Method for controlling grain structure of 6000-series aluminum alloy wire for rivets

Abstract

This invention relates to a method for controlling the grain structure of 6000 series aluminum alloy wire for rivets, belonging to the field of aluminum alloy processing technology. The purpose of this invention is to solve the problems of coarse, uneven, and difficult-to-control grain structure in 6000 series aluminum alloy wire for rivets. The method involves hot rolling a 6000 series aluminum alloy ingot that has undergone high-temperature homogenization treatment, followed by multiple cold drawing deformations without any heat treatment. After cold drawing with 70%~90% deformation to meet the dimensional tolerance requirements of the finished wire, it is then subjected to low-temperature annealing at 260℃~360℃ to obtain 6000 series aluminum alloy wire suitable for rivet upsetting. This invention improves the yield of 6000 series aluminum alloy wire upsetting, and the prepared rivets, nuts, bolts, pins, and other fasteners can be used in high-speed rail, luxury cars, light passenger vehicles, and even heavy-duty trucks, supporting the urgent needs of the transportation lightweighting field.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy processing technology, specifically relating to a method for controlling the grain structure of 6000 series aluminum alloy wire for rivets. Background Technology

[0002] Under the dual pressures of the global energy crisis and environmental protection, lightweighting in transportation has become an inevitable trend for high-quality development in sectors such as automobiles and high-speed rail. It not only effectively reduces fuel consumption and emissions but is also a core pathway for the transportation industry to achieve energy conservation and emission reduction, and to fulfill its "dual-carbon" goals. The overall plan for automotive development explicitly emphasizes that "lightweighting is of paramount importance," elevating it to a key national strategy and providing direction for the research and application of related lightweight materials and processing technologies.

[0003] Among numerous lightweight materials, aluminum and aluminum alloys have become the preferred materials in the current transportation lightweighting field due to their outstanding characteristics such as low density, high specific strength, excellent corrosion resistance, good processability and formability, and strong recyclability. Their applications now cover many key components such as automobile bodies, wheels, and fasteners. According to relevant research data, 60% of the fuel consumed by automobiles is due to the vehicle's own weight. For every 10% reduction in vehicle weight, fuel consumption can be reduced by 10% to 15%. Aluminum alloys have a density only one-third that of steel and a specific strength superior to some alloy steels. They can significantly reduce the weight of transportation equipment while ensuring the structural strength of components. Therefore, their application in high-end transportation equipment is increasing year by year.

[0004] With the accelerating pace of automotive lightweighting, market demand for mid-to-high-end aluminum alloy fasteners has reached new heights. This is especially true in high-end models such as new energy vehicles and luxury sedans, where aluminum alloy rivets and bolts, as key connecting components, directly impact the vehicle's structural stability, safety, and lightweighting effectiveness. However, the development of China's automotive fastener industry is currently lagging far behind the overall automotive industry, exhibiting an imbalance of "overcapacity in low-end products and insufficient supply in high-end products." The long-term reliance on imports for high-end aluminum alloy fasteners not only increases production costs for downstream enterprises but also hinders the independent advancement of my country's automotive lightweighting strategy. Against this backdrop, at a critical juncture in the fastener industry's transition from high-speed growth to high-quality growth, breaking through the core technological barriers of high-end aluminum alloy fasteners and achieving product upgrades has become an urgent need for industry development, bringing new opportunities and challenges to the research and development of related material processing technologies.

[0005] 6000 series aluminum alloys belong to the Al-Mg-Si series of heat-treatable alloys, possessing multiple advantages such as moderate strength, excellent formability, strong corrosion resistance, good weldability, and easy coloring. They are widely used in transportation, construction, sports, and other fields, and have received particular attention in the automotive lightweighting sector, making them a key research material for automotive body panels, wheels, and other components. Currently, 6000 series aluminum alloys are widely used in the manufacture of wheels for high-speed trains, luxury cars, light passenger vehicles, and even heavy-duty trucks. Simultaneously, considering the requirements for corrosion protection and assembly compatibility, their application in automotive structural connections is gradually expanding, and they are beginning to be used in the production of aluminum alloy nuts, bolts, pin sleeves, and various custom-machined fasteners, becoming a key supporting material for automotive lightweighting. Among these, 6000 series aluminum alloy wire serves as the core blank for manufacturing aluminum alloy rivets; its quality directly determines the mechanical properties, surface quality, and service reliability of the rivets, and is of great significance for the localization of high-end aluminum alloy fasteners.

[0006] However, in actual production, 6000 series aluminum alloy wire for rivets is more prone to structural defects such as coarse grains, coarse grain rings, and uneven grain distribution compared to other series of aluminum alloy wires. These defects are also difficult to control, severely restricting its application in high-end rivet manufacturing. A deeper analysis reveals that, as an Al-Mg-Si alloy, the grain refinement of 6000 series aluminum alloys mainly relies on the effects of Cr and a small amount of Mn. These elements form dispersed phases such as AlCrFeSi, which inhibit grain growth. However, due to the limited quantity and moderate thermal stability of these dispersed phases, these trace elements cannot fully exert their "strong pinning" effect on grain boundaries, resulting in weak resistance to recrystallization and grain growth in 6000 series aluminum alloy wire. During wire preparation and subsequent processing, once exposed to high temperatures, the dispersed phases in the alloy are prone to coarsening, losing their pinning effect on grain boundaries. With weakened grain boundary constraint, grains grow rapidly, forming coarse-grained structures.

[0007] The defects of coarse and uneven grain distribution can seriously affect the performance and subsequent processing quality of 6000 series aluminum alloy wire used for rivets. On the one hand, coarse grains lead to poor uniformity of wire structure and fluctuations in mechanical properties. During rivet manufacturing, when the wire is subjected to plastic deformation such as upsetting and stamping, it is prone to cracking due to stress concentration, significantly reducing the yield of rivets. On the other hand, after rivet upsetting, coarse grains can cause surface quality problems such as pitting and unevenness on the rivet surface, which cannot meet the stringent requirements of high-end automotive fasteners for surface precision and assembly performance, ultimately rendering aluminum alloy rivets, bolts, and other fasteners unusable. In addition, existing methods for controlling the grain structure of 6000 series aluminum alloy wire often suffer from complex processes, unstable control effects, and poor adaptability, making it difficult to effectively solve the core pain points of coarse, uneven, and difficult-to-control grains in 6000 series aluminum alloy wire used for rivets, and failing to meet the needs of large-scale production of high-end aluminum alloy rivets.

[0008] In summary, with the deepening of the transportation lightweighting strategy and the increasingly urgent demand for the localization of high-end aluminum alloy fasteners, it is of great practical significance and industrial application value to develop a control method that can effectively solve the problems of coarse, uneven and difficult-to-control grain structure of 6000 series aluminum alloy wire for rivets, improve the uniformity of wire structure, enhance the quality and performance of wire and subsequent rivet products, break through the technical bottleneck of high-end aluminum alloy fasteners, and promote the product upgrading of the fastener industry. Summary of the Invention

[0009] The purpose of this invention is to solve the problems of coarse, uneven, and difficult-to-control grain structure of 6000 series aluminum alloy wire for rivets, and to provide a method for controlling the grain structure of 6000 series aluminum alloy wire for rivets.

[0010] The method for controlling the grain structure of 6000 series aluminum alloy wire for rivets according to the present invention is carried out according to the following steps:

[0011] 1. The 6000 series aluminum alloy ingot is machined and hot-rolled to obtain hot-rolled wire rod billets;

[0012] 2. Cold draw the hot-rolled wire rod billet until it meets the dimensional tolerance requirements of the finished wire rod.

[0013] 3. After cold drawing, the wire is annealed in a furnace to obtain 6000 series aluminum alloy wire that can be used for rivet upsetting.

[0014] The beneficial effects of this invention are:

[0015] 1. This invention develops a method for controlling the grain structure of 6000 series aluminum alloy wire. During homogenization annealing at 500℃~550℃, it prevents compositional segregation and coarse second-phase residue, causing dispersed fine MgSi2 particles to pin the grain boundaries and hinder excessive grain growth. By avoiding any intermediate annealing before and during cold drawing of the hot-rolled wire blank, it prevents prolonged high-temperature atomic diffusion, accelerated grain boundary migration, and grain engulfment leading to exponential grain size growth. Alternating hot rolling with flat and vertical rolls and Y-rolls gradually refines the ingot by subjecting it to alternating forces in different directions, preventing the formation of coarse grain rings due to surface friction energy storage. Furthermore, 20-30 passes of deformation achieve over 95% deformation, further refining the grains. Finally, 3-5 cold deformation passes, with the cold deformation amount controlled at 70%~90%, generate a large number of dislocations within the grains, significantly increasing energy storage and dramatically increasing the recrystallization nucleation rate, further refining the grains. To prevent the uncontrolled and excessive growth of grains in the 6000 series aluminum alloy rivet wire during manufacturing, which could lead to a rough surface finish after rivet upsetting and affect user experience.

[0016] 2. This invention develops a method for controlling the grain structure of 6000 series aluminum alloy wire.

[0017] This invention develops a method for controlling the grain structure of 6000 series aluminum alloy wire, which can achieve fine and uniform grain structure control. During rivet upsetting, the fine grains allow dislocation (slip) to be activated simultaneously in multiple grains during deformation, without having to squeeze into a few grains to support the structure. This results in more dispersed and easier deformation. The fine and uniform grains also disperse stress, allowing the entire structure to deform together, reducing the risk of localized fracture. This invention also results in less anisotropy in the microstructure and better overall plasticity and ductility. In contrast, 6000 series aluminum alloy wire prepared by conventional methods is prone to problems such as coarse grains and coarse grain rings. Coarse and uneven grains are prone to localized stress concentration, with a few grains deforming and cracking first. Therefore, when users use aluminum alloy wire for rivet upsetting, cracking is likely to occur, especially when the cold upsetting deformation is large due to the differences in rivet shape, the cracking rate will increase significantly. The high-end 6000 aluminum alloy fasteners prepared generally have certain requirements for the aluminum alloy nail type. The upsetting deformation is large, which puts forward higher requirements for the grain structure of aluminum alloy wire. The grain size of this invention can reach as fine as 20~30μm, which is the choice of fastener wire for the automotive, high-speed rail and other transportation fields, supporting the urgent need in the field of high-quality wire.

[0018] This invention is applicable to high-end 6000 series aluminum alloy wires with diameters of φ1.6mm~φ20mm used for annealed rivets that require high-quality grain structure. Attached Figure Description

[0019] Figure 1 Photograph of the grain structure of 6061 wire prepared in Example 1;

[0020] Figure 2 Photograph of the grain structure of standard 6061 wire;

[0021] Figure 3 A photograph of the 6061 wire prepared in Example 1. Detailed Implementation

[0022] Specific Implementation Method 1: This implementation method for controlling the grain structure of 6000 series aluminum alloy wire for rivets specifically follows these steps:

[0023] 1. The 6000 series aluminum alloy ingot is machined and hot-rolled to obtain hot-rolled wire rod billets;

[0024] 2. Cold draw the hot-rolled wire rod billet until it meets the dimensional tolerance requirements of the finished wire rod.

[0025] 3. After cold drawing, the wire is annealed in a furnace to obtain 6000 series aluminum alloy wire that can be used for rivet upsetting.

[0026] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the 6000 series aluminum alloy ingot mentioned in step one is a homogenized annealed ingot. Everything else is the same as in Specific Implementation Method One.

[0027] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 2 in that the homogenized annealed ingot is subjected to homogenization annealing treatment at 500℃~550℃. Everything else is the same as in Specific Implementation Method 2.

[0028] 6000 series aluminum alloy ingots are prone to compositional segregation and coarse second phases. This temperature range allows for sufficient diffusion of components within the ingot, eliminating compositional segregation and promoting the uniform precipitation of fine MgSi2 dispersed phases. MgSi2 dispersed phases, acting as "grain boundary pinning particles," firmly anchor grain boundaries, hindering grain boundary migration and suppressing grain growth from the source. This prevents the formation of coarse grains during the ingot casting stage and provides a uniform microstructure basis for subsequent grain refinement.

[0029] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method Three in that: after homogenization annealing, it is directly hot-rolled in a single, uniform rolling process to a diameter of 13.8mm. Everything else is the same as in Specific Implementation Method Three.

[0030] Hot rolling is performed directly after homogenization annealing, which avoids the coarsening of the dispersed phase caused by the ingot cooling and then heating. This ensures the fine size and uniform distribution of MgSi2 particles, which continue to play a pinning role. At the same time, the metal undergoes plastic deformation during hot rolling, and the grains break under stress, providing a large number of nucleation sites for recrystallization, thus initially achieving grain refinement.

[0031] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that the hot rolling process involves 18 to 30 hot deformation passes to achieve a deformation rate of over 95%. Everything else is the same as in Specific Implementation Method Four.

[0032] In this embodiment, alternating hot rolling with flat and vertical rolls and Y-shaped rolls is used to subject the ingot to alternating forces in multiple directions. This avoids the concentration of surface friction energy caused by deformation in one direction, thereby effectively eliminating the "coarse grain ring" defect. The cumulative deformation amount in multiple passes reaches more than 95%, which can repeatedly break the grains inside the ingot, forming a large number of fine deformed grains. At the same time, the large deformation amount will generate a large number of dislocations in the grains, accumulating a high amount of deformation energy, providing sufficient energy for recrystallization nucleation in the subsequent cold drawing and annealing processes, further refining the grains. Moreover, multi-directional deformation can promote the growth of grains towards the equiaxed grain direction, avoiding the non-uniform structure caused by preferential grain orientation.

[0033] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method One in that no intermediate annealing is performed on the hot-rolled wire rod billet before and during cold drawing in step two. Everything else is the same as in Specific Implementation Method One.

[0034] Intermediate annealing exposes the wire to a high-temperature environment, leading to increased atomic diffusion and accelerated grain boundary migration. This causes the originally fine grains to undergo "grain engulfment," resulting in exponential grain size growth and negating the initial grain refinement effect. This implementation method prevents prolonged high-temperature operation from causing increased atomic diffusion, accelerated grain boundary migration, and grain engulfment that leads to exponential grain size growth.

[0035] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method One in that the cold drawing in step two involves 3 to 5 cold deformations, with the cold deformation amount controlled at 70% to 90%. Everything else is the same as in Specific Implementation Method One.

[0036] Multiple cold drawing processes subject the wire to continuous plastic deformation, further increasing the intragranular dislocation density and significantly enhancing deformation energy storage. This substantially improves the recrystallization nucleation rate during subsequent annealing (nucleation rate is positively correlated with deformation energy storage). Simultaneously, cold deformation can break the preferred orientation of grains, promoting further transformation of grains towards equiaxed grains, improving the uniformity of the microstructure, and laying the foundation for ultimately obtaining fine and uniform equiaxed grains.

[0037] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method One in that the annealing temperature in step three is 260℃~360℃, and the holding time is 1 hour. Everything else is the same as in Specific Implementation Method One.

[0038] This embodiment prevents grains from growing wildly due to high temperatures, while obtaining recrystallized grains above the recrystallization temperature point, resulting in fine and uniform grains that are easy to form during cold heading and riveting.

[0039] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method One in that the 6000 series aluminum alloy wire suitable for rivet upsetting has equiaxed grains. Everything else is the same as in Specific Implementation Method One.

[0040] In this embodiment, the equiaxed grains are symmetrical in shape, resulting in uniform properties in all directions. During deformation, the slip system is easy to activate, the stress distribution is uniform, and it is easier to plastically deform and less prone to cracking.

[0041] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that the grain level index of the 6000 series aluminum alloy wire suitable for rivet upsetting is ≥4. Everything else is the same as in Specific Implementation Method Nine.

[0042] In this embodiment, the 6000 series aluminum alloy wires available for rivet upsetting should have fine grains with a grain level index ≥ 4. Fine grains and numerous grain boundaries can hinder dislocation movement, preventing dislocations from accumulating in one place and causing stress concentration, resulting in more uniform deformation, improved plasticity, and easier cold upsetting.

[0043] The beneficial effects of the present invention are verified using the following embodiments:

[0044] Example 1: A method for controlling the grain structure of 6000 series aluminum alloy wire for rivets is specifically carried out according to the following steps:

[0045] 1. The 6000 series aluminum alloy ingot is machined and then homogenized at a high temperature of 500~550℃ for 16 hours to obtain fine MgSi2 particles pinning the grain boundaries. After homogenization annealing, it is directly hot rolled in one piece and then hot rolled to a specification of 13.8mm through 18 passes of hot rolling deformation.

[0046] Second, four cold drawing deformation processes are then performed to successively draw the 13.8mm 6061 aluminum alloy wire to specifications of 12.56mm, 11.13mm, 9.6mm, and 8.6mm, thus obtaining 6061 cold-drawn wire.

[0047] Third, the cold-drawn wire is annealed at a temperature of 260℃~360℃ for 1 hour to obtain a recrystallized structure with fine and uniform grains, resulting in 6000 series aluminum alloy wire suitable for rivet upsetting. In this embodiment, the 6061 wire has a tensile strength ≤155MPa and an elongation ≥25MPa.

[0048] In this embodiment, the 6061 wire showed no coarse crystal rings under low magnification, with a grain level index of 5 and a core-surface grain level index difference of 1, indicating good uniformity, which is beneficial for rivet upsetting.

[0049] In this embodiment, the rivets were prepared using 6000 series aluminum alloy wire, as shown in the physical example. Figure 3 As shown, the grain structure is as follows Figure 1 As shown, this high-end 6000 series aluminum alloy wire with a diameter of φ1.6mm~φ20mm is suitable for annealed rivets with high requirements for grain structure. It has great application potential and is the choice for fastener wire in the automotive, high-speed rail and other transportation fields, supporting the urgent demand in the field of high-quality wire.

Claims

1. A method for controlling the grain structure of 6000 series aluminum alloy wire for rivets, characterized in that... The specific steps for controlling the grain structure of 6000 series aluminum alloy wire used for rivets are as follows:

1. The 6000 series aluminum alloy ingot is machined and hot-rolled to obtain hot-rolled wire rod billets; 2. Cold draw the hot-rolled wire rod billet until it meets the dimensional tolerance requirements of the finished wire rod.

3. After cold drawing, the wire is annealed in a furnace to obtain 6000 series aluminum alloy wire that can be used for rivet upsetting.

2. The method for controlling the grain structure of 6000 series aluminum alloy wire for rivets according to claim 1, characterized in that... The 6000 series aluminum alloy ingot mentioned in step one is a homogenized annealed ingot.

3. The method for controlling the grain structure of 6000 series aluminum alloy wire for rivets according to claim 2, characterized in that... The homogenized annealed ingot is subjected to homogenization annealing treatment at 500℃~550℃.

4. The method for controlling the grain structure of 6000 series aluminum alloy wire for rivets according to claim 3, characterized in that... After homogenization annealing, the material is directly hot-rolled to a 13.8mm diameter using a uniform rolling process.

5. The method for controlling the grain structure of 6000 series aluminum alloy wire for rivets according to claim 4, characterized in that... The hot rolling process achieves a deformation rate of over 95% through 18 to 30 hot deformation passes.

6. The method for controlling the grain structure of 6000 series aluminum alloy wire for rivets according to claim 1, characterized in that... In step two, no intermediate annealing is performed on the hot-rolled wire rod billet before and during cold drawing.

7. The method for controlling the grain structure of 6000 series aluminum alloy wire for rivets according to claim 1, characterized in that... The cold drawing described in step two involves 3 to 5 cold deformations, with the cold deformation amount controlled at 70% to 90%.

8. The method for controlling the grain structure of 6000 series aluminum alloy wire for rivets according to claim 1, characterized in that... The annealing temperature in step three is 260℃~360℃, and the holding time is 1 hour.

9. The method for controlling the grain structure of 6000 series aluminum alloy wire for rivets according to claim 1, characterized in that... The grain structure of the 6000 series aluminum alloy ingot mentioned in step one is equiaxed grains.

10. A method for controlling the grain structure of 6000 series aluminum alloy wire for rivets according to claim 9, characterized in that... The grain level index of the 6000 series aluminum alloy ingot mentioned in step one is ≥4.

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