A medium frequency melting method for extrusion ingots with reduced black lines of anodized aluminum

Abstract

The invention belongs to the technical field of preparation of non-ferrous metal materials, and particularly relates to a medium-frequency smelting method for an extrusion ingot for reducing black lines of anodized aluminum. The method comprises the following steps: mixing various components of an aluminum alloy, then smelting at 720-750°C, placing the smelted aluminum alloy in a medium-frequency furnace for refining, wherein the refining comprises refining agent refining and argon refining; the refining agent refining comprises the following steps: adding a refining agent to the smelted aluminum alloy, wherein the medium gas is argon gas, heating the medium-frequency furnace for a period of time, closing the medium-frequency furnace, and standing for a total of at least 10 minutes, and then slagging; after the argon refining is completed, standing for at least 5 minutes, and then slagging; the method can reduce the hydrogen content, improve the effect of the aluminum alloy after anodizing treatment, and especially reduce the phenomenon of black lines of anodized aluminum.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of nonferrous metal materials, and in particular relates to a medium frequency melting method for an extrusion ingot for reducing black lines of anodized aluminum. Background Art

[0002] Al-Mg-Si alloy, i.e. 6XXX series aluminum alloy, has the characteristics of high strength in the solution aging state, good plasticity and excellent weldability. These characteristics enable the alloy to maintain high surface quality and performance after anodizing. Anodizing is an electrochemical process in which a metal is used as an anode in an appropriate electrolyte and an external current is applied to form an oxide film on its surface. For Al-Mg-Si alloy extrusion materials, this process can significantly improve its surface hardness, wear resistance, corrosion resistance and decorative properties.

[0003] Anodizing is a common method for aluminum alloy surface treatment. While improving the surface quality, it may also cause invisible defects to appear, such as black lines, color differences, etc., which may not meet the use requirements. There are many factors that affect the anodizing effect, including ingot raw materials, extrusion process, mechanical polishing and pre-treatment, etc.

[0004] Purification of aluminum alloy melt is one of the basic guarantee measures for producing high-quality aluminum castings. When the gas and inclusion content in aluminum alloy exceeds the standard, its casting performance and mechanical properties will be seriously affected. Therefore, it is an indispensable link to purify the aluminum alloy melt before casting. At present, the main methods of melt treatment in the furnace are adsorption purification, including blowing method and flux method. The blowing method is to blow inert gas (such as nitrogen, argon) into the aluminum melt to form bubbles. During the floating process, the bubbles will absorb the gas and oxide inclusions in the melt and bring them to the surface of the melt. This method has a significant effect on hydrogen removal. Flux method: During the smelting process of aluminum alloy, add appropriate flux. The flux reacts physically and chemically with the impurities in the melt to generate light solid phase components that enter the slag, which are removed during the slag removal operation to purify the melt.

[0005] The hydrogen content in aluminum alloy melt is high, while the solubility of hydrogen in solid aluminum is extremely low, but the solubility in liquid aluminum is very high. In addition, the furnace of the medium frequency furnace is deeper than that of the general rectangular furnace. Due to the influence of the surface tension and liquid static pressure of the aluminum alloy melt, it is relatively difficult for hydrogen and other gases to escape from the melt, and it is more difficult for inclusions to float, which increases the difficulty of removing gases and inclusions. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a medium frequency melting method for extrusion ingots to reduce the black lines of anodizing, reduce the hydrogen content, improve the effect of aluminum alloy after anodizing treatment, especially reduce the black lines of anodizing.

[0007] The embodiment of the present invention provides a medium frequency melting method for an extrusion ingot with reduced black lines of anodized aluminum, wherein the components of the aluminum alloy are mixed, and then melted at 720-750° C. (preferably 725° C.), and the melted aluminum alloy is placed in a medium frequency furnace for refining, wherein the refining includes refining agent refining and argon gas refining;

[0008] The refining agent refining is as follows: adding the refining agent to the smelted aluminum alloy, the medium gas is argon, turning on the intermediate frequency furnace for heating for a period of time, closing the intermediate frequency furnace, and standing, the total time of closing the intermediate frequency furnace and standing is at least 10 minutes (preferably 13 minutes to 20 minutes, more preferably closing the intermediate frequency furnace for 5-6 minutes and standing for 8-10 minutes), and then slagging;

[0009] After the argon refining is completed, the mixture is allowed to stand for at least 5 minutes (preferably 8-10 minutes), and then the slag is removed;

[0010] When the refining agent is refined, the starting temperature is 720-730°C, the medium frequency furnace is turned on for heating for 5-15 minutes (preferably 10 minutes), and the power of the medium frequency furnace is turned on for heating at 10-15% of the rated power (preferably 12-15%).

[0011] Preferably, the refining agent is mk4357B, and 0.8-1.2 kg of the refining agent is added to 1 ton of aluminum alloy.

[0012] Preferably, during the argon refining, medium frequency heating is turned on, heated to 725-735° C., argon is introduced, the argon flow rate is 30-50 L / min, and the argon refining time is 10-15 min, preferably 12 min.

[0013] Preferably, after argon refining is completed and slag is removed, degassing, online grain refinement, filtration, casting, homogenization treatment, and cooling are performed to obtain an ingot for extrusion with reduced black lines of anodized metal.

[0014] Preferably, each component of the aluminum alloy is preheated before smelting, the preheating temperature is 200-300° C., and the preheating time is not less than 1 hour.

[0015] Preferably, before the preheating, the aluminum block is firstly subjected to alkali washing, the alkali being sodium hydroxide with a pH value of 10-12.5, and after the alkali washing, it is rinsed and dried.

[0016] Preferably, the preheating temperature is 250° C. and the preheating time is 2 h.

[0017] Preferably, online grain refinement uses Al-5Ti-B for wire feeding, and the wire feeding ratio is 1.5kg / 1tAl; plate filtration is used for filtration; casting is semi-continuous casting, the casting end temperature is 680-705°C, and the steady-state casting speed is 75-80mm / min; the temperature of homogenization treatment is 560-570°C, and the holding time is 16-20h.

[0018] Preferably, the aluminum alloy includes the following components in weight percentage: Si: 0.7-1.3%, Fe: 0-0.2%, Mn: 0.4-1.0%, Mg: 0.6-1.2%, Ti≤0.05%, and the balance is Al and unavoidable impurities.

[0019] More preferably, the aluminum alloy comprises the following weight percentage components: Si: 0.7-0.8%, Fe: 0.07-0.12%, Mn: 0.6-0.8%, Mg: 0.8-1.0%, Ti: 0.02-0.04%, and the balance is Al and inevitable impurities. Most preferably, it comprises the following weight percentage components: Si: 0.75%, Fe: 0.09%, Mn: 0.7%, Mg: 0.9%, Ti: 0.02%, and the balance is Al and inevitable impurities.

[0020] The beneficial effect of the present invention is that, generally speaking, during the aluminum alloy refining process, the furnace is not turned on for heating, and the slag is directly removed without standing after refining. The present invention firstly increases the degree of chemical reaction between the melt and the refining agent during the degassing process by using a refining agent in combination with medium-frequency heating to assist in refining in the furnace, thereby improving the degassing effect. At the same time, the slag removal process is optimized, and the slag is removed after standing for a certain period of time after refining and degassing. The effective standing after refining with the refining agent can reduce the re-involvement of the slag reacted by the first refining into the melt during the second refining, and the standing after two refinings provides time for inclusions and gas to float, reducing the hydrogen content and slag content of the melt (the slag content will affect the hydrogen content result), thereby improving the quality of the melt.

[0021] The present invention removes the oxide scale on the surface of the raw materials by cleaning and pre-baking them, and preheats the metal to gradually heat up under milder conditions, which helps reduce the oxidation slag and air absorption of the metal during the smelting process, thereby improving the purity and quality of the melt. Refining agents are used in combination with medium-frequency heating to assist in refining in the furnace, which increases the degree of reaction between the melt and the refining agent during the degassing process, thereby improving the degassing effect. At the same time, the slag removal process is optimized, and slag removal is performed after refining and degassing to reduce the second refining from re-involving the slag reacted by the first refining into the melt, thereby improving the quality of the melt. The above process is used to improve the quality of the ingot product from many aspects, thereby reducing the further expansion of defects during the extrusion process, and further reducing the phenomenon of black lines in anodized aluminum. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the scanning result of Example 1.

[0023] Figure 2 This is the scanning result of Example 2.

[0024] Figure 3 This is the scanning result of Comparative Example 1.

[0025] Figure 4 This is the scanning result of Comparative Example 2.

[0026] Figure 5 This is the scanning result of Comparative Example 3. DETAILED DESCRIPTION Example 1

[0027] A medium frequency melting method for an extrusion ingot with reduced black lines of anodized aluminum is provided. The ingredients of the aluminum alloy melt are composed of the following components by weight percentage: Si: 0.75%, Fe: 0.09%, Mn: 0.7%, Mg: 0.9%, Ti: 0.02%, and the balance is Al and unavoidable impurities.

[0028] The steps are:

[0029] The first step is to clean the aluminum ingots. The aluminum ingots are alkaline washed with sodium hydroxide solution with a pH value of 12. After alkaline washing, they are rinsed with water and finally dried with hot air.

[0030] Metal baking and preheating, bake and preheat the master alloy and pure metal materials. Before feeding the aluminum-silicon master alloy, aluminum-iron master alloy, aluminum-manganese master alloy, aluminum-magnesium master alloy, and aluminum-titanium master alloy, put the raw materials into a resistance furnace for baking and preheating. The preheating temperature is 250°C and the time is 2 hours.

[0031] Prepare the cleaned and baked raw materials, calculate and prepare the ingredients according to the designed component requirements, put them into the smelting furnace, heat and melt them at 725℃ in the smelting furnace for 3 hours.

[0032] The second step is refining with refining agent. The refining agent is mk4357B, and the starting temperature is 725℃. The refining time of the refining agent is 15min, the medium gas is argon, and the refining agent addition ratio is 1kg / 1tAl. In the first half of the refining process (i.e. the first 10min), the medium frequency heating is turned on (stirring will be done when the medium frequency heating is turned on), and low power heating is adopted, with the power being 15% of the rated power (the rated power is 1000kw). In the second half of the refining process (i.e. the last 5min), the medium frequency heating is turned off.

[0033] The third step is to continue to turn off the medium frequency heating, let it stand for 10 minutes and then skim off the slag on the surface of the aluminum liquid.

[0034] The fourth step is to turn on the medium frequency heating (use low power heating, the power is 15% of the rated power (rated power is 1000kw), and stir at the same time), and heat to 730℃.

[0035] The fifth step is the second argon refining for 12 minutes, which is carried out with argon gas at a flow rate of 40 L / min.

[0036] Step 6: Turn off the medium frequency heating, let it stand for 10 minutes, and then perform the second slag removal to remove all the slag on the surface of the aluminum liquid. After the slag removal is completed, adjust the melt temperature to 720℃ to measure hydrogen in the furnace.

[0037] Step 7: After the hydrogen measurement is completed, casting is carried out.

[0038] Casting includes the following steps:

[0039] The first step is online processing. The degassing method is a combination of furnace degassing and online degassing, and the medium gas is argon. Then online grain refinement is carried out. The operation is to use Al-5Ti-B for wire feeding, and the wire feeding ratio is 1.5kg / 1tAl. Finally, filtration is carried out. The filtration method is plate filtration, 30PPi+50PPi.

[0040] The second step is semi-continuous casting. The semi-continuous casting parameters are: casting end temperature 690-700℃, steady-state casting speed 78mm / min.

[0041] The third step is homogenization treatment, the homogenization temperature is 565℃, the holding time is 16h, and the cooling method is air cooling + water mist cooling. After homogenization, machining is performed to obtain the extruded billet of target size. Example 2

[0042] Compared with Example 1, the difference is:

[0043] 1. In the medium frequency smelting method, the refining time of the second step refining agent is 12 minutes, the time of opening the medium frequency furnace heating is 6 minutes, the time of closing the medium frequency furnace heating is 6 minutes, and the heating power of the medium frequency furnace is 12% of the rated power.

[0044] 2. In the medium frequency smelting method, the standing time in the third step is 8 minutes, and then the slag is removed.

[0045] 3. In the medium frequency smelting method, the standing time in the sixth step is 8 minutes, and then the slag is removed.

[0046] The rest is the same as Example 1.

[0047] Comparative Examples 1-6

[0048] The differences between the medium frequency melting methods of comparative examples 1-6 and the medium frequency melting method of embodiment 1 are shown in Table 1, and the differences mainly lie in the second step, the third step and the sixth step in the medium frequency melting method.

[0049] The hydrogen content of the aluminum alloy after refining was measured (unit: mL / 100gAl). The results are shown in Table 1.

[0050] Table 1 Refining methods and hydrogen contents of different embodiments and comparative examples

[0051]

[0052] It can be seen from Table 1 that when aluminum alloy is refined with a refining agent, the heating is first turned on and then turned off, and then the slag is removed after standing. Combined with standing and then removing the slag after argon refining, the hydrogen content of the aluminum alloy can be significantly reduced and the refining effect can be improved.

[0053] The ingots obtained in the above examples and comparative examples were subjected to extrusion tests and anodic oxidation trials. During the extrusion test, the extrusion die preheating temperature was 480°C, the ingot casting temperature was 550°C, and the metal outflow rate was 3m / min. After the profile was prepared, it was dyed by anodic oxidation. The aluminum alloys of Examples 1-2 and Comparative Examples 1-3 were scanned, and the scan results were as follows: Figure 1-5 As shown, it can be seen that the method of Example 1-2 effectively eliminates the black line phenomenon of anodizing treatment and effectively improves the quality of anodizing.

[0054] A person skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of protection of the present application is limited to these examples. In line with the concept of the present application, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of different aspects of one or more embodiments of the present application as described above, which are not provided in detail for the sake of simplicity.

[0055] One or more embodiments of the present application are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the present application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of the present application should be included in the protection scope of the present application.

Claims

1. A medium frequency melting method for extrusion ingots to reduce black lines of anodized steel, characterized in that: The components of the aluminum alloy are mixed, and then smelted at 720-750° C. The smelted aluminum alloy is placed in a medium frequency furnace for refining, wherein the refining includes refining agent refining and argon gas refining; The refining agent refining is to add the refining agent to the smelted aluminum alloy, the medium gas is argon, the medium frequency furnace is turned on for heating for a period of time, the medium frequency furnace is turned off, and the medium frequency furnace is left to stand, the total time of turning off the medium frequency furnace and standing is at least 10 minutes, and then the slag is removed; After the argon refining is completed, the mixture is allowed to stand for at least 5 minutes, and then the slag is removed; When the refining agent is refined, the starting temperature is 720-730°C, the medium frequency furnace is turned on for heating for 5-15 minutes, and the power of the medium frequency furnace is turned on for heating at 10-15% of the rated power; The aluminum alloy includes the following components in weight percentage: Si: 0.7-1.3%, Fe: 0-0.2%, Mn: 0.4-1.0%, Mg: 0.6-1.2%, Ti≤0.05%, and the balance is Al and unavoidable impurities.

2. The method according to claim 1, characterized in that: During the argon refining, medium frequency heating is turned on, heated to 725-735° C., and argon is introduced at a flow rate of 30-50 L / min.

3. The method according to claim 1 or 2, characterized in that: After argon refining is completed and slag is removed, degassing, online grain refinement, filtration, casting, homogenization treatment, cooling are carried out to obtain an ingot for extrusion with reduced black lines of anodizing.

4. The method according to claim 1 or 2, characterized in that: Each component of the aluminum alloy is preheated before smelting, the preheating temperature is 200-300°C, and the preheating time is not less than 1 hour.

5. The method according to claim 4, characterized in that: Before the preheating, the aluminum block is firstly subjected to alkali washing, wherein the alkali is sodium hydroxide and the pH value is 10-12.

5. After the alkali washing, the aluminum block is rinsed and dried.

6. The method according to claim 4, characterized in that: The preheating temperature is 250°C and the preheating time is 2h.

7. The method according to claim 3, characterized in that: Online grain refinement uses Al-5Ti-B for wire feeding, and the wire feeding ratio is 1.5kg / 1tAl; plate filtration is used for filtration; casting is semi-continuous casting, the end temperature of casting is 680-705℃, and the steady-state casting speed is 75-80mm / min; the temperature of homogenization treatment is 560-570℃, and the holding time is 16-20h.

Images