Patent Application
20090098011
This invention relates to copper alloys, and in particular to copper-tin-nickel-phosphorus alloys with improved strength and formability.
There is a continued need for high strength copper alloys of good formability and reasonable cost for use in electrical connectors, and in particular for use in automotive electrical connectors. Current connector alloys in the low cost Cu—Sn—Ni—P family lack the combination of properties of practical strength (77 KSI), intermediate conductivity (37% IACS), excellent formability, and decent stress relaxation (65% at 150° C.). Formability in the document is measured by forming a strip by roller bending it 90° about a die of known radii. The ratio of the smallest die radii that the strip can be formed without cracking is divided over the strip thickness. Bends were measured both parallel (bad way, BW) and perpendicular (good way, GW) to the direction of rolling. Table 1 shows currently available Cu—Sn—Ni—P alloys:
C19025 comes close to achieving the desired properties but lacks the strength with acceptable formability; C40820 has the strength and superior formability but does not have the electrical conductivity.
Embodiments of the present invention provide a copper-tin-nickel-phosphorus alloy with an improved combination or properties, and in particular improved combination of yield strength and formability. In one preferred embodiment the alloy comprises between about 1% and about 2% Sn; between about 0.3% and about 1% Ni; between about 0.05% and about 0.15% P, and at least one of between about 0.01% and about 0.20% Mg and about 0.02% and about 0.4% Fe, the balance being copper. The addition of iron can be used as a low cost substitute for of Mg if good stress relaxation is not required for the application. More preferably the alloy comprises between about 1.1% and about 1.8% Sn, between about 0.4% and about 0.9% Ni, between about 0.05% and about 0.14% P, and between about 0.05 and about 0.15 Mg. Fe may be substituted for some of the Mg. Most preferably the alloy comprises, between about 1.2% and about 1.5% Sn; between about 0.5% and about 0.7% Ni; between about 0.09% and about 0.13% P, and between about 0.02% and about 0.06% Mg, the balance being copper. The alloy is preferably processed to have a yield strength of at least about 77 KSI, electrical conductivity of at least about 37% IACS, and formability (90° GW/BW) of 1.0/1.0. The alloy preferably also has a stress relaxation of 65% at 150° C.
The Sn gives the alloy solid solution strengthening. Ni and Mg are added to form precipitates of phosphorus with the added benefit of Mg increasing strength without lowering the electrical conductivity. The metal (Ni+Mg) to P ratio (the M/P ratio) is preferably controlled to a range of 4 to 8.5. If the ratio falls below 4 strengthening is not obtained and if is greater that 8.5 the material does not achieve 40% IACS.
In accordance with the preferred embodiment of this invention, the alloy is processed by melting and casting, hot rolling from about 850° C. to about 1000° C. cold rolling up to about 75% annealing between about 450° C.-about 600° C., cold rolling up to about a 60% reduction followed by annealing at 425° C. to about 600° C., cold rolling to about 50% prior to the final anneal between about 400° C. and 550° C. A final cold roll reduction is given to achieve the desired thickness and mechanical strength prior to a thermal stress relief treatment. In another preferred embodiment the processing includes a double final anneal treatment and the elimination of an upstream anneal which improves formability and strength respectively.
Embodiments of the present invention provide a copper-tin-nickel-phosphorus alloy with an improved combination or properties, and in particular improved combination of yield strength and formability. In one preferred embodiment the alloy comprises between about 1% and about 2% Sn; between about 0.3% and about 1% Ni; between about 0.05% and about 0.15% P, and at least one of between about 0.01% and about 0.20% Mg and about 0.02% and about 0.4% Fe, the balance being copper. The addition of iron can be used as a low cost substitute for of Mg if good stress relaxation is not required for the application.
More preferably the alloy comprises, between about 1.2% and about 1.5% Sn; between about 0.5% and about 0.7% Ni; between about 0.09% and about 0.13% P, and between about 0.02% and about 0.06% Mg, the balance being copper. The alloy is preferably processed to have a yield strength of at least about 77 KSI, electrical conductivity of at least about 37% IACS, and formability (90° GW/BW) of 1.0/1.0. The alloy preferably also has a stress relaxation of 65% at 150° C.
The Sn gives the alloy solid solution strengthening. Ni and Mg are added to form precipitates of phosphorus with the added benefit of Mg increasing strength without lowering the electrical conductivity. The M/P ration is preferably controlled to a range of 4 to 8.5. If the ratio falls below 4 strengthening is not obtained and if is greater that 8.5 the material does not achieve 40% IACS.
In accordance with the preferred embodiment of this invention, the alloy is processed by melting and casting, hot rolling from 850-1000° C. cold rolling up to about 75% annealing between 450-600° C., cold rolling about 60% followed by annealing at 425-600° C., cold rolling about 50% prior to the final anneal between 400-550° C. A final cold roll reduction is given to achieve the desired thickness and mechanical strength prior to a thermal stress relief treatment. In another preferred embodiment the processing includes a double final anneal treatment and the elimination of an upstream anneal which improves formability and strength respectively.
A series of 10 pound laboratory ingots with the compositions listed in Table 2 were melted in silica crucibles and cast into steel molds which were after gating 4″×4″×1.75″. After soaking for 2 hours at 900° C. they were hot rolled in three passes to 1.1″ (1.6″/1.35/1.1″), reheated at 900° C. for 10 minutes, and further reduced by hot rolling in three passes to 0.50″ (0.9″/0.7″/0.5″), followed by a water quench. After trimming and milling to remove the surface oxide, the alloys were cold rolled to 0.120″ and annealed at 570° C. for 2 hours. The alloys were cleaned and cold rolled to 0.048″ and annealed at 525° C. for 2 hours. The alloys were cold rolled to 0.030″ and annealed at 500° C. for 2 hours. The final cold roll was 60% to 0.012″ and a stress relief heat treatment was performed at 250° C. for 2 hours.
From the data in Example 2, it was determined that the Ni level is preferably at least 0.5 and the best overall alloys had a Ni/P ratio of 7-9. All the bends were poor due to the presence of contamination of sulfur forming long stringers as shown in
A series of 10 pound laboratory ingots with the compositions listed in Table 3 were melted in silica crucibles and cast into steel molds which were after gating 4″×4″×1.75″. After soaking for 2 hours at 900° C. they were hot rolled in three passes to 1.1″ (1.6″/1.35/1.1″), reheated at 900° C. for 10 minutes, and further reduced by hot rolling in three passes to 0.50″ (0.9″/0.7″/0.5″), followed by a water quench. After trimming and milling to remove the surface oxide, the alloys were cold rolled to 0.120″ and annealed at 570° C. for 2 hours. The alloys were cleaned and cold rolled to 0.048″ and annealed at 525° C. for 2 hours. The alloys were cold rolled to 0.024″ and annealed at 450° C. for 8 hours. The final cold roll was 50% to 0.012″ and a stress relief heat treatment was performed at 250° C. for 2 hours.
In general the strengths are low with the exception of alloys K293 and K294. Both these alloys contained more Sn than any of the others by about 0.5% correlating higher Sn levels to higher strength. The strengths of K286, K287 and K288 indicate the benefit of Mg as opposed to alloys of very close composition but without Mg, K282 and K284. It is notable that there is no drop in conductivity (the % IACS) accompanying the increase in yield strength. There was an increase in strength with the addition of iron to K291 and Mg in K289 both without Ni. The conductivity for the iron containing alloy is lower than the Mg containing alloy by about 4% IACS. Both of these alloys are almost perfectly balanced; Mg/P ratio is 1.81 for K289 close to the ideal of 1.2 and the Fe/P ratio for K291 is 4.00 which is also close to the ideal of 3.6. Iron is a more effective strengthener but leads to lower conductivity.
A series of 10 pound laboratory ingots with the compositions listed in Table 4 were melted in silica crucibles and cast into steel molds which were after gating 4″×4″×1.75″. After soaking for 2 hours at 900° C. they were hot rolled in three passes to 1.1″ (1.6″/1.35/1.1″), reheated at 900° C. for 10 minutes, and further reduced by hot rolling in three passes to 0.50″ (0.9″/0.7″/0.5″), followed by a water quench. After trimming and milling to remove the surface oxide, the alloys were cold rolled to 0.120″ and annealed at 570° C. for 2 hours. The alloys were cleaned and cold rolled to 0.048″ and annealed at 525° C. for 2 hours. The alloys were cold rolled to 0.024″ and annealed at 450° C. for 4 hours only for the single anneal condition and for 450° C. for 4 hours plus 375° C. for another 4 hours constituting the double anneal condition. The final cold roll was 50% to 0.012″ and a stress relief heat treatment was performed at 250° C. for 2 hours for both conditions.
Higher Sn levels helped the strength levels considerably but at lower conductivities. Compare alloys K320 and K319; 7 KSI difference in YS and 3% IACS in conductivity. The trend holds for those alloys with iron (K312 and K313) and those with magnesium (K 314 and K315) although the impact on strength is less than those without any other addition. There was no overall advantage of zinc K311 in contrast to K310; strength is increased but with lower conductivity. The double anneal showed an increase in formability (i.e., a decrease in the 90° bend radii that can be achieved). Slight increases in the conductivities are also noted.
A series of 10 pound laboratory ingots with the compositions listed in Table 4 were melted in silica crucibles and cast into steel molds which were after gating 4″×4″×1.75″. After soaking for 2 hours at 90° C. they were hot rolled in three passes to 1.1″ (1.6″/1.35/1.1″), reheated at 900° C. for 10 minutes, and further reduced by hot rolling in three passes to 0.50″ (0.9″/0.7″/0.5″), followed by a water quench. After trimming and milling to remove the surface oxide, the alloys were cold rolled to 0.120″ and annealed at 570° C. for 2 hours. The alloys were cleaned and cold rolled to 0.048″ and annealed at 525° C. for 2 hours. The alloys were cold rolled to 0.024″ and annealed at 450° C. for 4 hours only plus 375° C. for another 4 hours. The final cold roll was 50% to 0.012″ and a stress relief heat treatment was performed at 250° C. for 2 hours.
Thirteen of the twenty-two alloys in this group had yield strengths of 75 KSI or above. Six contained iron (K338, K339, K345, K346, K355 and K361) none of which made electrical conductivity of 40% IACS, although K338 is the closest at 38% IACS. Four contained Mg (K350, K351, K352 and K356) and 3 of these 4 exceeded 40% IACS. Note that K350 which did not achieve 40% IACS had a metal to phosphorus ratio of 9, greater that the recommended 8.5. Three of the alloys with yield strengths of 75 ksi or greater contained neither iron nor Mg (K343, K345, and K348), but none of these alloys had conductivities of 40% IACS.
All the data for Mg containing alloys and Mg-free alloys are combined in Tables 6 and 7. These data are from example 2, (Table 3 alloys which were double annealed and included in Tables 6 and 7), Example 3 (Table 4), and Example 4 (Table 5), and include data from Example 3. The process used for all the alloys is identical to the process used in the final double anneal of 4 (or 8 hours; see note) at 450° C.+4 hours at 375° C.
Overall the YS in Table 6 with Mg are higher than those in Table 7 without Mg. Only a few Mg-free alloys reach a minimum YS of 75 KSI: K293, K294, K310, K326, K343, K345, and K348, with corresponding electrical conductivities of: 42.2, 38.5, 38.5, 38.5, 38.4, 38.6 and 32.8% IACS respectively. Note with the exception of K293 none of the alloys achieve 40% IACS. Alloys K293, K294 and K326 all have properties of YS and conductivities close to C19025 but have better bends. In contrast the Mg alloys in Table 6 all have YS of at least 75 KSI with the exception of K289 and K290 (which had no Ni and an M/P ratio below 4). The electrical conductivities of all the alloys are at or above 40% IACS except for K318 (38.7% IACS) with an M/P of 7.66 and K350 (38.1% IACS) with an M/P ratio of 9.02. As the metal to phosphorus ratio increases the conductivity decreases and the combination of desirable properties becomes more difficult to reach. The addition of Mg enables the combination of yield strength over 75 KSI and conductivity of at least 40% IACS achievable when employing appropriate processing and maintaining an M/P ratio between 4 and 8.5.
A series of 10 pound laboratory ingots with the compositions listed in Table 8 were melted in silica crucibles and cast into steel molds which were after gating 4″×4″×1.75″. After soaking for 2 hours at 900° C. they were hot rolled in three passes to 1.1″ (1.6″/1.35/1.1″), reheated at 900° C. for 10 minutes, and further reduced by hot rolling in three passes to 0.50″ (0.9″/0.7″/0.5″), followed by a water quench. After trimming and milling to remove the surface oxide, the alloys were cold rolled to 0.080″ and annealed at 550° C. for 2 hours. The alloys were cleaned and cold rolled to 0.036″ and annealed at 450° C. for 4 hours only plus 375° C. for another 4 hours. The final cold roll was 60% to 0.012″ and a stress relief heat treatment was performed at 250° C. for 2 hours.
Increased cold work improved strength for all alloys. However, the Mg containing alloy with an M/P ratio below 9 (K352) was the only one to improve YS white maintaining or improving conductivity.
A series of 10 pound laboratory ingots with the compositions listed in Table 3 were melted in silica crucibles and cast into steel molds which were after gating 4″×4″×1.75″. After soaking for 2 hours at 900° C. they were hot rolled in three passes to 1.1″ (1.6″/1.35/1.1″), reheated at 900° C. for 10 minutes, and further reduced by hot rolling in three passes to 0.50″ (0.9″/0.7″/0.5″), followed by a water quench. After trimming and milling to remove the surface oxide, the alloys were cold rolled to 0.120″ and annealed at 570° C. for 2 hours. The alloys were cleaned and cold rolled to 0.048″ and annealed at 525° C. for 2 hours. The alloys were cold rolled to 0.024″ and annealed at 450° C. for 4 hours minimum. The final cold roll was 50% to 0.012″ and a stress relief heat treatment was performed at 250° C. for 2 hours. The samples were subjected to stress relaxation testing at 150° C. for 1000 hrs. The results are given in Table 9 below:
Alloys K291 and K312 with iron did not maintain 60% of the initial stress. The results are similar between the two despite the presence of Ni in K312. K314 with Ni and Mg combination maintained more than 65% of the initial stress.
A set of Mg and Mg-free alloys were processed using the indicated schedules. Tables 10 and 11 summarize the results. Both sets of alloys achieved yield strengths over 80 KSI. The Mg-containing alloys, all exceeded the target conductivity of 38% IACS, whereas the Mg-free alloys, with the exception of K412, did not. In addition, the formability of the Mg-containing alloys was generally better.
Plant processing was conducted on six alloys whose nominal compositions are set forth in Table 12. The processes are detailed in Table 13, where Process 1 is a laboratory process for comparison purposes, and Processes 2, 3, and 4 are plant processes.
The chemistry given in the Table 12 is the analyzed chemistry for the cast bars. Alloy 6 lies within the CDA range for C19025 and is present as a comparative example. All alloys were processed the same way: They were all hot rolled from 900° C., coil milled and then cold rolled to 0.125 or 0.100 gauge.
The resulting properties at final gage are shown in Table 14. Alloy 6 processed using Processes 3 and 4 possessed the expected properties for this alloy, having higher yield strength and poorer bends for Process 4 versus Process 3. Alloy 5 had a lower yield strength (YS) and poorer bad way bends when processed according to Process 2 in contrast to the Process 3 metal. Alloy 3 had comparable yield strength and conductivity for both the Process 2 and Process 3 processing but metal processed according to Process 3 had better bad way bends.
Processes 3 and 4 generally gave the best results. The results for Processes 1 and 2 on alloys 1 and 4 show slightly different results if the process is conducted in the plant (Process 2) rather than in the lab (Process 1) may have caused grain growth. Table 15 shows that the double anneal process (Process 2) gives good bends when simulated in the lab.
Plant processed alloys were subjected to stress relaxation testing at 150° C. Results for the transverse direction only are shown below in Table 16. All alloys except for alloy 2 had at least 65% stress remaining after 1000 h at 150° C.
This application claims priority to U.S. Provisional Patent Application Ser. No. 60/979,064, filed Oct. 10, 2007, the entire disclosure of which is incorporated herein.
| Number | Date | Country | |
|---|---|---|---|
| 60979064 | Oct 2007 | US |
