A method of producing a 6xxx series aluminium alloy

Abstract

The application discloses a preparation method of a 6xxx series aluminum alloy, and the whole section of the extruded bar can be in a completely fine-grained state by reducing the addition of Cr elements and Mn elements and combining a high-temperature and high-speed extrusion process, so that the demand of a cold forging process on the quality of raw materials can be met, and the extrusion production efficiency can be greatly improved, and the method has the advantages of economic, effective and industrialized production. In addition, by optimizing a three-stage solid solution treatment, quenching treatment and three-stage aging treatment process, the morphology characteristics of intracrystalline and grain boundary precipitated phases can be effectively controlled, the effect of improving the intergranular corrosion resistance of the aluminum alloy is achieved, meanwhile, the intracrystalline precipitated phases of the aluminum alloy are in a fine and dispersed distribution, and the grain boundary precipitated phases are in an intermittent distribution, so that the mechanical properties of the aluminum alloy are effectively improved.

Description

Technical Field

[0001] The present invention relates to a method for preparing an aluminum alloy, and in particular to a method for preparing a 6xxx series aluminum alloy. Background Art

[0002] Aluminum alloys are widely used in bicycle manufacturing due to their high specific strength, excellent hot and cold working properties, weldability, and corrosion resistance. Early bicycles primarily used medium-strength aluminum alloys such as 6063 and 6061 for frames, wheels, and handlebars. Seamless tubing was predominantly used to ensure safety during use. With advancements in hot extrusion die technology, seamless tubing has gradually been replaced by seamed tubing to reduce production costs. In recent years, an increasing number of medium-, high-, and high-strength aluminum alloys, such as 6013, 6066, 6069, 7003, and 7075, have been widely used to meet market demand for lightweighting. At the same time, forging has been adopted instead of machining to improve component physical properties, reduce raw material loss during the manufacturing process, and ultimately increase service life and reduce production costs. However, forging, especially cold forging, places high demands on the raw material's microstructure and properties. The material often requires both a fine-grained structure and an annealed state to prevent surface peeling and cracking during the cold forging process. This paper takes 6061 aluminum alloy as the object, focusing on the influence of alloy composition, hot extrusion temperature and hot extrusion speed on the microstructure of extruded bars. It shows the influence of different microstructures of bars on the quality of hub components after cold forging, in order to provide data support for reducing production costs and improving the application of 6xxx alloys in automobiles. Summary of the Invention

[0003] Based on this, in order to solve the problem in the prior art that extrusion processing parameters have a significant impact on the properties of aluminum alloys, the present invention provides a method for preparing 6xxx series aluminum alloys, and the specific technical solution is as follows:

[0004] A method for preparing a 6xxx series aluminum alloy, wherein the 6xxx series aluminum alloy comprises Si, Fe, Cu, Mn, Mg, Cr, Zn, Ti, and Al elements, wherein the mass percentage of Si is 0.55% to 0.65%; the mass percentage of Fe is 0.11% to 0.15%; the mass percentage of Cu is 0.15% to 0.18%; the mass percentage of Mn is 0.01% to 0.05%; the mass percentage of Mg is 0.85% to 0.90%; the mass percentage of Cr is 0.05% to 0.07%; the mass percentage of Zn is 0.01%; the mass percentage of Ti is 0.02%; the remainder is Al;

[0005] The preparation method comprises the following steps:

[0006] Step S1: preparing the aluminum alloy according to the composition ratio of Si, Fe, Cu, Mn, Mg, Cr, Zn, Ti and Al elements;

[0007] Step S2: smelting the ingredients and performing slag removal during the smelting process;

[0008] Step S3: Casting process, in which online degassing and deslagging are performed throughout the casting process;

[0009] Step S4: After the casting is completed, the ingot is transferred to a homogenizing furnace for uniform post-treatment, and then the ingot is quickly transferred to a cooling chamber for rapid cooling to room temperature, and then extruded by an extruder. At the outlet of the extruder, the extruded rod is cooled by online water cooling so that the rod is quickly cooled to less than 50°C within 2 minutes to obtain a rod;

[0010] Step S5: subjecting the rod to three-stage solution treatment, quenching treatment, three-stage aging treatment, alkali washing, water washing, and pickling to obtain a 6xxx series aluminum alloy;

[0011] The temperature of the extrusion treatment is 515° C. to 525° C., and the speed of the extrusion treatment is 10 m / min to 18 m / min.

[0012] Furthermore, the smelting treatment is carried out at a temperature of 760° C. to 810° C. and for a time of 1 hour to 3 hours.

[0013] Furthermore, the casting process speed is 40 mm / min to 50 mm / min, the cooling water flow rate is 1000 L / min to 1500 L / min, and the cooling water temperature is ≤35°C.

[0014] Furthermore, the homogenization treatment is carried out at a temperature of 520° C. to 550° C. for 5 to 6 hours.

[0015] Furthermore, the temperature of the extrusion process is 520° C., and the speed of the extrusion process is 15 m / min.

[0016] Furthermore, the three-stage solution treatment is: solution treating the rod at 400°C to 420°C for 10h to 12h, then solution treating at 450°C to 510°C for 5h to 8h, and finally solution treating at 520°C to 550°C for 1h to 5h.

[0017] Furthermore, the quenching treatment is: quenching the rod after the three-stage solid solution treatment using water with a pressure of 5KPa to 10KPa for 50s to 150s.

[0018] Furthermore, the three-stage aging treatment includes a first aging treatment, a second aging treatment, and a third aging treatment. In the first aging treatment, the quenched bar is transferred to a preheated aging furnace, and a high-frequency electromagnetic wave generator is installed in the aging furnace. The temperature of the first aging treatment is 120°C to 150°C, and the time is 1h to 2h; the temperature of the second aging treatment is 155°C to 160°C, and the time is 2.5h to 3h; the temperature of the third aging treatment is 100°C to 120°C, and the time is 1h to 3h.

[0019] Furthermore, the first aging treatment adjusts the frequency of the electromagnetic wave to 150KHz-220KHz; the second aging treatment adjusts the frequency of the electromagnetic wave to 120KHz-150KHz; and the third aging treatment adjusts the frequency of the electromagnetic wave to 100KHz-120KHz.

[0020] The above scheme can significantly improve the comprehensive mechanical properties of 6xxx aluminum alloy by optimizing the composition of 6xxx aluminum alloy and the parameters of the extrusion process. Specifically, the addition of Cr and Mn elements combined with the high-temperature and high-speed extrusion process can make the entire cross-section of the extruded bar completely fine-grained, which can meet the requirements of the cold forging process for the quality of raw materials. At the same time, it can also greatly improve the extrusion production efficiency, with the advantages of economic and effective industrial production. In addition, by optimizing the three-stage solution treatment, quenching treatment, and three-stage aging treatment process, the morphology characteristics of the intragranular and grain boundary precipitation phases can be effectively regulated to achieve the effect of improving the intergranular corrosion resistance of the aluminum alloy. At the same time, the precipitation phases within the aluminum alloy crystals are finely dispersed and the precipitation phases at the grain boundaries are discontinuously distributed, thereby effectively improving the mechanical properties of the aluminum alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the grain structure of the 6xxx series aluminum alloy prepared in Example 1, Example 2 and Comparative Example 2, and Figure 1 a and d are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Example 1; Figure 1 b and e are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Example 2; Figure 1 Figures c and f are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Comparative Example 2;

[0022] Figure 2 is a schematic diagram of the grain structure of the 6xxx series aluminum alloy of Comparative Examples 4 to 6, and Figure 2 a and b are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Comparative Example 4; Figure 2 b and e are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Comparative Example 5; Figure 2Figures c and f are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Comparative Example 6;

[0023] Figure 3 Schematic diagram of the grain structure of the 6xxx series aluminum alloys of 7-8 and Example 3, and Figure 3 a and d are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Comparative Example 7; Figure 3 b and e are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Comparative Example 8; Figure 3 c and f are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Example 3;

[0024] Figure 4 Schematic diagram of the forging quality of the 6xxx series aluminum alloy prepared in Example 3;

[0025] Figure 5 Schematic diagram of the forging quality of the 6xxx series aluminum alloy prepared in Comparative Example 9;

[0026] Figure 6 Schematic diagram of the forging quality of the 6xxx series aluminum alloy prepared in comparative example 10. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with its embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not limit the scope of protection of the present invention.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0029] In one embodiment of the present invention, a method for preparing a 6xxx series aluminum alloy is provided, wherein the 6xxx series aluminum alloy includes Si, Fe, Cu, Mn, Mg, Cr, Zn, Ti, and Al elements, wherein the mass percentage of Si is 0.55% to 0.65%; the mass percentage of Fe is 0.11% to 0.15%; the mass percentage of Cu is 0.15% to 0.18%; the mass percentage of Mn is 0.01% to 0.05%; the mass percentage of Mg is 0.85% to 0.90%; the mass percentage of Cr is 0.05% to 0.07%; the mass percentage of Zn is 0.01%; the mass percentage of Ti is 0.02%; the remainder is Al;

[0030] The preparation method comprises the following steps:

[0031] Step S1: preparing the aluminum alloy according to the composition ratio of Si, Fe, Cu, Mn, Mg, Cr, Zn, Ti and Al elements;

[0032] Step S2: smelting the ingredients and performing slag removal during the smelting process;

[0033] Step S3: Casting process, in which online degassing and deslagging are performed throughout the casting process;

[0034] Step S4: After the casting is completed, the ingot is transferred to a homogenizing furnace for uniform post-treatment, and then the ingot is quickly transferred to a cooling chamber for rapid cooling to room temperature, and then extruded by an extruder. At the outlet of the extruder, the extruded rod is cooled by online water cooling so that the rod is quickly cooled to less than 50°C within 2 minutes to obtain a rod;

[0035] Step S5: subjecting the rod to three-stage solution treatment, quenching treatment, three-stage aging treatment, alkali washing, water washing, and pickling to obtain a 6xxx series aluminum alloy;

[0036] The temperature of the extrusion treatment is 515° C. to 525° C., and the speed of the extrusion treatment is 10 m / min to 18 m / min.

[0037] In one embodiment, the smelting treatment is carried out at a temperature of 760° C. to 810° C. and for a time of 1 hour to 3 hours.

[0038] In one embodiment, the casting process speed is 40 mm / min to 50 mm / min, the cooling water flow rate is 1000 L / min to 1500 L / min, and the cooling water temperature is ≤35°C.

[0039] In one embodiment, the homogenization treatment is carried out at a temperature of 520° C. to 550° C. for 5 to 6 hours.

[0040] In one embodiment, the extrusion temperature is 520° C. and the extrusion speed is 15 m / min.

[0041] In one embodiment, the three-stage solution treatment is: solution treating the rod at 400℃~420℃ for 10h~12h, then solution treating at 450℃~510℃ for 5h~8h, and finally solution treating at 520℃~550℃ for 1h~5h.

[0042] In one embodiment, the quenching treatment is: quenching the rod after the three-stage solid solution treatment using water with a pressure of 5KPa to 10KPa for 50s to 150s.

[0043] In one embodiment, the three-stage aging treatment includes a first aging treatment, a second aging treatment, and a third aging treatment. The first aging treatment is to transfer the quenched bar to a preheated aging furnace, and a high-frequency electromagnetic wave generator is set in the aging furnace. The first aging treatment temperature is 120°C to 150°C, and the time is 1h to 2h; the second aging treatment temperature is 155°C to 160°C, and the time is 2.5h to 3h; the third aging treatment temperature is 100°C to 120°C, and the time is 1h to 3h.

[0044] In one embodiment, the first aging treatment adjusts the electromagnetic wave frequency to 150KHz-220KHz; the second aging treatment adjusts the electromagnetic wave frequency to 120KHz-150KHz; and the third aging treatment adjusts the electromagnetic wave frequency to 100KHz-120KHz.

[0045] The above scheme can significantly improve the comprehensive mechanical properties of 6xxx aluminum alloy by optimizing the composition of 6xxx aluminum alloy and the parameters of extrusion treatment. Specifically, this application can make the surface completely fine-grained by reducing the addition of Cr and Mn elements, and combining high-temperature and high-speed extrusion process, which can meet the requirements of cold forging process for raw material quality, and at the same time greatly improve the extrusion production efficiency, with the advantages of economic and effective industrial production. In addition, by optimizing the three-stage solution treatment, quenching treatment, and three-stage aging treatment process, the morphology characteristics of the intragranular and grain boundary precipitation phases can be effectively regulated to achieve the effect of improving the intergranular corrosion resistance of the aluminum alloy. At the same time, the precipitation phases within the aluminum alloy crystals are finely dispersed and the precipitation phases at the grain boundaries are discontinuously distributed, thereby effectively improving the mechanical properties of the aluminum alloy.

[0046] The embodiments of the present invention will be described in detail below with reference to specific examples.

[0047] Example 1:

[0048] A method for preparing a 6xxx aluminum alloy comprises the following steps:

[0049] Step S1: preparing the aluminum alloy according to the composition ratio of Si, Fe, Cu, Mn, Mg, Cr, Zn, Ti and Al elements;

[0050] Step S2: smelting the ingredients at 780°C for 3 hours, and performing slag removal during the smelting process;

[0051] Step S3: Casting process, wherein the entire casting process is subjected to online degassing and deslagging treatment, and the casting process speed is 40 mm / min, the cooling water flow rate is 1000 L / min, and the cooling water temperature is ≤35°C;

[0052] Step S4: After the casting is completed, the ingot is transferred to a homogenizing furnace for uniform post-treatment at 520°C for 5 hours, and then the ingot is quickly transferred to a cooling chamber for rapid cooling to room temperature, and then extruded by an extruder, and the extrusion temperature is 520°C, the extrusion speed is 15m / min, and the extruded rod is cooled by online water cooling at the outlet of the extruder so that the rod is quickly cooled to less than 50°C within 2 minutes to obtain a rod;

[0053] Step S5: subjecting the rod to a three-stage solution treatment, wherein the three-stage solution treatment comprises: subjecting the rod to a solution treatment at 400° C. for 10 hours, then to a solution treatment at 450° C. for 8 hours, and finally to a solution treatment at 520° C. for 5 hours; then subjecting the rod after the three-stage solution treatment to a quenching treatment for 150 seconds using water at a pressure of 5 kPa; and then subjecting the rod to a three-stage aging treatment, wherein the three-stage aging treatment comprises a first aging treatment, a second aging treatment, and a third aging treatment, wherein the first aging treatment transfers the quenched rod to a preheated aging furnace, and a high-frequency electromagnetic wave generator is provided in the aging furnace, wherein the first aging treatment temperature is 120° C., the electromagnetic wave frequency is 150 kHz, and the time is 1 hour; the second aging treatment temperature is 155° C., the electromagnetic wave frequency is 150 kHz, and the time is 3 hours; and the third aging treatment temperature is 100° C., the electromagnetic wave frequency is 120 kHz, and the time is 1 hour;

[0054] Step S6: The rods after the three-stage aging treatment are alkali washed, water washed, and pickled to obtain a 6xxx series aluminum alloy.

[0055] Example 2:

[0056] A method for preparing a 6xxx aluminum alloy comprises the following steps:

[0057] Step S1: preparing the aluminum alloy according to the composition ratio of Si, Fe, Cu, Mn, Mg, Cr, Zn, Ti and Al elements;

[0058] Step S2: smelting the ingredients at 760°C for 3 hours, and performing slag removal during the smelting process;

[0059] Step S3: Casting process, wherein online degassing and deslagging are performed throughout the casting process, and the casting process speed is 40 mm / min, the cooling water flow rate is 1500 L / min, and the cooling water temperature is ≤35°C;

[0060] Step S4: After the casting is completed, the ingot is transferred to a homogenizing furnace for uniform post-treatment at 550°C for 6 hours, and then the ingot is quickly transferred to a cooling chamber for rapid cooling to room temperature, and then extruded by an extruder, and the extrusion temperature is 520°C, the extrusion speed is 15m / min, and the extruded rod is cooled by online water cooling at the outlet of the extruder so that the rod is quickly cooled to less than 50°C within 2 minutes to obtain a rod;

[0061] Step S5: subjecting the rod to a three-stage solution treatment, wherein the three-stage solution treatment comprises: subjecting the rod to a solution treatment at 420° C. for 10 hours, then to a solution treatment at 450° C. for 5 hours, and finally to a solution treatment at 520° C. for 4 hours; then subjecting the rod after the three-stage solution treatment to a quenching treatment for 150 seconds using water at a pressure of 10 kPa; and then subjecting the rod to a three-stage aging treatment, wherein the three-stage aging treatment comprises a first aging treatment, a second aging treatment, and a third aging treatment, wherein the first aging treatment transfers the quenched rod to a preheated aging furnace, and a high-frequency electromagnetic wave generator is provided in the aging furnace, wherein the first aging treatment temperature is 150° C., the electromagnetic wave frequency is 220 kHz, and the time is 2 hours; the second aging treatment temperature is 160° C., the electromagnetic wave frequency is 150 kHz, and the time is 2.5 hours; and the third aging treatment temperature is 1120° C., the electromagnetic wave frequency is 120 kHz, and the time is 3 hours;

[0062] Step S6: The rods after the three-stage aging treatment are alkali washed, water washed, and pickled to obtain a 6xxx series aluminum alloy.

[0063] Example 3:

[0064] A method for preparing a 6xxx aluminum alloy comprises the following steps:

[0065] Step S1: preparing the aluminum alloy according to the composition ratio of Si, Fe, Cu, Mn, Mg, Cr, Zn, Ti and Al elements;

[0066] Step S2: smelting the ingredients at 800°C for 3 hours, and performing slag removal during the smelting process;

[0067] Step S3: Casting process, wherein the entire casting process is subjected to online degassing and deslagging treatment, and the casting process speed is 45 mm / min, the cooling water flow rate is 1200 L / min, and the cooling water temperature is ≤35°C;

[0068] Step S4: After the casting is completed, the ingot is transferred to a homogenizing furnace for homogenizing post-treatment at 540℃ for 6h, and then the ingot is rapidly transferred to a cooling chamber for rapid cooling to room temperature, and then the extrusion treatment is performed by an extruder, the temperature of the extrusion treatment is 520℃, the speed of the extrusion treatment is 15m / min, and the extruded rod is cooled to below 50℃ within 2min by online water cooling at the outlet of the extruder to obtain a rod;

[0069] Step S5: The rod is subjected to three-stage solid solution treatment, i.e., solid solution treatment at 420℃ for 11h, then solid solution treatment at 460℃ for 8h, and finally solid solution treatment at 540℃ for 4h, and then the rod after the three-stage solid solution treatment is quenched by water with a pressure of 8KPa for 100s, and then three-stage aging treatment is performed, which includes first aging treatment, second aging treatment and third aging treatment, the first aging treatment is to transfer the quenched rod to a preheated aging furnace, a high-frequency electromagnetic wave generating device is arranged in the aging furnace, the first aging treatment temperature is 135℃, the electromagnetic wave frequency is 220KHz, and the time is 2h, the second aging treatment temperature is 160℃, the electromagnetic wave frequency is 140KHz, and the time is 3h, and the third aging treatment temperature is 120℃, the electromagnetic wave frequency is 120KHz, and the time is 2h.

[0070] Step S6: After the three-stage aging treatment, the rod is subjected to alkali washing, water washing and acid washing to obtain a 6xxx series aluminum alloy.

[0071] The components and component proportions of Examples 1-3 are shown in Table 1.

[0072] Comparative Examples 1-3:

[0073] Comparative Examples 1-3 differ from Example 3 in that the components and component proportions are different, and the other aspects are the same as Example 3, the components and component proportions of Comparative Examples 1-3 are shown in Table 1.

[0074] Comparative Examples 4-6:

[0075] Comparative Examples 4-6 differ from Example 3 in that the process parameters of the extrusion treatment are different, the process parameters of the extrusion treatment of Comparative Examples 4-6 are shown in Table 2.

[0076] Comparative Examples 7-8:

[0077] Comparative Examples 7-8 differ from Example 3 in that the process parameters of the extrusion treatment are different, the process parameters of the extrusion treatment of Comparative Examples 7-8 are shown in Table 2.

[0078] Comparative Example 9:

[0079] The difference from Example 3 is the different preparation method. Other aspects are the same as Example 3. The preparation method of Comparative Example 9 comprises the following steps:

[0080] A method for preparing a 6xxx aluminum alloy comprises the following steps:

[0081] Step S1: preparing the aluminum alloy according to the composition ratio of Si, Fe, Cu, Mn, Mg, Cr, Zn, Ti and Al elements;

[0082] Step S2: smelting the ingredients at 800°C for 3 hours, and performing slag removal during the smelting process;

[0083] Step S3: Casting process, wherein the entire casting process is subjected to online degassing and deslagging treatment, and the casting process speed is 45 mm / min, the cooling water flow rate is 1200 L / min, and the cooling water temperature is ≤35°C;

[0084] Step S4: After the casting is completed, the ingot is transferred to a homogenizing furnace for uniform post-treatment at 540°C for 6 hours, and then the ingot is quickly transferred to a cooling chamber for rapid cooling to room temperature, and then extruded by an extruder, and the extrusion temperature is 520°C, the extrusion speed is 15m / min, and the extruded rod is cooled by online water cooling at the outlet of the extruder so that the rod is quickly cooled to less than 50°C within 2 minutes to obtain a rod;

[0085] Step S5: solution treating the rod at 420° C. for 15 h, and then aging treating the rod at 200° C. for 12 h;

[0086] Step S6: The aging-treated rod is subjected to alkali washing, water washing, and pickling to obtain a 6xxx series aluminum alloy.

[0087] Comparative Example 10:

[0088] The difference between Comparative Example 10 and Example 3 is that the preparation method of Comparative Example 10 includes the following steps, and the rest is the same as Example 3.

[0089] A method for preparing a 6xxx aluminum alloy comprises the following steps:

[0090] Step S1: preparing the aluminum alloy according to the composition ratio of Si, Fe, Cu, Mn, Mg, Cr, Zn, Ti and Al elements;

[0091] Step S2: smelting the ingredients at 800°C for 3 hours, and performing slag removal during the smelting process;

[0092] Step S3: Casting process, wherein the entire casting process is subjected to online degassing and deslagging treatment, and the casting process speed is 45 mm / min, the cooling water flow rate is 1200 L / min, and the cooling water temperature is ≤35°C;

[0093] Step S4: After the casting is completed, the ingot is transferred to a homogenizing furnace for uniform post-treatment at 400°C for 8 hours, and then the ingot is quickly transferred to a cooling chamber for rapid cooling to room temperature, and then extruded by an extruder, and the extrusion temperature is 520°C, the extrusion speed is 15m / min, and the extruded rod is cooled by online water cooling at the outlet of the extruder so that the rod is quickly cooled to less than 50°C within 2 minutes to obtain a rod;

[0094] Step S5: performing a solution treatment on the bar at 400° C. for 2 h, and then performing a cold forging treatment.

[0095] Table 1: Ingredients and ratios

[0096]

[0097]

[0098] Table 2: Process parameters of extrusion treatment

[0099]

[0100] The performance of the 6xxx aluminum alloys prepared in Examples 1 to 5 and the 6xxx aluminum alloys prepared in Comparative Examples 1 to 10 was analyzed. Specifically, the room temperature tensile strength, elongation, and high temperature tensile strength (350°C) were tested in accordance with national standards. The results are shown in Table 3 below.

[0101]

[0102]

[0103] From the data analysis in Table 3, it can be seen that the present application has a significant effect on the mechanical properties of the prepared 6xxx aluminum alloy by optimizing the composition and component ratio. When combined with the process parameters, a material with excellent mechanical properties can be obtained.

[0104] from Figures 1 to 3 Analysis shows that Figure 1 Schematic diagram of the grain structure of the 6xxx series aluminum alloy prepared in Example 1, Example 2 and Comparative Example 2, and Figure 1 a and d are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Example 1; Figure 1 b and e are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Example 2; Figure 1c and f in the figure are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Comparative Example 2; Figure 1 It can be seen from (a), (b), and (c) that with the increase of Cr and Mn element addition, the depth of the coarse grain ring of the extruded rod gradually decreases. Figure 1 (d), (e), and (f) further demonstrate the effects of different Cr and Mn element additions on the grain structure morphology. It can be seen from the figure that the coarse-grained layer of Example 1 is composed of irregularly shaped coarse grains, while the internal grain structure is a fibrous structure elongated along the extrusion direction. Compared with Example 1, the coarse-grained layer of Example 2 is composed of long, coarse grains along the extrusion direction, and the grain structure in the middle of the rod is still a fibrous structure consistent along the extrusion direction. At the same time, there is a fine-grained region between the surface coarse-grained layer and the core fiber crystals, and the grain size of this region is within 20 μm. For Comparative Example 2, which has the highest Cr and Mn content, no coarse-grained ring structure is formed on the surface of the rod under the extrusion process conditions. For Example 1, due to its low Cr and Mn addition, the small amount of CrAl7 and MnAl6 high-temperature phase particles formed in the matrix have limited pinning effect on dislocations, and the recrystallization occurring on the surface of the extruded rod grows rapidly, eventually forming a thicker coarse-grained layer. As for Example 2, due to the increase in the amount of Cr and Mn added, the inhibitory effect on the growth of grains after recrystallization is enhanced, the area on the surface of the extruded bar that meets the requirements of recrystallization growth is reduced, and at the same time, a fine-grained area is formed between the surface and the core where recrystallization occurs but cannot grow. For Comparative Example 2 in which Cr and Mn elements are further added, due to the presence of a large amount of CrAl7 and MnAl6 high-temperature phase particles in the matrix. Therefore, by adding a certain amount of Cr and Mn alloy elements, the surface of the bar after extrusion can be made free of coarse grain rings, which can meet the requirements of the bar cold forging process. However, the addition of a large amount of Cr and Mn elements not only increases the energy consumption during production, but also increases the cost of raw materials. Therefore, within the allowable range of the national standard composition of the alloy, as little Cr and Mn elements as possible are added.

[0105] Figure 2 is a schematic diagram of the grain structure of the 6xxx series aluminum alloy of Comparative Examples 4 to 6, and Figure 2 a and b are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Comparative Example 4; Figure 2 b and e are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Comparative Example 5; Figure 2Figures c and f are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Comparative Example 6; after the extrusion temperature is reduced from 480°C to 420°C, due to the reduction in the energy of the entire system, the area where the material recrystallization activation energy is reached is reduced, and the recrystallization process occurs only on the surface of the bar where severe friction occurs with the working surface of the die. The depth of the coarse grain ring of the bar is significantly improved, from the original 5.5mm to 1.3mm, but the grain size of the surface of the bar increases. Since the coarse grains have poor ductility and are prone to cracking on the surface of the product during cold forging, they are not conducive to the cold forging processing and forming of the material. When the extrusion temperature is increased from 480°C to 520°C, due to the increase in the energy of the entire system, more areas meet the conditions for the material to recrystallize. Therefore, the area where the recrystallization process occurs is expanded, and the depth of the coarse grain ring of the bar is increased, from the original 5.5mm to 8.2mm, but the grain size of the coarse grain ring area, especially the surface of the bar, is refined, which is conducive to the cold forging processing and forming of the material.

[0106] Figure 3 Schematic diagram of the grain structure of the 6xxx series aluminum alloys of 7-8 and Example 3, and Figure 3 a and d are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Comparative Example 7; Figure 3 b and e are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Comparative Example 8; Figure 3 c and f are schematic diagrams of the grain structure morphology of the 6xxx series aluminum alloy of Example 3; while the extrusion temperature is maintained at 520°C, the extrusion speed is greatly increased to 5m / min, 10m / min and 15m / min, respectively. The grain structure photos of the extruded bars are shown in FIG. Figure 3 As shown in the figure, as the extrusion speed increases, the recrystallization area inside the extruded rod gradually expands under various extrusion speed conditions. The recrystallization depth reaches 10mm under the extrusion speed of 5m / min, the recrystallization depth reaches 13mm under the extrusion speed of 10m / min, and the recrystallization process occurs throughout the entire cross-section of the extruded rod under the extrusion speed of 15m / min. Except for the coarse grain ring under the extrusion speed of 5m / min, the recrystallization area inside the rod under the conditions of 10m / min and 15m / min gradually expands, but its grain size has reached a fine-grained structure state, with an average grain size of about 300μm.

[0107] from Figures 4-6 analyze, Figure 4 Schematic diagram of the forging quality of the 6xxx series aluminum alloy prepared in Example 3; Figure 5 Schematic diagram of the forging quality of the 6xxx series aluminum alloy prepared in Comparative Example 9; Figure 6 Schematic diagram of the forging quality of the 6xxx series aluminum alloy prepared in Comparative Example 10. Figures 4-6It can be known from the analysis that the cold forging forming process of the state samples of Example 3, Comparative Example 9 and Comparative Example 10 can be successfully completed, the surface quality of the products after forging is best, and the requirements of the cold forging process on the internal organization quality of the raw material can be completely met; the surface of the product after forging of Comparative Example 9 is rough due to the coarse crystal layer on the surface, and the rough feeling is particularly obvious in the free deformation part; the surface layer of the finished product after forging of Comparative Example 10 has obvious crystal spots, and there is a phenomenon of delayed crystal cracking in some corner positions. Therefore, the 6xxx series aluminum alloy prepared in the application has excellent forging performance and has a wider application space.

[0108] The technical features of the above-described embodiments can be combined arbitrarily, and to make the description simple, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the description.

[0109] The above-described embodiments only express several implementation manners of the application, the description is more specific and detailed, but it should not be understood as the limitation of the patent scope of the application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made, which all belong to the protection scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims.

Claims

1. A method for preparing a 6xxx series aluminum alloy, characterized in that: The 6xxx series aluminum alloy includes Si, Fe, Cu, Mn, Mg, Cr, Zn, Ti and Al elements, wherein the mass percentage of Si is 0.55% to 0.65%; the mass percentage of Fe is 0.11% to 0.15%; the mass percentage of Cu is 0.15% to 0.18%; the mass percentage of Mn is 0.01% to 0.05%; the mass percentage of Mg is 0.85% to 0.90%; the mass percentage of Cr is 0.05% to 0.07%; the mass percentage of Zn is 0.01%; the mass percentage of Ti is 0.02%; the balance is Al; The preparation method comprises the following steps: Step S1: preparing the aluminum alloy according to the composition ratio of Si, Fe, Cu, Mn, Mg, Cr, Zn, Ti and Al elements; Step S2: smelting the ingredients and performing slag removal during the smelting process; Step S3: Casting process, in which online degassing and deslagging are performed throughout the casting process; Step S4: After the casting is completed, the ingot is transferred to a homogenizing furnace for uniform post-treatment, and then the ingot is quickly transferred to a cooling chamber for rapid cooling to room temperature, and then extruded by an extruder. At the outlet of the extruder, the extruded rod is cooled by online water cooling so that the rod is quickly cooled to less than 50°C within 2 minutes to obtain a rod; Step S5: subjecting the rod to three-stage solution treatment, quenching treatment, three-stage aging treatment, alkali washing, water washing, and pickling to obtain a 6xxx series aluminum alloy; The extrusion temperature is 515°C to 525°C, and the extrusion speed is 10m / min to 18m / min. The three-stage solution treatment comprises: solution treating the rod at 400°C to 420°C for 10 hours to 12 hours, then solution treating at 450°C to 510°C for 5 hours to 8 hours, and finally solution treating at 520°C to 550°C for 1 hour to 5 hours; The three-stage aging treatment includes a first aging treatment, a second aging treatment, and a third aging treatment. In the first aging treatment, the quenched bar is transferred to a preheated aging furnace, and a high-frequency electromagnetic wave generator is installed in the aging furnace. The temperature of the first aging treatment is 120°C to 150°C, and the time is 1h to 2h; the temperature of the second aging treatment is 155°C to 160°C, and the time is 2.5h to 3h; the temperature of the third aging treatment is 100°C to 120°C, and the time is 1h to 3h.

2. The preparation method according to claim 1, characterized in that The smelting treatment is performed at a temperature of 760° C. to 810° C. and for a time of 1 hour to 3 hours.

3. The preparation method according to claim 1, characterized in that The casting process speed is 40 mm / min to 50 mm / min, the cooling water flow rate is 1000 L / min to 1500 L / min, and the cooling water temperature is ≤35°C.

4. The preparation method according to claim 1, characterized in that The homogenization treatment is carried out at a temperature of 520° C. to 550° C. for 5 to 6 hours.

5. The preparation method according to claim 1, characterized in that The extrusion temperature is 520° C., and the extrusion speed is 15 m / min.

6. The preparation method according to claim 1, characterized in that The quenching treatment is as follows: the rod after the three-stage solid solution treatment is quenched in water with a pressure of 5KPa to 10KPa for 50s to 150s.

7. The preparation method according to claim 6, characterized in that The first aging treatment adjusts the frequency of the electromagnetic wave to 150KHz-220KHz; the second aging treatment adjusts the frequency of the electromagnetic wave to 120KHz-150KHz; and the third aging treatment adjusts the frequency of the electromagnetic wave to 100KHz-120KHz.

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