GB1146040A - Improvements relating to high strength brazed articles - Google Patents

Abstract

1,146,040. Brazing. OLIN MATHIESON CHEMICAL CORP. 24 May, 1966, No. 23183/66. Heading B3R. [Also in Division C7] An article comprises two members of the same or different aluminium bronze alloy containing 9À0-11À8% aluminium joined by a filler metal having a melting point above 1049‹ F. but below the melting point of the aluminium bronze alloy. The aluminium bronze alloy may be the binary aluminium copper alloy or may include 0À05-5% of at least one additional element to a total of less than 10% and preferably less than 5%. The additional elements may be iron 2-5%; chromium 0À4-2À0%; titanium 0À4-2%; zirconium 0À05-0À2%; molybdenum 0À4-2%; columbium 0À4-2%; vanadium 0À4-2% and mixtures thereof. The aluminium content of the bronze is preferably 9À4-10À4% and in addition to the additional elements mentioned above the alloy may contain as incidental impurities tin, zinc, lead, nickel, silicon, silver, phosphorus, magnesium, antimony, bismuth and arsenic. The aluminium bronze is provided in the temper worked condition by working at 1850-1000‹ F. followed by working at a temperature below 500‹ F., the working being e.g. rolling, forging, extrusion, drawing and swaging. The worked alloy may be annealed and includes 5-95% beta phase and the remainder alpha. A brazing flux and filler metal or self fluxing filler metal are applied to the surfaces to be joined which may be of the same or different alloy, the assembly is heated to 1100-1850‹ F. at which temperature the aluminium bronze is converted to a higher proportion of both phase and then the assembly is quenched e.g. with water to below 1000‹ F. at greater than 300‹ F. per minute preferably at 10,000‹ F. per minute to below 800‹ F. The flux may be applied in paste form and the filler may be a powder mixed with the flux paste or a wire. The filler metal has a melting point preferably between 1300‹ F. and below 1700‹ F. and may be e.g. 50% silver, 16% copper, 16% zinc and 18% cadmium; 15% silver, 80% copper and 5% phosphorus or 56% silver, 22% copper, 17% zinc and 5% tin. Copper base alloy containing 5-7% phosphorous; 52% copper, 48% zinc and 52% copper, 45% zinc and 3% tin may also be used. The flux may contain a mixture of sodium, potassium, zinc, lithium and aluminium chlorides; lithium fluoride; boron oxide; potassium borate and sodium borate. The brazed article may be tempered by heating for 20 minutes at 500-900‹ F. and this may be effected by carrying out an additional soldering step on the brazed article. In an example an alloy of 9À8% aluminium, 4% iron, balance copper is hot rolled at 1300-1600‹ F., then cold rolled and then further cold rolled with intermediate annealing. Blanks from the alloy are degreased, pickled in sulphuric acid and potassium dichromate and abraded with steel wool and then brushed with a flux of A filler comprising an alloy of 93% copper, 7% phosphorus is applied between the overlapped parts and the assembly is heated in an electric furnace at 1850‹ F. to cause the filler to flow. On removal from the furnace the assembly is cooled with compressed air at a rate greater than 300‹ F. per minute to below 800‹ F. and then allowed to cool to room temperature. The brazed joint shows 30% beta, 70% alpha phase, a uniformly fine grain size about 0À030 mm. and no penetration of the filler into the aluminium bronze. Heat exchanger tubes may be brazed from aluminium bronze strip.