A preparation method for improving surface quality of high-strength 6-series aluminum alloy extruded profiles

Abstract

The application relates to a preparation method for improving the surface quality of high-strength 6-series aluminum alloy extruded profiles, and belongs to the technical field of aluminum alloy materials.The alloy composition is as follows: 1.5-1.7% of Si, 0.7-1.0% of Cu, 0.9-1.2% of Mn, 1.3-1.7% of Mg, 0.15-0.25% of Cr, 0.03-0.05% of Ti, 0.3% of Fe and 0.2% of rare earth elements, impurities are less than 0.05% individually, the total amount is not less than 0.15%, and the balance is Al.In the technical scheme, the rare earth elements are added, TiB2 aggregation can be prevented, the dispersity is further improved, the roughness of the aluminum alloy surface is reduced, the surface quality of the aluminum alloy is improved, the profile surface roughness is reduced from 4.6-5.0 mu m to 2.0-2.5 mu m, and the improvement effect is excellent.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aluminum alloy materials, and particularly relates to a preparation method for improving the surface quality of high-strength 6-series aluminum alloy extruded profiles. BACKGROUND

[0002] 6xxx series aluminum alloys have silicon (Si) and magnesium (Mg) as the main alloying elements, and Al as the main element. These alloys have good strength and ductility, enhanced corrosion resistance, easy formability and anodizability. In addition, they also have good weldability, which makes them strong candidates for structural applications. Mg and Si are added in proportions required to form a quasi-binary alloy (Al-Mg2Si), in which the alloy has (Mg: Si is 1.73:1), or the Si content is higher than the balanced magnesium silicide (Mg2Si) formation. The formation of Mg2Si is beneficial to the heat treatment and the range of strength improvement.

[0003] Aluminum matrix composites (AMMC) are widely used in aerospace, aviation and automotive industries due to their excellent mechanical and tribological properties. AMMCs have high strength, high Young's modulus, improved corrosion resistance, creep, fatigue and wear strength. They are durable and almost maintenance-free, so they are suitable structural materials for various industries. The use of AMMCs meets the continuous demand for strong, lightweight and high-performance equipment.

[0004] In the prior art, for particle reinforced AMMCs, the size of the reinforcing particles has a significant impact on their performance. In-situ reinforcing particles can be sub-micron or even nanometer. These particles improve the strength, hardness and wear resistance of the matrix while maintaining good plasticity. In addition, the high-temperature performance of the material will also be significantly improved. However, the specific surface energy of nanoparticles is large, and nanoparticles are prone to agglomeration, which greatly limits the strengthening and toughening effect and the surface quality of 6-series aluminum alloys. SUMMARY

[0005] The purpose of the present application is to provide a preparation method for improving the surface quality of high-strength 6-series aluminum alloy extruded profiles. By synthesizing TiB2 and MgAl2O4 in-situ in the aluminum melt system, the effect of refining the grain is achieved. Secondly, the MgAl2O4 (spinel) synthesized in the system can also be used to improve the adhesion quality between the metal and the ceramic (TiB2) by enhancing the interfacial bonding. By adding rare earth elements, the agglomeration of TiB2 can be prevented, further improving the dispersibility, reducing the roughness of the aluminum alloy surface, and achieving the effect of improving the surface quality of the aluminum alloy.

[0006] The technical problem to be solved by the present application is that in-situ reinforced particles can be submicron or even nanometer level. These particles improve the strength, hardness and wear resistance of the matrix while maintaining good plasticity. In addition, the high temperature performance of the material will also be significantly improved. However, the specific surface energy of nanoparticles is large, and nanoparticles are prone to agglomeration, which greatly limits the strengthening and toughening effect and the surface quality of the 6 series aluminum alloy.

[0007] The object of the present application can be achieved by the following technical solutions:

[0008] A preparation method for improving the surface quality of high-strength 6 series aluminum alloy extruded profiles, comprising the following steps:

[0009] 1) Melting and casting process: aluminum ingots, aluminum silicon intermediate alloy, aluminum manganese intermediate alloy, aluminum chromium intermediate alloy, aluminum copper intermediate alloy and aluminum-based reinforcing materials are added to a crucible furnace, the crucible furnace is heated to 720-780℃, after the materials are completely melted, magnesium ingots, granular refining agents and rare earth elements are pressed in, the melt is refined under an argon atmosphere, after refining is completed, a slag remover is sprinkled to remove slag, then a covering agent is sprinkled into the melt, the temperature is controlled at 760-780℃, the standing time is half an hour, the melt temperature is 770-790℃, the casting plate temperature is preferably controlled at 710-730℃, and the casting speed is 80-100mm / s;

[0010] 2) Primary homogenization process: the homogenization temperature is 550-565℃, the holding time is 6-10h, and the natural cooling is to room temperature;

[0011] 3) Secondary homogenization process: after the primary homogenization process, the sample is heated from ambient temperature to 175-300℃, the holding time is 4-12h, and then the natural cooling is to room temperature;

[0012] 4) Extrusion process: the extrusion ingot rod temperature is 450-500℃, the profile speed is 5-10m / min, and the cooling intensity is greater than or equal to 550℃ / min;

[0013] The alloy composition is: 1.5-1.7% Si, 0.7-1.0% Cu, 0.9-1.2% Mn, 1.3-1.7% Mg, 0.15-0.25% Cr, 0.03-0.05% Ti, 0.3% Fe and 0.2% rare earth elements, the impurities are less than 0.05% individually, the total amount is not less than 0.15%, and the balance is Al.

[0014] Further, the temperature rising rate of the primary homogenization process and the secondary homogenization process is 5℃ / min.

[0015] It is to be noted that if a conventional one-step homogenization is used, the heating temperature will quickly exceed the precipitation temperature range of the metastable Mg2Si or Q phase (150°C to 350°C). In the present invention, the metastable Mg2Si and Q phase is precipitated in only 40 minutes at a heating rate of 5°C / min. In the solute depleted zone, the precipitation of nucleation sites of the α-Al(Mn,Cr)Si dispersoids is insufficient due to the lack of driving force. For example, in the heavily Si segregated zone, the precipitation of the metastable Mg2Si and Q phase will be extremely difficult. Therefore, in the center of the grains and dendrite arms, the metastable Mg2Si is insufficient and the Q phase is precipitated. As a result, when the heating temperature reaches the precipitation temperature of the α-Al(Mn,Cr)Si dispersoids, the α-Al(Mn,Cr)Si dispersoids must precipitate without nucleation sites, resulting in the formation of a coarse dispersoid zone (a region where the dispersoids are not uniformly distributed).

[0016] If a two-step homogenization is used, the first step of heat treatment will provide sufficient time for Mg and Si to precipitate. The isothermal holding of the first step of heat treatment is particularly important for the precipitation of the heavily segregated zone, which has a weak driving force for precipitation. In addition, the diffusion of solute elements also helps to obtain a more uniform distribution of β-Mg2Si and Q-AlMgSiCu. The more uniform precipitation of nucleation sites will improve the distribution of the α-Al(Mn,Cr)Si dispersoids. Therefore, the amount of coarse dispersoid zone is significantly reduced compared to the one-step homogenization condition.

[0017] Further, the covering agent is silicon carbide, and the particle size is 10-20 μm.

[0018] Further, the preparation process of the aluminum-based reinforcing material is as follows:

[0019] Aluminum powder, magnesium powder and boric acid are used as starting materials, the size of Al and Mg powder particles ranges from 40 to 60 μm, the magnesium powder, boric acid and aluminum powder are mixed in a mass ratio of 2:2:9, the mixture is ball milled at a ball powder mass ratio of 10:1 and a rotation speed of 650 rpm for 12 hours, the weight fraction of Mg in the mixed powder after ball milling pretreatment is about 15.38wt%, then pure aluminum powder is added to the mixture to control the amount of whiskers formed during sintering. By adding 54.48wt% of Al powder to the mixture, the mass fraction of Mg is reduced to 7wt%.

[0020] Further, the granular refining agent is prepared by the following steps:

[0021] First, K2TiF6 powder and KBF4 powder are placed in an electric resistance furnace (economic considerations, simple reaction process, easy to industrialize batch production). Then the powders are heated to 200°C and kept for 4 hours to completely remove the crystal water. After cooling, the two powders are mixed and ground to obtain a powder reactant with a particle size of <200 μm.

[0022] The above process mainly realizes in-situ synthesis of TiB2, and plays a role in refining grains in cooperation with stirring processing.

[0023] Further, the rare earth element is selected from one of La, Er, Y and Ce.

[0024] It should be noted that MgAl2O4 at the matrix-reinforcement interface can prevent the formation of harmful Al4C3, which acts as a diffusion barrier and limits the decomposition of the reinforcement particles (i.e., SiC), thereby reducing the mechanical properties of the Al-SiC composite. After adding Mg to the Al-SiC composite, a strong chemical bond is formed, thereby forming a layer between the MgAl2O4 matrix and the reinforcement.

[0025] Advantages of the present application:

[0026] (1) In the technical scheme of the present application, the addition of rare earth to the aluminum alloy system increases the rare earth-rich phase in the TiAl3 phase and the TiB2 phase. The decomposition of the rare earth phase releases rare earth elements, making it difficult for TiB2 to aggregate or deposit and inhibiting the growth of TiAl3, so that more particles become effective nucleation substrates. The addition of rare earth promotes the transition of the beta-Al5FeSi phase to the alpha-Al 15 (Mn,Fe)3Si2 phase, improving the strength of the aluminum alloy.

[0027] (2) In the technical scheme of the present application, the secondary homogenization process can significantly change the distribution of alpha-Al(Mn,Cr)Si dispersoids, enhancing the mechanical properties of the aluminum alloy profile.

[0028] (3) In the technical scheme of the present application, TiB2 grain refiner is generated by in-situ polymerization, the size of the grain refiner is refined, and the nucleation effect is better. The synthesized MgAl2O4 (spinel) in the system can also be used to improve the adhesion between the metal and the ceramic (TiB2) by enhancing the interfacial bonding,

[0029] (4) In the technical scheme of the present application, the addition of rare earth elements can prevent the aggregation and deposition of TiB2, further improve the dispersibility, reduce the surface roughness of the aluminum alloy, and improve the surface quality of the aluminum alloy. The surface roughness of the profile is reduced from 4.6-5.0 μm to 2.0-2.5 μm, and the improvement effect is excellent. DETAILED DESCRIPTION

[0030] With reference to the drawings and embodiments of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0031] In the present application:

[0032] The preparation process of the aluminum-based reinforcing material is as follows:

[0033] Aluminum powder, magnesium powder and boric acid are used as starting materials, the size of Al and Mg powder particles ranges from 40 to 60 μm, the magnesium powder, boric acid and aluminum powder are mixed in a mass ratio of 2:2:9, the mixture is high-energy ball milled at a ball-to-powder mass ratio of 10:1 and a rotation speed of 650 rpm for 12 h, the weight fraction of Mg in the mixed powder after ball milling pretreatment is about 15.38 wt%, then pure aluminum powder is added to the mixture to control the amount of whiskers formed during sintering. By adding 54.48 wt% of Al powder to the mixture, the mass fraction of Mg is reduced to 7 wt%.

[0034] The grain refiner is prepared by the following steps:

[0035] Firstly, K2TiF6 powder and KBF4 powder are put into a resistance furnace. Then the powders are heated to 200℃ and kept for 4 hours to completely remove the crystal water. After cooling, the two powders are mixed and ground to obtain powder reactants with a particle size of <200 μm. Example 1

[0036] A preparation method for improving the surface quality of high-strength 6-series aluminum alloy extruded profiles, comprising the following steps:

[0037] 1) Melting and casting process: aluminum ingots, aluminum-silicon intermediate alloy, aluminum-manganese intermediate alloy, aluminum-chromium intermediate alloy, aluminum-copper intermediate alloy and aluminum-based reinforcing material are added into a crucible furnace, the crucible furnace is heated to 760℃, after the materials are completely melted, magnesium ingots, grain refiner and rare earth element La are pressed in, the melt is refined under argon atmosphere, after the refining is completed, a slag remover is scattered to remove slag, then a covering agent is scattered into the melt, the standing temperature is controlled at 770℃, the standing time is half an hour, the melt is cast when the melt temperature is 780℃, the casting plate temperature is preferably controlled at 720℃, and the casting speed is 90 mm / s;

[0038] 2) Primary homogenization process: the homogenization temperature is 550-565℃, the holding time is 6-10 h, and the natural cooling is to room temperature;

[0039] 3) Secondary homogenization process: after the primary homogenization process, the sample is heated from ambient temperature to 175-300°C, and the holding time is 4-12h, and then naturally cooled to room temperature;

[0040] 4) Extrusion process: the extrusion ingot rod temperature is 480°C, the profile speed is 7m / min, and the cooling intensity is ≥550°C / min;

[0041] The alloy composition is: 1.5-1.7% Si, 0.7-1.0% Cu, 0.9-1.2% Mn, 1.3-1.7% Mg, 0.15-0.25% Cr, 0.03-0.05% Ti, 0.3% Fe, and 0.2% rare earth element La, the individual impurities are less than 0.05%, the total amount is not less than 0.15%, and the balance is Al.

[0042] The covering agent is silicon carbide, and the particle size is 10-20μm. Example 2

[0043] The alloy composition is: 1.6% Si, 0.8% Cu, 1.1% Mn, 1.5% Mg, 0.2% Cr, 0.04% Ti, 0.3% Fe, and 0.2% rare earth element Er, the individual impurities are less than 0.05%, the total amount is not less than 0.15%, and the balance is Al. Example 3

[0044] The alloy composition is: 1.6% Si, 0.8% Cu, 1.1% Mn, 1.5% Mg, 0.2% Cr, 0.04% Ti, 0.3% Fe, and 0.2% rare earth element Er, the individual impurities are less than 0.05%, the total amount is not less than 0.15%, and the balance is Al. Example 4

[0045] The alloy composition is: 1.6% Si, 0.8% Cu, 1.1% Mn, 1.5% Mg, 0.2% Cr, 0.04% Ti, 0.3% Fe, and 0.2% rare earth element Er, the individual impurities are less than 0.05%, the total amount is not less than 0.15%, and the balance is Al.

[0046] Comparative Example 1

[0047] The difference between this comparative example and Example 4 is that the granular refining agent TiB2 is directly added, and the remaining steps and raw materials are the same as Example 4.

[0048] Comparative Example 2

[0049] The difference between this comparative example and Example 4 is that no rare earth element is added, and the remaining steps and raw materials are the same as Example 4.

[0050] Comparative Example 3

[0051] The difference between the present comparative example and example 4 is that no aluminum-based reinforcing material is added, and the remaining steps and raw materials are implemented synchronously with example 4.

[0052] Comparative example 4

[0053] The difference between the present comparative example and example 4 is that no secondary homogenization process is performed, and the remaining steps and raw materials are implemented synchronously with example 4.

[0054] The aluminum alloy profiles prepared in examples 1-4 and comparative examples 1-3 are subjected to performance testing according to GB / T 6892, and the test results are shown in Table 1 below:

[0055] Table 1

[0056]

[0057] As can be seen from Table 1 above, the in-situ synthesized grain refiner in the present application can strengthen the strength of the alloy, and the cooperation of the rare earth element and the aluminum-based reinforcing material can improve the surface quality of the aluminum alloy profile. The two homogenization processes significantly increase the mechanical strength of the aluminum alloy profile.

[0058] In the description of the specification, the description of the reference terms "one embodiment", "example", "specific example" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are contained in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0059] The above is only an example and description of the present application, and those skilled in the art can make various modifications or supplements or use similar ways to replace the described specific embodiments, as long as they do not deviate from the invention or exceed the scope defined by the present claims, and should belong to the protection scope of the present application.

Claims

1. A method for improving surface quality of extruded profiles of high-strength 6-series aluminium alloys, characterized in that: The method comprises the following steps: 1) a melting process: aluminum ingot, aluminum silicon intermediate alloy, aluminum manganese intermediate alloy, aluminum chromium intermediate alloy, aluminum copper intermediate alloy and aluminum-based reinforcing material are added into a crucible furnace, the crucible furnace is heated to 720-780℃, after the materials are completely melted, magnesium ingot, granular refining agent and rare earth elements are pressed in, the melt is refined under an argon atmosphere, after the refining is completed, a slag removing agent is scattered to remove slag, then a covering agent is scattered into the melt, the standing temperature is controlled at 760-780℃, the standing time is half an hour, the melt is started to be cast when the melt temperature is 770-790℃, the casting plate temperature is controlled at 710-730℃, and the casting speed is 80-100mm / s; The granular refining agent is prepared by the following steps: Firstly, K2TiF6 powder and KBF4 powder are put into an electric resistance furnace, then the powders are heated to 200℃ and kept for 4 hours to completely remove crystal water, after cooling, the two kinds of powders are mixed and ground to obtain powder reactants with a particle size of <200μm; The preparation process of the aluminum-based reinforcing material is as follows: Magnesium powder, boric acid and aluminum powder are mixed according to a mass ratio of 2:2:9, the mixture is high-energy ball milled at a ball powder mass ratio of 10:1 and a rotating speed of 650rpm for 12h, the weight fraction of Mg in the mixed powder after the ball milling pretreatment is 15.38wt%, then pure aluminum powder is added into the mixed powder to control the amount of whiskers formed in the sintering process, by adding 54.48wt% of Al powder into the mixed powder, the mass fraction of Mg is reduced to 7wt%; 2) a primary homogenization process: the homogenization holding temperature is 550-565℃, the holding time is 6-10h, and the natural cooling is to room temperature; 3) a secondary homogenization process: after the primary homogenization process, the sample is heated from ambient temperature to 175-300℃, the holding time is 4-12h, and then the natural cooling is to room temperature; The heating rate of the primary homogenization process and the secondary homogenization process is 5℃ / min; 4) an extrusion process: the extrusion ingot rod temperature is 450-500℃, the profile speed is 5-10m / min, and the cooling intensity is ≥550℃ / min; The 6-series aluminum alloy composition is: 1.5-1.7%Si, 0.7-1.0%Cu, 0.9-1.2%Mn, 1.3-1.7%Mg, 0.15-0.25%Cr, 0.03-0.05%Ti, 0.3%Fe and 0.2% rare earth elements, the impurities are less than 0.05% individually, the total amount is not less than 0.15%, and the balance is Al.

2. The method for improving the surface quality of high-strength 6-series aluminum alloy extruded profiles according to claim 1, characterized in that: The covering agent is silicon carbide with a particle size of 10-20μm.

3. The method of claim 1, wherein the method is characterized by: The size range of the aluminum powder and magnesium powder particles is 40-60μm.

4. The method of claim 1, wherein the method is characterized by: The rare earth element is selected from one of La, Er, Y and Ce. The method comprises the following steps:

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