Process for treating copper-nickel alloys for use in brazed assemblies and product

The present invention relates to a process for maintaining the fine grain size of and providing excellent bend formability, hot ductility and strength properties to a copper-nickel-manganese alloy to be exposed to elevated temperatures. The process of the present invention includes a final cold working step during which the material to be fabricated into a desired article and/or exposed to the elevated temperatures has its thickness reduced by about 4% to about 30%, preferably from about 5% to about 25%. The alloys described herein have particular utility in brazed articles or assemblies.

This application is related to co-pending U.S. patent application Ser. No. 
587,570, filed Mar. 9, 1984, to Mahulikar et al. 
The present invention relates to a process for. treating copper-nickel 
alloys to enable them to retain a relatively fine grain structure and 
exhibit excellent bend formability, ductility and strength properties 
after exposure to elevated temperatures. 
It is well known that copper-nickel alloys are particularly well adapted 
for use in those environments where resistance to corrosion and mechanical 
strength are required. Applications for these alloys include tubing for 
heat exchangers such as radiators and oil coolers, salt water lines such 
as fire lines and sanitary lines, sheathing for lifeboats, fuel lines and 
pressure-containing parts in valves and fittings which are used at 
elevated temperatures. Often during fabrication into a final product, the 
alloys are subjected to elevated temperatures such as those associated 
with brazing. One particular family of copper-nickel alloys that have been 
used in a variety of applications because of their ductility and ability 
to withstand high temperatures are copper-nickel-manganese alloys. U.S. 
Pat. Nos. 1,525,047 to Rath, 2,074,604 to Bolton et al., 2,144,279 to 
Whitman, 2,215,905 to Kihlgren and 4,169,729 to Popplewell et al. 
illustrate several copper-nickel-manganese alloys and their applications. 
In addition to being exposed to elevated temperatures, these 
copper-nickel-maganese alloys often undergo fabrication operations such as 
stamping and bending. Consequently, it becomes desirable that the alloy 
being processed exhibit both good formability and ductility. When 
fabricated into articles such as tubing, it is also desirable that the 
alloy exhibit relatively high strength properties. 
In order to maintain the lowest possible cost, cupro-nickel strip materials 
are often processed directly to finish gage and annealed. The materials 
processed in this manner often show extreme grain growth after exposure to 
elevated temperatures. It is not unusual for brazed cupro-nickel materials 
to exhibit grain growth in excess of 2mm. Materials having such a grain 
size may be undesirably low in strength. 
It is an object of the present invention to provide a copper-nickel alloy 
having the ability to maintain a relatively fine grain structure when 
exposed to elevated temperatures. 
It is a further object of the present invention to provide a copper-nickel 
alloy as above having improved ductility and bend formability. 
It is a further object of the present invention to provide a process for 
providing such a copper-nickel alloy. 
It is a further object of the present invention to provide a copper-nickel 
alloy as above which has particular utility in brazed assemblies. 
Further objects and advantages of the present invention will become 
apparent from a consideration of the following specification. 
Alloys in accordance with the present invention consist essentially of from 
about 5% to about 45% nickel, from about 0.1% to about 1.1% manganese and 
the balance essentially copper. The higher nickel contents are generally 
used where strength is required and/or more aggressive environments are 
encountered in service. While not mandatory, the alloys may also contain 
phosphorous in an amount less than about 0.002%. As used herein, the 
percentages for each addition are weight percentages. In a preferred 
embodiment, the alloys of the present invention consist essentially of 
from about 5% to about 35% nickel, from about 0.6% to about 1% manganese 
and the balance essentially copper. 
The alloys may be processed in any desired manner to a strip material 
having a desired thickness, a desired temper and a desired grain size. 
Preferably, the strip material possesses an average grain size of about 
10.mu. to about 100.mu. prior to the treatment of the present invention. 
In accordance with the present invention, the strip material is then 
subjected to a final cold working step which reduces its thickness from 
about 4% to about 30%. It has been discovered that such a final cold 
working step enables the material to substantially maintain a relatively 
fine grain structure when exposed to elevated temperatures during 
subsequent processing. This is surprising because relatively low 
reductions normally cause exaggerated grain growth during conventional 
heat treatments such as annealing. As well as maintaining a relatively 
fine grain structure, alloys processed in accordance with the present 
invention exhibit excellent bend formability, ductility and strength 
during and after exposure to elevated temperatures. This combination of 
properties and grain structure is highly desirable in a material to be 
brazed. 
In a preferred manner of performing the present invention, the final cold 
working step is performed by cold rolling the strip material in a single 
pass through a rolling mill to obtain the strip material thickness 
reduction. In a most preferred embodiment, the final cold working step 
comprises reducing the strip material thickness by about 5% to about 25%. 
Alloys processed in accordance with the present invention have utility in 
assemblies subjected to high temperature processes and techniques, 
particularly brazed assemblies. Good brazing materials need to exhibit 
good bend formability, hot ductility and strength properties. Alloys 
processed in accordance with the present invention exhibit such 
properties. In addition, alloys processed in accordance with the present 
invention are able to substantially maintain relatively fine grain 
structures after exposure to elevated temperatures. This is directly 
attributable to the final cold working step which acts as a grain 
refinement treatment. 
As previously discussed, alloys in accordance with the present invention 
consist essentially of from about 5% to about 45% nickel, from about 0.1% 
to about 1.1% manganese and the balance essentially copper. In a preferred 
embodiment, the copper-base alloys consist essentially of from about 5% to 
about 35% nickel, from about 0.6% to about 1% manganese and the balance 
essentially copper. If desired, the alloys may contain phosphorous in an 
amount less than about 0.002%; however, this is not required. Conventional 
brass mill impurities may be tolerated in the alloys of the present 
invention but should preferably be kept at a minimum. 
Ordinarily, copper nickel alloys that are exposed to high temperatures such 
as those associated with brazing experience grain coarsening. This grain 
coarsening adversely impacts the material and reduces the overall strength 
of the material. It has been found that alloys processed in accordance 
with the process of the present invention are able to maintain relatively 
fine grain structures after exposure to elevated temperatures. As a 
result, the alloys exhibit improved strength and improved ductility at 
elevated temperatures. The improved ductility is particularly desirable 
because greater elongation percentages may be obtained at the elevated 
temperatures. As a result, cracking in assemblies subjected to relatively 
high temperature heat treatments such as brazing is significantly reduced. 
As well as exhibiting improved strength and ductility, alloys processed in 
accordance with the present invention exhibit excellent bend formability. 
This is particularly desirable where the material is to be subjected 
during fabrication to forming operations such as stamping and bending. For 
good bend formability, a minimum bend radius of 1t is desirable where t is 
the thickness of the material being bent. 
The alloys of the present invention may be cast in any desired manner. For 
example, they may be cast using continuous casting, direct chill casting 
or Durville casting. Any suitable pouring temperature may be used during 
casting. Generally, the pouring temperature will preferably be in the 
range of about 1000.degree. C. to about 1300.degree. C. Most preferably, 
the pouring temperature is in the range of about 1050.degree. C. to about 
1150.degree. C. 
After casting, the alloys may be processed in any desired manner into a 
strip material having a desired thickness, a desired temper and a desired 
grain structure. In a preferred embodiment, the strip material has an 
average grain size in the range of about 10.mu. to about 100.mu.. 
Preferably, the alloys will be processed by breaking down the cast ingot 
into a strip material such as a sheet or plate using a hot working 
operation such as hot rolling followed by a cold working operation such as 
cold rolling. During cold rolling, the alloy may be subjected to one or 
more passes through a rolling mill until it reaches the desired thickness 
or gage. If necessary, one or more interanneals may be performed during 
the cold rolling operation. To provide the desired temper, the strip 
material may be annealed after cold working to the desired thickness. The 
various hot rolling, cold rolling and/or annealing steps may be performed 
using any conventional technique and apparatus known in the art. 
The hot rolling step may be performed with any suitable initial 
temperature. Preferably, the initial hot rolling temperature is in the 
range of about 700.degree. C. to about 1050.degree. C. Most preferably, 
the initial hot rolling temperature is in the range of about 780.degree. 
C. to about 1000.degree. C. Any suitable cooling rate may be used to cool 
the strip material from hot rolling. 
The alloys of the present invention are believed to be capable of cold 
rolling reductions in excess of 90%; however, the cold rolling reduction 
preferably is between 10% and 80%. The cold rolling operation may be 
performed in one or more rolling passes. 
Annealing temperatures in the range of about 550.degree. C. to about 
900.degree. C. for at least one minute to about 24 hours may be used for 
the interanneals and/or the final anneal to a desired temper. Preferably, 
the final anneal and/or the interanneals are performed at an annealing 
temperature in the range of about 700.degree. C. to about 850.degree. C. 
for at least about one hour to about 12 hours. 
After the strip material has been processed to have a desired thickness, a 
desired temper and a desired grain structure, it is subjected to a final 
cold working step. The final cold working step preferably reduces the 
strip material thickness from about 4% to about 30%. In a most preferred 
embodiment, the strip material thickness is reduced from about 5% to about 
25%. The final cold working step may be performed in any desired manner 
using any conventional technique and apparatus known in the art. 
Preferably, the cold orking step comprises cold rolling the strip material 
to obtain the reduction in thickness. The cold rolling step may be 
performed by one or more passes of the strip material through a 
conventional rolling mill. 
It has been discovered that performing this final cold working step as the 
last processing step before fabrication into a desired article and/or 
exposure to elevated temperatures enables the copper alloys of the present 
invention to maintain a relatively fine grain structure. It is believed 
that grain structures having an average grain size in the range of about 
100.mu. to about 200.mu. are achievable using the final cold working step 
of the present invention. Further, alloys processed in accordance with the 
present invention exhibit excellent bend formability, hot ductility and 
strength before, during and after exposure to elevated temperatures. This 
renders the alloys particularly suitable for use in brazed assemblies such 
as tubing for radiators or heat exchangers. 
After the processing has been completed, the strip material may be 
fabricated into any desired article. As previously stated, alloys 
processed in accordance with the present invention readily lend themselves 
for use in brazed assemblies such as tubing. When used in such assemblies, 
the alloys of the present invention demonstrate excellent brazing 
characteristics and may be used with any suitable filler material. For 
example, they may be used with filler materials such as copper alloys 
C11000 and C12200. Of course, the temperatures used in brazing depend upon 
the filler material being used. For copper alloys such as C11000 and 
C12200, the brazing temperature is typically in the range of about 
1065.degree. C. to about 1120.degree. C., generally about 1090.degree. C. 
At these temperatures, alloys processed in accordance with the present 
invention are able to maintain relatively fine grain structures as well as 
excellent ductility, formability and strength properties. It should be 
noted that the ductility at elevated temperatures property, or hot 
ductility, exhibited by the present alloys facilitate fabrication 
operations in general. 
The present invention and improvements resulting therefrom will be more 
readily apparent from a consideration of the following illustrative 
examples.

EXAMPLE I 
Two alloys were prepared having the nominal compositions set forth in Table 
I below. 
TABLE I 
______________________________________ 
Alloy Ni (%) Mn (%) Cu (%) 
______________________________________ 
A 21 0.6 bal. 
B 21 1.0 bal. 
______________________________________ 
The alloys were Durville cast and processed in the following manner. The 
alloys were soaked at 980.degree. C. for 40 minutes and then hot rolled to 
0.3". The plates were then coil milled and cold rolled down to 0.050" 
gage. Samples of each alloy were then given one of the following three 
treatments. 
The first treatment comprised further cold rolling the samples down to 
0.020" gage and then annealing each sample at 700.degree. C. for 1 hour to 
a soft temper. The second treatment comprised cold rolling the samples 
down to 0.020" gage, annealing each sample at 700.degree. C. for 1 hour to 
a soft temper and performing a final 10% cold reduction. The third 
treatment comprised first annealing each sample at 700.degree. C. for 1 
hour and then performing the second treatment. All of the treated samples 
were then braze heat treated at 1090.degree. C. for 30 minutes and the 
grain size was recorded. The brazing heat treatment consisted of placing 
the test samples in a chamber and heating them to the desired temperature. 
The results of the grain size measurements are recorded in Table II. 
TABLE II 
______________________________________ 
Grain Size After 
Brazing Heat 
Treatment Alloy Treatment (mm) 
______________________________________ 
1 A &gt;1 
1 B &gt;1 
2 A .about.0.2 
2 B .about.0.2 
3 A .about.0.2 
3 B .about.0.2 
______________________________________ 
From this data, it can be seen that treatment 1 resulted in excessive 
undesirable grain growth whereas the alloys processed by treatments 2 and 
3 exhibted a fine grain structure. The data also shows that the grain 
refinement effect after brazing using the final cold working step of the 
present invention may be obtained irrespective of the number of previous 
anneals employed. 
EXAMPLE II 
To demonstrate the bend formability properties of materials treated in 
accordance with the present invention, bend formability tests were carried 
out on a manganese modified copper-nickel alloy. The alloy had the same 
nominal composition as alloy B in Example I. 
Samples of the alloy were given different final cold reductions ranging 
from 5% to 37%. Thereafter, standard 90.degree. bend tests were carried 
out in good and bad way directions. The results are given in Table III. 
TABLE III 
______________________________________ 
Cold Rolling (%) 
5 10 20 25 37 
Minimum Bend sharp sharp 0.55 0.6 0.7 
Radius/Thickness (L)* 
Minimum Bend sharp 0.24 0.55 0.6 1.4 
Radius/Thickness (T)** 
______________________________________ 
*(L) = good way 
**(T) = bad way 
For good bend formability, a minimum bend radius of 1t is the maximum limit 
where t is the thickness of the material being tested. The results at the 
5%, 10%, 20% and 25% cold reductions were acceptable while the results at 
the 37% cold reduction were unacceptable. 
It is believed that thsse examples demonstrate the benefits, e.g. improved 
ductility, bend formability and strength, the ability to maintain a fine 
grain structure when exposed to elevated temperatures and improved brazing 
ability which can be obtained by processing copper-nickel-manganese alloys 
in accordance with the present invention. Alloys processed in accordance 
with the present invention readily lend themselves to applications, such 
as tubing for heat exchangers, radiators, and transmission oil coolers, 
where such properties are required. 
While the nickel content of the alloys of the present invention has been 
described as being from about 5% to about 45%, the nickel content may be 
as great as about 65% without adversely affecting the desirable properties 
of the alloys. 
The U.S. patents set forth in the application are intended to be 
incorporated by reference herein. 
It is apparent that there has been provided in accordance with this 
invention a process for treating copper-nickel alloys for use in brazed 
assemblies which fully satisfy the objects, means and advantages set forth 
hereinbefore. While the invention has been described in combination with 
specific embodiments thereof, it is evident that many alternatives, 
modifications and variations will be apparent to those skilled in the art 
in light of the foregoing description. Accordingly, it is intended to 
embrace all such alternatives, modifications and variations as fall within 
the spirit and broad scope of the appended claims.