A 6-series aluminum alloy sheet with high stamping performance and its processing technology

Abstract

This invention discloses a 6-series aluminum alloy sheet with high stamping performance and its processing technology, belonging to the field of aluminum alloy material technology. The aluminum alloy, by mass percentage, comprises the following raw material components: Si 0.4–0.9 wt%, Mg 0.4–0.8 wt%, Cu 0.01–0.25 wt%, Mn ≤0.06 wt%, Cr ≤0.03 wt%, Zn ≤0.03 wt%, Ti ≤0.05 wt%, Fe ≤0.10 wt%, with the remainder being Al and unavoidable impurities. This invention, by adjusting the content of each element in the aluminum alloy and subjecting the aluminum alloy ingot containing the above components to homogenization, extrusion, quenching, aging, and stamping treatments, enables the 6-series aluminum alloy profile to possess high strength and formability, making it suitable for the stamping of aluminum alloy back plates.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy material technology, specifically relating to a 6-series aluminum alloy sheet with high stamping performance and its processing technology, which is particularly suitable for the manufacture of electronic product casings (such as tablet and laptop casings), and can achieve a balance between low cost, high strength and excellent anodized appearance. Background Technology

[0002] Aluminum alloys are widely used in the manufacture of electronic product casings (such as tablets and laptops) due to their lightweight nature and excellent anodized appearance. There are two main manufacturing methods for electronic product casings:

[0003] 1) 5xxx series aluminum alloys Electronic product casings are typically made from 5052 / 5252 alloys and their modified alloys through stamping. However, 5052 / 5252 alloys have lower mechanical properties (yield strength 180MPa) and a darker color after anodizing (compared to 6063 aluminum alloy). Using higher-strength / alloyed 5-series aluminum alloys to manufacture casings results in reduced stamping performance (prone to cracking, high internal stress requiring annealing leading to decreased mechanical properties) and a poorer anodized appearance (high Mg content causes a darker anodized color; and more pronounced surface texture, requiring sandblasting for masking). 2) 6xxx series aluminum alloys Electronic product casings are typically manufactured using 6063 aluminum alloy with full CNC machining. 6063 has excellent anodizing properties and high mechanical properties (yield strength 230 MPa), making it the preferred material for electronic product casings. However, 6063 aluminum alloy has poor stamping performance, and the full CNC manufacturing method is costly, which does not meet the current industry's need for cost reduction.

[0004] Therefore, it is necessary to develop a stampable 6-series aluminum alloy to meet the requirements of low cost, high strength, and high anodized appearance for electronic product casings. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a 6-series aluminum alloy sheet material with high stamping performance and its processing technology. Through composition optimization and processing technology optimization, the material simultaneously possesses excellent stamping performance, high mechanical properties, and superior anodized appearance, meeting the manufacturing requirements of low cost, high strength, and easy processing for electronic product casings.

[0006] The objective of this invention is achieved through the following technical solution: A 6-series aluminum alloy sheet with high stamping performance comprises the following raw material components by mass percentage: Si 0.4-0.9 wt%, Mg 0.4-0.8 wt%, Cu 0.01-0.25 wt%, Mn ≤0.06 wt%, Cr ≤0.03 wt%, Zn ≤0.03 wt%, Ti ≤0.05 wt%, Fe ≤0.10 wt%, with the remainder being Al and unavoidable impurities.

[0007] Furthermore, the Si content - Mg content ≥ 0.05~0.15wt%.

[0008] Furthermore, the thickness of the 6-series aluminum alloy sheet is 0.8–1.6 mm.

[0009] The processing technology for the aforementioned high stamping performance 6-series aluminum alloy sheet includes the following steps: Raw materials are weighed according to the mass percentage of each element in the aluminum alloy and then smelted and cast to obtain ingots. The ingots with the above-mentioned components are homogenized and held at 560-580℃ for 8-24 hours, and then cooled to room temperature at 5-15℃ / h. The homogenized material is extruded, with the extrusion bar temperature controlled at 480–550℃, the extrusion bar speed at 0.6–1.5 mm / s, and the extrusion outlet temperature controlled at 420–480℃. The extruded material is quenched using a 0.1-0.5% salt water mist cooling method. Aging treatment: immediately after quenching, age at 80–120℃ for 30 min–8 h; After aging treatment and cooling to room temperature, the aged material is stamped at a stamping speed of 0.3–0.8 mm / s, with a punch radius of 2–5 mm, a die radius of 3–6 mm, and a stamping gap of 8–12% of the material thickness.

[0010] Furthermore, after aging treatment, the volume fraction of atomic clusters in the 6-series aluminum alloy sheet is 0.03–0.10%.

[0011] Furthermore, before the stamping process, the aged material is degreased by soaking it in a 5-8 wt% sodium carbonate solution at 40-50°C for 5-8 minutes.

[0012] Si and Mg are the main alloying elements in 6-series aluminum alloys. They can form the strengthening phase Mg₂Si, which is crucial for ensuring the material's mechanical strength. To ensure high yield strength, the Si and Mg contents must be controlled. However, high alloying leads to increased deformation resistance and decreased stamping performance. Mg also negatively impacts stamping performance, while Si improves work hardening, thus enhancing stamping performance. However, excessive Si can cause the material to appear grayish and dull after sandblasting and anodizing, affecting its appearance. Therefore, this invention controls the Si content at 0.4–0.9 wt% and the Mg content at 0.4–0.8 wt%, achieving a balance between strength, stamping performance, and anodizing properties. Specifically, limiting the Si content to ≥ Mg content + 0.05–0.15 wt% further enhances work hardening and optimizes stamping performance.

[0013] Cu can improve the work hardening ability of materials, which is beneficial to improving stamping performance. However, Cu has an adverse effect on the corrosion resistance and surface brightness after anodizing. Excessive Cu content can lead to darkening and discoloration of the anodized surface. Therefore, this invention limits the Cu content to 0.01-0.25 wt% to minimize the negative impact on corrosion resistance and anodized appearance while improving stamping performance.

[0014] Mn, Cr, Zn, and Fe are the limiting elements. While Mn and Cr can control grain size, excessive addition can easily form fibrous crystals, leading to discoloration after anodizing and affecting appearance consistency. Zn has no beneficial effect on the material's mechanical properties, stamping performance, or anodizing performance, and therefore needs to be strictly limited. Fe is an unavoidable impurity in the raw materials; excessive Fe can cause discoloration and mottling after anodizing, reducing appearance quality. Therefore, this invention limits Mn ≤ 0.06 wt%, Cr ≤ 0.03 wt%, Zn ≤ 0.03 wt%, and Fe ≤ 0.10 wt% to ensure stable appearance quality and overall performance of the material.

[0015] Ti primarily plays a role in controlling the grain size in the as-cast state, preventing excessively large ingot grains from affecting subsequent processing performance. However, excessively high Ti content can lead to "black line" defects after anodizing, affecting the appearance. Therefore, Ti content is limited to ≤0.05 wt%. By holding the ingot at 560–580℃ for 8–24 hours (stirring every 4 hours at a speed of 20 r / min for 5 minutes each time), the coarse second phase in the ingot can be fully dissolved, eliminating component segregation and homogenizing the microstructure. Subsequently, cooling to room temperature at a slow cooling rate of 5–15℃ / h will precipitate fine and uniform soluble second phase in the microstructure, providing a good microstructure basis for subsequent extrusion molding and aging treatment, and avoiding stress concentration and cracking problems caused by uneven microstructure during stamping. By controlling the extrusion bar temperature to 480–550℃, the extrusion bar speed to 0.6–1.5 mm / s, and the extrusion outlet temperature to 420–480℃, the material can be formed in a suitable plastic state, avoiding excessive temperature leading to grain growth and excessive temperature leading to increased deformation resistance. At the same time, it ensures the shape accuracy and microstructure uniformity of the extruded parts, providing good base material properties for subsequent stamping. Cooling is achieved using a 0.1%–0.5% salt water mist, with the water mist pressure controlled at 0.2–0.5 MPa. The distance between the water mist nozzle and the material surface is 150–250 mm, and the cooling time is 3–8 minutes, ensuring rapid cooling of the material to below 150°C. Compared to traditional water-cooling, this method offers moderate cooling intensity, ensuring rapid material cooling, fixing the supersaturation of solute and vacancies to give the material high plasticity, which is beneficial for stamping. It also effectively controls the material's planar clearance, reduces quenching deformation and internal stress, and avoids crack formation. Compared to high-concentration salt water quenching, it significantly reduces residual stress and improves the material's dimensional stability.

[0016] Immediately after quenching, the material undergoes an aging treatment at 80–120℃ for 30 min–8 h, with nitrogen gas used for protection during the aging process. After aging, it is cooled to room temperature at a rate of 20–30℃ / h. This process forms fine atomic clusters with a volume fraction of 0.03–0.10% in the material microstructure. These atomic clusters do not significantly increase the yield strength of the material, ensuring that the material has low strength and high plasticity before stamping, facilitating stamping. After stamping, the atomic clusters can further grow into a strengthening phase through subsequent natural aging, significantly improving the mechanical strength of the material and meeting the requirements for electronic product casings. This aging process design achieves the dual requirements of "easy processing before stamping and high strength after stamping," solving the problem of traditional 6-series aluminum alloys struggling to balance strength and formability.

[0017] After aging treatment and cooling to room temperature, the aluminum alloy sheet is stamped. The stamping temperature is controlled at room temperature to avoid excessively high or low temperatures affecting stamping performance. The stamping speed is controlled at 0.3–0.8 mm / s to ensure smooth material deformation and reduce stress concentration. The fillet radius of the stamping punch is 2–5 mm, and the fillet radius of the die is 3–6 mm to avoid sharp corners causing material cracking. The stamping clearance is controlled at 8–12% of the material thickness to ensure dimensional accuracy and surface quality of the stamped parts. Before stamping, the material surface needs to be degreased using a 5–8 wt% sodium carbonate solution, soaked at 40–50°C for 5–8 minutes to remove surface oil and impurities, preventing defects such as scratches, jamming, and cracking during stamping. After stamping, a prototype of the electronic product casing is obtained, which can be further surface treated such as anodizing as required.

[0018] This invention optimizes the composition and processing technology of 6-series aluminum alloys, enabling the material to achieve high formability while maintaining high strength, thus having broad market application prospects. Detailed Implementation

[0019] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0020] Example 1 The raw material composition of 6-series aluminum alloy sheet, by mass percentage, includes: Si: 0.45wt%, Mg: 0.4wt%, Cu: 0.01wt%, Mn: 0.02wt%, Cr: 0.01wt%, Zn: 0.01wt%, Ti: 0.02wt%, Fe: 0.05wt%, with the remainder being Al and unavoidable impurities; Weigh the raw materials according to the above composition, put them into a graphite crucible melting furnace, control the melting temperature at 720℃, introduce argon gas for protection (argon gas flow rate 0.3L / min), stir at 30r / min for 15min, let the melt stand for 10min (standing temperature 710℃), and then cast it using a semi-continuous casting method at a casting speed of 80mm / min, a casting temperature of 690℃, and a cooling water flow of 15m³ / h to obtain an ingot. The ingots with the above composition were homogenized, and then kept at 560℃ for 24 hours, and then cooled to room temperature at 5℃ / h. The homogenized material is extruded with an extrusion bar temperature of 480℃, an extrusion bar speed of 0.6mm / s, and an extrusion outlet temperature of 420℃. The extruded material was quenched using a 0.1% salt water mist cooling system with a water mist pressure of 0.2 MPa, a water mist nozzle distance of 150 mm from the material surface, and a cooling time of 3 minutes, cooling to below 145°C. Aging treatment: immediately after quenching, age at 80℃ for 8 hours. After aging, cool to room temperature at 20℃ / h to obtain a 6-series aluminum alloy sheet with a thickness of 0.8mm. After aging and cooling to room temperature, the sheet metal is stamped. The stamping temperature is room temperature, the stamping speed is 0.3 mm / s, the radius of the punch corner is 2 mm, the radius of the die corner is 3 mm, and the stamping gap is 8% of the material thickness. Before stamping, the sheet metal is soaked in a 5 wt% sodium carbonate solution (40℃) for 5 minutes to remove surface oil. After stamping, the prototype of the electronic product shell is obtained.

[0021] According to the test results, in this embodiment, the volume fraction of atomic clusters in the 6-series aluminum alloy sheet after aging is 0.03%, the yield strength is 230MPa, the stamping performance is qualified (main strain ε1=0.32), the color is uniform and the brightness is good after anodizing, and there are no defects such as material marks or discoloration. The surface roughness Ra=0.6μm, which can meet the stamping manufacturing requirements of electronic product shells.

[0022] Example 2 The 6-series aluminum alloy sheet, by weight percentage, comprises: Si: 0.65wt%, Mg: 0.55wt%, Cu: 0.13wt%, Mn: 0.04wt%, Cr: 0.02wt%, Zn: 0.02wt%, Ti: 0.03wt%, Fe: 0.08wt%, with the remainder being Al and unavoidable impurities; the sheet thickness is 1.2mm.

[0023] Weigh the raw materials according to the above composition, put them into a graphite crucible melting furnace, control the melting temperature at 740℃, introduce argon gas for protection (argon gas flow rate 0.5L / min), stir at 40r / min for 20min, let the melt stand for 15min (standing temperature 720℃), and then cast it using a semi-continuous casting method at a casting speed of 100mm / min, a casting temperature of 700℃, and a cooling water flow rate of 20m³ / h to obtain an ingot. The ingots with the above composition were homogenized, and then kept at 570℃ for 16 hours, and then cooled to room temperature at 10℃ / h. The homogenized material is extruded with an extrusion bar temperature of 515℃, an extrusion bar speed of 1.0 mm / s, and an extrusion outlet temperature of 450℃. The extruded material was quenched using a 0.3% salt water mist cooling system with a water mist pressure of 0.35 MPa, a water mist nozzle distance of 200 mm from the material surface, and a cooling time of 5 min, cooling to below 135℃. Aging treatment: immediately after quenching, the aluminum alloy is aged at 100℃ for 4 hours. After aging, it is cooled to room temperature at 25℃ / h to obtain a 6-series aluminum alloy sheet with a thickness of 1.2mm. After aging and cooling to room temperature, the sheet metal is stamped. The stamping temperature is room temperature, the stamping speed is 0.5 mm / s, the punch radius is 3.5 mm, the die radius is 4.5 mm, and the stamping gap is 10% of the material thickness. Before stamping, the sheet metal is soaked in a 6.5 wt% sodium carbonate solution (45℃) for 6.5 min for degreasing to remove surface oil. After stamping, the prototype of the electronic product casing is obtained.

[0024] According to the test results, in this embodiment, the volume fraction of atomic clusters in the 6-series aluminum alloy sheet after aging is 0.06%, the yield strength is 250MPa, the stamping performance is excellent (main strain ε1=0.38), the color is uniform and the brightness is high after anodizing, there are no appearance defects, and the surface roughness Ra=0.5μm, which can meet the stamping manufacturing requirements of electronic product shells.

[0025] Example 3 The raw material composition of 6-series aluminum alloy sheet, by mass percentage, includes: Si: 0.9wt%, Mg: 0.8wt%, Cu: 0.25wt%, Mn: 0.06wt%, Cr: 0.03wt%, Zn: 0.03wt%, Ti: 0.05wt%, Fe: 0.10wt%, with the remainder being Al and unavoidable impurities; Weigh the raw materials according to the above composition, put them into a graphite crucible melting furnace, control the melting temperature at 760℃, introduce argon gas for protection (argon gas flow rate 0.8L / min), stir at 50r / min for 25min, let the melt stand for 20min (standing temperature 730℃), and then cast it using a semi-continuous casting method at a casting speed of 120mm / min, a casting temperature of 710℃, and a cooling water flow rate of 25m³ / h to obtain an ingot. The ingots with the above composition were homogenized, and then kept at 580℃ for 8 hours, and then cooled to room temperature at 15℃ / h. The homogenized material is extruded with an extrusion bar temperature of 550℃, an extrusion bar speed of 1.5mm / s, and an extrusion outlet temperature of 480℃. The extruded material is quenched using a 0.5% brine solution for mist cooling; Aging treatment: immediately after quenching, the aluminum alloy is aged at 120℃ for 30 minutes. After aging, it is cooled to room temperature at 30℃ / h to obtain a 6-series aluminum alloy sheet with a thickness of 1.6mm. After aging and cooling to room temperature, the sheet metal is stamped. The stamping temperature is room temperature, the stamping speed is 0.8 mm / s, the radius of the punch corner is 5 mm, the radius of the die corner is 6 mm, and the stamping gap is 12% of the material thickness. Before stamping, the sheet metal is soaked in an 8 wt% sodium carbonate solution (50℃) for 8 minutes to remove surface oil. After stamping, the prototype of the electronic product shell is obtained.

[0026] According to the test results, in this embodiment, the volume fraction of atomic clusters in the 6-series aluminum alloy sheet after aging is 0.10%, the yield strength is 260MPa, the stamping performance is qualified (main strain ε1=0.31), the color is uniform after anodizing, and there are no defects such as material marks, discoloration, or black lines. The surface roughness Ra=0.7μm, which can meet the stamping manufacturing requirements of electronic product shells.

[0027] Comparative Example 1 (Conventional 5052 Aluminum Alloy) The material is made of conventional 5052 aluminum alloy. By mass percentage, its raw material composition includes: Mg: 2.5wt%, Cr: 0.15wt%, Fe: 0.25wt%, with the remainder being Al and unavoidable impurities. The processing technology adopts the conventional stamping process for 5052 aluminum alloy, specifically: Melting and casting: The material is placed in a graphite crucible melting furnace at a melting temperature of 710–730℃ without argon protection. The stirring speed is 25–35 r / min, the stirring time is 10–15 min, and the melt is allowed to stand for 8–12 min (standing temperature 700–720℃). The semi-continuous casting speed is 70–90 mm / min, the casting temperature is 680–700℃, and the cooling water flow rate is 12–18 m³ / h. Homogenization process: Hold at 480-500℃ for 12-18 hours, then allow to cool naturally to room temperature (cooling rate approximately 25-35℃ / h), without intermediate stirring steps; Cold rolling: Cold rolling temperature is room temperature, rolling speed is 1.0~1.8mm / s, and the thickness after rolling is 0.8~1.6mm; Annealing treatment: Hold at 300-320℃ for 2-3 hours, then cool naturally to room temperature to release internal stress from cold rolling; Surface treatment before stamping: coarse sandblasting (sand particle size 80-100 mesh) to remove surface texture.

[0028] Tests showed that the comparative material had a yield strength of 180 MPa and passed stamping performance tests. However, after anodizing, the color was dark and there were obvious material marks, which needed to be covered with coarse sand. The appearance quality was poor and the mechanical properties were insufficient.

[0029] Comparative Example 2 (Conventional 6063 Aluminum Alloy) It uses conventional 6063 aluminum alloy, and its raw material composition by mass percentage includes: Si: 0.6wt%, Mg: 0.3wt%, with the remainder being Al and unavoidable impurities; Its processing technology is as follows: Melting and casting: graphite crucible melting furnace, melting temperature 720~740℃, argon flow rate 0.2~0.4L / min, stirring speed 30~40r / min, stirring time 15~20min, melt settling time 10~15min (settling temperature 710~720℃), semi-continuous casting speed 90~110mm / min, casting temperature 690~700℃, cooling water flow rate 18~22m³ / h; Homogenization process: Hold at 520-540℃ for 10-16 hours, cool at a rate of 10-15℃ / h, without intermediate stirring steps; Extrusion molding: Extrusion bar temperature 460~490℃, extrusion bar speed 0.8~1.2mm / s, extrusion outlet temperature 390~420℃, and thick slabs are obtained after extrusion; 5. Artificial aging: Hold at 520-540℃ for 1-2 hours, then cool with water (cooling rate ≥100℃ / min) to room temperature; 6. Artificial aging: Hold at 170-180℃ for 8-10 hours, then cool naturally to room temperature. Full CNC machining: CNC milling machine is used for machining at a speed of 8000-10000 r / min and a feed rate of 1500-2000 mm / min. The machine is gradually milled to remove excess material and obtain the outline and details of the electronic product casing.

[0030] Testing revealed that the comparative material has a yield strength of 230 MPa and an excellent anodized appearance, but its stamping performance is extremely poor (main strain ε1=0.18), making it impossible to stamp and requiring full CNC machining, which results in high manufacturing costs.

[0031] Comparative Example 3 The 6-series aluminum alloy, by mass percentage, comprises the following raw material components: Si: 1.0 wt%, Mg: 0.9 wt%, Cu: 0.3 wt%, Mn: 0.08 wt%, with the remainder being Al and unavoidable impurities; the processing technology is the same as in Example 2 of this invention.

[0032] Testing revealed that the comparative material had a volume fraction of 0.12% atomic clusters after aging and a yield strength of 270 MPa. However, it exhibited poor stamping performance (main strain ε1=0.25), and its color turned grayish and dark after anodizing, with discoloration defects, failing to meet the requirements for electronic product casings.

[0033] As can be seen from the comparison of the above embodiments and comparative examples, the 6-series aluminum alloy sheet material and its processing technology of the present invention can effectively solve the technical defects of existing 5-series and 6-series aluminum alloys, and achieve a comprehensive balance of high stamping performance, high strength and excellent anodized appearance. Moreover, the processing cost is low, the process is stable, and it is suitable for mass production, with extremely high practical value and market promotion prospects.

[0034] Based on the disclosure in the foregoing specification, those skilled in the art can make appropriate changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A 6000-series aluminum alloy sheet having high draw formability, characterized by: By mass percentage, it includes the following raw material components: Si 0.4–0.9 wt%, Mg 0.4–0.8 wt%, Cu 0.01–0.25 wt%, Mn ≤0.06 wt%, Cr ≤0.03 wt%, Zn ≤0.03 wt%, Ti ≤0.05 wt%, Fe ≤0.10 wt%, with the remainder being Al and unavoidable impurities.

2. The high-stretch formability 6-series aluminum alloy sheet of claim 1, wherein: Si content - Mg content ≥ 0.05~0.15wt%.

3. The high-stretch formability 6-series aluminum alloy sheet of claim 1, wherein: The thickness of the 6-series aluminum alloy sheet is 0.8–1.6 mm.

4. A process for working a high-stretch formability 6-series aluminum alloy sheet according to claim 1, 2 or 3, characterized in that: Includes the following steps: Raw materials are weighed according to the mass percentage of each element in the aluminum alloy and then smelted and cast to obtain ingots. The ingots with the above-mentioned components are homogenized and held at 560-580℃ for 8-24 hours, and then cooled to room temperature at 5-15℃ / h. The homogenized material is extruded, with the extrusion bar temperature controlled at 480–550℃, the extrusion bar speed at 0.6–1.5 mm / s, and the extrusion outlet temperature controlled at 420–480℃. The extruded material is quenched using a 0.1-0.5% salt water mist cooling method. Aging treatment: immediately after quenching, age at 80–120℃ for 30 min–8 h; After aging treatment and cooling to room temperature, the aged material is stamped at a stamping speed of 0.3–0.8 mm / s, with a punch radius of 2–5 mm, a die radius of 3–6 mm, and a stamping gap of 8–12% of the material thickness.

5. The processing technology for 6-series aluminum alloy sheets with high stamping performance according to claim 4, characterized in that: After aging treatment, the volume fraction of atomic clusters in the 6-series aluminum alloy sheet is 0.03–0.10%.

6. The processing technology for 6-series aluminum alloy sheets with high stamping performance according to claim 4, characterized in that: Before the stamping process, the aged material is degreased by immersing it in a 5-8 wt% sodium carbonate solution at 40-50°C for 5-8 minutes.