Al-cerium-silicon casting alloy with high temperature creep resistance, preparation method and application

Abstract

The application discloses an Al-Ce-Si casting alloy with high-temperature creep resistance, a preparation method and application, and the composition of the Al-Ce-Si casting alloy is as follows: Ce 10-13%, Si 0.5-2.5%, Ta 0.1-0.35%, and the balance of Al and inevitable impurity elements. The application is beneficial to strengthening the weak eutectic colony boundary and hindering the rapid expansion of cracks along the boundary by adding Si, and finally improves the mechanical properties of the Al-Ce casting alloy. Moreover, the addition of trace Ta elements is beneficial to reducing the stress concentration and crack initiation of the alloy, and the creep cavities are not easy to be generated at the phase boundary in the creep process. The yield strength of the Al-Ce-Si casting alloy of the application is 115-140 MPa at room temperature, the tensile strength is 213-230 MPa, the yield strength is 80-97 MPa at high temperature 300 DEG C, the tensile strength is 128-136 MPa, and the steady-state creep rate is lower than 7.45*10 ‑9 s ‑1 -4 after 100h of creep at 300 DEG C and tensile stress 15 MPa, and the Al-Ce-Si casting alloy has excellent mechanical properties and high-temperature creep resistance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of aluminum alloy materials, and particularly relates to an Al-Ce-Si cast alloy with high-temperature creep resistance, a preparation method and application. BACKGROUND

[0002] Lightening the weight of an automobile can improve fuel utilization, save limited resources, reduce the emission of greenhouse gases, and improve the stability of automobile driving and the comfort of passengers, so all automobile enterprises in the world are constantly seeking structural materials for lightening automobiles. Aluminum alloy materials are favored in the automobile industry due to their high specific strength, good thermal conductivity, small density and easy processing, and are often used in automobile parts such as automobile body panels, oil pans, cylinder covers and engine pistons. Among them, the lightening effect of aluminum alloy manufacturing for automobile engines is the most significant, which can reduce the weight by more than 30%. Among automobile engine parts, about 100% of the pistons and 75% of the cylinder shells are cast aluminum alloys.

[0003] At present, modern automobile engines are developing towards high power and high density, and the service environment of engine parts is becoming more and more severe, which needs to withstand the coupling effect of high temperature and load for a long time. The working temperature of the automobile engine piston can reach 300 DEG C, and it also needs to withstand the pressure action when the compressed gas. The mechanical properties of conventional cast aluminum alloys for automobile engines in the casting state are difficult to meet the service requirements, and usually need to be subjected to subsequent heat treatment, which leads to a complicated preparation process of the parts and an increase in production cost. In addition, the conventional cast aluminum alloy for automobile engines has poor heat resistance, and easily causes the second phase to coarsen or dissolve at 300 DEG C, resulting in a sharp decrease in the high-temperature performance of the parts, and the parts are prone to creep and deformation or even failure under the action of high temperature and load.

[0004] The Al-Ce cast alloy has excellent thermal stability, good fluidity and low thermal cracking tendency, and can be used without heat treatment, which is an ideal material for the next generation of automobile engine parts. Ce is a cheap rare earth element, and its resources are relatively abundant, which is often a byproduct of extracting expensive rare earth elements, and will not greatly increase the production cost when used as the main alloying element of Al. Ce and Al form Chinese character-shaped Al 11 Ce3phase at 645 DEG C. Since the diffusion rate and solid solubility of Ce in Al are very low, the Al 11 Ce3phase is not easy to coarsen at high temperature, which is beneficial to the high-temperature performance of the alloy.

[0005] However, the Al 11 Ce3phase has weak strengthening ability to the alloy, which leads to low room temperature and high temperature strength of the Al-Ce cast alloy, and it is difficult to meet the requirements of modern high-power automobile engines. In addition, the coarse blocky primary Al 11Ce3 phase is prone to stress concentration and even breakage under stress, and micro cracks are formed in the aluminum matrix, which not only damages the mechanical properties of the alloy, but also is not conducive to the creep resistance of the alloy. Therefore, it is necessary to further improve the high temperature strength and creep resistance of the Al-Ce casting alloy. SUMMARY

[0006] The purpose of the present application is to overcome at least one deficiency of the prior art, and to provide an Al-Ce-Si casting alloy with high temperature creep resistance, a preparation method and application.

[0007] The technical solution adopted by the present application is:

[0008] In a first aspect, the present application provides an Al-Ce-Si casting alloy with high temperature creep resistance, the composition of the alloy is: Ce 10-13%, Si 0.5-2.5%, Ta 0.1-0.35%, the balance being Al and unavoidable impurity elements.

[0009] In some examples, the amount of Si / Ta in the Al-Ce-Si casting alloy is greater than or equal to 3 by mass percent.

[0010] In some examples, the composition of the Al-Ce-Si casting alloy is: Ce 11.5%, Si 2%, Ta 0.3%, the balance being Al and unavoidable impurity elements.

[0011] In some examples, the content of unavoidable impurity elements in the Al-Ce-Si casting alloy is ≤0.1% by mass percent.

[0012] In some examples, the steady-state creep rate of the Al-Ce-Si casting alloy after 100h of creep at 300℃ and a tensile stress of 15 MPa is ≤7.45x10-9 s-1.

[0013] In a second aspect, the present application provides a preparation method for the Al-Ce-Si casting alloy provided in the first aspect, which comprises the following steps:

[0014] 1) batching: weighing Al raw material, Ce raw material, Si raw material and Ta raw material according to the proportion and preheating;

[0015] 2) melting: heating the preheated pure aluminum to 750-800℃, after complete melting, sequentially adding preheated Ce raw material, Si raw material and Ta raw material, stirring uniformly after complete melting, and then reducing to 725-735℃ for 20-30 min;

[0016] 3) Refining: refining by isolating oxygen, then holding at 720-730 DEG C for 10-15 min, then pouring after slagging and removing the film after cooling, to obtain Al-Ce-Si alloy ingot.

[0017] In some examples, the preheating temperature in step 1) is 150-170 DEG C, and the preheating time is 30-40 min.

[0018] In some examples, the refining time of step 3) is 6-10 min.

[0019] In some examples, the Ce raw material is Al-20Ce alloy, the Si raw material is Al-20Si alloy, and the Ta raw material is Al-5Ta alloy.

[0020] In a third aspect, the application provides the use of the Al-Ce-Si casting alloy provided in the first aspect in the preparation of engine parts.

[0021] The beneficial effects of the application are:

[0022] The application selects Si element to add to the Al-Ce casting alloy, and controls the Si content at 0.5-2.5%, which can effectively improve the strength of the alloy. On the one hand, after Si is added to the alloy, there is a eutectic reaction of L→ α-Al + AlCeSi during solidification, and finally a lamellar eutectic structure with small spacing is formed. Compared with the Chinese character-shaped Al 11 Ce3 phase, the lamellar AlCeSi phase has a longer coarsening time at high temperature and has higher heat resistance, greatly improving the high temperature strength of the alloy. On the other hand, Si can modify the morphology of Al 11 Ce3 phase, promote the Al 11 Ce3 phase to change from Chinese character-shaped to fibrous and distribute on the eutectic colony boundary, which is beneficial to strengthening the weak eutectic colony boundary and hindering the rapid expansion of cracks along the boundary, and finally improves the mechanical properties of the Al-Ce casting alloy.

[0023] The microstructure of the Al-Ce-Si casting alloy of the application contains a large amount of lamellar AlCeSi phase. Unlike the Chinese character-shaped Al 11 Ce3 phase, the length and width of the AlCeSi phase in three-dimensional morphology are larger. Transmission electron microscopy characterization of the alloy structure after high temperature tensile creep test found that the three-dimensional morphology characteristics of the AlCeSi phase can more effectively hinder the movement of dislocations in space, resulting in a large number of dislocation pile-ups near the phase boundary, thereby improving the high temperature creep resistance of the Al-Ce-Si casting alloy.

[0024] The Al-Ce-Si casting alloy of the application adds a small amount of Ta element, which modifies the primary Al 11The morphology and size of Ce3 phase. When Ta element is not contained, the primary Al 11 The Ce3 phase presents long block with square cross section and the size is more than 90 μm. The primary phase does not have the effect of strengthening the aluminum matrix, but rather splits the continuity of the alloy and easily breaks to produce micro cracks, reducing the strength and plasticity of the alloy. After adding Ta element, because the solid solubility of Ta in the aluminum matrix is small, Ta is expelled from the solid phase during the solidification process and enriched in the front of the solid-liquid interface, hindering the growth of the primary Al 11 Ce3 phase, and promoting the primary Al 11 The Ce3 phase is transformed from long block to starburst, and the size is reduced to 30-40 μm. The primary Al 11 The refinement and morphology change of the Ce3 phase are beneficial to reduce the stress concentration and crack initiation of the alloy, and the creep cavities are not easy to produce at the phase boundary during the creep process, enhancing the high temperature creep resistance of the alloy.

[0025] The yield strength of the Al-Ce-Si casting alloy of the present application at room temperature is 115-140 MPa, the tensile strength is 213-230 MPa, the yield strength at high temperature 300℃ is 80-97 MPa, the tensile strength is 128-136 MPa, and the steady-state creep rate after creep for 100h at 300℃ and tensile stress 15 MPa is less than 7.45×10 -9 s -1 The alloy can be used without heat treatment, which is beneficial to save production cost, shorten production cycle and energy saving and emission reduction. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is the metallographic structure picture of the Al-Ce-Si casting alloy prepared in Example 3.

[0027] Figure 2 is the metallographic structure picture of the Al-Ce casting alloy without adding Si and Ta prepared in Comparative Example 2.

[0028] Figure 3 is the transmission electron microscope bright field picture of the Al-Ce-Si casting alloy prepared in Example 3 after creep for 100h at 300℃ / 15 MPa. DETAILED DESCRIPTION

[0029] The present application will be described in detail below in combination with examples, comparative examples and experimental data.

[0030] The chemical composition of the alloy in each embodiment is, in percentage by weight: Ce 10-13%, Si 0.5-2.5%, Ta 0.1-0.35%, unavoidable impurity element content ≤0.1%, and the balance of Al. The raw materials are selected as 99.9% industrial pure aluminum, Al-20Ce, Al-20Si and Al-5Ta intermediate alloy.

[0031] Unless otherwise specified, the instruments, raw materials and reagents involved in the following examples and comparative examples can be obtained through a regular commercial channel.

[0032] Unless otherwise specified, the detection and experimental methods in the following examples and comparative examples are conventional detection and experimental methods in the prior art. Among them, the room temperature tensile test is carried out according to GB / T 228.1-2010, the high temperature tensile test is carried out according to GB / T 228.2-2015, and the high temperature tensile creep test and the acquisition of steady-state creep rate are carried out according to GB / T 2039-2012.

[0033] The following description is only a preferred embodiment of the present application and does not limit the present application. It should be understood that any modification, equivalent replacement, partial improvement, etc. made without departing from the spirit and principles of the present application is considered within the protection scope of the present application.

[0034] Example 1

[0035] The preparation method of the Al-Ce-Si casting alloy of the present embodiment is as follows:

[0036] 1) According to the weight percentage of the constituent elements, take Ce: 10 wt%, Si: 0.5 wt%, Ta: 0.15 wt%, and the balance of Al; first, preheat the above raw materials in a dry box at 160℃ for 35 min;

[0037] 2) Put pure Al into the crucible in the melting furnace, and the melting temperature is 770℃; after the pure Al is completely melted, sequentially add the preheated Al-20Ce, Al-20Si and Al-5Ta intermediate alloy, and after completely melting, stir uniformly, and reduce the furnace temperature to 725℃ and keep for 20 min;

[0038] 3) After the holding is completed, introduce dry high-purity argon into the melt for 8 min, and then adjust the furnace temperature to 720℃ again and keep for 15 min;

[0039] 4) After slagging, the alloy melt is poured into a cast iron mold, and after cooling and demolding, the alloy ingot is obtained.

[0040] Example 2

[0041] The preparation method of the Al-Ce-Si casting alloy of the present embodiment is as follows:

[0042] 1) The weight percentage of the constituent elements is taken as Ce: 12 wt%, Si: 1 wt%, Ta: 0.2 wt%, and the balance is Al; first, the above raw materials are preheated at 160°C in a drying box for 35 min;

[0043] 2) Put pure Al into the crucible in the smelting furnace, and the smelting temperature is 780°C; after the pure Al is completely melted, preheated Al-20Ce, Al-20Si and Al-5Ta intermediate alloy are added in turn, and after completely melted, the temperature is reduced to 730°C and kept for 20 min;

[0044] 3) After the holding is completed, dry high-purity argon is introduced into the melt for 8 min, and then the temperature is adjusted to 725°C again and kept for 15 min;

[0045] 4) After slagging, the alloy melt is poured into a cast iron mold, and after cooling and demolding, an alloy ingot is obtained.

[0046] Example 3

[0047] The preparation method of the Al-Ce-Si casting alloy of this example is as follows:

[0048] 1) The weight percentage of the constituent elements is taken as Ce: 11.5 wt%, Si: 2 wt%, Ta: 0.3 wt%, and the balance is Al; first, the above raw materials are preheated at 160°C in a drying box for 35 min;

[0049] 2) Put pure Al into the crucible in the smelting furnace, and the smelting temperature is 790°C; after the pure Al is completely melted, preheated Al-20Ce, Al-20Si and Al-5Ta intermediate alloy are added in turn, and after completely melted, the temperature is reduced to 735°C and kept for 20 min;

[0050] 3) After the holding is completed, dry high-purity argon is introduced into the melt for 8 min, and then the temperature is adjusted to 730°C again and kept for 15 min;

[0051] 4) After slagging, the alloy melt is poured into a cast iron mold, and after cooling and demolding, an alloy ingot is obtained.

[0052] The metallographic structure picture of the Al-Ce-Si casting alloy prepared in this example is shown in Figure 1 .

[0053] Example 4

[0054] The preparation method of the Al-Ce-Si casting alloy of this example is as follows:

[0055] 1) Ce: 12 wt%, Si: 1.5 wt%, Ta: 0.35 wt%, balance Al in terms of weight percentage; first preheat the above raw materials in a drying box at 160°C for 35 min;

[0056] 2) Put pure Al into the crucible in the smelting furnace, and the smelting temperature is 790°C; after the pure Al is completely melted, preheated Al-20Ce, Al-20Si and Al-5Ta intermediate alloys are sequentially added, and after completely melted, the temperature is stirred uniformly, and the furnace temperature is reduced to 735°C for 20 min;

[0057] 3) After the holding is completed, dry high-purity argon is introduced into the melt for 8 min, and then the furnace temperature is adjusted to 730°C for 15 min;

[0058] 4) After slagging, the alloy melt is poured into a cast iron mold, and after cooling and demolding, an alloy ingot is obtained.

[0059] Example 5

[0060] The preparation method of the Al-Ce-Si casting alloy of this example is as follows:

[0061] 1) Ce: 13 wt%, Si: 2.5 wt%, Ta: 0.3 wt%, balance Al in terms of weight percentage; first preheat the above raw materials in a drying box at 160°C for 35 min;

[0062] 2) Put pure Al into the crucible in the smelting furnace, and the smelting temperature is 800°C; after the pure Al is completely melted, preheated Al-20Ce, Al-20Si and Al-5Ta intermediate alloys are sequentially added, and after completely melted, the temperature is stirred uniformly, and the furnace temperature is reduced to 735°C for 20 min;

[0063] 3) After the holding is completed, dry high-purity argon is introduced into the melt for 8 min, and then the furnace temperature is adjusted to 730°C for 15 min;

[0064] 4) After slagging, the alloy melt is poured into a cast iron mold, and after cooling and demolding, an alloy ingot is obtained.

[0065] Comparative Example 1

[0066] The preparation method of the casting alloy of this comparative example is as follows:

[0067] 1) Ce: 10 wt%, balance Al in terms of weight percentage; first preheat the above raw materials in a drying box at 160°C for 35 min;

[0068] 2) Put pure Al into the crucible in the smelting furnace, the smelting temperature is 770℃; after the pure Al is completely melted, preheated Al-20Ce intermediate alloy is added, after completely melted, stir uniformly, and reduce the furnace temperature to 725℃ for 20 min;

[0069] 3) After the holding is completed, dry high-purity argon gas is introduced into the melt for 8 min, and then the furnace temperature is adjusted to 720℃ for 15 min again;

[0070] 4) After slagging, the alloy melt is poured into a cast iron mold, and after cooling and demolding, an alloy ingot is obtained.

[0071] Comparative Example 2

[0072] The preparation method of the casting alloy of the present comparative example is as follows:

[0073] 1) According to the weight percentage of the constituent elements, take Ce: 13 wt%, and the balance is Al; first preheat the above raw materials in a dry box at 160℃ for 35 min;

[0074] 2) Put pure Al into the crucible in the smelting furnace, the smelting temperature is 770℃; after the pure Al is completely melted, preheated Al-20Ce intermediate alloy is added, after completely melted, stir uniformly, and reduce the furnace temperature to 725℃ for 20 min;

[0075] 3) After the holding is completed, dry high-purity argon gas is introduced into the melt for 8 min, and then the furnace temperature is adjusted to 720℃ for 15 min again;

[0076] 4) After slagging, the alloy melt is poured into a cast iron mold, and after cooling and demolding, an alloy ingot is obtained.

[0077] The metallographic structure picture of the casting alloy prepared in this comparative example is shown in Figure 2 .

[0078] Comparative Example 3

[0079] The preparation method of the casting alloy of the present comparative example is as follows:

[0080] 1) According to the weight percentage of the constituent elements, take Ce: 10 wt%, Si: 4 wt%, Ta: 1 wt%, and the balance is Al; first preheat the above raw materials in a dry box at 160℃ for 35 min;

[0081] 2) Put pure Al into the crucible in the smelting furnace, the smelting temperature is 790℃; after the pure Al is completely melted, preheated Al-20Ce, Al-20Si and Al-5Ta intermediate alloys are added in turn, after completely melted, stir uniformly, and reduce the furnace temperature to 730℃ for 20 min;

[0082] 3) After the holding, dry high-purity argon gas is introduced into the melt for 8 min for refining, and then the furnace temperature is adjusted to 720°C again for holding for 15 min;

[0083] 4) After the slagging, the alloy melt is poured into a cast iron mold, and after cooling and demolding, an alloy ingot is obtained.

[0084] Comparative Example 4

[0085] The preparation method of the cast alloy of the present comparative example is as follows:

[0086] 1) According to the weight percentage of the constituent elements, Ce: 12 wt%, Si: 1.5 wt%, and the balance is Al; first, the above raw materials are preheated at 160°C in a dry box for 35 min;

[0087] 2) The pure Al is placed into the crucible in the smelting furnace, and the smelting temperature is 780°C; after the pure Al is completely melted, the preheated Al-20Ce, Al-20Si intermediate alloy is added in turn, and after completely melted, it is stirred uniformly, and the furnace temperature is reduced to 730°C for holding for 20 min;

[0088] 3) After the holding, dry high-purity argon gas is introduced into the melt for 8 min for refining, and then the furnace temperature is adjusted to 720°C again for holding for 15 min;

[0089] 4) After the slagging, the alloy melt is poured into a cast iron mold, and after cooling and demolding, an alloy ingot is obtained.

[0090] Performance detection:

[0091] The alloys prepared in each example and comparative example are subjected to room temperature tensile and high temperature tensile tests, and the compositions of Ce, Si, and Ta in each example are shown in Table 1 below, and the rest is Al and unavoidable impurity elements, and the content of impurities is not more than 0.1 wt%.

[0092] Table 1

[0093]

[0094] According to the standards of GB / T 228.1-2010, GB / T 228.2-2015, and GB / T 2039-2012, the room temperature and high temperature mechanical properties and creep properties of Examples 1-5 and Comparative Examples 1-4 are tested. The performance test results are shown in Table 2.

[0095] Table 2

[0096]

[0097] As can be seen from Table 2, the mechanical properties and high-temperature creep resistance of the alloy prepared by the present application are significantly improved compared with the control group. This is because the addition of Si forms a large number of lamellar eutectic structures with small spacing in the alloy structure, producing significant strengthening effect; on the other hand, the addition of Si forms AlCeSi phase with more resistance to coarsening, which is beneficial to the heat resistance and high-temperature strength of the Al-Ce-Si alloy. Si also promotes the formation of Al 11 Ce3 phase changes from Chinese character shape to fibrous shape and is distributed on the eutectic colony boundary, which can strengthen the alloy matrix and hinder the crack propagation along the boundary.

[0098] Figure 3 is the transmission electron microscope bright field picture of the Al-Ce-Si cast alloy prepared in Example 3 after creep for 100 h at 300℃ / 15 MPa, from which Figure 3 It can be seen that Ta plays a very good modification role, making the primary Al 11 Ce3 phase is refined and the morphology changes to star-shaped, which is beneficial to improve the alloy performance. These lamellar AlCeSi phases have the characteristics of long and wide in three-dimensional morphology, which more effectively hinders the movement of dislocation in the creep process, thereby improving the high-temperature creep resistance of the alloy.

[0099] The above is a further detailed description of the present application, which cannot be regarded as a limitation on the specific implementation of the present application. For ordinary skilled persons in the technical field to which the present application belongs, simple deduction or replacement without departing from the concept of the present application is within the protection scope of the present application.

Claims

1. A high-temperature creep-resistant Al-Ce-Si casting alloy, characterized in that, The alloy has the following composition by mass percentage: Ce 10-13%, Si 0.5-2.5%, Ta 0.1-0.35%, with the balance being Al and unavoidable impurity elements, and the Si / Ta ratio is greater than or equal to 3 by mass percentage.

2. The Al-Ce-Si casting alloy according to claim 1, characterized in that, The alloy has the following composition by mass percentage: Ce 11.5%, Si 2%, Ta 0.3%, with the balance being Al and unavoidable impurity elements.

3. The Al-Ce-Si casting alloy according to claim 1, characterized in that, The content of the unavoidable impurity elements is ≤0.1% by mass percentage.

4. The Al-Ce-Si casting alloy according to claim 1, characterized in that, The steady-state creep rate of the Al-Ce-Si cast alloy after creeping for 100 hours at 300℃ and under a tensile stress of 15 MPa is ≤7.45×10⁻⁶. -9 s -1 .

5. The method for preparing the Al-Ce-Si casting alloy according to any one of claims 1 to 4, characterized in that, Includes the following steps: 1) Batching: Weigh Al raw materials, Ce raw materials, Si raw materials, and Ta raw materials according to the proportions and preheat them; 2) Melting: Heat the preheated pure aluminum to 750-800℃ and melt it completely. Then add the preheated Ce raw material, Si raw material and Ta raw material in sequence. After they are completely melted, stir them evenly and then lower the temperature to 725-735℃ and hold for 20-30 minutes. 3) Refining: Refining in the absence of oxygen, then holding at 720-730℃ for 10-15 minutes, then removing slag and casting, cooling and demolding to obtain Al-Ce-Si alloy ingots.

6. The preparation method according to claim 5, characterized in that, The preheating temperature in step 1) is 150-170℃, and the preheating time is 30-40 min.

7. The preparation method according to claim 5, characterized in that, The refining time in step 3) is 6 to 10 minutes.

8. The preparation method according to claim 5, characterized in that, The Ce raw material is an Al-20Ce alloy, the Si raw material is an Al-20Si alloy, and the Ta raw material is an Al-5Ta alloy.

9. The application of the Al-Ce-Si casting alloy according to any one of claims 1 to 4 in the manufacture of engine parts.

Images