 deg.C. Next, a chemical film substantially consisting of at least K3AlF6 and selectively KAlF4 is provided. As the alkali aq. soln. used in the degreasing stage, an aq. soln. of sodium hydroxide or potassium hydroxide is preferable. Since this chemical film has the function of substituting Al oxide and does not have holding power so much, when the clad layer reaches the m.p., it allows the fluidizing of the clad lower layer.