TITANIUM-COPPER ALLOY STRIP CONTAINING NB AND AL AND METHOD FOR PRODUCING SAME

Abstract

The present invention discloses a Nb and Al-containing titanium-copper alloy strip, characterized in that the weight percentage composition of the titanium-copper alloy strip comprises: 2.00-4.50 wt % Ti, 0.005-0.4 wt % Nb, and 0.01-0.5 wt % Al, balance being Cu and unavoidable impurities. Preferably, in the microstructure of the titanium-copper alloy strip, the number of Nb and Al-containing intermetallic compound particles with a particle size of 50-500 nm is not less than 1×10.sup.5/mm.sup.2, and the number of Nb and Al-containing intermetallic compound particles with a particle size greater than 1 μm is not more than 1×10.sup.3/mm.sup.2. Under the condition of ensuring excellent bendability, the titanium-copper alloy strip has excellent stability, especially the stability of mechanical properties at high temperatures. The present invention also relates to a method for producing the titanium-copper alloy strip.

Claims

1. A Nb and Al-containing titanium-copper alloy strip, characterized in that the weight percentage composition of the titanium-copper alloy strip comprises: 2.0-4.5 wt % Ti, 0.005-0.40 wt % Nb, and 0.01-0.50 wt % Al, balance being Cu and unavoidable impurities.

2. The Nb and Al-containing titanium-copper alloy strip according to claim 1, characterized in that the weight percentage composition of the titanium-copper alloy strip comprises: 2.5-4.0 wt % Ti, preferably 2.9-3.5 wt % Ti; and/or 0.01-0.3 wt % Nb; and/or 0.05-0.3 wt % Al.

3. The Nb and Al-containing titanium-copper alloy strip according to claim 1, characterized in that in the titanium-copper alloy strip, the number of Nb and Al-containing intermetallic compound particles with a particle size of 50-500 nm is not less than 1×10.sup.5/mm.sup.2, and the number of Nb and Al-containing intermetallic compound particles with a particle size greater than 1 μm is not more than 1×10.sup.3/mm.sup.2.

4. The Nb and Al-containing titanium-copper alloy strip according to claim 1, characterized in that the titanium-copper alloy strip has a decline rate of hardness H<5% after being held at 500° C. in atmospheric environment for 1 hour.

5. The Nb and Al-containing titanium-copper alloy strip according to claim 1, characterized in that: (1) the titanium-copper alloy strip has a ratio of the bending radius parallel to the rolling direction to the thickness of the strip R.sub.1/T≤0.5, and a ratio of the bending radius perpendicular to the rolling direction to the thickness of the strip R.sub.2/T≤1.0; and/or (2) the titanium-copper alloy strip has a yield strength of greater than 900 MPa and an electrical conductivity of 10-20% IACS.

6. The Nb and Al-containing titanium-copper alloy strip according to claim 1, characterized in that the weight percentage composition of the titanium-copper alloy strip also comprises a total amount of 0-0.50wt % of one or more selected from Ni, Co, Fe, Sn, Mn, Si, Cr, Mg, B, Zr, and Ag.

7. A method for preparing the Nb and Al-containing titanium-copper alloy strip according to claim 1, comprising the following steps: 1) Casting: the copper alloy raw materials are melted at 1200-1400° C. by using vacuum or gas-protected smelting method; 2) hot working: the ingot is subjected to hot working at a temperature of 700-980° C., and the cross-sectional area of the ingot is controlled to have a reduction of not less than 75% by the hot working; 3) Milling: the material obtained by hot working is subjected to milling; 4) First cold rolling: the cross-sectional area of the material is controlled to have a reduction of not less than 70%; 5) Solid solution treatment: the cold-rolled material is heated to a temperature of 700-950° C. and held for 1-100 s, followed by water cooling or air cooling, wherein the cooling rate is 10-250° C./s; 6) Intermediate cold rolling: the cross-sectional area of the material is controlled to have a reduction of 5-99%; 7) First aging: a temperature of 350-500° C. is held for 0.5-24 h under inactive gas protection; 8). Final cold rolling: the cross-sectional area is controlled to have a reduction of 5-80%;

9. Second aging: a temperature of 200-550° C. is held for 1 min-10 h under inactive gas protection.

8. The method according to claim 7, wherein one or more of the followings are satisfied: The casting in step 1) is iron mold casting, horizontal continuous casting or vertical semi-continuous casting; The hot working in step 2) is hot forging, hot rolling, or a combination thereof; In step 3), the material is milled up and down 0.5-2.0 mm to remove surface defects; In step 6), multi-pass cold rolling is carried out, and the reduction in single pass is controlled at 5-20%; The solid solution treatment in step 5) and the intermediate cold rolling in step 6) are used as a step unit, and the step unit is repeated at least twice, wherein the cross-sectional area of the intermediate cold-rolled material between two adjacent solid solution treatments is reduced by ≥30%; and The aging in step 7) and/or step 9) is performed in an atmosphere containing hydrogen, nitrogen, argon, or any mixture of these gases.

9. The method according to claim 7, wherein in step 1), the smelting process includes three steps, the first step: adding electrolytic copper and Nb-containing master alloy simultaneously in a smelting furnace and smelting; the second step: upon completely melting of the electrolytic copper and the Nb-containing master alloy, adding Ti-containing, Al-containing raw materials and optionally one or more raw materials containing one or more of Ni, Co, Fe, Sn, Mn, Si, Cr, Mg, B, Zr and Ag in sequence; the third step: upon melting of all the raw materials, refining at 1300±50° C. for 30-60 minutes, and then casting an ingot.

10. The method according to claim 9, wherein the Nb-containing master alloy is a Cu—Nb master alloy or a Nb—Ti master alloy, and the Ti-containing, Al-containing raw materials are pure Ti, pure Al or Ti and/or Al-containing master alloy, and the one or more raw materials containing one or more of Ni, Co, Fe, Sn, Mn, Si, Cr, Mg, B, Zr and Ag are elementary substances of these elements or master alloys containing these elements.

Description

DESCRIPTION OF THE DRAWINGS

[0050] FIG. 1 is the metallographic structure of the Cu—Ti—Nb—Al alloy strip according to the present invention.

[0051] FIG. 2 shows the metallographic structure of a Cu—Ti alloy strip in the prior arts.

[0052] FIG. 3 shows the metallographic structure of a Cu—Ti—Nb alloy strip in the prior arts.

[0053] FIG. 4 shows the metallographic structure of a Cu—Ti—Al alloy strip in the prior arts.

[0054] FIG. 5 is the scanning electron micrograph of a Nb and Al-containing intermetallic compound in the Cu—Ti—Nb—Al alloy strip according to the present invention.

EMBODIMENTS

[0055] The present invention will be further described in detail below by reference with the drawings and examples.

[0056] 20 example alloys and 10 comparative example alloys were designed. Each alloy was prepared according to the requirements of the addition amount of alloy raw materials (see Table 1 below) using forementioned two-step smelting method of adding alloy raw materials: the first step: electrolytic copper and Cu—Nb master alloy were added simultaneously in a smelting furnace and smelted; the second step: after the electrolytic copper and Cu—Nb master alloy were completely melted, according to the composition in Table 1, pure Ti, pure Al and elementary substances of optional elements selected from Ni, Co, Fe, Sn, Mn, Si, Cr, Mg, B, Zr and Ag were added successively; the third step: after all the raw materials were melted, refining was carried out at 1300±50° C. for 30-60 min. After smelting, a rectangular ingot was cast by a vertical semi-continuous casting method.

[0057] The ingot was held at 800-950° C. for 1-12 h and then hot rolled, the hot rolling speed was 50-120 m/min, the reduction in single pass of rolling was controlled at 10-30%, and the final rolling temperature was 650° C. or higher, after hot rolling, on-line water cooling was performed, followed by milling.

[0058] Subsequently, the first cold rolling was carried out, and the total cold rolling reduction was controlled above 80%.

[0059] After the first cold rolling, solid solution treatment was carried out. The temperature for the solid solution treatment was 700-950° C., the holding time was 1-100 s, and the cooling rate was 10-250° C./s.

[0060] After the solid solution treatment, an intermediate cold rolling was carried out. The rolling reduction was controlled at 30-60%, and the reduction in single pass was controlled at 5-20%.

[0061] After the intermediate cold rolling, the second solid solution treatment was carried out. The temperature for the solid solution treatment was 700-950° C., the holding time was 1-100 s, and the cooling rate was 10° C./s-250° C./s.

[0062] After the second solid solution treatment, an intermediate cold rolling was carried out again. The rolling reduction was controlled at 10-60%, and the reduction in single pass was controlled at 5-20%.

[0063] It should be noted that although a specific rolling reduction and two solution treatments and two intermediate cold rolling were involved in the above intermediate cold rolling steps, according to the actual product specifications, the rolling reduction can be varied within the range of 5-99%, and the solid solution treatment and the intermediate cold rolling can be carried out once or twice or more.

[0064] Subsequently, the first aging was carried out in an atmosphere containing hydrogen, nitrogen, argon, or any mixture of these gases. The aging temperature was 400° C. and the holding time was 4 h.

[0065] After the first aging, the final cold rolling was carried out, and the rolling reduction was controlled at 10-30%. It should be noted that although a specific rolling reduction was involved in the final cold rolling step here, the rolling reduction can be varied within the range of 5-80% according to the actual product specifications.

[0066] Finally, the second aging was carried out in an atmosphere containing hydrogen, nitrogen, argon, or any mixture of these gases. The aging temperature was 350° C. and the holding time was 4 h.

[0067] It should be noted that although a specific gas atmosphere was used in the first and second aging processes, it should be understood that other inert gases may also be used as the protective atmosphere.

[0068] Subsequently, the number of Nb and Al-containing intermetallic compound particles with a particle size of 50-500 nm and the number of Nb and Al-containing intermetallic compound particles with a particle size >1 μm in the alloy were measured, and the mechanical properties, electrical conductivity, bendability and the stability of mechanical properties at high temperature of the resulting alloy strip were tested.

[0069] It should be noted that, in order to avoid making the specification of the present application excessively lengthy, the detailed process parameters of Example 12 are described below as an example. Although the detailed process parameters of other examples are not recorded, it should be understood that the disclosures of the specification are sufficient for those skilled in the art to implement the invention claimed in this application, and such disclosures can also fully support the protection scope claimed by the claims.

[0070] In Example 12, the specification of the thickness of the finished product was 0.15 mm, and the specific process was as follows:

[0071] The ingredients of the alloy were added according to the amount of the raw materials of the alloy in Example 12 and smelted. The first step: electrolytic copper and Cu-Nb master alloy were added simultaneously in a smelting furnace and smelted; the second step: after the electrolytic copper and Cu—Nb master alloy were completely melted, pure Ti, pure Al and pure Co were added successively; the third step: after all the raw materials were melted, refining was carried out at 1300° C. for 45 min. After the smelting, a rectangular ingot was cast by a vertical semi-continuous casting method.

[0072] The ingot was held at 930° C. for 8 h and then hot rolled. The hot rolling speed was 110 m/min, the single pass reduction of rolling was 30%, and the final rolling temperature was 650° C. or higher, after the hot rolling, on-line water cooling was carried out, followed by milling.

[0073] Subsequently, the first cold rolling was carried out, and the total cold rolling reduction was 90%.

[0074] After the first cold rolling, solid solution treatment was carried out. The temperature for the solid solution treatment was 700° C., the holding time was 80 s, and the cooling rate was 100° C./s.

[0075] After the solid solution treatment, an intermediate cold rolling was carried out. The rolling reduction was controlled at 55%, and the reduction in single pass was controlled at 20%.

[0076] After the intermediate cold rolling, the second solid solution treatment was carried out. The solid solution temperature was 950° C., the holding time was 5 s, and the cooling rate was 200° C./s.

[0077] After the second solid solution treatment, an intermediate cold rolling was carried out again. The rolling reduction was controlled at 20%, and the reduction in single pass was controlled at 5%.

[0078] Subsequently, the first aging was carried out in an atmosphere containing a mixture of hydrogen and argon. The aging temperature was 400° C. and the holding time was 4 h.

[0079] After the first aging, the final cold rolling was carried out. The rolling reduction was 20%, and the final thickness was 0.15 mm.

[0080] Finally, the second aging was carried out in an atmosphere containing a mixture of hydrogen and argon at a temperature of 350° C. for 4 hours to obtain the finished material.

[0081] Standard Tests:

[0082] The room temperature tensile test was carried out on the electronic universal mechanical testing machine in accordance with “GB/T228.1-2010, Metallic Material Tensile Test, Part 1: Room Temperature Test Method”. The sample adopts a rectangular cross-section proportional sample with a proportionality factor of 5.65. The yield strength of the strips of the examples of the present invention and the comparative examples given in Table 1 below was the yield strength in the direction parallel to rolling direction.

[0083] The electrical conductivity was tested in accordance with “GB/T3048-2007, Test Method for Electrical Properties of Wires and Cables, Part 2: Metallic Material Resistivity Test”, expressed in %IACS.

[0084] The bendability was measured by the following method: take a long strip sample of the copper alloy strip in the rolling direction (i.e. good direction), and take a long strip sample perpendicular to the rolling direction (i.e. bad direction). The width of the samples was 10 mm. A 90° V-shaped punch with different radii at the tip was used to bend the long strip samples, and the outer surface of the bend was observed using a stereomicroscope. The bendability was expressed by the minimum bending radius/strip thickness (R/T) without cracks on the surface. When R/T value is 0, the minimum bending radius R is 0 and the bendability is the best.

[0085] The average grain size was measured in accordance with the test method of “YS/T 347-2004, Measuring Method for Average Grain Size of Copper and Copper Alloy”.

[0086] The stability test of mechanical properties at high temperature was carried out with reference to “GB/T33370-2016, Measuring method for Softening Temperature of Copper and CopperAlloy”. The sample was held at 500° C. in air for 1 hour and then air-cooled to test the hardness of the sample. the decline rate of hardness H (%) of the sample after being held at a certain high temperature compared with the original sample is used to characterize the stability of the mechanical properties of the sample at high temperature. The lower the decline rate of hardness H at the same temperature, the better the stability of the mechanical properties at high temperature.

[0087] The grain size and the distribution of intermetallic compound particles of the alloys were observed by metallographic microscope. The intermetallic compound particles in the alloy were observed using scanning electron microscope and their size and quantity were counted. The specific operation mode was as follows: a section parallel to the rolling direction of copper alloy strip was taken, and a rectangle of 25 μm×40 μm (1000 μm.sup.2) was taken as basic unit to observe its microstructure; 10 rectangles at different positions in the field of vision were selected, and the number of particles with a particle size between 50-500 nm and the number of particles with a particle size greater than 1 μm in each rectangle were counted. Finally, the average value was taken as the judgment basis, and the particle size was defined as the maximum size of particles.

[0088] According to Examples 1-20, it can be found that by reasonable control of the content of Ti, Nb, and Al, the copper alloys of all the examples in the present invention have achieved the properties of yield strength ≥900 MPa, electrical conductivity ≥10% IACS while exhibiting excellent bendability, i.e. the ratio of the bending radius parallel to rolling direction (i.e. good direction) to the thickness of strip (R.sub.1/T) ≤0.5, the ratio of the bending radius perpendicular to rolling direction (i.e. bad direction) to the thickness of strip (R.sub.2/T)≤1.0. After 500° C. soaking tests, it was found that the alloy samples in Example 1-20 had a decline rate of hardness H<5%.

[0089] Examples 1-20 and Comparative Examples 1-10 reflected the effects of different Nb and Al contents and the number of Nb and Al-containing intermetallic compound particles on the comprehensive properties of the titanium-copper alloy strip. Meanwhile, Examples 1-20 also showed that addition of one or more optional elements selected from Si, Zn, Co, Fe, Sn, Mn, Mg, Cr, B, Ag, and Zr in a reasonable small amount improved the strength and high temperature stability of the alloy to a certain extent.

[0090] The composition, the number of Nb and Al-containing intermetallic compound particles and the property test results of the titanium-copper alloy strips of Examples 1-20 and Comparative Examples 1-10 were shown in Table 1.

[0091] Although the yield strength and bending property of the titanium-copper alloy strips of Comparative Examples 1-5 meet the requirements, because Nb and Al were not added (Comparative Example 1) or Nb and Al were not added simultaneously (Comparative Example 2-5), there was no Nb and Al-containing intermetallic compound particles in the matrix, so the decline rate of hardness H was high (H>10%). Although both Nb and Al were added in Comparative Examples 6 and 7, the Nb content was insufficient in Comparative Example 6, and the Al content was insufficient in Comparative Example 7, which could not produce sufficient Nb and Al-containing intermetallic compound particles, therefore, exhibiting a weak strengthening effect, therefore, the decline rate of hardness H was still high (H>10%) .

[0092] Comparative examples 8-10 showed that although the decline rate of hardness H<5%, the yield strength and bendability of the titanium-copper alloy were adversely affected due to the excessive Al and/or Nb content. Especially when Al and Nb contents were simultaneously excessive, they agglomerated into large precipitate particles, which was disadvantageous for improving the strength of the alloy, and increased the risk of cracking during bending (R.sub.1/T and R.sub.2/T were larger in Comparative Example 10).

TABLE-US-00001 TABLE 1 Composition, number of Nb and Al-containing intermetallic compound particles and property test results of Examples and Comparative Examples Nb and Al-containing inter- metallic compound particles Number of Number of Properties Element content particles with particles with Decline Cu Ti Nb Al Other particle particle Yield rate of wt wt wt wt wt size of 50-500 size > 1 μm × strength Conductivity 90°Bending 90°Bending hardness Example % % % % % nm × 10.sup.4/mm.sup.2 10.sup.2/mm.sup.2 MPa % IACS GW R.sub.1/T BW R.sub.2/T H % 1 Rem. 2.07 0.305 0.012 — 21 3 903 20.0 0 0 4.6 2 Rem. 2.35 0.135 0.244 — 88 5 911 19.1 0 0.1 3.5 3 Rem. 2.59 0.048 0.098 — 58 4 919 17.9 0 0.2 4.8 4 Rem. 2.84 0.013 0.169 — 15 3 924 17.5 0.2 0.4 4.5 5 Rem. 3.10 0.063 0.058 — 78 4 913 16.2 0 0.4 3.9 6 Rem. 3.21 0.032 0.015 — 35 1 935 15.6 0 0.4 4.1 7 Rem. 3.25 0.212 0.124 — 91 4 949 15.1 0.1 0.4 2.9 8 Rem. 3.27 0.006 0.215 — 14 5 955 14.3 0.2 0.6 4.7 9 Rem. 3.36 0.084 0.154 — 77 4 954 13.1 0.2 0.6 3.9 10 Rem. 3.41 0.113 0.301 — 58 6 946 12.9 0.2 0.4 4.5 11 Rem. 3.46 0.294 0.195 Ni: 0.15 102 5 959 13.2 0.4 0.8 3.1 B: 0.05 12 Rem. 3.49 0.168 0.169 Co: 0.05 81 5 957 12.3 0.4 0.8 3.8 13 Rem. 3.51 0.068 0.188 Fe: 0.25 44 4 968 12.4 0.4 0.6 2.9 14 Rem. 3.59 0.156 0.023 Sn: 0.14 36 5 979 11.0 0.4 0.6 4.2 15 Rem. 3.61 0.137 0.224 Mn: 0.18 74 6 975 11.6 0.4 0.4 4.5 16 Rem. 3.69 0.021 0.058 Si: 0.08 60 6 982 10.7 0 0.4 3.8 17 Rem. 3.75 0.368 0.119 Cr: 0.19 99 4 988 10.5 0.4 0.8 3.7 18 Rem. 3.96 0.116 0.01 Mg: 0.30 19 5 984 10.3 0.4 0.8 4.1 19 Rem. 4.11 0.156 0.455 Zr: 0.09 87 7 979 10.2 0.4 0.6 3.6 20 Rem. 4.33 0.075 0.364 Ag: 0.26 51 4 991 10.1 0.4 0.6 3.3 Nb and Al-containing inter- metallic compound particles Number of particles with Number of Properties Element content particle particles with Decline Comparative Cu Ti Nb Al Other size of particle Yield rate of examples wt wt wt wt wt 50-500 nm × size > 1 μm strength Conductivity 90°Bending 90°Bending hardness No. % % % % % 10.sup.4/mm.sup.2 10.sup.3/mm.sup.2 MPa % IACS GW R.sub.1/T BW R.sub.2/T H % 1 Rem. 3.22 — — — — — 921 13.2 0 0.4 12.8 2 Rem. 3.25 — 0.084 — — — 926 14.1 0.2 0.4 10.7 3 Rem. 3.23 — 0.203 — — — 914 13.3 0.2 0.4 10.5 4 Rem. 3.26 0.046 — — — — 917 14.9 0.4 0.6 11.3 5 Rem. 3.30 0.115 — — — — 909 15.1 0.2 0.6 11.2 6 Rem. 3.34 0.003 0.086 — 0.7 2 945 15.7 0 0.2 10.2 7 Rem. 3.30 0.08 0.002 — 1.0 2 957 14.8 0.2 0.2 10.5 8 Rem. 2.99 0.61 0.19  — 67 13 889 16.6 0.8 1.0 3.9 9 Rem. 3.15 0.083 0.568 — 75 11 878 16.5 0.6 0.8 4.3 10 Rem. 3.25 0.583 0.668 — 63 26 904 12.0 1.6 2.0 4.5