A tungsten alloy wire material for a diamond wire busbar and a method of manufacturing the same

Abstract

The application discloses a tungsten alloy wire material for diamond wire bus and a preparation method thereof, and relates to the technical field of hard silicon material cutting wire material. The tungsten alloy wire material is prepared by using hydride, carbon and tungsten powder as raw materials or carbide and tungsten powder as raw materials. When the hydride, carbon and tungsten powder are used as raw materials, the percentage of the hydride in the total mass is 0.80-7.50%, the hydride is one or more of HfH2, TaH, TiH2 and ZrH4, and the particle size of the hydride is 0.5-1.5 microns. The carbon is carbon powder or carbon nanotube, the particle size of the carbon powder or carbon nanotube is less than or equal to 1.0 micron, and the percentage of the carbon in the total mass is 0.10-1.5%. When the carbide and tungsten powder are used as raw materials, the carbide is one or more of TiC, ZrC, TaC and HfC, the particle size of the carbide is 0.5-1.0 micron, the percentage of the carbide in the total mass is 1.0-8.0%, and the particle size of the tungsten powder is less than or equal to 3.0 microns.

Description

Technical Field

[0001] This invention relates to the field of hard silicon material cutting wire technology, specifically to a tungsten alloy wire for diamond wire busbars and its preparation method. Background Technology

[0002] The technical performance of diamond wire directly affects the quality of silicon wafers and the manufacturing cost of photovoltaic modules, making it a core technology for cost reduction in photovoltaic companies. Generally speaking, the finer the diameter, the higher the strength, the lower the breakage rate, and the higher the breaking force of the diamond wire, the better the quality of the cut silicon wafers, the higher the yield rate, and the smaller the thickness. Furthermore, the silicon material loss rate during cutting is lower, thus bringing more profits to silicon wafer manufacturers. Currently, mass-produced diamond wire busbars are mainly made of 92 or 100 carbon steel. However, due to the thinner diameter, defects in the carbon steel raw material, such as inclusions, careless handling, and insufficient strength, lead to problems such as high wire breakage and weak cutting force at the customer end. Even using ultra-strong carbon steel cannot meet industry demands. Therefore, finding alternative busbar materials is of great significance for diamond wire cutting.

[0003] Tungsten wire boasts advantages such as a high melting point, good flexibility, high tensile strength, strong fatigue resistance, high temperature resistance, corrosion and oxidation resistance, and low breakage rate. Moreover, tungsten wire has greater potential for finer wires, theoretically down to below 30μm, making it highly favored by diamond wire busbars. It is expected to replace high-carbon steel wire on a large scale in the future and has attracted much attention in the industry.

[0004] For example, patent application CN113215463B discloses a tungsten alloy wire made of tungsten and yttrium oxides. This technology obtains an alloy wire with ultra-high strength and good toughness by doping yttrium oxides. The process involves obtaining yttrium-doped tungsten oxide powder through liquid-liquid doping, solid-liquid doping, and solid-solid doping, then reducing it to alloy powder. The tungsten alloy wire is then obtained through isostatic pressing, pre-sintering, sintering, multi-roll milling, multi-pass rotary forging, and drawing. This patent obtains fine-grained and uniformly distributed yttrium oxide particles by controlling the doping process. The deep deformation processing of the alloy material through multi-roll rolling refines the dispersed yttrium oxide particles, thereby improving the strength and toughness of the tungsten wire. The final tungsten alloy wire has a maximum tensile strength of 6510 MPa.

[0005] Patent application CN115679174A discloses an ultra-strong tungsten wire. Through the action of a dispersed second phase (one or more of rare earth oxides, zirconium oxide, and titanium oxide) and a solid solution strengthening phase (one or more of rhenium, molybdenum, hafnium, niobium, iron, and cobalt), this technology is based on a composite approach of fine grain strengthening, dispersion strengthening, and solid solution strengthening. It uses a carbon source as a nucleation center to reduce and prepare nanoscale tungsten powder and a dispersed second phase, and utilizes the excellent "rhenium effect" of rhenium to significantly improve the breaking strength of the alloy wire. The prepared tungsten wire has a diameter of less than 37 μm and a tensile strength higher than 5200 MPa, with the optimal composition reaching 7200 MPa.

[0006] The patent application CN114211049A discloses a technical solution that improves the tensile strength of tungsten wire by doping it with rhenium and / or lanthanum. The process involves two reductions of the mixed powder, isostatic pressing, pre-sintering, hammer melting sintering, rotary forging, annealing, continuous rotary forging, and drawing to ultimately obtain tungsten alloy wires with a diameter of 30–50 μm and a strength ≥5100 MPa (between 5100 and 5800 MPa). This technology uses liquid-liquid doping with Re and La rare earth elements to reduce the size of metal precipitates, resulting in a denser microstructure and a comprehensive improvement in both the strength and plasticity of the tungsten wire, giving it high tensile strength and flexibility at a small diameter.

[0007] The tensile strength of high-strength tungsten wires prepared by the above-mentioned existing technologies is mostly between 5000 and 6000 MPa, and the best can only reach 7200 MPa, which cannot meet the higher requirements. Therefore, how to further improve the tensile strength of high-strength tungsten wires is a technical barrier that urgently needs to be solved. Summary of the Invention

[0008] To address the aforementioned problems in the prior art, this invention provides a tungsten alloy wire for diamond wire busbars and its preparation method, thereby solving the technical challenge that the prior art cannot further improve the tensile strength of tungsten wire.

[0009] The technical solution adopted in this invention is as follows:

[0010] A tungsten alloy wire for diamond wire busbars is made from hydrides, carbon, and tungsten powder, or from carbides and tungsten powder.

[0011] When using hydrides, carbon, and tungsten powder as raw materials, the percentage of hydrides in the total mass of the material is 0.80–7.50%, and the hydrides are one or more of HfH2, TaH, TiH2, and ZrH4, with a particle size of 0.5–1.5 μm; the carbon is carbon powder or carbon nanotubes, with a particle size ≤1.0 μm, and the percentage of carbon in the total mass of the material is 0.10–1.5%; the remainder is tungsten powder, and the raw material particle size of the tungsten powder is ≤3.0 μm;

[0012] When carbides and tungsten powder are used as raw materials, the carbides are one or more of TiC, ZrC, TaC, and HfC, the particle size of the carbides is 0.5 to 1.0 μm, and the percentage of carbides in the total mass of the material is 1.0 to 8.0%; the residue is tungsten powder, and the raw material particle size of the tungsten powder is ≤3.0 μm.

[0013] A method for preparing tungsten alloy wire for diamond wire busbars includes the following steps:

[0014] (1) Mixing: Hydride, carbon, tungsten powder or carbide and tungsten powder are mixed evenly to obtain tungsten alloy powder.

[0015] (2) Cold isostatic pressing: The tungsten alloy powder obtained in step (1) is pressed into a compact by cold isostatic pressing;

[0016] (3) Sintering: The pressed billet obtained in step (2) is pre-sintered in a medium-frequency sintering furnace, and then the temperature is raised to the target temperature for sintering densification treatment to obtain sintered billet strips;

[0017] (4) Blanking and drawing: The obtained sintered blank is subjected to multiple rounds of rotary forging or multiple rounds of rolling, and finally drawn, with multiple rounds of annealing in between, to obtain high-strength tungsten wire with a diameter of 20-45μm.

[0018] Furthermore, in step (1), one of the following is used for mixing: ball mill, three-dimensional mixer, spiral mixer, V-type mixer, double cone mixer and rapid mixer. During the mixing process, argon gas is introduced for protection, the speed of the mixer is 200-500 r / min, and the mixing time is 24-36 h.

[0019] Furthermore, when using a ball mill, the ball-to-material ratio is 3:1 to 6:1.

[0020] Furthermore, in step (2), the pressure of cold isostatic pressing is 150-300 MPa, and the holding time is 60-200 s.

[0021] Furthermore, in step (3), both pre-sintering and sintering are carried out in a hydrogen atmosphere. The pre-sintering temperature is 1300-1500℃ and the holding time is 150-180min; the sintering temperature is 2100-2300℃ and the holding time is 4-6h.

[0022] In summary, compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] This invention can mix tungsten powder, hydrides, and carbon or carbide powder in various ways. During the mixing process, high-speed rotation causes the agglomeration of the original tungsten powder to disappear and the alloy powder to become uniform and refined. The strength of the tungsten wire is enhanced by dispersion strengthening and fine grain strengthening of carbides (TiC, ZrC, TaC, HfC) or carbides formed by hydrides and carbon. Finally, high-strength tungsten wire with a particle size of 20-45 μm and a tensile strength of up to 8600 MPa is prepared. Attached Figure Description

[0024] Figure 1 These are morphology images of the original tungsten powder used in Example 1 at different magnification ratios;

[0025] Figure 2 The images show the morphology of the mixed powder after ball milling in Example 1 at different scales. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and various embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments.

[0027] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in these embodiments, unless otherwise specified, employs conventional testing methods in the art. The terminology used in this invention is merely for describing particular implementations and is not intended to limit the scope of the disclosure.

[0028] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; other raw materials, reagents, test methods and techniques not specifically mentioned herein refer to raw materials and reagents commonly used by one of ordinary skill in the art, as well as commonly employed test methods and techniques.

[0029] Electron microscopy was used to examine the tungsten powder before and after mixing, as well as the mixed tungsten powder, in the following examples, taking Example 1 as an example. Figure 1 This is a morphology image of tungsten powder before ball milling. Figure 2 The image shows the morphology of the mixed powder after ball milling. It is easy to see that the original tungsten powder before ball milling exhibited tungsten powder agglomeration, while the mixed powder after ball milling showed no obvious agglomeration and the powder particle size became finer. The conclusions obtained from other embodiments are roughly the same, and will not be elaborated further here.

[0030] Example 1

[0031] This embodiment provides a process for preparing tungsten alloy wire for diamond wire busbars:

[0032] Step 1: Mixing

[0033] HfH2, carbon powder, tungsten balls, and tungsten powder were loaded into a ball mill for ball milling and then sieved to obtain alloy powder. The weight percentage of HfH2 in the total powder was 1.00%, the weight percentage of carbon powder was 0.12%, the ball-to-powder ratio was 4:1, the ball mill was protected by argon gas, the ball milling speed was 350 r / min, and the ball milling time was 30 h.

[0034] Step 2: Cold isostatic pressing

[0035] The alloy powder obtained in step one is pressed into a compact by cold isostatic pressing. The pressure of cold isostatic pressing is 220 MPa and the holding time is 140 s.

[0036] Step 3: Sintering

[0037] The pressed billets were pre-sintered in a medium-frequency induction furnace, and then further heated to the target temperature for densification treatment to obtain sintered billet strips. Both pre-sintering and sintering were carried out in a hydrogen atmosphere. The pre-sintering temperature was 1400℃, and the holding time was 165 min; the sintering temperature was 2200℃, and the holding time was 5 h. The density of the sintered billet strips was 99.2%.

[0038] Step 4: Rotary forging and drawing

[0039] The sintered billet obtained in step three is subjected to multiple rotary forgings and then drawn, with multiple annealings in between, to obtain a high-strength tungsten wire with a diameter of 35μm and a tensile strength of 7100MPa.

[0040] Example 2

[0041] This embodiment provides a process for preparing tungsten alloy wire for diamond wire busbars:

[0042] Step 1: Mixing

[0043] HfH2, ZrH4, carbon powder, tungsten balls, and tungsten powder were mixed together in a ball mill and then sieved to obtain alloy powder. HfH2 accounted for 4.00% of the total powder by weight, ZrH4 accounted for 3.00%, and carbon powder accounted for 0.90%. The ball-to-powder ratio was 4:1. The ball mill was protected by argon gas, the milling speed was 350 r / min, and the milling time was 30 h.

[0044] The cold isostatic pressing, sintering, spinning, and drawing processes are all the same as those in Example 1.

[0045] The final result is a high-strength tungsten wire with a diameter of 35μm and a tensile strength of 7500MPa.

[0046] Example 3

[0047] This embodiment provides a process for preparing tungsten alloy wire for diamond wire busbars:

[0048] Step 1: Mixing

[0049] TaH, ZrH4, TiH2, carbon powder, tungsten balls, and tungsten powder were loaded into a ball mill and ball-milled. After sieving, alloy powder was obtained. The weight percentage of TaH in the total powder was 3.00%, ZrH4 was 2.00%, TiH2 was 1.00%, and carbon powder was 1.0%. The ball-to-powder ratio was 4:1. Argon gas was introduced into the ball mill for protection. The ball milling speed was 350 r / min, and the ball milling time was 30 h.

[0050] The cold isostatic pressing, sintering, spinning, and drawing processes are all the same as those in Example 1.

[0051] The final result is a high-strength tungsten wire with a diameter of 35 μm and a tensile strength of 8600 MPa.

[0052] Example 4

[0053] This embodiment provides a process for preparing tungsten alloy wire for diamond wire busbars:

[0054] Step 1: Mixing

[0055] HfH2, carbon powder, and tungsten powder were mixed together in a three-dimensional mixer and then sieved to obtain alloy powder. HfH2 accounted for 1.00% of the total powder by weight, and carbon powder accounted for 0.12% of the total powder by weight. Argon gas was introduced into the three-dimensional mixer for protection, the mixing speed was 250 r / min, and the mixing time was 32 h.

[0056] The cold isostatic pressing, sintering, spinning, and drawing processes are all the same as those in Example 1.

[0057] The final result is a high-strength tungsten wire with a diameter of 35μm and a tensile strength of 7000MPa.

[0058] Example 5

[0059] This embodiment provides a process for preparing tungsten alloy wire for diamond wire busbars:

[0060] Step 1: Mixing

[0061] HfH2, ZrH4, carbon powder, and tungsten powder were mixed together in a double cone mixer and then sieved to obtain alloy powder. HfH2 accounted for 4.00% of the total powder by weight, ZrH4 accounted for 3.00% of the total powder by weight, and carbon powder accounted for 0.90% of the total powder by weight. The mixer was protected by argon gas, the mixer speed was 200 r / min, and the mixing time was 36 h.

[0062] The cold isostatic pressing, sintering, spinning, and drawing processes are all the same as those in Example 1.

[0063] The final result is a high-strength tungsten wire with a diameter of 35 μm and a tensile strength of 7650 MPa.

[0064] Example 6

[0065] This embodiment provides a process for preparing tungsten alloy wire for diamond wire busbars:

[0066] Step 1: Mixing

[0067] TaC powder, HfC powder, balls, and tungsten powder were fed into a ball mill for ball milling and sieving to obtain alloy powder. The carbide powder accounted for 6.0% of the total powder by weight, the ratio of TaC powder to HfC powder was 2:1, the ball-to-powder ratio was 5:1, the ball mill was purged with argon gas for protection, the ball milling speed was 400 r / min, and the ball milling time was 32 h.

[0068] Step 2: Cold isostatic pressing

[0069] The alloy powder obtained in step one is pressed into a compact by cold isostatic pressing. The pressure of cold isostatic pressing is 280 MPa and the holding time is 80 s.

[0070] Step 3: Sintering

[0071] The pressed billets were pre-sintered in a medium-frequency induction furnace, and then further heated to the target temperature for densification treatment to obtain sintered billets. Both pre-sintering and sintering were carried out in a hydrogen atmosphere. The pre-sintering temperature was 1500℃, and the holding time was 160 min; the sintering temperature was 2300℃, and the holding time was 5 h. The density of the sintered billets was 99.6%.

[0072] Step 4: Rotary forging and drawing

[0073] The sintered billet obtained in step three is subjected to multiple rotary forgings and then drawn, with multiple annealings in between, to obtain a high-strength tungsten wire with a diameter of 45μm and a tensile strength of 7720MPa.

[0074] Example 7

[0075] This embodiment provides a process for preparing tungsten alloy wire for diamond wire busbars:

[0076] Step 1: Mixing

[0077] ZrC powder, TaC powder, HfC powder, balls, and tungsten powder were fed into a ball mill for ball milling and sieving to obtain alloy powder. The carbide powder accounted for 6.0% of the total powder by weight, the ratio of ZrC powder, TaC powder, and HfC powder was 3:2:1, the ball-to-powder ratio was 5:1, the ball mill was purged with argon gas for protection, the ball milling speed was 400 r / min, and the ball milling time was 32 h.

[0078] The cold isostatic pressing, sintering, spinning, and drawing processes are all the same as those in Example 6.

[0079] The final result is a high-strength tungsten wire with a diameter of 45 μm and a tensile strength of 8060 MPa.

[0080] Example 8

[0081] This embodiment provides a process for preparing tungsten alloy wire for diamond wire busbars:

[0082] Step 1: Mixing

[0083] ZrC powder, TaC powder, HfC, and tungsten powder were mixed together in a three-dimensional mixer and then sieved to obtain alloy powder. The carbide powder accounted for 6.0% of the total powder by weight, and the ratio of ZrC powder, TaC powder, and HfC powder was 3:2:1. The three-dimensional mixer was protected by argon gas, the mixing speed was 250 r / min, and the mixing time was 32 h.

[0084] The cold isostatic pressing, sintering, spin forging and drawing processes are the same as those in Example 6, and a high-strength tungsten wire with a diameter of 45 μm and a tensile strength of 7950 MPa is finally obtained.

[0085] The cold isostatic pressing, sintering, spin forging and drawing processes are the same as those in Example 1, and a high-strength tungsten wire with a diameter of 35 μm and a tensile strength of 8450 MPa is finally obtained.

[0086] Comparative Example 1

[0087] This comparative example provides a process for preparing tungsten alloy wire for diamond wire busbars:

[0088] Step 1: Mixing

[0089] HfH2, carbon powder, tungsten balls, and tungsten powder were loaded into a ball mill for ball milling and then sieved to obtain alloy powder. The weight percentage of HfH2 in the total powder was 0.70%, the weight percentage of carbon powder was 0.10%, the ball-to-powder ratio was 4:1, the ball mill was protected by argon gas, the ball milling speed was 350 r / min, and the ball milling time was 30 h.

[0090] The cold isostatic pressing, sintering, rotary forging, and drawing processes are the same as those in Example 1.

[0091] The final tungsten wire with a diameter of 35 μm and a tensile strength of 5800 MPa was obtained.

[0092] Comparative Example 2

[0093] This comparative example provides a process for preparing tungsten alloy wire for diamond wire busbars:

[0094] Step 1: Mixing

[0095] HfH2, carbon powder, tungsten balls, and tungsten powder were loaded into a ball mill for ball milling and then sieved to obtain alloy powder. HfH2 accounted for 8.00% of the total powder by weight, carbon powder accounted for 0.80% of the total powder by weight, the ball-to-powder ratio was 4:1, the ball mill was protected by argon gas, the ball milling speed was 350 r / min, and the ball milling time was 30 h.

[0096] The cold isostatic pressing, sintering, rotary forging, and drawing processes are the same as those in Example 1.

[0097] The final tungsten wire with a diameter of 35 μm and a tensile strength of 5350 MPa was obtained.

[0098] Comparative Example 3

[0099] This comparative example provides a process for preparing tungsten alloy wire for diamond wire busbars:

[0100] Step 1: Mixing

[0101] TaC powder, HfC powder, balls, and tungsten powder were fed into a ball mill for ball milling and sieving to obtain alloy powder. The carbide powder accounted for 9.0% of the total powder by weight, the ratio of TaC powder to HfC powder was 2:1, the ball-to-powder ratio was 5:1, the ball mill was purged with argon gas for protection, the ball milling speed was 400 r / min, and the ball milling time was 32 h.

[0102] The cold isostatic pressing, sintering, rotary forging, and drawing processes are the same as those in Example 6.

[0103] The final tungsten wire with a diameter of 45 μm and a tensile strength of 6030 MPa was obtained.

[0104] Comparative Example 4

[0105] This comparative example is for preparing conventional pure tungsten wire.

[0106] Tungsten powder with a particle size ≤1.0μm was loaded into a cold isostatic press and pressed to obtain a compact. The cold isostatic pressing process, pre-sintering and sintering, and rotary forging and drawing processes were the same as those in Example 6.

[0107] The final tungsten wire with a diameter of 45 μm and a tensile strength of 3560 MPa was obtained.

[0108] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A tungsten alloy wire for diamond wire busbars, characterized in that, Made from hydrides, carbon, and tungsten powder, or from carbides and tungsten powder. When using hydrides, carbon, and tungsten powder as raw materials, the percentage of hydrides in the total mass of the material is 0.80–7.50%, and the hydrides are one or more of HfH2, TaH, TiH2, and ZrH4, with a particle size of 0.5–1.5 μm; the carbon is carbon powder or carbon nanotubes, with a particle size ≤1.0 μm, and the percentage of carbon in the total mass of the material is 0.10–1.5%; the remainder is tungsten powder, and the raw material particle size of the tungsten powder is ≤3.0 μm; When carbides and tungsten powder are used as raw materials, the carbides are one or more of TiC, ZrC, TaC, and HfC, the particle size of the carbides is 0.5 to 1.0 μm, and the percentage of carbides in the total mass of the material is 1.0 to 8.0%; the residue is tungsten powder, and the raw material particle size of the tungsten powder is ≤3.0 μm. The preparation process of the tungsten alloy wire for the diamond wire busbar includes the following steps: (1) Mixing: Hydride, carbon, tungsten powder or carbide and tungsten powder are mixed evenly to obtain tungsten alloy powder. The mixing is carried out using one of the following: ball mill, three-dimensional mixer, spiral mixer, V-type mixer, double cone mixer and rapid mixer. During the mixing process, argon gas is introduced for protection. The speed of the mixer is 200-500 r / min and the mixing time is 24-36 h. (2) Cold isostatic pressing: The tungsten alloy powder obtained in step (1) is pressed by cold isostatic pressing to obtain a compact. The pressure of cold isostatic pressing is 150-300 MPa and the holding time is 60-200 s. (3) Sintering: The pressed billet obtained in step (2) is pre-sintered in a medium-frequency sintering furnace, and then the temperature is raised to the target temperature for sintering densification treatment to obtain sintered billet strips. Both pre-sintering and sintering are carried out in a hydrogen atmosphere. The pre-sintering temperature is 1300-1500℃ and the holding time is 150-180min; the sintering temperature is 2100-2300℃ and the holding time is 4-6h. (4) Blanking and drawing: The obtained sintered blank is subjected to multiple rounds of rotary forging or multiple rounds of rolling, and finally drawn, with multiple rounds of annealing in between, to obtain high-strength tungsten wire with a diameter of 20-45μm.

2. A method for preparing tungsten alloy wire for diamond wire busbars as described in claim 1, characterized in that, Includes the following steps: (1) Mixing: Hydride, carbon, tungsten powder or carbide and tungsten powder are mixed evenly to obtain tungsten alloy powder. The mixing is carried out using one of the following: ball mill, three-dimensional mixer, spiral mixer, V-type mixer, double cone mixer and rapid mixer. During the mixing process, argon gas is introduced for protection. The speed of the mixer is 200-500 r / min and the mixing time is 24-36 h. (2) Cold isostatic pressing: The tungsten alloy powder obtained in step (1) is pressed by cold isostatic pressing to obtain a compact. The pressure of cold isostatic pressing is 150-300 MPa and the holding time is 60-200 s. (3) Sintering: The pressed billet obtained in step (2) is pre-sintered in a medium-frequency sintering furnace, and then the temperature is raised to the target temperature for sintering densification treatment to obtain sintered billet strips. Both pre-sintering and sintering are carried out in a hydrogen atmosphere. The pre-sintering temperature is 1300-1500℃ and the holding time is 150-180min; the sintering temperature is 2100-2300℃ and the holding time is 4-6h. (4) Blanking and drawing: The obtained sintered blank is subjected to multiple rounds of rotary forging or multiple rounds of rolling, and finally drawn, with multiple rounds of annealing in between, to obtain high-strength tungsten wire with a diameter of 20-45μm.

3. The method for preparing tungsten alloy wire for diamond wire busbars as described in claim 2, characterized in that, When using a ball mill, the ball-to-material ratio is 3:1 to 6:1.

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