Heat-treatable brazed die-casting aluminum alloy as well as preparation method and brazing optimization process of heat-treatable brazed die-casting aluminum alloy

Abstract

The invention discloses a heat-treatable braze-weldable die-casting aluminum alloy and a preparation method and a brazing optimization process thereof, high-content Mg and Si elements are introduced into the aluminum alloy in a breakthrough mode, a fine and dispersed nanoscale Mg2Si strengthening phase is separated out at the grain boundary after the Mg and Si elements are subjected to brazing and T5 treatment, the strength of the aluminum alloy can be remarkably improved, meanwhile, rare earth is introduced for strengthening, and the strength of the aluminum alloy is improved. The rare earth content is 5.0-10.0%, the rare earth is a hypoeutectic component and has excellent fluidity, meanwhile, La and Ce form an Al11Re3 eutectic phase (the proportion is larger than 30.6%), the high-temperature stability and strength of the aluminum alloy can be improved, Rb in the brazing flux and Mg can form a compound during brazing, inhibition of Mg on the brazing flux is reduced, and the aluminum alloy can be subjected to heat treatment strengthening to meet performance requirements under matching.

Description

Technical Field

[0001] This invention relates to the field of alloy technology, specifically to a heat-treatable brazable die-cast aluminum alloy, its preparation method, and optimized brazing process. Background Technology

[0002] Brazing is a method of achieving permanent connection by wetting the surface of the base material with a filler metal (with a melting point lower than the base material) at high temperature and utilizing capillary action. The brazing temperature for aluminum alloys is around 610℃.

[0003] High-pressure die casting (HPDC) is widely used due to its high efficiency and near-net-shape forming characteristics. However, traditional die-cast aluminum alloys suffer from low solid-liquid phase temperatures, making it difficult to meet the brazing sealing requirements of precision components such as thermal management systems. Currently, brazable aluminum alloys can be broadly classified into three categories: Al-Mn, Al-Ni (Al-Fe-Ni, Al-Mn-Ni), and Al-RE. Existing technologies typically improve the high-temperature stability of the alloy by adding a high proportion of rare earth elements (La, Ce), and combine them with elements such as Fe, Mn, and Cr to improve anti-adhesion properties and grain refinement. While this can meet the brazing requirements, the added elements have low solid solubility, making it impossible to improve material strength through heat treatment. This low strength leads to easy deformation during post-brazing processing, resulting in low yield rates in mass production and a significant increase in costs.

[0004] Furthermore, traditional brazable die-cast aluminum alloys require strict control of Mg and Si content because high Mg and Si content can affect brazing quality. During the brazing process, elements such as Mg will react chemically with surface oxides, such as generating MgO and Al2MgO4, and react chemically with flux to generate MgF2, KMgF3, K2MgF4, etc., which seriously affect brazing quality and needs to be improved. Summary of the Invention

[0005] To address at least one of the aforementioned technical deficiencies, the present invention provides the following technical solution: The first aspect of this invention discloses a heat-treatable, brazable, die-cast aluminum alloy, comprising, by weight, the following components: La, Ce: 5.0%~10.0%; Ni: 0.05%~3.0%; Mg: 0.05%~0.5%; Si: 0.05%~0.5%; V: 0.03%~0.3%; Mn: 0.3%~0.6%; Fe: 0.3%–0.6%, the remainder being Al and unavoidable impurities.

[0006] Furthermore, the mass ratio of La to Ce is 2:3.

[0007] A second aspect of this invention discloses a method for preparing a heat-treatable, brazable die-cast aluminum alloy, comprising the following steps: Step 1: Melt, refine, degas, and remove slag from La, Ce, Ni, Si, V, Mn, Fe, and Al; Step 2: Add Mg into the furnace in the form of an intermediate alloy, so that the mass ratio of La, Ce, Ni, Mg, Si, V, Mn, Fe and Al in the furnace meets the ratio described in claim 1; Step 3: When the density equivalent is ≤0.2%, the molten metal in the furnace is injected into the mold for high-pressure die casting. The mold vacuum degree is 10-35 mBar, the casting pressure is 45-95 MPa, the filling speed is 35-65 m / s, the mold temperature is 120-200℃, and the aluminum liquid temperature is 680-720℃.

[0008] Furthermore, in step 1, La, Ce, Ni, V, Mn, and Fe are all added to the furnace in the form of Al master alloy.

[0009] Furthermore, in step 1, the aluminum alloy refining agent is pressed into the molten metal in the furnace through a degassing machine for refining, and argon gas is introduced. After degassing, the slag is removed and the mixture is left to stand.

[0010] Furthermore, in step 3, the gas content of the molten metal is detected and the density equivalent is calculated. If the density equivalent is >0.2%, the refining and degassing steps continue.

[0011] The third aspect of this invention discloses an optimized brazing process for die-cast aluminum alloys, comprising the following steps: First, the die-cast aluminum alloy prepared above is brazed using a flux containing Rb; Second, the brazed aluminum alloy is strengthened by heat treatment.

[0012] Furthermore, the composition of the flux, by weight, is as follows:

[0013] Furthermore, the heat treatment strengthening parameters are as follows: hold at 180-200℃ for 1.5-3 hours.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This aluminum alloy has made a breakthrough by introducing high content of Mg and Si elements, breaking the industry's prejudice. After brazing and T5 treatment, Mg and Si elements precipitate fine and dispersed nano-sized Mg2Si strengthening phases at the grain boundaries, which can significantly improve the strength of the aluminum alloy.

[0015] 2. This aluminum alloy is strengthened by introducing rare earth elements, with a rare earth content of 5.0-10.0%. It is a hypoeutectic composition, exhibiting excellent fluidity. Simultaneously, La+Ce forms Al... 11The Re3 eutectic phase (accounting for more than 30.6%) can improve the high-temperature stability and matrix strength of aluminum alloys.

[0016] 3. High-Temperature Strength: Nickel's high melting point (1455℃) and stability allow it to maintain its performance at high temperatures. Adding nickel to aluminum alloys forms stable intermetallic compounds (such as Al3Ni). These phases are less prone to coarsening at high temperatures, effectively hindering dislocation movement and thus improving the alloy's high-temperature strength and creep resistance. Furthermore, the addition of nickel optimizes the oxide film structure, enhancing the alloy's corrosion resistance in specific corrosive environments (such as sulfur-containing or alkaline media).

[0017] 4. Multi-component microalloying: Fe and Mn form the Al6Mn dispersed phase, which can inhibit grain growth and improve anti-adhesion properties; V and Al can form stable intermetallic compounds (such as Al7V). These nanoscale precipitates act as non-uniform nucleation sites during solidification, which can inhibit excessive grain growth and thus refine α-Al grains. Vanadium can reduce the segregation tendency of alloying elements (such as rare earth and magnesium) during solidification, especially for cast aluminum alloys with high rare earth content (such as La+Ce=5%-10%), avoiding hot cracking or performance fluctuations caused by local compositional inhomogeneity.

[0018] 5. In this process, a flux containing Rb is used for brazing. During the brazing process, Rb reacts with the high content of Mg in the aluminum alloy to form RbMgF3 and / or Rb4Mg3F. 10 The presence of compounds such as magnesium reduces the inhibition of flux, greatly improving the brazing performance of high-Mg cast aluminum alloys. Subsequently, heat treatment strengthens the aluminum alloy by forming a Mg2Si strengthening phase from Mg and Si, thereby improving the mechanical and other properties of the aluminum alloy. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a SEM image of the aluminum alloy after brazing in Example 1.

[0021] Figure 2 Metallographic images of the weld corner positions of Comparative Example 1, Comparative Example 2, and Example 8.

[0022] Figure 3 It is a temperature curve during brazing. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0024] The component mass ratios of the aluminum alloys in each embodiment are shown in Table 1, and the preparation methods of the aluminum alloys in each embodiment are as follows: Step 1: Material preparation. The raw materials are as follows: A00 aluminum ingot, Al(La+Ce)40, AlMg50, 3303Si, AlNi10, AlV10, AlMn10 and AlFe10 master alloy as raw materials, with the mass ratio of La to Ce being 2:3.

[0025] The furnace is gradually heated to bake away the moisture inside. During the heating process, A00 aluminum ingots, weighed according to the ratio, are placed on the side of the furnace for baking and then put into the furnace. The furnace is heated and melted to obtain molten aluminum.

[0026] After the A00 aluminum ingot is melted, the Al(La+Ce)40, 3303Si, AlV10, AlNi10, AlMn10 and AlFe10 master alloys are placed on the side of the furnace for baking and then put into the furnace. The furnace temperature is 720℃. Stir until fully dissolved and let stand.

[0027] The aluminum alloy refining agent (560RF sodium-free refining agent) was forced in using a degasser for refining. 99.999% argon gas was introduced and the refining time was 15 minutes. After degassing, the slag was removed and the mixture was allowed to stand.

[0028] Step 2: Add the AlMg50 master alloy into the furnace until it melts.

[0029] If the aluminum alloy composition reaches the preset mass percentage, then the gas content is tested and the density equivalent is calculated to be ≤0.2%. If not, the elements that have not reached the preset mass percentage are added to achieve the preset mass percentage.

[0030] Step 3: Detect the gas content, and when the density equivalent is ≤0.2%, inject the molten metal in the furnace into the mold for high-pressure die casting. High-pressure die casting is carried out using a 500T high-pressure die casting equipment. Mold vacuum degree: 25mBar, casting pressure: 80MPa, injection speed: 50m / s, mold temperature: 130℃, and temperature of aluminum alloy liquid at injection: 690±2℃.

[0031] Table 1. Component Table

[0032] Note: Aluminum and unavoidable impurities are not shown in Table 1.

[0033] Meanwhile, common aluminum alloys on the market were used as a comparison, and the composition of aluminum alloys is shown in Table 2.

[0034] Table 2, Component Table

[0035] Note: Aluminum and unavoidable impurities are not shown in Table 2.

[0036] The aluminum alloys in the embodiments and comparative examples were brazed and heat-treated as follows; The optimized brazing process for aluminum alloys includes the following steps: First, the die-cast aluminum alloy prepared above is brazed using a flux containing Rb. The flux composition, by mass, is as follows: 20 wt.% (kAlF4 + Rb3AlF6) aqueous solution, with a kAlF4 to Rb3AlF6 mass ratio of 1:1. Nitrogen is used as the shielding gas during brazing. The temperature profile during brazing is shown below. Figure 3 As shown, the time was 1 hour, after which the furnace temperature was cooled down to 280°C (i.e., furnace cooling), and then cooled down to room temperature by air (i.e., air cooling).

[0037] Second, the brazed aluminum alloy is subjected to heat treatment for strengthening at a temperature of 200℃ for 2 hours.

[0038] The aluminum alloys in each embodiment and comparative example were tested for performance and solidus temperature before and after brazing. The mechanical properties were tested in accordance with the requirements of GB / T228-2021, and the test data are shown in Tables 3 and 4.

[0039] Table 3. Performance Test Data

[0040] Table 4: Mechanical properties after brazing heat treatment

[0041] According to the results in Tables 3 and 4 above, within the composition range of this invention, after brazing and T5 heat treatment, the alloy achieves a tensile strength of over 259 MPa, a yield strength of over 130 MPa, an elongation of over 12%, and a Brinell hardness greater than 80 HBW, indicating excellent brazing quality. Based on the test performance data of Comparative Example 1 and... Figure 2 It can be seen that when Mg and Si are not added to the alloy, the as-cast strength is low, the strength is not improved by heat treatment, and there are voids at the weld after brazing. Based on the test performance data of Comparative Example 2 and... Figure 2 It is evident that when more than 0.5% of Mg and Si are added to the alloy, the solidus line drops sharply, and melting occurs during the brazing process, making brazing impossible. This indicates that the Mg and Si content has a significant impact on the alloy strength and brazing performance, and their content must be strictly controlled. Comparative Example 3 shows that traditional Al-Si materials cannot be brazed. Comparative Examples 4 and 5 show that Al-Mn and Al-Ni alloys without the addition of Mg and Si have low strength, and the strength is not improved after heat treatment; furthermore, porosity exists at the weld seam after brazing.

[0042] Figure 1 The image shows a SEM image of the brazed aluminum alloy. It can be seen that the α-Al grains are rounded and about 10 μm in size, and the Al-(La+Ce) eutectic is uniformly distributed at the grain boundaries. Figure 2 The metallographic image of the weld joint shows that the weld joint of this aluminum alloy is relatively full with no obvious pores, indicating that the alloy has excellent brazing performance. In contrast, the aluminum alloy in Comparative Example 1 / 2 has low strength, and the material softens and deforms during the brazing process, resulting in a loose weld and a large number of pores in the weld.

[0043] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A heat-treatable, brazable die-cast aluminum alloy, characterized in that, By mass, it includes the following components: La, Ce: 5.0%~10.0%; Ni: 0.05%~3.0%; Mg: 0.05%~0.5%; Si: 0.05%~0.5%; V：0.03%～0.3%； Mn: 0.3%~0.6%; Fe: 0.3%–0.6%, the remainder being Al and unavoidable impurities.

2. The heat-treatable, brazable die-cast aluminum alloy as described in claim 1, characterized in that: The mass ratio of La to Ce is 2:

3.

3. A method for preparing a heat-treatable, brazable die-cast aluminum alloy, characterized in that: Includes the following steps: Step 1: Melt, refine, degas, and remove slag from La, Ce, Ni, Si, V, Mn, Fe, and Al; Step 2: Add Mg into the furnace in the form of an intermediate alloy, so that the mass ratio of La, Ce, Ni, Mg, Si, V, Mn, Fe and Al in the furnace meets the ratio described in claim 1; Step 3: When the density equivalent is ≤0.2%, the molten metal in the furnace is injected into the mold for high-pressure die casting. The mold vacuum degree is 10-35 mBar, the casting pressure is 45-95 MPa, the filling speed is 35-65 m / s, the mold temperature is 120-200℃, and the aluminum liquid temperature is 680-720℃.

4. The method for preparing a heat-treatable, brazable die-cast aluminum alloy as described in claim 3, characterized in that: In step 1, La, Ce, Ni, V, Mn, and Fe are all added to the furnace in the form of Al master alloy.

5. The method for preparing a heat-treatable, brazable die-cast aluminum alloy as described in claim 3, characterized in that: In step 1, the aluminum alloy refining agent is pressed into the molten metal in the furnace through a degassing machine for refining, and argon gas is introduced. After degassing, the slag is removed and the mixture is left to stand.

6. The method for preparing a heat-treatable, brazable die-cast aluminum alloy as described in claim 3, characterized in that: In step 3, the gas content of the molten metal is detected and the density equivalent is calculated. If the density equivalent is >0.2%, the refining and degassing steps continue.

7. An optimized brazing process for die-cast aluminum alloys, characterized in that: Includes the following steps: First, the die-cast aluminum alloy prepared according to any one of claims 3-6 is brazed using a flux containing Rb; Second, the brazed aluminum alloy is strengthened by heat treatment.

8. The optimized brazing process for die-cast aluminum alloys as described in claim 7, characterized in that: The flux composition by weight is as follows:

9. The optimized brazing process for die-cast aluminum alloys as described in claim 7, characterized in that: The heat treatment strengthening parameters are as follows: hold at 180-200℃ for 1.5-3 hours.

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