Strong-strain low-temperature rolling grain refining method for preparing ultra-high-purity aluminum target material

Abstract

The invention discloses a strong-strain low-temperature rolling grain refining method for preparing an ultra-high-purity aluminum target material, and relates to the technical field of ultra-high-purity aluminum target material preparation. The method comprises the steps of blank preparation and homogenization, cryogenic environment establishment and blank pre-cooling, single-pass cryogenic strong shear rolling, after-rolling cryogenic maintenance and low-temperature stabilization treatment and subsequent finishing and machining, and a composite strong shear strain field is constructed through the synergistic effect of the cryogenic environment, asymmetrical rolling, lateral constraint and roller internal cooling. And grain extreme refinement and orientation randomization are synchronously realized in single-pass rolling. According to the method, a traditional multi-pass accumulative deformation mode is abandoned, the problem that fine grains and isotropy are difficult to achieve synchronously in the prior art is solved, an equiaxial ultra-fine grain non-texture structure is obtained, the use requirements of high-end manufacturing fields such as semiconductors and panel display on the target material can be met, and a reliable technical approach is provided for efficient preparation of the ultra-pure aluminum target material.

Description

Technical Field

[0001] This invention relates to the field of ultra-high purity aluminum target material preparation technology, specifically to a high-strain low-temperature rolling method for refining grains in the preparation of ultra-high purity aluminum targets. Background Technology

[0002] Ultra-high purity aluminum sputtering targets are indispensable key raw materials in high-end manufacturing fields such as semiconductors and flat panel displays. The microstructure of the target, especially the grain size and orientation distribution, directly determines the quality, uniformity, and performance of the sputtered film. An ideal target microstructure should have fine grains and random orientation to ensure stable sputtering rates and uniform film thickness. Therefore, how to efficiently and reliably prepare ultra-high purity aluminum targets with both nanoscale fine grains and highly isotropic microstructure has always been an important direction for technological solutions in this field.

[0003] To refine grain size, existing technologies generally employ multi-pass, multi-process deformation processing paths. For example, invention patent CN110205590A discloses a rolling method for ultra-high purity aluminum sputtering targets. This method achieves large deformation through a two-pass strategy of "first rolling with half reduction, then biting in and retracting, and finally rolling with full reduction." However, it essentially still falls under the category of multi-pass rolling and does not involve ultra-low temperature environments, resulting in limited grain refinement capabilities and a final grain size of approximately 150 micrometers. Another existing technology, CN107119244B, describes a method for preparing highly preferred oriented fine-grained ultra-high purity aluminum targets. Its process includes hot rolling at 50°C to 300°C followed by cold rolling, with the reduction per pass controlled at 40% to 50%, and temperature rise controlled by inter-pass cooling. While this method can achieve fine grains, the multi-pass rolling process easily introduces strong rolling texture, leading to anisotropic target properties. In addition, there are technical solutions that use a composite process of "multi-directional forging + room temperature multi-pass rolling", which is more complicated and cannot solve the problems of fine grains and isotropy in a single deformation.

[0004] In summary, existing technologies all rely on a multi-pass, multi-process cumulative deformation mode. Their limitation lies in the inability to simultaneously achieve nanoscale grain refinement and the formation of highly random equiaxed, textureless microstructure in ultra-high purity aluminum within a single rolling deformation process. Multiple processes lead to complex workflows and low efficiency; while simply pursuing large reductions in a single-pass rolling process inevitably results in strong texture. Therefore, there is an urgent need to develop a novel rolling deformation principle and process that can synergistically address the contradictory requirements of grain refinement and isotropy within a compact process.

[0005] The present invention was proposed to overcome the shortcomings of the prior art. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a high-strain low-temperature rolling method for refining grains in the preparation of ultra-high purity aluminum sputtering targets. By leveraging the synergistic effects of cryogenic environment, asynchronous rolling, lateral constraint, and internal cooling of the rolls, a dynamically changing composite high-shear strain field is constructed. This allows for the simultaneous and extreme refinement and randomization of ultra-high purity aluminum grains in a single-pass rolling process, abandoning the traditional multi-pass processing mode and efficiently obtaining nanoscale equiaxed untextured structures, thus meeting the stringent requirements of high-end sputtering targets for microstructure.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for refining grains by high-strain low-temperature rolling for preparing ultra-high purity aluminum targets, comprising the following steps:

[0008] Step 1, Billet Preparation and Homogenization: The ultra-high purity aluminum ingot is machined to obtain a slab, which is then subjected to high-temperature homogenization treatment;

[0009] Step 2, Cryogenic Environment Establishment and Billet Pre-cooling: The billet is placed in a liquid nitrogen environment for pre-cooling, so that the overall temperature of the billet drops to below -150°C;

[0010] Step 3, Single-pass cryogenic shear rolling: The pre-cooled slab is fed into a rolling mill for single-pass rolling under continuous cooling in a liquid nitrogen atmosphere or by liquid nitrogen spray. There is a linear velocity difference between the upper and lower work rolls of the rolling mill, with a speed ratio ranging from 1.2 to 2.0. A lateral restraint device is installed at the roll gap entrance of the rolling mill. This lateral restraint device is closely fitted to both sides of the slab in the width direction to restrict the width direction flow of the slab during rolling. The reduction in this single-pass rolling is 70% to 85%.

[0011] Step 4, Post-rolling cryogenic holding and low-temperature stabilization treatment: After a single rolling pass is completed, the rolled plate is immediately immersed in liquid nitrogen for 10 to 30 minutes, and then slowly warmed up to room temperature in a low-temperature environment of -50°C to 0°C.

[0012] Step 5, Subsequent finishing and processing: The treated sheet material is leveled, cut and surface-processed to obtain the finished ultra-high purity aluminum sputtering target material.

[0013] By combining single-pass, asynchronous rolling, lateral confinement, and cryogenic environment, a composite strong shear strain field is constructed, which can simultaneously achieve extreme grain refinement and randomization of grain orientation in a single rolling process, thereby obtaining nano-equiaxed non-textured structures that are difficult to achieve in traditional multi-process methods in the shortest possible step.

[0014] Furthermore, in step one, the purity of the ultra-high purity aluminum is not less than 99.999%;

[0015] The high-temperature homogenization treatment is carried out at a temperature of 450°C to 600°C, with a holding time of 10 hours to 48 hours, and the treatment atmosphere is a vacuum or a high-purity inert gas protective atmosphere.

[0016] By setting the raw material purity and homogenization process parameters as described above, a pure and uniformly composed billet base can be provided for subsequent ultra-low temperature severe plastic deformation, ensuring the consistency of deformation and the overall uniformity of the final microstructure.

[0017] Furthermore, in step two, the pre-cooling time is 30 minutes to 2 hours to ensure that the core temperature of the slab remains stable below -150°C.

[0018] By setting the precooling time and core temperature, the billet cross section is ensured to reach and stabilize at an ultra-low temperature state uniformly before rolling, thereby enabling uniform deformation and overall nano-sizing.

[0019] Furthermore, in step three, the lateral restraint device is a high-strength alloy baffle fixedly installed on the mill stand. The gap between the high-strength alloy baffle and the slab width direction on one side is less than 0.5 mm, and the height of the baffle is not less than the thickness of the slab before rolling.

[0020] By setting up lateral constraint devices and their tiny gap fit with the slab, the additional multi-directional shear generated by the forced lateral widening is suppressed, thereby enhancing the complexity and multi-directionality of the strain field and directly promoting the formation of equiaxed atextured structures.

[0021] Furthermore, in step three, both the upper and lower work rolls of the rolling mill are equipped with internal cooling channels. During the rolling process, liquid nitrogen or ultra-low temperature cooling media are continuously introduced into these internal cooling channels to maintain the surface temperature of the work rolls at an ultra-low temperature.

[0022] By using the internal cooling channels of the rolls, the temperature of the deformation zone can be actively and precisely controlled, continuously removing deformation heat to ensure that the entire process is kept in an ultra-low temperature window, effectively suppressing dynamic recovery and recrystallization, and ensuring the stable forming of nanostructures.

[0023] Furthermore, in step three, the single-pass rolling process creates a dynamically changing composite shear strain field inside the slab. This composite shear strain field is composed of the dominant shear strain generated by asynchronous rolling and the additional multi-directional shear strain generated by lateral constraints.

[0024] By setting a dynamically changing composite shear strain field, it is possible to achieve simultaneous refinement and randomization within a single pass, and the complexity of its strain path replaces the function of traditional multi-pass multi-directional deformation.

[0025] Furthermore, in step four, the rate of temperature increase to slowly return to room temperature is no greater than 5°C / min.

[0026] By setting a strict post-rolling heating rate, it is possible to safely release micro-stress while maximally suppressing recrystallization and grain growth, thus ensuring the complete preservation of the rolled ultrafine nanostructure.

[0027] Furthermore, through the single-pass deep cryogenic shear rolling and subsequent processing, the finished ultra-high purity aluminum sputtering target material forms an equiaxed ultrafine grain structure with an average grain size between 50nm and 200nm, and the grain orientation is highly randomly distributed.

[0028] The microstructure of the target material prepared by this method is characterized by ultrafine equiaxed grains, which can give the target material higher strength and thermal stability, while the highly random grain orientation ensures that the sputtering rate is uniform in all directions, thereby obtaining a deposited film with extremely uniform thickness and composition.

[0029] Compared with existing technologies, this high-strain low-temperature rolling method for refining grains in the preparation of ultra-high purity aluminum targets has the following advantages:

[0030] I. This invention constructs a dynamically changing composite strong shear strain field through the synergistic effect of cryogenic environment, asynchronous rolling, lateral constraint, and internal cooling of the rolls. It simultaneously achieves extreme grain refinement and randomization of grain orientation in ultra-high purity aluminum during single-pass rolling, abandoning the multi-pass cumulative deformation mode of existing technologies. It effectively avoids the texture strengthening problem caused by multiple processes and successfully obtains equiaxed ultrafine grain textureless structure, meeting the requirements of high-end manufacturing fields such as semiconductors and flat panel displays for the quality and uniformity of sputtered film of target materials. Thus, it solves the technical problem that existing technologies cannot simultaneously achieve fine grains and isotropy.

[0031] Second, this invention simplifies the process route by replacing traditional multi-pass processing with single-pass rolling, which significantly shortens the production process and improves production efficiency. At the same time, through billet homogenization treatment, precise deep cryogenic precooling and post-rolling low-temperature stabilization treatment, it ensures the consistency of billet deformation and the uniformity of finished product structure, effectively suppresses grain growth and recrystallization, and ensures the stable preservation of ultrafine grain structure.

[0032] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0034] Figure 1 This is a flowchart illustrating the preparation method of the present invention;

[0035] Figure 2 This is a schematic diagram illustrating the principle of the composite strong shear strain field of the present invention;

[0036] Figure 3 This is a diagram of the cryogenic environment and equipment collaborative control system of the present invention;

[0037] Figure 4 This is a comparison diagram of the effects of grain refinement and orientation randomization in this invention. Detailed Implementation

[0038] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0039] Example 1

[0040] like Figures 1 to 4 As shown, this embodiment selects a medium combination of process parameters. By setting a homogenization temperature of 500℃, a holding time of 24h, a precooling time of 1h, a roll linear speed ratio of 1.5, a rolling reduction of 75%, a liquid nitrogen holding time of 20min after rolling, and a low-temperature stabilization heating rate of 3℃ / min, the implementation effect of the core process of this invention under normal working conditions is verified, ensuring that the target material product obtains an ultrafine-grained and randomly oriented microstructure.

[0041] In this embodiment, the detailed implementation process of the preparation method is as follows:

[0042] Billet preparation and homogenization:

[0043] Specifically, a Φ300mm ultra-high purity aluminum ingot was selected and machined using a gantry milling machine to remove the oxide scale, casting defect layer, and excess edges from the ingot surface, resulting in a slab with a thickness of 20mm, a width of 300mm, and a length of 500mm. During the machining process, the cutting speed was controlled at 150m / min and the feed rate at 0.2mm / r to avoid the machining heat causing the local temperature of the slab to rise above 50℃, thus preventing any impact on the subsequent homogenization effect.

[0044] The processed slab is placed in a vacuum annealing furnace for high-temperature homogenization. First, the furnace door is closed, and the vacuum pump is started to evacuate the furnace to a vacuum level of ≤5×10⁻⁶. - The furnace temperature was initially increased to 500℃ at a rate of 5℃ / min, then maintained at that temperature for 24 hours, with real-time monitoring of temperature fluctuations to ensure the temperature difference did not exceed ±5℃. The homogenization treatment aimed to eliminate component segregation and casting stress within the ingot, ensuring uniform diffusion of aluminum atoms and forming a single-phase structure with consistent composition. This provided a pure and uniform billet base for subsequent intense cryogenic plastic deformation. After the holding period, the billet was cooled to room temperature with the furnace, and the furnace door was opened to remove it.

[0045] Establishment of cryogenic environment and pre-cooling of billet:

[0046] For example, prepare a liquid nitrogen immersion tank with a volume of 1m³. The tank is equipped with a detachable support made of stainless steel to prevent reaction with the liquid nitrogen. Place the homogenized slab stably on the support, ensuring the slab does not directly contact the tank to prevent stress caused by excessively rapid localized cooling. Then, slowly inject liquid nitrogen into the immersion tank at a rate of 10L / min until the slab is completely submerged. At this point, the slab begins pre-cooling.

[0047] To monitor the core temperature of the slab in real time, holes with a diameter of 2 mm and a depth of 150 mm were drilled at the center of the slab's width and thickness. K-type thermocouples were inserted into these holes and connected to a data logger, recording temperature data every 1 minute. The pre-cooling process lasted 1 hour, during which evaporated liquid nitrogen was replenished to maintain the liquid nitrogen level at least 50 mm above the top surface of the slab. After 1 hour, the data logger showed that the core temperature of the slab stabilized at -165℃, meeting the requirement of below -150℃, and the pre-cooling stage was completed.

[0048] Single-pass deep cryogenic shear rolling:

[0049] First, the rolling mill was debugged and prepared. The mill used was a twin-roll reversible rolling mill with a work roll diameter of 300mm and a roll body length of 500mm. Both the upper and lower work rolls of the mill were equipped with internal cooling channels. Specifically, eight Φ8mm through holes were evenly distributed circumferentially inside the roll body, parallel to the roll shaft, extending to the roll neck at both ends, and connected to a liquid nitrogen delivery pipeline via a rotary joint. Before rolling, the liquid nitrogen delivery pump was started, and liquid nitrogen was introduced into the internal cooling channels of the rolls at a flow rate controlled at 5L / min for 30 minutes, reducing the surface temperature of the work rolls to below -150℃. The roll surface temperature was monitored using an infrared thermometer to ensure temperature stability.

[0050] A lateral restraint device is installed at the entrance of the rolling mill roll gap. This device consists of high-strength alloy baffles fixedly installed on both sides of the rolling mill stand. The baffles are made of H13 hot work die steel, quenched and tempered to a hardness of HRC50-55, exhibiting good wear resistance and low-temperature stability. The baffle dimensions are: height 25mm, 20mm greater than the slab thickness before rolling; width 500mm, consistent with the slab length; thickness 20mm. During installation, the positioning bolts on the stand are adjusted to ensure that the gap between the baffle and the slab in the width direction is 0.3mm on one side and less than 0.5mm, ensuring a tight fit between the baffle and both sides of the slab and restricting the slab's width-direction flow during rolling.

[0051] The pre-cooled slab is quickly removed from the liquid nitrogen immersion tank and fed into the roll gap of the rolling mill via a conveyor roller conveyor. During the conveying process, a liquid nitrogen spraying device continuously cools the surface of the slab at a flow rate of 3 L / min, ensuring that the temperature of the slab does not exceed -150℃ before entering the roll gap. The linear speed of the upper work roll of the rolling mill is set to 1.5 m / s, and the linear speed of the lower work roll is set to 1.0 m / s, with a linear speed ratio of 1.5, falling within the range of 1.2-2.0. The reduction per pass is set to 75%, meaning the slab is rolled from 20 mm thick to 5 mm thick.

[0052] During the rolling process, the different linear speeds of the upper and lower rolls generate dominant shear strain within the slab. Simultaneously, the lateral restraint device restricts the slab's lateral width expansion, causing it to be compressed in the width direction, generating additional multi-directional shear strain. These two factors couple to form a dynamically changing composite shear strain field. An infrared thermometer monitors the slab temperature at the roll gap in real time, ensuring the slab temperature remains below -150℃ throughout the rolling process to prevent temperature rise due to deformation heat. The rolling process lasts 10 seconds, allowing the slab to successfully pass through the roll gap, completing a single-pass deep cryogenic shear rolling process.

[0053] Post-rolling cryogenic retention and low-temperature stabilization treatment:

[0054] After a single rolling pass, the rolled sheet is immediately placed in a liquid nitrogen tank for cryogenic holding. The liquid nitrogen depth in the tank is 300 mm to ensure the sheet is completely immersed in the liquid nitrogen. The holding time is set to 20 minutes, during which the sheet temperature is monitored by thermocouples and maintained at approximately -196°C. The purpose is to fix the ultrafine grain structure formed during the rolling process and inhibit grain growth.

[0055] After 20 minutes, the substrate was removed from the liquid nitrogen storage tank and placed in a cryogenic incubator for low-temperature stabilization. The initial temperature of the incubator was set to -50℃. After placing the substrate inside, the programmed temperature control system was activated, and the temperature was slowly increased to room temperature (25℃) at a rate of 3℃ / min for approximately 25 hours. The purpose of slow heating was to safely release the micro-stress within the substrate while minimizing recrystallization and grain growth, ensuring the complete preservation of the ultrafine nanostructure. During the heating process, the temperature inside the incubator was recorded every hour to ensure that the heating rate met the requirements.

[0056] Subsequent finishing and processing:

[0057] After the low-temperature stabilization treatment, the sheet material is removed and first leveled using a multi-roller leveling machine. The leveling machine has 11 rollers with a roller diameter of 80mm and a leveling speed of 0.5m / min. Through repeated leveling, the flatness error of the sheet material is reduced to ≤0.1mm / m. After leveling, the sheet material is cut using a plasma cutter to remove irregular parts at both ends, resulting in a target blank with dimensions of 5mm thickness, 300mm width, and 490mm length.

[0058] The target blank undergoes surface processing. First, a surface grinder is used for grinding with a diamond wheel (120 mesh), at a grinding speed of 30 m / s and a feed rate of 0.01 mm / r, reducing the surface roughness of the plate to Ra ≤ 1.6 μm. Then, a polishing machine is used for precision polishing with alumina polishing paste (0.5 μm particle size) at a polishing speed of 1 m / min, further reducing the surface roughness to Ra ≤ 0.8 μm, meeting the surface quality requirements of the sputtering target. Finally, the target is cleaned and dried to obtain the finished ultra-high purity aluminum sputtering target.

[0059] In summary, this embodiment successfully prepared ultra-high purity aluminum sputtering targets through the detailed process steps described above. Testing revealed that the average grain size of the finished product was 120 nm, with highly randomized grain orientation and no obvious preferred texture. The entire process is compact, achieving extreme grain refinement and randomized orientation through a single-pass rolling and subsequent processing. Compared to traditional multi-pass processes, the process is simplified by more than 60%, significantly improving production efficiency. Furthermore, the finished product exhibits excellent microstructure uniformity, meeting the requirements of high-end manufacturing fields such as semiconductors and flat panel displays for sputtering targets.

[0060] Example 2

[0061] like Figures 1 to 4As shown, this embodiment sets a lower limit of 450℃ for homogenization temperature, an upper limit of 48h for holding time, an upper limit of 2h for precooling time, a lower limit of 1.2 for roll linear speed ratio, a middle and upper limit of 80% for rolling reduction, an upper limit of 30min for post-rolling liquid nitrogen holding, and an upper limit of 5℃ / min for low-temperature stabilization heating rate to verify the feasibility and stability of the technical solution of the present invention under extreme parameter conditions.

[0062] In this embodiment, the detailed implementation process of the preparation method is as follows:

[0063] Billet preparation and homogenization:

[0064] A Φ300mm ultra-high purity aluminum ingot was selected and machined using a CNC milling machine. The machining parameters were: cutting speed 120m / min, feed rate 0.15mm / r, and depth of cut 2mm. The ingot was machined into a slab with a thickness of 25mm, a width of 350mm, and a length of 600mm. After machining, the burrs and oil stains on the surface of the slab were removed, and it was cleaned with anhydrous ethanol and dried.

[0065] The slab was placed in a high-purity argon-protected annealing furnace for high-temperature homogenization. The furnace chamber volume was 2 m³, and high-purity argon gas (≥99.999%) was introduced as the protective atmosphere at a flow rate of 2 L / min. After purging the air from the furnace, the furnace temperature was raised to 450℃ at a heating rate of 3℃ / min. After reaching the set temperature, it was held at that temperature for 48 hours, during which the oxygen content of the furnace atmosphere was monitored to ensure that the oxygen content was ≤5×10⁻⁶. -6 To prevent oxidation of the slab, heating was stopped after 48 hours, but argon gas was continued to be introduced. The slab was then cooled to room temperature in the furnace and removed. At this point, the component segregation inside the slab had been completely eliminated, and the microstructure was well homogeneous.

[0066] Establishment of cryogenic environment and pre-cooling of billet:

[0067] Prepare a liquid nitrogen immersion tank with a volume of 1.5 m³. The tank is equipped with a multi-layered stainless steel support. Place the homogenized slab on the bottom support, with a 50 mm gap between the slabs to ensure that the liquid nitrogen can fully surround the slab. Pour liquid nitrogen into the immersion tank at a rate of 15 L / min until the liquid nitrogen level is 100 mm above the top surface of the slab.

[0068] Holes were drilled at the center of three different locations on the slab, namely the head, middle, and tail, and K-type thermocouples were inserted and connected to a multi-channel data logger to monitor the core temperature of the slab in real time. The pre-cooling time was set to 2 hours, during which liquid nitrogen was added every 30 minutes to maintain a stable liquid nitrogen level. After 2 hours, the data logger showed that the temperature at all three measuring points was stable at -170℃, meeting the requirement of below -150℃, and the pre-cooling was completed.

[0069] Single-pass deep cryogenic shear rolling:

[0070] The rolling mill was commissioned. The mill used was a four-high reversible mill with a work roll diameter of 350mm and a support roll diameter of 800mm. Both the upper and lower work rolls were equipped with 10 internal cooling channels, each Φ10mm, connected to a liquid nitrogen storage tank via a rotary joint. Before rolling, liquid nitrogen was introduced into the internal cooling channels of the rolls at a flow rate of 6L / min for 40 minutes to lower the surface temperature of the work rolls to below -160℃. The temperature was confirmed to be within the acceptable range using an infrared thermometer.

[0071] The lateral restraint device is installed. The baffle is made of Cr12MoV alloy tool steel, cryogenically treated, with a hardness of HRC55-60. Its dimensions are: height 30mm, greater than the slab thickness by 25mm; width 600mm; thickness 25mm. During installation, the positioning mechanism is adjusted to ensure a 0.2mm gap on one side between the baffle and the slab in the width direction, guaranteeing a tight fit and restricting lateral flow.

[0072] The pre-cooled slab is fed into the rolling mill via a conveyor roller conveyor equipped with a liquid nitrogen spraying device. The spraying flow rate is 4 L / min to keep the slab surface cooled. The linear speed of the upper work roll is set to 1.2 m / s, the linear speed of the lower work roll is set to 1.0 m / s, the linear speed ratio is 1.2, and the single-pass reduction is 80%, that is, the slab is rolled from 25 mm thick to 5 mm thick.

[0073] During the rolling process, the combined shear strain field drastically refines the grains inside the slab. The temperature of the slab at the roll gap is monitored by thermocouples and consistently maintained below -155℃, ensuring that the deformation heat is carried away in a timely manner. Due to the large reduction, the rolling force of the mill is adjusted to 1500kN to ensure that the slab can be smoothly bitten in and rolled. The rolling time is 15s, and there are no phenomena such as roll jamming or slab cracking.

[0074] Post-rolling cryogenic retention and low-temperature stabilization treatment:

[0075] After rolling, the sheet material is immediately transferred to a liquid nitrogen incubator filled with liquid nitrogen, completely immersing the sheet material in the nitrogen for 30 minutes. The temperature of the sheet material is monitored by a temperature sensor and maintained at -196℃. After 30 minutes, the sheet material is removed and placed in a low-temperature constant temperature chamber with an initial temperature set at -40℃. The temperature control system is activated, and the temperature is slowly increased to room temperature at a rate of 5℃ / min. The heating process lasts for approximately 23 hours, during which the heating rate is monitored in real time to ensure that it does not exceed the set value.

[0076] Subsequent finishing and processing:

[0077] The plate material, heated to room temperature, was leveled using a 13-roll leveler at a speed of 0.4 m / min. After three rounds of leveling, the flatness error of the plate material was ≤0.08 mm / m. Subsequently, the plate material was cut using a laser cutting machine to obtain a target blank with a thickness of 5 mm, a width of 350 mm, and a length of 590 mm, with a cutting accuracy of ±0.5 mm.

[0078] The target blank undergoes surface treatment. First, it is ground with an abrasive wheel at a speed of 25 m / s and a feed rate of 0.008 mm / r to achieve a surface roughness of Ra ≤ 1.2 μm. Then, it is precision polished using diamond polishing paste with a particle size of 0.3 μm at a polishing speed of 0.8 m / min, ultimately achieving a surface roughness of Ra ≤ 0.6 μm. After cleaning and drying, the finished ultra-high purity aluminum sputtering target is obtained.

[0079] In summary, this embodiment successfully prepared qualified ultra-high purity aluminum sputtering targets. Testing revealed that the average grain size of the finished product was 90 nm, with random grain orientation and no preferred texture. Even under conditions of prolonged homogenization, prolonged precooling, high pressure, and upper limit heating rate, the process maintained good stability and operability. The prepared target material exhibited uniform microstructure and stable performance, demonstrating that the technical solution of this invention has a wide process window and can adapt to different production needs.

[0080] Example 3

[0081] like Figure 1 As shown in Figure 4, in this embodiment, the homogenization temperature is set to 600℃, the upper limit is 10h, the holding time is 10h, the lower limit is 30min, the lower limit is 30min, the upper limit is 2.0, the upper limit is 70% of the rolling reduction, the lower limit is 10min of liquid nitrogen after rolling, and the lower limit is 2℃ / min of low temperature stabilization heating rate, which further verifies the universality of the technical solution of the present invention.

[0082] In this embodiment, the detailed implementation process of the preparation method is as follows:

[0083] Billet preparation and homogenization:

[0084] A Φ300mm ultra-high purity aluminum ingot was selected and machined using a machining center at a cutting speed of 200m / min and a feed rate of 0.25mm / r to form a slab with a thickness of 18mm, a width of 280mm, and a length of 450mm. After machining, the surface oxide scale and machining marks were removed, and the slab was cleaned with acetone and then dried.

[0085] Place the slab into a vacuum annealing furnace and evacuate it to a vacuum level of ≤3×10. -The furnace temperature was increased to 600℃ at a rate of 8℃ / min, and held for 10 hours. During this period, the furnace temperature was monitored, and the temperature difference was controlled within ±8℃. Due to the high homogenization temperature and short holding time, over-burning of the slab was avoided by shortening the heating rate and strictly controlling the holding time. After the holding period, the slab was cooled to room temperature with the furnace, and then removed. The internal composition of the slab was found to be uniform with no obvious segregation.

[0086] Establishment of cryogenic environment and pre-cooling of billet:

[0087] Prepare a liquid nitrogen immersion tank with a volume of 0.8 m³. Place the slab on the support inside the tank and inject liquid nitrogen at a rate of 8 L / min until the slab is completely submerged. Insert a thermocouple into the core of the slab and connect it to a data logger. Set the pre-cooling time to 30 min. Due to the relatively thin slab thickness of 18 mm, heat transfer is rapid. After 30 min, the data logger shows that the core temperature of the slab stabilizes at -160℃, meeting the pre-cooling requirements. Pre-cooling is complete.

[0088] Single-pass deep cryogenic shear rolling:

[0089] The mill was debugged. The work roll diameter was 280mm. The internal cooling channels of the upper and lower work rolls consisted of six Φ8mm through holes. Liquid nitrogen was introduced at a flow rate of 4L / min for 20 minutes to reduce the roll surface temperature to below -150℃. Lateral restraint devices were installed. The baffles were made of W18Cr4V high-speed steel with a hardness of HRC60-62. The baffles were 22mm high, 18mm thicker than the slab thickness, 450mm wide, and 18mm thick. After installation, the clearance on one side was 0.4mm.

[0090] The pre-cooled slab was fed into the rolling mill via a conveyor roller conveyor. During the conveying process, liquid nitrogen was sprayed at a flow rate of 2 L / min to maintain the slab temperature. The linear speed of the upper work roll was set to 2.0 m / s, the linear speed of the lower work roll to 1.0 m / s, the linear speed ratio to be 2.0, and the single-pass reduction to be 70%, meaning the slab thickness was rolled from 18 mm to 5.4 mm. During the rolling process, due to the high linear speed ratio, the dominant shear strain was significant. Combined with the additional shear strain from lateral constraints, a strong composite shear strain field was formed, rapidly refining the grains. Infrared thermometer monitoring showed that the slab temperature remained below -152℃ during the rolling process, with a rolling time of 8 seconds, successfully completing the rolling operation.

[0091] Post-rolling cryogenic retention and low-temperature stabilization treatment:

[0092] After rolling, the sheet is immediately placed in a liquid nitrogen tank and held for 10 minutes, with the temperature stabilized at -196℃. After 10 minutes, the sheet is removed and placed in a low-temperature constant temperature chamber with an initial temperature set at -30℃. The temperature is then slowly increased to room temperature at a rate of 2℃ / min for approximately 32 hours to ensure that stress is fully released and the grain structure is stable.

[0093] Subsequent finishing and processing:

[0094] The sheet metal was leveled using a 9-roll leveler at a speed of 0.6 m / min, resulting in a flatness error ≤0.1 mm / m. The sheet metal was then cut using a plasma cutter to obtain a target blank with a thickness of 5.4 mm, a width of 280 mm, and a length of 440 mm. The target blank was then surface-ground at a speed of 35 m / s and a feed rate of 0.01 mm / r, achieving a surface roughness Ra ≤1.5 μm. Following this, polishing was performed using alumina polishing paste with a particle size of 0.4 μm, resulting in a surface roughness Ra ≤0.7 μm. After cleaning and drying, the finished ultra-high purity aluminum sputtering target was obtained.

[0095] In summary, this embodiment successfully prepared an ultra-high purity aluminum sputtering target. Testing revealed that the average grain size of the finished product was 150 nm, with a highly randomized grain orientation. Even under conditions of high-temperature short-time homogenization, short-time pre-cooling, high-speed ratio, and low heating rate, effective grain refinement and randomized orientation could still be achieved. The process flow was stable and reliable, further demonstrating the universality and feasibility of the technical solution of this invention, and providing technical support for target preparation under different production conditions.

[0096] Comparative Example

[0097] like Figure 4 As shown, this comparative example uses the existing multi-pass rolling process, without employing a cryogenic environment, lateral restraint device, or asynchronous rolling. Instead, it refines the grains solely through room temperature multi-pass rolling to demonstrate the advantages of the present invention.

[0098] In this comparative example, the detailed implementation process of the preparation method is as follows:

[0099] Billet preparation and homogenization:

[0100] Ultra-high purity aluminum ingots with the same purity of 99.999% as in Example 1 were selected and processed into slabs with the same dimensions as in Example 1: 20mm thick, 300mm wide, and 500mm long. The slabs were placed in a vacuum annealing furnace and held at 500℃ for 24 hours. The homogenization process was the same as in Example 1 to ensure that the basic conditions of the slabs were the same.

[0101] Multi-pass room temperature rolling:

[0102] After homogenization, the slab is cooled to room temperature in the furnace and then rolled in multiple passes at room temperature (25°C). The rolling mill used is a conventional twin-roll mill with no internal cooling channels for the upper and lower work rolls. The linear speed ratio is 1.0, and no lateral restraint device is installed at the roll gap entrance of the mill.

[0103] The total reduction was set at 75% (consistent with Example 1), and rolling was completed in three passes. The first pass reduced the slab by 30%, from 20mm to 14mm; the second pass reduced the slab by 30%, from 14mm to 9.8mm; and the third pass reduced the slab by 21.4%, from 9.8mm to 7.7mm. After each pass, the slab was air-cooled to room temperature before the next pass to avoid grain growth caused by rolling heat. During the rolling process, the rolling force of the mill was adjusted to ensure smooth slab entry and rolling.

[0104] Post-rolling processing and finishing:

[0105] After rolling, the plate was naturally cooled to room temperature, and then leveled, cut and surface-processed. The finishing process was completely consistent with that in Example 1, and a comparative sample of ultra-high purity aluminum sputtering target was obtained.

[0106] In summary, this comparative example employs a multi-pass room temperature synchronous rolling process from existing technologies, without utilizing the cryogenic environment, lateral constraint device, and asynchronous rolling technology of this invention. Testing revealed that the average grain size of the comparative sample was 120 μm, significantly larger than the 50-200 nm of the embodiments of this invention, and the grain orientation exhibited a distinct rolling texture, indicating a preferred orientation. Furthermore, the comparative example involved numerous rolling passes, resulting in a complex process flow and production efficiency only about 40% of that of Example 1. The comparison clearly demonstrates that the technical solution of this invention can achieve extreme grain refinement and orientation randomization in a single-pass process, significantly outperforming existing technologies and offering advantages such as shorter process flow, higher efficiency, and better product performance.

[0107] The simplified table of core information for the examples and comparative examples is as follows:

[0108] To clearly demonstrate the process and effect differences between the embodiments of the present invention and the comparative examples, the following table summarizes the core process parameters, key equipment features, and finished product structure features of each case for easy and intuitive comparison.

[0109] Case types Homogenization temperature / time Pre-cooling time Roll linear speed ratio Rolling reduction Post-rolling cryogenic holding time Low temperature stabilization heating rate Key equipment characteristics Finished grain size Grain orientation distribution Example 1 500℃ / 24h 1h 1.5 75% 20min 3℃ / min Cryogenic environment, lateral restraint device, asynchronous rolling, internal cooling of rolls 120nm Highly random Example 2 450℃ / 48h 2h 1.2 80% 30min 5℃ / min Cryogenic environment, lateral restraint device, asynchronous rolling, internal cooling of rolls 90nm Highly random Example 3 600℃ / 10h 30min 2.0 70% 10min 2℃ / min Cryogenic environment, lateral restraint device, asynchronous rolling, internal cooling of rolls 150nm Highly random Comparative Example 500℃ / 24h none 1.0 75% (3 passes) none None (natural cooling at room temperature) Room temperature environment, no lateral constraints, synchronous rolling, and no internal cooling of the rolls. 120μm Clearly preferential texture

[0110] In summary, as shown in the table above, although the process parameters differ in the three embodiments of the present invention, they all achieve an ultrafine grain structure of 50-200 nm after a single-pass rolling process through the synergistic effect of cryogenic environment, lateral constraint device, asynchronous rolling, and internal cooling of the rolls. Furthermore, the grain orientation is highly random, meeting the requirements for high-end sputtering targets. In contrast, the comparative embodiment, using existing multi-pass room temperature synchronous rolling technology, lacks the core equipment features of the present invention, resulting in a finished product grain size much larger than that of the embodiments of the present invention, and exhibiting a significant preferred texture. This comparison fully verifies the innovation and superiority of the technical solution of the present invention. By constructing a composite strong shear strain field, it achieves simultaneous grain refinement and orientation randomization within a single pass, simplifying the process flow, improving production efficiency, and ensuring product performance. This provides an efficient and reliable technical approach for the preparation of ultra-high purity aluminum sputtering targets.

[0111] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for refining grains by high-strain low-temperature rolling for preparing ultra-high purity aluminum sputtering targets, characterized in that, This includes the following steps: Step 1, Billet Preparation and Homogenization: The ultra-high purity aluminum ingot is machined to obtain a slab, which is then subjected to high-temperature homogenization treatment; Step 2, Cryogenic Environment Establishment and Billet Pre-cooling: The billet is placed in a liquid nitrogen environment for pre-cooling, so that the overall temperature of the billet drops to below -150°C; Step 3, Single-pass cryogenic shear rolling: The pre-cooled slab is fed into a rolling mill for single-pass rolling under continuous cooling in a liquid nitrogen atmosphere or by liquid nitrogen spray. There is a linear velocity difference between the upper and lower work rolls of the rolling mill, with a speed ratio ranging from 1.2 to 2.

0. A lateral restraint device is installed at the roll gap entrance of the rolling mill. This lateral restraint device is closely fitted to both sides of the slab in the width direction to restrict the width direction flow of the slab during rolling. The reduction in this single-pass rolling is 70% to 85%. Step 4, Post-rolling cryogenic holding and low-temperature stabilization treatment: After a single rolling pass is completed, the rolled plate is immediately immersed in liquid nitrogen for 10 to 30 minutes, and then slowly warmed up to room temperature in a low-temperature environment of -50°C to 0°C. Step 5, Subsequent finishing and processing: The treated sheet material is leveled, cut and surface-processed to obtain the finished ultra-high purity aluminum sputtering target material.

2. The method for refining grains by high-strain low-temperature rolling for preparing ultra-high purity aluminum targets according to claim 1, characterized in that, In step one, the purity of the ultra-high purity aluminum is not less than 99.999%. The high-temperature homogenization treatment is carried out at a temperature of 450°C to 600°C, with a holding time of 10 hours to 48 hours, and the treatment atmosphere is a vacuum or a high-purity inert gas protective atmosphere.

3. The method for refining grains by high-strain low-temperature rolling for preparing ultra-high purity aluminum targets according to claim 1, characterized in that, In step two, the pre-cooling time is 30 minutes to 2 hours to ensure that the core temperature of the slab is stable below -150°C.

4. The method for refining grains by high-strain low-temperature rolling for preparing ultra-high purity aluminum targets according to claim 1, characterized in that, In step three, the lateral restraint device is a high-strength alloy baffle fixedly installed on the mill stand. The gap between the high-strength alloy baffle and the slab width direction on one side is less than 0.5 mm, and the height of the baffle is not less than the thickness of the slab before rolling.

5. The method for refining grains by high-strain low-temperature rolling for preparing ultra-high purity aluminum targets according to claim 1, characterized in that, In step three, both the upper and lower work rolls of the rolling mill are equipped with internal cooling channels. Liquid nitrogen or ultra-low temperature cooling media are continuously introduced into these internal cooling channels during the rolling process to maintain the surface temperature of the work rolls at an ultra-low temperature.

6. The method for refining grains by high-strain low-temperature rolling for preparing ultra-high purity aluminum targets according to claim 1, characterized in that, In step three, the single-pass rolling process creates a dynamically changing composite shear strain field inside the slab. This composite shear strain field is composed of the dominant shear strain generated by asynchronous rolling and the additional multi-directional shear strain generated by lateral constraints.

7. The method for refining grains by high-strain low-temperature rolling for preparing ultra-high purity aluminum targets according to claim 1, characterized in that, In step four, the rate of temperature rise to room temperature should not exceed 5°C / min.

8. The method for refining grains by high-strain low-temperature rolling for preparing ultra-high purity aluminum targets according to claim 1, characterized in that, Through the single-pass deep cryogenic shear rolling and subsequent processing, the finished ultra-high purity aluminum sputtering target material forms an equiaxed ultrafine grain structure with an average grain size between 50nm and 200nm, and the grain orientation is highly randomized.

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