A method for reducing casting defects of cast aluminum alloy

Abstract

A method for reducing casting defects of cast aluminum alloys, including aluminum alloy batching, heating, melting and refining, addition of Al-M master alloy, temperature control treatment, pouring and other steps, the process improves the performance of aluminum alloy products. The present invention utilizes the addition of Al-M master alloy and temperature control treatment to precipitate high-melting-point and high-density Al-M intermetallic compounds in the molten metal, promotes its sedimentation by adsorption on the surface of the double-layer oxide film, shortens the sedimentation time and improves the rate, and finally achieves the purpose of improving the purity of the molten metal; at the same time, it can also effectively reduce pores, shrinkage holes and other hole-like defects, and improve the comprehensive performance of aluminum alloy castings. The preparation method of the present invention is simple, easy to operate, and highly practical, which is conducive to its wide application in manufacturing industries such as automotive aluminum alloy parts.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material processing, and in particular relates to a method for reducing casting defects of cast aluminum alloy. Background Art

[0002] Alloy melting is the first step in the casting forming process and is also a key step that directly determines the quality of the casting. Therefore, improving alloy melting technology is of great significance to ensure the subsequent casting process.

[0003] Liquid aluminum alloy reacts strongly with moisture and oxygen in the environment, so it is always covered with an oxide film, which is transiently formed, rough, dry and very stable. The surface turbulence generated during the melting and refining process causes the surface oxide film to be drawn into the molten metal to form double-layer oxide films and bubbles and other entrapment defects, which are the starting point for defects such as pores, shrinkage holes, and thermal cracks, and are important factors affecting the consistency of mechanical properties such as tensile strength, elongation and fatigue strength of castings. At present, the melting technology, degassing and impurity removal technology widely used in the foundry industry will introduce a large amount of double-layer oxide film into the molten metal. At the same time, because the density of the double-layer oxide film is close to that of the liquid aluminum alloy, it is difficult for the double-layer oxide film to escape and be removed from the molten metal without external intervention. The foundry industry lacks effective technology to reduce or even eliminate the defects of the double-layer oxide film. Summary of the invention

[0004] The purpose of the present invention is to propose a method for reducing casting defects of cast aluminum alloys in view of the shortcomings of existing molten metal purification treatment technologies, so as to effectively reduce casting defects in liquid aluminum alloys, especially double-layer oxide film defects.

[0005] In order to achieve the above technical objectives, the present invention adopts the following technical solutions.

[0006] A method for reducing casting defects of cast aluminum alloys described in the present invention comprises the following steps.

[0007] Step 1: Batching: Calculate the theoretical batching amount according to the raw material composition and target composition and take into account the actual burning loss. All raw materials are peeled off the surface oxide layer with an angle grinder and then dried in a drying oven at 200-300℃ to complete the batching.

[0008] Step 2: Furnace cleaning and drying: Clean and wash the inner cavity of the melting furnace, preheat to 300-500℃ and keep warm for 2-3 hours to fully remove moisture, etc.

[0009] Step 3: Add materials for melting: First, add standard grade aluminum alloy ingots or pure aluminum and aluminum master alloy and other raw materials into the preheated melting furnace, heat up with the furnace to 60-115℃ above the alloy liquidus temperature, and let it stand for 15-30min after it is completely melted.

[0010] Step 4: Refining: Use standard liquid aluminum alloy refining process (degassing, impurity removal) to purify the molten metal. After slag removal, adjust the molten metal temperature to 90-105℃ above the alloy liquidus temperature and let it stand for 15-25min.

[0011] Step 5: Add Al-M master alloy: first remove the surface oxide scale of the Al-M master alloy. If the Al-M master alloy is in block form, place it in a high-temperature resistant filter bag, immerse it in the molten metal, and slowly stir the molten metal to melt the Al-M master alloy quickly. If the Al-M master alloy is in rod or wire form, directly immerse it gradually in the molten metal, and slowly move the Al-M master alloy to melt it quickly.

[0012] The M in the Al-M master alloy is a high melting point element with low solubility in Al, and can form an intermetallic compound or a solid solution based on the intermetallic compound with Al. The M element can be V, Ti, Fe, Mo, Nb, W, Cr, Zr or Sc, etc.

[0013] The amount of the Al-M master alloy added is measured based on the amount of the M element added, and accounts for 0.01%-0.5% of the total weight of the molten metal.

[0014] Step 6: Temperature control treatment: Lower the temperature of the melt to 10-40°C above the alloy liquidus temperature, and then raise the temperature to the required pouring temperature.

[0015] During the temperature control treatment, the metal should be kept in a static state, and the temperature control treatment process should be no less than 30 minutes.

[0016] Step 7: Casting: Use gravity casting, counter-gravity casting, pressure casting, tilt casting and other casting techniques to complete the casting.

[0017] The beneficial effects of the present invention are:

[0018] (1) The present invention adds an appropriate amount of Al-M master alloy and uses temperature control treatment to precipitate high-melting-point and high-density Al-M intermetallic compounds in the molten metal, and promotes its sedimentation by adsorbing on the surface of the double-layer oxide film, thereby shortening the sedimentation time and increasing the rate, and ultimately achieving the purpose of improving the purity of the molten metal.

[0019] (2) The present invention can not only reduce double-layer film defects, but also effectively reduce hole defects such as pores and shrinkage holes, thereby improving the comprehensive performance of aluminum alloy castings.

[0020] (3) The present invention is applicable to Al-Si based cast aluminum alloys, Al-Cu based cast aluminum alloys, and Al-Mg based cast aluminum alloys.

[0021] (4) The preparation method of the present invention is simple, easy to operate, highly practical, and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the tensile fracture morphology of the sample in Example 1.

[0023] Figure 2 This is the tensile fracture morphology of the sample in Example 2.

[0024] Figure 3 This is the tensile fracture morphology of the sample in Example 6.

[0025] Figure 4 This is a hole-type casting defect of the sample in Example 1.

[0026] Figure 5 This is the double-layer oxide film casting defect of the sample in Example 1.

[0027] Figure 6 This is the tensile fracture morphology of the sample in Example 7. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and through examples. It should be noted that the accompanying drawings and specific examples are for explanation rather than limitation of the present invention. Example 1

[0029] (1) Alloy composition (mass percentage) of A356 alloy is as follows: Si is 6.50, Mg is 0.30, Cu is 0.1, Fe≤0.12, Mn≤0.05, Zn≤0.05, and the balance is aluminum.

[0030] (2) The alloy with the above ratio was heated to 720°C to melt and then allowed to stand for 20 minutes.

[0031] (3) After degassing, removing impurities and slag, keep the molten metal at 720℃ and let it stand for 30 minutes.

[0032] (4) After pouring the molten metal, the casting is completed in the metal mold. Example 2

[0033] (1) Alloy composition (mass percentage) of A356 alloy is as follows: Si is 6.50, Mg is 0.30, Cu is 0.1, Fe≤0.12, Mn≤0.05, Zn≤0.05, and the balance is aluminum.

[0034] (2) The alloy with the above ratio was heated to 720°C and melted, and then allowed to stand for 20 minutes.

[0035] (3) After degassing, impurity removal and slag removal, keep the molten metal at 720℃ and let it stand for 20 minutes.

[0036] (4) Gradually add rod-shaped Al-10Ti in an amount such that the Ti content in the molten metal is 0.2%.

[0037] (5) Let it stand and keep warm for 30 minutes, then pour the molten metal into the metal mold to complete the pouring. Example 3

[0038] (1) Alloy composition (mass percentage) of A356 alloy is as follows: Si is 6.50, Mg is 0.30, Cu is 0.1, Fe≤0.12, Mn≤0.05, Zn≤0.05, and the balance is aluminum.

[0039] (2) The alloy with the above ratio was heated to 720°C and melted, and then allowed to stand for 20 minutes.

[0040] (3) After degassing, impurity removal and slag removal, keep the molten metal at 720℃ and let it stand for 20 minutes.

[0041] (4) Gradually add rod-shaped Al-10Ti in an amount such that the Ti content in the molten metal is 0.2%.

[0042] (5) Lower the temperature of the molten metal to 690°C and then raise it to the pouring temperature of 700°C, which takes a total of 30 minutes.

[0043] (6) After pouring the molten metal, it solidifies in the metal mold. Example 4

[0044] (1) Alloy composition (mass percentage) of A356 alloy is as follows: Si is 6.50, Mg is 0.30, Cu is 0.1, Fe≤0.12, Mn≤0.05, Zn≤0.05, and the balance is aluminum.

[0045] (2) The alloy with the above ratio was heated to 720°C and melted, and then allowed to stand for 20 minutes.

[0046] (3) After degassing, impurity removal and slag removal, keep the molten metal at 720℃ and let it stand for 20 minutes.

[0047] (4) Gradually add rod-shaped Al-10Ti in an amount such that the Ti content in the molten metal is 0.2%.

[0048] (5) Lower the temperature of the molten metal to 680°C and then raise it to the pouring temperature of 700°C, which takes a total of 40 minutes.

[0049] (6) After the molten metal is poured, it solidifies in the metal mold. Example 5

[0050] (1) Alloy composition (mass percentage) of A356 alloy is as follows: Si is 6.50, Mg is 0.30, Cu is 0.1, Fe≤0.12, Mn≤0.05, Zn≤0.05, and the balance is aluminum.

[0051] (2) The alloy with the above ratio was heated to 720°C and melted, and then allowed to stand for 20 minutes.

[0052] (3) After degassing, impurity removal and slag removal, keep the molten metal at 720℃ and let it stand for 20 minutes.

[0053] (4) Gradually add rod-shaped Al-10Ti in an amount such that the Ti content in the molten metal is 0.2%.

[0054] (5) Lower the temperature of the molten metal to 650°C and then raise it to the pouring temperature of 700°C, which takes a total of 50 min.

[0055] (6) After the molten metal is poured, it solidifies in the metal mold. Example 6

[0056] (1) Alloy composition (mass percentage) of A356 alloy is as follows: Si is 6.50, Mg is 0.30, Cu is 0.1, Fe≤0.12, Mn≤0.05, Zn≤0.05, and the balance is aluminum.

[0057] (2) The alloy with the above ratio was heated to 720°C and melted, and then allowed to stand for 20 minutes.

[0058] (3) After degassing, removing impurities and slag, keep the molten metal at 720℃ and let it stand and keep warm for 20 minutes.

[0059] (4) Gradually add rod-shaped Al-10Ti in an amount such that the Ti content in the molten metal is 0.2%.

[0060] (5) Lower the temperature of the molten metal to 630°C and then raise it to the pouring temperature of 700°C, which takes a total of 60 min.

[0061] (6) After the molten metal is poured, it solidifies in the metal mold. Example 7

[0062] (1) Alloy composition (mass percentage) of A356 alloy is as follows: Si is 6.50, Mg is 0.30, Cu is 0.1, Fe≤0.12, Mn≤0.05, Zn≤0.05, and the balance is aluminum.

[0063] (2) The alloy with the above ratio was heated to 720°C and melted, and then allowed to stand for 20 minutes.

[0064] (3) After degassing, impurity removal and slag removal, keep the molten metal at 720℃ and let it stand for 20 minutes.

[0065] (4) Gradually add rod-shaped Al-10Nb in an amount such that the Nb content of the molten metal is 0.1%.

[0066] (5) Lower the temperature of the molten metal to 630°C and then raise it to the pouring temperature of 700°C, which takes a total of 60 min.

[0067] (6) After the molten metal is poured, it solidifies in the metal mold.

[0068] The results of the tensile properties of the samples of Examples 1 to 7 are shown in Table 1. The tensile fracture morphology is shown in Table 1. Figure 1-Figure 6 There are typical hole-like casting defects and double-layer oxide film on the tensile fracture of the samples in Example 1 and Example 2. Typical casting defects of the sample in Example 1 are as follows: Figure 4 and Figure 5 The tensile fracture of the sample in Example 6 is a typical ductile fracture, and no casting defects are found. The tensile fracture of Example 7 is a typical ductile fracture, and no casting defects are found on the fracture.

[0069] Table 1 Tensile properties of samples of Examples 1-6

[0070] Sample No. Tensile strength (MPa) Elongation (%) Remark Example 1 175 7.1 Without Al-10Ti Example 2 176 7.3 Add Al-10Ti Example 3 177 8.5 Add Al-10Ti and control the temperature to 690℃ Example 4 184 9.7 Add Al-10Ti and control the temperature to 680℃ Example 5 185 11.2 Add Al-10Ti and control the temperature to 650℃ Example 6 198 14.1 Add Al-10Ti and control the temperature to 630℃ Example 7 203 14.6 Add Al-10Nb and control the temperature to 630℃

[0071] As can be seen from Table 1, by comparing the above embodiments and comparative examples, the castings prepared by the process of the present invention have significantly improved tensile strength and elongation compared with the castings in the comparative examples. This is because the process of the present invention adds a temperature control treatment, which promotes the precipitation of high-melting-point AM intermetallic compounds, and then promotes the co-sedimentation of defects such as double-layer oxide films, thereby improving the melt quality and the final casting performance.

Claims

1. A method for reducing casting defects of cast aluminum alloys, Its characteristics are The steps include: Step 1: Calculate the theoretical batching amount according to the raw material composition and target composition and consider the actual burning loss. All raw materials are peeled off the surface oxide layer with an angle grinder and then dried in a drying oven at 200-300℃ to complete the batching; Step 2: Clean and wash the inner cavity of the melting furnace, preheat to 300-500℃ and keep warm for 2-3 hours to fully remove moisture; Step 3: First, add standard grade aluminum alloy ingots or pure aluminum and aluminum master alloys into the preheated melting furnace, heat up to 60-115°C above the alloy liquidus temperature, and stand for 15-30 minutes after it is completely melted; Step 4: Use standard liquid aluminum alloy refining process to purify the molten metal. After slag removal, adjust the temperature of the molten metal to 90-105℃ above the alloy liquidus temperature and keep it at room temperature for 15-25min. Step 5: first remove the surface oxide scale of the Al-M master alloy. If the Al-M master alloy is in block form, place it in a high temperature resistant filter bag, immerse it in the molten metal described in step 4, and slowly stir the molten metal to quickly melt the Al-M master alloy. If the Al-M master alloy is in rod or wire form, directly immerse it in the molten metal step by step, and slowly move the Al-M master alloy to quickly melt it. The M in the Al-M master alloy is a high melting point element, has low solubility in Al, and can form an intermetallic compound or a solid solution based on the intermetallic compound with Al; The amount of Al-M master alloy added is based on the amount of M element added, and accounts for 0.01%-0.5% of the total weight of the molten metal; Step 6: Temperature control treatment: lower the temperature of the melt to 10-40°C above the alloy liquidus temperature, and then raise the temperature to the required pouring temperature; during the temperature control treatment, the metal should be kept in a static state, and the temperature control treatment process should be no less than 30 minutes; Step 7: Use gravity casting, counter-gravity casting, pressure casting, tilt casting and other casting techniques to complete the casting; The cast aluminum alloy is an Al-Si cast aluminum alloy, an Al-Cu cast aluminum alloy, or an Al-Mg cast aluminum alloy.

2. A method for reducing casting defects of cast aluminum alloy according to claim 1, Its characteristics are The M element is V, Ti, Fe, Mo, Nb, W, Cr, Zr or Sc.

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