Silver braze alloy

Abstract: The present invention relates to a silver braze alloy having improved wetting properties. The silver braze alloy consists essentially of from about 52.25 wt% to about 57.0 wt% silver, from about 38.95 to about 43.0 wt% copper, from about 0.5 wt% to about 5.5 wt%, preferably from about 1.0 wt% to about 5.5 wt%, manganese, and up to about 2.5 wt%, preferably from about 1.5 wt% to about 2.5 wt%, nickel. The alloy further may contain 0.15 wt% total of other trace elements.

Description: The present invention relates to a silver brazing alloy and to a method of brazing metal parts. It is known to torch braze, induction braze, furnace braze, or vacuum braze metal parts, such as steel parts, using non-ferrous brazing alloys, also known as filler metals. Typical filler metals include silver, gold, nickel, and copper brazing alloys. Silver brazing alloys are more costly and, in general, melt at lower temperatures than copper alloys. One silver brazing alloy which has been used in the prior art is an alloy containing 56 wt% silver, 42 wt% copper, and 2.0 wt% nickel. Despite the wide spread use of this silver brazing alloy, there remains a need for an alloy which has improved brazing characteristics, particularly wettability. Silver solder or braze alloys with contents of Mn and/or Ni together with Cu are already disclosed in the prior art such as in the JP publications 57-149092, 57-149093 or in the US-A-2303272. Furthermore, brazing of steel or stainless steel alloys is usually effected by the known braze filler alloys "Braze 580" and "Braze 655" on the base of silver with the participation of Cu and Mn of further containing Ni (Braze 655). Accordingly, it would be desirable to provide a silver braze alloy having improved wettability. It is further desirable to provide an improved brazing method which does not require nickel plating of a stainless steel substrate prior to brazing. The foregoing desires are attained by the silver braze alloy as defined in claims 1-5 and the brazing method as defined in claims 6-13. Certain preferred embodiments of the silver braze alloy and the method of the present invention, will now be described in greater detail by way of example only and with reference to the accompanying drawing. The figure is a graph showing the wetting angle which can be obtained by the preferred alloys in accordance with the present invention as a function of the manganese content of the alloy. A silver braze alloy in accordance with the present invention consists of from 52.25 wt% to 57.0 wt% silver, from 38.95 wt% to 43.0 wt% copper, from 0.5 wt% to 5.5 wt%, preferably from 1.0 wt% to 5.5 wt%, manganese and up to about 2.5 wt%, preferably from 1.5 wt% to 2.5 wt%, nickel. The alloys of the present invention may also contain up to about 0.15 wt% total of tolerated unavoidable trace impurities such as iron, zinc, silicon, phosphorous, sulfur, platinum, palladium, lead, gold, aluminum, magnesium, tin, germanium, carbon, and oxygen. A manganese addition within the foregoing ranges has been found to improve the brazing characteristics of the alloy of the present invention, particularly the wetting characteristics, as compared to a silver-copper-nickel brazing alloy consisting of 56wt% silver, 42 wt% copper, and 2.0 wt% nickel. Particularly useful brazing alloys in accordance with the present invention include: (1) a silver brazing alloy consisting essentially of 56 wt% silver, 42 wt% copper and 2.0 wt% manganese; and (2) a silver brazing alloy consisting of 0.5 to 5.5 wt% manganese with the remaining composition Al,Cu,Ni proportional to the 56:42:2 ratio. The silver braze alloys of the present invention may be formed in any suitable manner known in the art and may be cast using any suitable technique known in the art into any desired form. For example, the silver braze alloys of the present invention can be in strip form, wire form, rod form, sheet form, foil form, pig form, powder form, shot form, chip form, paste form. The silver braze alloys of the present invention may be brazed at a temperature in the range of from about 900°C to about 1050°C, preferably from about 950°C to about 1050°C, for a time sufficient to melt the brazing alloy onto a substrate formed from a ferrous material such as steel and stainless steel. Using the alloys of the present invention, brazing can be done using a furnace, locally using a torch, using an induction heater, dipped in a braze or flux bath, resistance heated, laser heated, or infrared heated. Depending on the brazing technique being employed, brazing may be carried out in an inert gas atmosphere, such as an argon atmosphere, or some other type of protective atmosphere. The silver braze alloy of the present invention melts at the aforementioned brazing temperatures and readily wets the ferrous substrate material to be joined without melting the ferrous substrate material. The silver braze alloys of the present invention may be used to braze steel surfaces, particularly stainless steel surfaces. One of the advantages of the silver braze alloys of the present invention is that in an inert gas atmosphere, such as an argon atmosphere, no flux needs to be used and no nickel plating of the ferrous substrate material is required. It has been found that the silver brazing alloys of the present invention have better wettability and flow characteristics than other brazing alloys such as an alloy consisting of 56 wt% silver, 42 wt% copper, and 2.0 wt% nickel. To demonstrate the improved properties of the alloys of the present invention, a controlled amount of braze alloy consistent with the alloys of the present invention were applied to a series of stainless steel pieces. The braze volume was kept small to prevent excessive spreading of the alloy during the test. Each sample was then heated to a braze temperature of 900°C or 1000°C in a brazing furnace under a protective argon atmosphere. The braze alloy under the aforementioned brazing conditions melted and formed a wetting angle with the stainless steel piece. The angle at the line of contact between the liquid or solidified braze alloy and the stainless steel piece was then measured. This was done either in situ or after the piece had been cooled to room temperature. The resulting angle is an indicator of wettability. The lower the contact or wetting angle, the better the wetting behaviour between the silver braze alloy and the base material. As can be seen from Fig. 1, the braze alloys of the present invention heated to a temperature of 1000°C exhibited wetting angles in the range of from approximately 1 degree to about 19 degrees and braze alloys of the present invention heated to a temperature of 900°C exhibited wetting angles which ranged from approximately 1 degree to about 37 degrees. The typical wetting angle for a 56Ag-42Cu-2Ni alloy can range anywhere from 10 to 90 degrees depending on the surface conditions of the stainless steel and the brazing temperature. As can be seen from the foregoing discussion, the silver brazing alloys of the present invention significantly reduce this wide range of wetting variability, producing generally low wetting angles and improved braze flow. The foregoing test shows that the higher the manganese content of the alloy, the lower the wetting angle. Fig. 1 clearly shows that alloys in accordance with the present invention having a manganese content greater than 1.0 wt% to 5.0 wt% provide excellent wettability properties. It is apparent that there has been provided in accordance with the present invention a silver braze alloy which fully meets the foregoing objects, means and advantages.

Claims: A silver braze alloy consisting of from 52.25 wt% to 57.0 wt% silver, from 38.95 to 43.0 wt% copper, from 0.5 wt% to 5.5 wt% manganese, up to about 2.5 wt% nickel, and up to 0.15 wt% total of tolerated unavoidable impurities. A silver braze alloy according to claim 1, wherein said nickel content of said alloy is in a range from 1.5 wt% to 2.5 wt%. A silver braze alloy according to claim 1 or 2, wherein said manganese content is in a range from 1.0 wt% to 5.5 wt%. A silver braze alloy consisting of 56 wt% silver, 42 wt% copper, 2.0 wt% manganese, and unavoidable impurities. A silver braze alloy consisting of 0.5 to 5.5 wt% manganese with the remaining composition apart from unavoidable impurities, being silver, copper and nickel in the proportional ratio of 56:42:2 respectively. A method for brazing an article comprising of: (1) providing an article formed from a ferrous material; (2) applying a brazing material to said article formed from an alloy consisting of from 52.25 wt% to 57.0 wt% silver, from about 38.95 wt% to 43.0 wt% copper, from 0.5 wt% to 5.5 wt% manganese, up to about 2.5 wt% nickel and up to 0.15 wt% total of tolerated unavoidable impurities; and (3) heating said article and said brazing material at a temperature in the range of from 900°C to 1050°C for a time sufficient to melt said brazing material. The method of claim 6, wherein said heating step comprises heating said article and said brazing material at a temperature in the range of from 950°C to about 1050°C. The method of claim 6 or 7, wherein said brazing material applying step comprises applying a brazing material consisting of about 56 wt% silver, 42 wt% copper, 2.0 wt% manganese and unavoidable inpurities. The method of claim 6 or 7, wherein said brazing material applying step comprises applying a brazing material consisting of 0.5 to 5.5 wt% manganese with the remaining composition apart from unavoidable impurities, being silver, copper and nickel in the proportional ratio of 56:42:2 respectively. The method according to claim 6, 7 or 8, wherein said brazing material being applied has a nickel content in the range of from about 1.5 wt% to about 2.5 wt%. The method according to any of claims 6 to 10, wherein said brazing material being applied has a manganese content in the range of from 1.0 wt% to 5.5 wt%. The method according to any of claims 6 to 11, wherein said article providing step comprises providing an article formed from steel. The method according to claim 12, wherein said article providing step comprises providing an article formed from stainless steel.

Inventors: HOSKING F MICHAEL, KHORUNOV VIKTOR FEDOROVICH, LIN WANGEN, MAKSYMOVA SVITLANA VASYLIVNA, SCHWARTZ BRIAN, HOSKING, F. MICHAEL, KHORUNOV, VIKTOR FEDOROVICH, LIN, WANGEN, MAKSYMOVA, SVITLANA VASYLIVNA, SCHWARTZ, BRIAN
Applicants: UNITED TECHNOLOGIES CORP, UNITED TECHNOLOGIES CORPORATION
Application year: 2001
Main classification: C22C5
IPC codes: B23K1, B23K35, C22C5, B23K103