Copper-based brazing material and use of the brazing material

Abstract

A copper-based brazing material comprises an alloy having nickel in a proportion of from 20 to 35 percent by weight, zinc in a proportion of from 5 to 20 percent by weight, manganese in a proportion of from 5 to 20 percent by weight, chromium in a proportion of from 1 to 10 percent by weight, silicon in a proportion of from 0.1 to 5 percent by weight and molybdenum in a proportion of from 0 to 7 percent by weight, each based on the total weight of the alloy, and the remainder being copper and unavoidable impurities. The alloy is in particular free from boron, phosphorus and lead. The brazing material can be used for induction brazing of components made of iron materials for exhaust systems in motor vehicles.

Claims

1. A copper-based brazing material for use in induction brazing of stainless steel, wherein the brazing material consists of an alloy having nickel in a proportion of from 25 to 30 percent by weight, zinc in a proportion of from 5 to 20 percent by weight, manganese in a proportion of from 5 to 20 percent by weight, chromium in a proportion of from 1 to 10 percent by weight, silicon in a proportion of from 0.1 to 5 percent by weight, and molybdenum in a proportion of from 0 to 7 percent by weight, each based on the total weight of the alloy, and the remainder being copper and unavoidable impurities, wherein the alloy is free from boron, phosphorus and lead; and wherein the brazing material is present in a form of a wire or of a foil.

2. The brazing material according to claim 1, wherein the brazing material has a liquidus temperature of at most 1,150° C.

3. The brazing material according to claim 1, wherein the proportion of zinc is within a range of from 5 to 15 percent by weight.

4. The brazing material according to claim 1, wherein the proportion of manganese is within a range of from 7 to 19 percent by weight.

5. The brazing material according to claim 1, wherein the proportion of chromium is within a range of from 3 to 10 percent by weight.

6. The brazing material according to claim 1, wherein the alloy has molybdenum in a proportion of from 0.1 to 7 percent by weight.

7. The brazing material according to claim 1, wherein the brazing material has a liquidus temperature in a range of from 1,050° C. to 1,150° C.

8. The brazing material according to claim 1, wherein the proportion of silicon is within a range of from 0.3 to 1 percent by weight.

9. A copper-based brazing material for use in induction brazing of stainless steel, wherein the brazing material consists of an alloy having nickel in a proportion of 28 percent by weight, zinc in a proportion of 10 percent by weight, manganese in a proportion of 8 percent by weight, chromium in a proportion of 5 percent by weight, and silicon in a proportion of 0.5 percent by weight, each based on the total weight of the alloy, and the remainder being copper and unavoidable impurities, wherein the alloy is free from boron, phosphorus and lead.

10. A copper-based brazing material for use in induction brazing of stainless steel, wherein the brazing material consists of an alloy having nickel in a proportion of from 25 to 30 percent by weight, zinc in a proportion of from 5 to 12 percent by weight, manganese in a proportion of from 8 to 18 percent by weight, chromium in a proportion of from 4 to 10 percent by weight, silicon in a proportion of from 0.2 to 1 percent by weight, and molybdenum in a proportion of from 0 to 7 percent by weight, each based on the total weight of the alloy, and the remainder being copper and unavoidable impurities, wherein the alloy is free from boron, phosphorus and lead.

11. The brazing material according to claim 10, wherein the alloy has molybdenum in a proportion of from 0.5 to 2 percent by weight.

12. The brazing material according to claim 10, wherein the brazing material is present in the form of a wire or of a foil.

Description

DETAILED DESCRIPTION

(1) Further characteristics and advantages of the present invention can be inferred from the following description of preferred embodiments, which, however, shall not be considered as limiting.

Manufacturing Example

(2) To produce a brazing material of the present invention, metal powders are mixed in the proportions mentioned below and melted in a melting furnace:

(3) 48.5 percent by weight copper

(4) 28 percent by weight nickel

(5) 10 percent by weight zinc

(6) 8 percent by weight manganese

(7) 5 percent by weight chromium

(8) 0.5 percent by weight silicon.

(9) The melt was cast into a block and subsequently formed into a wire by hot rolling.

Test Results

(10) The brazing material thus obtained was subjected to the following tests:

(11) Wetting

(12) Wetting tests were performed at a conductive test stand under a controlled, low-oxygen atmosphere. A defined amount of brazing material was applied to a metal strip that is heated to the processing temperature over a short period of time by applying power. During heating and maintaining at the processing temperature, the solder wets the metallic surface and spreads. At the solder/metal phase boundary a specific contact angle occurs. The lower the contact angle, the better the wetting of the metallic surface by the solder. The contact angle was measured using a 3D microscope and a perpendicular metallographic microsection of the wetting plane.

(13) Salt Spray Test

(14) To simulate the corrosive attack against the brazed joint, pipe joints were brazed and subjected to a salt spray test. The salt spray test performed here is based on VDA621-415 and was modified as follows.

(15) To perform the test, specimens exhibiting the brazed joints were first maintained for 3.5 hours at a temperature of 500° C. and subsequently sprayed for 4 hours at 35° C. with a saline solution (5 percent by weight NaCl in distilled water). Then the specimens were exposed for 4 hours to a changing condensation water climate between 20° C. and 40° C. and 70% and 95% humidity. Subsequently, a room climate of 20° C. and 65% humidity was simulated for 12.5 hours. This four-part treatment cycle was repeated 20 times in total. Then microsections of the specimens were analysed for corrosive patches using a light microscope.

(16) The ageing test described corresponds to an exposure of the components of an exhaust system under normal operating conditions over a period of approximately 4 years.

(17) Condensate Corrosion

(18) For testing condensate corrosion, metal strips provided with solder are first maintained for 5 hours at a temperature of 500° C. Subsequently, the metal strips are exposed for 1 hour to a dry hot airflow and for 5 hours to a moist climate of 99.9% humidity at 80° C. During this time, the specimens are located above a bath containing a condensate solution of citric acid, sodium hydroxide, sodium chloride and distilled water. The cycle of hot airflow and moist climate is repeated 5 times in total. Overall, the sequence comprising heating in the furnace and 5 cycles of hot airflow and moist climate is repeated 10 times.

(19) Evaluation is performed using metallographic microsections and a three-dimensional image of the solder surface. With the use of this test, statements can be made on the corrosion resistance of the solder to the acidic condensate. Further, galvanic corrosion between the base material and the solder occurring in the peripheral area of the surface provided with solder can be determined quantitatively.

(20) Resistance to Oxidation

(21) Resistance to oxidation is evaluated using a cyclic oxidation test. To this end, a specimen of the brazing material with a known surface is cyclically heated to an application-oriented temperature of 650° C. in a furnace under air atmosphere, maintained at the temperature for a pre-determined period of time, and then cooled in air. This process is repeated 20 times, with the weight change of the specimen caused by formation or flaking of the oxide layer, based on the surface in mg/mm.sup.2, being continuously recorded.

(22) Melting Interval (DSC Analysis)

(23) To determine the melting interval, a DSC (Differential Scanning calorimetry) analysis was performed. The DSC measuring cell consists of a furnace and an integrated sensor equipped with corresponding footprints for specimen and reference crucibles. The surfaces of the sensor are linked with thermocouples or are themselves part of the thermocouples. Thus, both the temperature difference between specimen and reference sides (DSC signal) and the absolute temperature of the specimen or reference side can be determined.

(24) Gap Filling Capacity

(25) Pipe joints were induction-brazed under a protected atmosphere, and wetting and penetration depth of the solder into the gap at a gap width up to approximately 400 μm were measured metallographically.

(26) Mechanical Properties (Hardness, Tensile Strength)

(27) a) Tensile Strength

(28) To determine the tensile strength according to DIN 50125, centrally butt-brazed shape H tensile specimens were produced conductively and tested on a test machine (universal test machine ZWICK 1485).

(29) b) Hardness

(30) Vickers hardness HV.sub.0.1 was measured according to DIN EN ISO 6507-1. Microsections of the metal strips from the wetting tests that were conductively provided with solder were used as specimen material.

(31) On sheet steel, the brazing material of the present invention with the composition Cu48.5Ni28Zn10Mn8Cr5Si0.5 exhibits a contact angle of 12° and thus a very good wetting behaviour. In a commercially available copper solder (Bedra™ M122, Berkenhoff) a contact angle of 30° occurs under the same test conditions.

(32) In the salt spray test, no critical corrosion attack can be observed metallographically, either at the brazing material or at the phase boundary between the brazing material and the base substrate. The test for condensate corrosion shows a value for the volume wear of the brazing material of approximately 0.02 mm.sup.3/mm.sup.2, reaching the values obtained for traditional nickel alloys. The test for oxidation resistance shows the rapid formation of a strongly adhering oxide layer. After formation of this protective top layer only marginal weight changes can be detected. Thus, the oxidation resistance of the alloy of the present invention is sufficient for use at high temperatures, and the oxidation resistance of copper is by far exceeded.

(33) The DSC measurement showed a melting interval from 1,050° C. (solidus) to 1,140° C. (liquidus). The tensile strength of the brazed joint was 320 N/mm.sup.2 and the Vickers hardness HV.sub.0.1 was 180.

(34) The test results demonstrate the suitability of the brazing material of the present invention for use in induction brazing and additionally show that the brazed joint thus obtained is sufficiently resistant under the conditions prevailing in exhaust systems of motor vehicles and has the required mechanical strength and resistance to thermal cycling.

(35) Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.