High-toughness aluminum alloy splined hub and preparation method thereof

Abstract

The invention relates to a high-strength and high-toughness aluminum alloy splined hub and a preparation method thereof.The method comprises the following steps that S1, materials are prepared according to the components and content of aluminum alloy, and then alloy liquid is prepared through a smelting furnace; s2, after the alloy liquid is refined, a casting rod is manufactured through a continuous casting method; s3, after the cast rod is subjected to three-stage homogenization treatment, the cast rod is cooled to the room temperature; s4, the treated casting rod is subjected to extrusion deformation, and then water cooling is conducted; and S5, the treated casting rod is cut, preheated and forged, and then the aluminum alloy splined hub is obtained. And S6, the obtained aluminum alloy splined hub is firstly subjected to solution treatment and then subjected to two-stage aging treatment, and the aluminum alloy splined hub is obtained. The high-efficiency short-process technology of continuous casting, three-stage homogenization, large-extrusion-ratio deformation, forging and two-stage aging is innovatively researched and developed, the key performance of the prepared splined hub comprehensively breaks through, the yield strength at the room temperature is 460 MPa or above, the tensile strength is 490 MPa or above, and the elongation is 7.5% or above.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of automobile spline hub manufacturing, in particular to a high-toughness aluminum alloy spline hub and a preparation method thereof. BACKGROUND

[0002] Automobile lightening is the key to improving the endurance of the automobile, which has been included in the key field of the national Energy Saving and New Energy Automobile Technology Roadmap. The chassis connecting parts (such as spline hubs) need to bear complex alternating loads, and the strength, stiffness and fatigue resistance of the material are required to be strict. At present, the aluminum alloy chassis parts mainly use 6082 or 6061 alloy, and its process has significant bottlenecks: first, the existing alloy performance cannot meet the lightening upgrade demand, the strict Fe content limit (<0.15wt%) greatly increases the cost and restricts the application of recycled aluminum, and it is urgent to break through the material performance bottleneck through micro-alloying design; second, the deformation energy accumulated in the plastic deformation of the forging in the extrusion or forging process is easy to induce recrystallization during solid solution treatment, forming coarse grain structure, which seriously deteriorates the mechanical properties; third, the traditional production process is long and energy-consuming, and the homogenization treatment and multi-pass blanking process lead to low efficiency and high cost.

[0003] In the field of spline hub manufacturing, although the straight forging aluminum alloy technology has the advantages of light weight and high strength, its core process has been monopolized by American aluminum industry for a long time. The spline hub of heavy truck transmission shaft, as a key component for transmitting torque and dynamic load, currently mainly relies on steel forgings, and adopts one-way / multi-way die forging process, which has the problem of single forming of single piece and low efficiency. Especially worth noting is that there is no mature and reliable public report on high-strength aluminum alloy spline hub and its hot working process suitable for heavy trucks at home and abroad. The existing research and development of aluminum alloy spline hub faces the following core challenges: how to inhibit the grain boundary migration and abnormal grain growth during hot working (especially high temperature solid solution), and avoid coarse grain defects; how to simplify the process flow, improve the efficiency and reduce the cost on the premise of ensuring the high strength of the material; and how to design the alloy composition and process to have excellent comprehensive mechanical properties and high temperature stability. SUMMARY

[0004] In view of the problems of large weight and low strength of the existing aluminum alloy spline hub, the purpose of the present application is to provide a high-toughness aluminum alloy spline hub and a preparation method thereof.

[0005] Accordingly, the technical scheme adopted by the present application is as follows:

[0006] In a first aspect, the present application relates to a preparation method of a high-toughness aluminum alloy spline hub, comprising the following steps:

[0007] S1, preparing materials according to the composition and content of the aluminum alloy, and then preparing alloy liquid by a furnace;

[0008] S2, after refining the alloy liquid, the cast bar is prepared by a continuous casting method;

[0009] S3, after adopting three-stage homogenization treatment on the cast bar, the cast bar is cooled to room temperature;

[0010] S4, after the cast bar treated in step S3 is subjected to extrusion deformation, the cast bar is then water-cooled;

[0011] S5, after the cast bar treated in step S4 is subjected to cutting, preheating and forging, the aluminum alloy spline hub is obtained.

[0012] S6, the aluminum alloy spline hub obtained in step S5 is first subjected to solid solution treatment, and then subjected to two-stage aging treatment, thereby obtaining the high-strength and high-toughness aluminum alloy spline hub.

[0013] As a preferred scheme, in step S1, the aluminum alloy is a 6xxx series aluminum alloy.

[0014] As a preferred scheme, the 6xxx series aluminum alloy includes any one of a conventional 6xxx aluminum alloy material, a high-strength and high-toughness 6xxx aluminum alloy material, and a high-Fe-content 6xxx aluminum alloy material.

[0015] As a preferred scheme, in step S1, the aluminum alloy includes the following components in the following weight percentages: magnesium: 1.0-1.4%, silicon: 1.0-1.4%, manganese: 0.3-0.7%, copper: 0.3-0.7%, chromium: 0.1-0.3%, zinc: 0.1-0.2%, zirconium: 0.05-0.2%, erbium: 0.05-0.2%, iron: 0.1-0.5%, and the balance being aluminum and unavoidable impurities.

[0016] In the aluminum alloy, the added Zr and Er elements significantly optimize the material structure and performance through synergistic effect. The specific effects include: 1) inhibiting coarse grains and improving thermal stability: Zr forms high-density nanoscale Al3Zr phases, and Er promotes Al3(Er,Zr) composite phase heterogeneous nucleation; both of them pin dislocations and grain boundaries, effectively inhibit grain boundary migration during high-temperature solid solution, and ensure strength even if there are larger grains. 2) improving high-temperature mechanical properties: Er reduces the diffusion rate of Zr, so that the nanophase remains stable during high-temperature service, the creep resistance is improved, and the high load requirement of the spline hub is met.

[0017] As a preferred solution, in step S3, the specific conditions of the three-stage homogenization treatment are: first-stage homogenization treatment at 470 DEG C for 10-14h, second-stage homogenization treatment at 530 DEG C for 5-7h, and third-stage homogenization treatment at 545 DEG C for 5-7h. The three-stage homogenization treatment adopted in the application can precisely control the precipitation of Al3(Er,Zr) phase: the low-temperature stage provides nucleation sites, and the high-temperature stage realizes high-density dispersion distribution; this process simultaneously reduces the width of the non-precipitation zone, improves the recrystallization resistance, and thus improves the yield strength. The time of the first-stage homogenization treatment should not be too short, if it is less than 10h, the coarse non-equilibrium second phase cannot be fully dissolved, composition segregation remains, the risk of cracking during subsequent hot working increases, and the mechanical properties, corrosion resistance and surface quality of the material are significantly reduced.

[0018] The application adopts Zr / Er micro-alloying combined with three-stage homogenization treatment, breaks through the traditional strength-toughness inversion contradiction, inhibits coarse grains while realizing fine-grain strengthening, precipitation strengthening and dispersion strengthening threefold synergy, and provides high strength-toughness, fatigue resistance and high-temperature stability comprehensive performance for the spline hub.

[0019] As a preferred solution, in step S4, the specific conditions of the extrusion deformation are: extrusion ratio is 10-20, extrusion cylinder temperature is 460-490 DEG C, and both the mold and the cast bar temperature are 480-510 DEG C.

[0020] As a preferred solution, in step S5, the temperature of the preheating is 420-450 DEG C.

[0021] As a preferred solution, in step S6, the temperature of the solid solution treatment is 470 DEG C-480 DEG C, and the holding time is 1.5-2.5h. The solid solution treatment can make the large-size second phase particles in the aluminum alloy spline hub dissolve in the matrix, providing sufficient driving force for the subsequent aging process.

[0022] As a preferred solution, in step S6, after the pre-aging treatment and before the two-stage aging treatment, a quenching step is further included to improve the hardness of the aluminum alloy.

[0023] As a preferred solution, in step S6, the two-stage aging treatment is: 22-26 h of holding at 90-100 DEG C for the first-stage aging treatment, and 14-18 h of holding at 115-125 DEG C for the second-stage aging treatment. The two-stage aging treatment can shorten the peak aging time and further improve the strength and toughness. The first-stage aging treatment helps to improve the aging hardening response, so that the strength performance achieved in a short time can reach that achieved in a long time at a low temperature. Meanwhile, the residual stress generated by the severe plastic deformation can be effectively released during the heat treatment, and the deformation amount of the spline hub is reduced. If a single-stage aging treatment is adopted, or the two-stage aging treatment is adopted with the temperature and time exceeding the above-mentioned range, the mechanical properties of the aluminum alloy spline hub prepared will be poor.

[0024] In a second aspect, the present application relates to an aluminum alloy spline hub with high strength and toughness, which is prepared by the above method, and the weight percentage of each component in the material of the aluminum alloy spline hub is as follows: magnesium: 1.0-1.4%, silicon: 1.0-1.4%, manganese: 0.3-0.7%, copper: 0.3-0.7%, chromium: 0.1-0.3%, zinc: 0.1-0.2%, zirconium: 0.05-0.2%, erbium: 0.05-0.2%, iron: 0.1-0.5%, and the balance is aluminum and inevitable impurities.

[0025] As a preferred solution, the yield strength of the aluminum alloy spline hub at room temperature is above 460 MPa, the tensile strength is above 490 MPa, and the elongation is above 7.5%.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] 1. Short process hot working process innovation

[0028] The present application innovatively develops a high-efficiency short process of "continuous casting→three-stage homogenization→large extrusion ratio deformation→forging→two-stage aging". The three-stage homogenization can eliminate segregation in stages (low-temperature back-dissolution eutectic phase→medium-high temperature dissolution of coarse phase→high-temperature solid solution to form a supersaturated matrix), and avoid the easy overburning defect of single-stage treatment. The extrusion deformation with a large extrusion ratio can break the residual second phase and improve the uniformity of the structure. In the two-stage aging treatment, the first-stage aging can accelerate the hardening response, improve the peak aging hardness, release the residual stress, and reduce the risk of workpiece deformation.

[0029] 2. Cross-over improvement of mechanical properties

[0030] The key performance of the spline hub prepared by the present application is comprehensively broken through: the yield strength at room temperature is above 460 MPa, the tensile strength is above 490 MPa, and the elongation is above 7.5%. The product has high load capacity, fatigue resistance and high-temperature stability, and is suitable for complex stress environment. BRIEF DESCRIPTION OF DRAWINGS

[0031] Other features, objects, and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments thereof, when read in conjunction with the accompanying drawings:

[0032] Figure 1 Flow chart for producing aluminum alloy spline hub of the present application;

[0033] Figure 2 Microstructure chart of as-cast aluminum alloy proposed by the present application;

[0034] Figure 3 Microstructure chart of homogenized aluminum alloy proposed by the present application;

[0035] Figure 4 Microstructure chart of extruded aluminum alloy proposed by the present application;

[0036] Figure 5 Microstructure chart of forged aluminum alloy proposed by the present application;

[0037] Figure 6 Photo of aluminum alloy spline hub prepared by the process provided by the present application. DETAILED DESCRIPTION

[0038] The present application will be described in detail below with specific embodiments. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made. These all belong to the protection scope of the present application.

[0039] Example 1

[0040] This embodiment provides a method for preparing a high-toughness aluminum alloy spline hub, and the production process is as shown in Figure 1 The specific steps are as follows:

[0041] 1) Aluminum alloy smelting: according to the theoretical weight percentage of each component, the alloy is Al-1.0Mg-1.2Si-0.5Mn-0.47Cu-0.2Cr-0.15Zn-0.1Zr-0.13Er-0.48Fe, and pure Al, pure Mg, pure Zn, and intermediate alloys Al-Si, Al-Cu, Al-Mn, Al-Cr, Al-Zr, Al-Er are selected as raw materials. First, all raw materials (pure metals and intermediate alloys) are preheated to 200°C to remove moisture. Then pure aluminum is added and heated to 760-780°C to form a molten pool, and high-melting-point intermediate alloys Al-Mn, Al-Cr, Al-Zr, Al-Er are immediately added. After melting, continue stirring for 15-20 min. Then, reduce the temperature to 730-750°C and add Al-Si and Al-Cu intermediate alloys. Then, reduce the temperature to 680-700°C, first add pure zinc and stir for 5 min to dissolve, then use a graphite bell to compact pure magnesium and immerse it into the lower part of the melt, slowly move until completely dissolved, and continue stirring for 15-20 min. Then, in-furnace refining is carried out: rotate for 12 min with Ar+1.5% Cl2 mixed gas (flow rate 1.5 L / min), and after 5 min of standing, completely remove the slag. After that, the alloy liquid is transferred to the runner and subjected to out-of-furnace degassing in an SNIF degassing tank (vacuum degree ≤1 kPa), and then filtered through a 50 ppi ceramic foam filter. Finally, after standing at 710-720°C (≤20 min when containing Er / Zr), pouring is completed.

[0042] 2) Bar forming: the alloy liquid prepared in step 1) is used to manufacture a 200 mm diameter cast bar (its as-cast microstructure is shown in Figure 2 ) by conventional continuous casting technology. After cooling, the cast bar is placed in a resistance furnace for three-stage homogenization treatment. The three-stage homogenization treatment schedule is: first, increase to 470°C at a rate of 5°C / min, and hold for 12 h; then, increase to 530°C at a rate of 3°C / min, and hold for 6 h; and then, increase to 545°C at a rate of 3°C / min, and hold for 6 h. After homogenization treatment, air cooling is carried out: first, decrease to 300°C at a rate of 5°C / min, then cool to room temperature at a rate of 3°C / min, and finally form an aluminum alloy cast bar for spline hub (its microstructure is shown in Figure 3 ).

[0043] 3) Bar extrusion: according to the process requirements, design and process the extrusion die, adapt the structure size of the die cavity, set the extrusion ratio to 16, and complete the preparation work before cast ingot extrusion. During extrusion, the extrusion cylinder temperature is strictly controlled at 480°C, and the die and aluminum alloy cast bar for spline hub are kept at 500°C. The male and female dies are precisely closed to gradually reduce the diameter of the cast ingot. After extrusion, the male die is lifted by the ejector rod, the thin-walled formed part is ejected from the female die, and the whole extrusion process is completed by rapid water cooling. The microstructure of the thin-walled formed part after extrusion is shown in Figure 4shown.

[0044] 4) Bar cutting: cutting the thin-walled formed piece obtained after extrusion into a thin-walled blank piece of a predetermined length.

[0045] 5) Bar preheating: heating the thin-walled blank piece, and the heating temperature is 430℃.

[0046] 6) Forging: placing the preheated thin-walled blank piece into a female die, moving a male die downward, accurately closing the male die and the female die, preforming, forming, and finish forging the thin-walled blank piece by a conventional method to obtain an aluminum alloy spline hub, and a microstructure diagram of the aluminum alloy spline hub is shown in Figure 5 .

[0047] 7) Heat treatment: after the aluminum alloy spline hub is expanded and deburred, the oil stains and dirt on the surface of the aluminum alloy spline hub requiring heat treatment are cleaned, and the aluminum alloy spline hub is sent into a resistance furnace for heat treatment. First, the temperature of the heat treatment furnace is set to 470-480℃, and after the temperature of the heat treatment furnace reaches 470-480℃, the heat treatment is performed for 2h for solid solution treatment. Then, within 15s after the furnace door is opened, quenching is performed, and within 2h after the quenching is completed, two-stage aging treatment is performed, and the two-stage aging treatment system is: 90-100℃ x 24h + 120℃ x 16h.

[0048] A photo of the finally prepared high-toughness aluminum alloy spline hub is shown in Figure 6 , the actual content of each component of the high-toughness aluminum alloy spline hub is shown in Table 1, and the mechanical property test results are shown in Table 2.

[0049] Comparative Example 1

[0050] This comparative example provides a preparation method of a high-toughness aluminum alloy spline hub, which is basically the same as the method of Example 1, and the only difference is that in step 1) of this comparative example, the aluminum alloy used has a theoretical weight percentage of each component of Al-0.75Mg-0.63Si-0.43Mn-0.47Cu-0.1Cr-0.05Zn-0.1Zr-0.16Fe.

[0051] Table 1 Actual content of components of high-toughness aluminum alloy spline hub (.wt%)

[0052]

[0053] Table 2 Mechanical property test results of high-toughness aluminum alloy spline hub

[0054]

[0055] As can be seen from the results of Table 2, the yield strength of the aluminum alloy spline hub prepared in Example 1 is about 1.3 times that of the aluminum alloy spline hub prepared in Comparative Example 1, the tensile strength is about 1.2 times that of the aluminum alloy spline hub prepared in Comparative Example 1, and the elongation is also improved compared with Comparative Example 1. It is shown that the mechanical properties of the aluminum alloy spline hub prepared in Example 1 are obviously superior to those of the aluminum alloy spline hub prepared in Comparative Example 1.

[0056] The above description is only examples of the present application, and is not a limitation on the patent scope of the present application. Any equivalent structure or equivalent process transformation made by using the present application specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing a high-strength and tough aluminum alloy spline hub, characterized in that: The following steps are involved: S1. Prepare the materials according to the composition and content of the aluminum alloy, and then prepare the alloy liquid in the furnace; S2, after refining the alloy liquid, forming cast rods by continuous casting method; S3, subjecting the cast rod to three-stage homogenization treatment and then cooling it to room temperature; S4, extruding and deforming the cast rod after the treatment in step S3, and then cooling it with water; S5, cutting, preheating and forging the cast rod processed in step S4 to obtain an aluminum alloy spline hub; S6. The aluminum alloy spline hub obtained in step S5 is first subjected to a solution treatment and then subjected to a double-stage aging treatment to obtain a high-strength and toughness aluminum alloy spline hub.

2. The method for preparing a high-strength and tough aluminum alloy spline hub according to claim 1, characterized in that: In step S1, the aluminum alloy is a 6xxx series aluminum alloy.

3. The method for preparing a high-strength and tough aluminum alloy spline hub according to claim 1, wherein: In step S1, the aluminum alloy includes the following components in weight percentage: magnesium: 1.0-1.4%, silicon: 1.0-1.4%, manganese: 0.3-0.7%, copper: 0.3-0.7%, chromium: 0.1-0.3%, zinc: 0.1-0.2%, zirconium: 0.05-0.2%, erbium: 0.05-0.2%, iron: 0.1-0.5%, and the balance is aluminum and unavoidable impurities.

4. The method for preparing a high-strength and tough aluminum alloy spline hub according to claim 1, characterized in that: In step S3, the specific conditions of the three-stage homogenization treatment are: the first-stage homogenization treatment is performed at 470° C. for 10-14 hours, the second-stage homogenization treatment is performed at 530° C. for 5-7 hours, and the third-stage homogenization treatment is performed at 545° C. for 5-7 hours.

5. The method for preparing a high-strength and tough aluminum alloy spline hub according to claim 1, characterized in that: In step S4, the specific conditions of the extrusion deformation are: an extrusion ratio of 10-20, an extrusion barrel temperature of 460-490°C, and mold and cast rod temperatures of 480-510°C.

6. The method for preparing a high-strength and tough aluminum alloy spline hub according to claim 1, characterized in that: In step S5, the preheating temperature is 420-450°C.

7. The method for preparing a high-strength and tough aluminum alloy spline hub according to claim 1, characterized in that: In step S6, the temperature of the solution treatment is 470° C.-480° C., and the holding time is 1.5-2.5 h.

8. The method for preparing a high-strength and tough aluminum alloy spline hub according to claim 1, characterized in that: In step S6, the double-stage aging treatment is as follows: the first-stage aging treatment is carried out at a temperature of 90°C-100°C for 22-26 hours, and the second-stage aging treatment is carried out at a temperature of 115°C-125°C for 14-18 hours.

9. A high-strength and tough aluminum alloy spline hub prepared according to the method according to any one of claims 1 to 8, characterized in that: The weight percentages of the components in the material of the high-strength and tough aluminum alloy spline hub are as follows: magnesium: 1.0-1.4%, silicon: 1.0-1.4%, manganese: 0.3-0.7%, copper: 0.3-0.7%, chromium: 0.1-0.3%, zinc: 0.1-0.2%, zirconium: 0.05-0.2%, erbium: 0.05-0.2%, iron: 0.1-0.5%, and the balance is aluminum and unavoidable impurities.

10. The high-strength and tough aluminum alloy spline hub according to claim 9, characterized in that: The aluminum alloy spline hub has a yield strength of 460 MPa or more, a tensile strength of 490 MPa or more, and an elongation of 7.5% or more at room temperature.

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