GB825317A - Improvements in and relating to soldering metal articles - Google Patents

Abstract

825,317. Soldering. GENERAL MOTORS CORPORATION. Nov. 7, 1957 [Nov. 13, 1956], No. 34704/57. Class 83 (4). [Also in Group II] In soldering metal articles at least one of which consists of aluminium or aluminium alloy, the articles are immersed in a solution comprising an alkali metal hydroxide and an alkali metal zincate dissolved in a solvent to clean the aluminium or aluminium alloy article and plate a film of zinc thereon and are then immersed in molten solder by passing them through an interface between the solution and the solder. A bath 12 is prepared comprising a molten low-melting point solder 10 beneath a cover layer 14 having a boiling- point higher than that of the solder. The alkali metal hydroxide may be sodium, potassium or lithium, hydroxide. The solder may be a lead-tin eutectic, a tin-lead-cadmium eutectic, a 50% lead, 32% tin, 18% cadmium alloy, a 50/50 lead-tin-alloy, indium, an indium-tincadmium eutectic or a cadmium-tin-leadbismuth alloy. The cover layer may be prepared by reacting zinc oxide or metallic zinc with sodium hydroxide to form sodium zincate with excess sodium hydroxide and adding water 80 grams sodium hydroxide, 3 grams zinc oxide and 17 grams water are heated to produce a cover layer solution containing water, sodium hydroxide and sodium zincate. The ends of a pair of aluminium wires are twisted together and inserted into such a cover layer where the sodium hydroxide removes the aluminium oxide film from the wires and a zinc film is plated thereon. The wires are then passed into the solder below to form a soldered joint. Several immersions into the butt are made. Copper, nickel, or steel parts may similarly be soldered to aluminium or aluminium alloy parts. The water in the cover layer may be replaced by organic solvents, e.g. primary polyhydric alcohols such as glycols, diols or triols and organic materials having hydroxy groups including organic, e.g. citric acid are said to be useful to some extent. The preferred solvents are ethylene glycol; 1,3-propandiol; 1,4- butanediol; 2,2-bis-(hydroxy methyl) 1 butanol and pentaerythritol or mixtures thereof. 9 grams sodium hydroxide and 1 gram zinc oxide are heated to produce the reaction and 90 grams of ethylene glycol are added to form the cover layer solution. The parts to be solderedmay be first dipped in a preparatory bath containing 5% sodium zincate and sufficient sodium hydroxide to clean the parts and the bath may be made from 80 grams water, 16 grams sodium hydroxide and 4 grams zinc oxide. The joint may finally be painted or plastic coated.