A high anodizing quality die cast aluminum alloy formulation
By reducing the silicon and iron content and adding Sr-Ti composite refining agent, combined with argon refining and low-pressure die casting, the anodizing process was optimized, solving the problem of uneven oxide film on die-cast aluminum alloys and achieving high-quality anodizing effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Filing Date
- 2026-05-20
- Publication Date
- 2026-07-10
AI Technical Summary
The high silicon and iron content in existing die-cast aluminum alloys leads to the enrichment or exposure of impurity phases at the interface between the substrate and the film during the anodizing process, resulting in an uneven and dense oxide film, and causing problems such as color difference, pinholes and film peeling.
By reducing the silicon and iron content to ≤0.3% and ≤0.15% respectively, adding a specific mass ratio of Sr-Ti composite refining agent, and combining argon refining for degassing and slag removal with low-pressure die casting, the anodizing process is optimized to form a continuous and uniform oxide film layer.
It significantly reduces interface defects, obtains a uniform and dense oxide film, avoids color difference and pinholes, and improves the adhesion and gloss of the film.
Abstract
Description
Technical Field
[0001] This invention relates to the field of alloy materials and surface treatment technology, and discloses a high-quality anodized die-cast aluminum alloy formulation. Background Technology
[0002] In existing technologies, die-cast aluminum alloys typically use aluminum-silicon alloys. To meet the requirements of filling capacity and anti-sticking in the die-casting process, the silicon content is generally controlled at 6%-12%, and the iron content is controlled at 0.5%-1.2%. After melting, these alloys are die-cast, degreased, alkali-washed, and then directly placed in a sulfuric acid electrolyte for anodizing treatment, forming an oxide film layer on their surface.
[0003] The conventional die-cast aluminum alloys mentioned above have high silicon and iron content. During the anodizing process, the impurity phases formed by silicon and iron cannot be oxidized and consumed. They accumulate or become exposed at the interface between the substrate and the film layer, which destroys the continuity of the film layer. The core problem of the existing technology is that after anodizing, die-cast aluminum alloys are prone to color difference, pinholes and film layer peeling, and cannot form a uniform and dense anodized film layer. Summary of the Invention
[0004] In view of the defects in the existing aluminum-silicon die-cast aluminum alloys, such as high silicon and iron content, impurity phases are enriched or exposed at the interface between the substrate and the film layer during the anodizing process, which leads to color difference, pinholes and peeling of the oxide film and the inability to form a uniform and dense anodized film layer, this invention provides a high-quality anodized die-cast aluminum alloy formula and its preparation process.
[0005] To address the aforementioned technical problems, this invention provides a high-quality anodized die-casting aluminum alloy formulation. By mass percentage, the formulation comprises: Si ≤ 0.3%, Fe ≤ 0.15%, Mg 0.3%-0.8%, Mn 0.2%-0.5%, Cu 0.01%-0.05%, and Sr-Ti composite refining agent 0.05%-0.15%, with the balance being Al and unavoidable impurities. The mass ratio of Sr to Ti in the Sr-Ti composite refining agent is 1:(2-5). The preparation process of the high-quality anodized die-casting aluminum alloy formulation includes the following steps: melting alloy raw materials according to the stated proportions to obtain an alloy melt; introducing argon gas into the alloy melt for refining, degassing, and slag removal treatment; performing low-pressure die casting on the refined, degassed, and slag-removed alloy melt to obtain a die-cast blank; pre-treating the die-cast blank; and anodizing the pre-treated die-cast blank.
[0006] This invention significantly reduces the content of silicon and iron, thereby reducing the total amount of harmful impurity phases such as free silicon and iron-rich phases that do not participate in anodic oxidation film formation. This avoids the enrichment, exposure, and stress concentration of these non-conductive impurity phases at the interface between the substrate and the oxide film. Simultaneously, a specific mass ratio of Sr-Ti composite refining agent is added. Sr adsorbs at the growth interface of the eutectic silicon, altering its growth kinetics and transforming it from a needle-like or plate-like brittle phase into a granular or short rod-like structure. Ti reacts with Al to generate dispersed TiA. L3 intermetallic compounds, acting as heterogeneous nucleation cores, significantly refine the grains of the aluminum alloy matrix. The synergistic effect of these two compounds eliminates the local segregation of impurity phases and greatly reduces the sources of interface defects. Combined with argon refining, degassing, and slag removal processes to remove dissolved hydrogen and non-metallic inclusions from the melt, and then low-pressure die casting to achieve stable layer-by-layer filling of the melt, significantly reduces casting defects such as air entrapment, shrinkage porosity, and oxide inclusions. Finally, during the anodizing process, a continuous, uniform oxide film layer that is firmly bonded to the matrix can be formed, effectively solving the problems of color difference, pinholes, and film peeling in existing technologies.
[0007] Furthermore, in the above technical solution, by mass percentage, the Si content in the die-cast aluminum alloy formula is 0.05%-0.2%, and the Fe content is 0.03%-0.1%; the content of a single impurity in the unavoidable impurities is ≤0.02%; the pretreatment includes alkaline washing and acid washing for film removal, wherein the alkaline washing uses a sodium hydroxide solution with a mass fraction of 5%-8%, and the acid washing uses a nitric acid solution with a mass fraction of 10%-15%.
[0008] In practice, the Si and Fe contents are further limited to the above-mentioned optimal range, which can minimize the volume fraction of harmful impurity phases while ensuring the basic melting and die-casting process performance of the alloy; the content of a single unavoidable impurity is strictly controlled to prevent the formation of other unknown harmful intermetallic compounds; alkaline washing with sodium hydroxide solution of the above-mentioned concentration can quickly dissolve the natural oxide film and oil stains on the surface of the die-cast billet, and then acid washing with nitric acid solution removes the film, neutralizes the residual alkali solution and dissolves the silicon-containing black ash generated during the alkaline washing process, providing a clean and uniform substrate surface for subsequent anodizing.
[0009] Furthermore, in the above technical solution, the Sr-Ti composite refining agent is added in the form of an Al-Sr-Ti master alloy, wherein the mass fraction of Sr in the Al-Sr-Ti master alloy is 5%-10% and the mass fraction of Ti is 15%-25%; the Al-Sr-Ti master alloy is added at a temperature of 720℃-750℃, and after addition, it is stirred at a speed of 200-300r / min for 3-5min, and after standing for 10-15min, argon gas is introduced for refining, degassing and slag removal treatment.
[0010] In practice, adding Sr and Ti elements in the form of an Al-Sr-Ti master alloy can avoid severe burn-off and macroscopic segregation when pure metals are added, and significantly improve the element yield and distribution uniformity. Adding the master alloy in the temperature range of 720℃-750℃ can ensure rapid melting and dispersion of the master alloy, and effectively reduce the high-temperature oxidation burn-off of Sr elements. Through the above stirring and settling parameters, the master alloy can be fully dissolved and uniformly diffused throughout the melt, ensuring the consistency of the refining effect. Argon refining can then further remove any small non-metallic inclusions that may be generated during the refining process.
[0011] Furthermore, in the above technical solution, the refining, degassing, and slag removal treatment of the alloy melt by introducing argon gas is carried out using a rotary jetting device. The argon gas is introduced at a pressure of 0.2-0.4 MPa and a flow rate of 10-15 L / min. The rotor speed of the rotary jetting device is 400-600 r / min, and the refining time is 8-12 min. After refining, the alloy melt is allowed to stand for 15-20 min, and the surface slag is skimmed off.
[0012] In practice, a rotary jetting device is used to introduce argon gas, which breaks the argon gas into a large number of micron-sized fine bubbles, greatly increasing the gas-liquid contact area and significantly improving the degassing efficiency. The optimized combination of argon gas pressure, flow rate, and rotor speed ensures that the bubbles are evenly distributed in the melt and rise slowly, effectively carrying dissolved hydrogen and suspended inclusions in the melt. Controlling the refining time to 8-12 minutes achieves ideal degassing and slag removal effects while avoiding excessive oxidation of the melt and excessive temperature drop. After refining, the melt is allowed to stand and the surface scum is skimmed off, which allows the floating inclusions to be fully separated, further improving the purity of the melt.
[0013] Furthermore, in the above technical solution, the process parameters for low-pressure die casting include: filling pressure of 0.02-0.05 MPa, filling time of 3-6 s, holding pressure of 0.05-0.08 MPa, and holding time of 5-10 s; the injection temperature of the alloy melt is 680℃-710℃, the mold temperature is 200℃-250℃, and a release agent containing zirconium fluoride is sprayed onto the surface of the mold.
[0014] In practice, the aforementioned low-pressure die casting process parameters enable stable, layer-by-layer filling of the alloy melt, significantly reducing the generation of air entrapment and oxide inclusions. Appropriate injection temperature and mold temperature ensure good melt fluidity, avoiding defects such as cold shuts and incomplete filling, while controlling the solidification rate of the casting to prevent coarse grains. Spraying a release agent containing zirconium fluoride onto the mold surface forms a dense, high-temperature resistant isolation film, effectively preventing the casting from sticking to the mold and reducing the residue of the release agent on the casting surface, thus avoiding its adverse effects on the color and adhesion of the subsequent anodized film.
[0015] Furthermore, in the above technical solution, the pretreatment of the die-cast blank includes mechanical polishing, degreasing, and brightening steps in sequence; the degreasing uses a weak alkaline solution containing surfactant, at a temperature of 50℃-60℃, for 3-5 minutes; the brightening uses a mixed acid solution of nitric acid and phosphoric acid with a volume ratio of 1:1, at room temperature, for 1-2 minutes.
[0016] In practice, mechanical polishing is first used to remove the rough layer, flash, and obvious surface defects on the die-cast blank surface to improve surface smoothness. A weak alkaline solution containing surfactant is used for degreasing at the above-mentioned temperature and time, which can gently and efficiently remove surface oil stains while avoiding excessive corrosion of the aluminum alloy substrate by strong alkali. A brightening solution of nitric acid and phosphoric acid mixed in the above-mentioned proportion is used to selectively dissolve the micro protrusions and residual oxide film on the surface, so that the blank surface obtains a uniform metallic luster, laying the foundation for the formation of a uniform film layer in subsequent anodizing.
[0017] Furthermore, in the above technical solution, the electrolyte used in the anodic oxidation treatment comprises 150-180 g / L sulfuric acid, 5-10 g / L oxalic acid, and 3-8 g / L glycerol; the anodic oxidation treatment temperature is 18℃-22℃, and the current density is 1.0-1.5 A / dm³. 2 The oxidation time is 30-45 minutes, and a lead plate is used as the cathode.
[0018] In practice, sulfuric acid is used as the main electrolyte, providing the acidic environment and sulfate ions required for anodizing, promoting the formation and dissolution of the alumina film. Oxalic acid, as an additive, improves the hardness and wear resistance of the oxide film, while also broadening the current density operating range for anodizing. Glycerol, as a corrosion inhibitor, adsorbs onto the oxide film surface, slowing down the chemical dissolution of the oxide film by the electrolyte and improving the film's density. By controlling the electrolyte temperature, current density, and oxidation time, the growth rate and dissolution rate of the oxide film can reach a dynamic balance, forming a suitable and uniformly dense oxide film. Using a lead plate as the cathode provides excellent conductivity and resistance to sulfuric acid corrosion, ensuring the long-term stability of the anodizing process.
[0019] Furthermore, in the above technical solution, by mass percentage, the Mg content in the die-cast aluminum alloy formula is 0.4%-0.6%, the Mn content is 0.3%-0.4%, and the mass ratio of Mg to Mn is (1.2-1.5):1; the anodizing treatment further includes a sealing treatment, which uses deionized water at a temperature of 85℃-95℃ and a sealing time of 15-25 minutes.
[0020] In practice, limiting the content and mass ratio of Mg and Mn within the above range can form appropriate and uniformly distributed Al-Mn and Al-Mg-Mn intermetallic compounds. These compounds can improve the strength and corrosion resistance of the alloy without adversely affecting the color uniformity of the anodic oxide film. After anodizing, high-temperature deionized water is used for pore sealing treatment, which can cause the micropores of the oxide film to undergo a hydration reaction, generating hydrated alumina with volume expansion, thereby sealing the micropores and significantly improving the corrosion resistance, insulation and surface gloss of the oxide film.
[0021] Furthermore, in the above technical solution, after the low-pressure die casting is formed, the step of water mist cooling and quenching the die casting blank is also included. The cooling rate of the water mist cooling and quenching is 15℃ / s-25℃ / s, and after cooling to 150℃-200℃, it is air-cooled to room temperature. The grain size grade of the die casting blank is 6-8, and the size of the iron-rich phase in the microstructure of the die casting blank is ≤5μm.
[0022] In practice, after low-pressure die casting, water mist cooling quenching is performed at the above-mentioned cooling rate. This allows the alloy to quickly pass through the high-temperature phase transformation zone, suppressing the growth and coarsening of the iron-rich phase and controlling its size to within 5μm. At the same time, it further refines the matrix grains, achieving a grain size grade of 6-8. The fine iron-rich phase and uniform equiaxed grain structure can reduce the exposure and local segregation of impurity phases during anodizing, significantly improving the smoothness and gloss of the oxide film and effectively avoiding local color differences.
[0023] Furthermore, in the above technical solution, the Cu content in the die-cast aluminum alloy formula is 0.02%-0.04% by mass percentage; the anodizing treatment adopts a stepped voltage increase method, with an initial voltage of 10V, which is increased to the working voltage at a rate of 2V / min, and the working voltage is 12V-15V; after oxidation at the working voltage for 20-30min, the voltage is reduced to 8V at a rate of 1V / min and maintained for 5-10min.
[0024] In practice, limiting the Cu content to the range of 0.02%-0.04% allows for an appropriate increase in the strength and hardness of the alloy without affecting the color uniformity of the anodic oxide film. The aforementioned stepped voltage ramping method avoids localized current concentration caused by initial high voltage, slows the initial growth rate of the oxide film, and prevents the formation and expansion of pinholes. The subsequent slow voltage reduction and maintenance for a certain period allows for a more uniform pore structure in the oxide film, a stronger bond between the film and the substrate, and further improves the overall quality of the oxide film.
[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0026] 1. This technical solution reduces the number of impurity phases that do not participate in film formation and lowers the source of interface defects by limiting the silicon content to ≤0.3% and the iron content to ≤0.15%. By adding a strontium-titanium composite refiner with a strontium to titanium mass ratio of 1:(2-5), strontium changes the morphology of eutectic silicon and titanium refines the matrix grains. The two work together to eliminate the agglomeration of impurity phases. Combined with argon refining and low-pressure die casting, the hydrogen content of the melt and the risk of gas entrapment are reduced, avoiding color difference, pinholes and film peeling after anodizing, and obtaining a uniform and dense anodized film.
[0027] 2. By limiting the addition temperature and stirring / standing parameters of the aluminum-strontium-titanium master alloy, the uniform dissolution and full reaction of the refining agent were ensured. The use of a fluorinated zirconium release agent, mechanical polishing, and a specific concentration of nitric acid-phosphoric acid mixed acid brightening agent removed the surface segregation layer and residues. In the anodizing stage, a mixed electrolyte of sulfuric acid and oxalic acid containing glycerol was used, supplemented by a step-up voltage method, to slow down the local current concentration in the initial film formation and inhibit the expansion of pinholes. Combined with water mist cooling quenching, the size of the iron-rich phase was controlled within 5 micrometers, which improved the gloss and smoothness of the film. Detailed Implementation
[0028] The present invention will be further described in detail below with reference to embodiments. Those skilled in the art can reproduce the technical solution of the present invention and achieve its claimed technical effects based on the content disclosed in this specification. It should be noted that the following embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention. Any non-substantial improvements and adjustments made based on the core concept of the present invention should fall within the scope of protection of the present invention.
[0029] Example 1: This example provides a high-quality anodized die-cast aluminum alloy. By mass percentage, its composition is: Si 0.1%, Fe 0.05%, Mg 0.5%, Mn 0.35%, Cu 0.03%, Sr-Ti composite refining agent 0.1%, with the balance being Al and unavoidable impurities. Among the unavoidable impurities, the content of a single impurity is ≤0.02%, and the mass ratio of Sr to Ti in the Sr-Ti composite refining agent is 1:3.
[0030] Its preparation method includes the following steps:
[0031] Melting: Weigh out pure aluminum, pure magnesium, pure copper, aluminum-manganese master alloy, aluminum-silicon master alloy, and aluminum-iron master alloy according to the above proportions, put them into a medium-frequency induction melting furnace, heat them to 750℃ to completely melt them, and obtain the alloy melt.
[0032] Addition of refining agent: Cool the alloy melt to 735℃, add Al-Sr-Ti master alloy (where the mass fraction of Sr is 8% and the mass fraction of Ti is 24%), stir at 250r / min for 4min, and let stand for 12min.
[0033] Refining, degassing and slag removal: Argon gas is introduced into the alloy melt using a rotary jetting device for refining. The argon gas pressure is 0.3 MPa, the flow rate is 12 L / min, the rotor speed is 500 r / min, and the refining time is 10 min. After refining, the alloy melt is allowed to stand for 18 min to remove surface slag.
[0034] Low-pressure die casting: The alloy melt is heated to 695℃ for injection, the mold temperature is controlled at 225℃, and the mold surface is pre-sprayed with a release agent containing zirconium fluoride; the low-pressure die casting process parameters are: filling pressure 0.035MPa, filling time 4.5s, holding pressure 0.065MPa, holding time 7.5s, to obtain the die casting blank.
[0035] Water mist cooling quenching: Immediately after die casting, the die casting blank is subjected to water mist cooling quenching at a cooling rate of 20℃ / s. After cooling to 175℃, it is taken out and air-cooled to room temperature.
[0036] Pretreatment: The die-cast blanks are mechanically polished, degreased, and polished in sequence. Degreasing is performed using a weakly alkaline solution containing fatty alcohol polyoxyethylene ether at 55°C for 4 minutes. Polishing is performed using a mixed acid solution of nitric acid and phosphoric acid at a volume ratio of 1:1 at room temperature for 1.5 minutes.
[0037] Anodizing treatment: A mixed electrolyte of sulfuric acid, oxalic acid, and glycerol was used, with sulfuric acid concentration of 165 g / L, oxalic acid concentration of 7.5 g / L, and glycerol concentration of 5.5 g / L; the anodizing temperature was 20℃, and the current density was 1.25 A / dm³. 2 The cathode is made of lead plate; a stepped voltage increase method is adopted: the initial voltage is 10V, which is increased to 13.5V at a rate of 2V / min. After oxidation at this working voltage for 25min, the voltage is reduced to 8V at a rate of 1V / min and maintained for 7.5min.
[0038] Sealing treatment: Place the anodized blank in deionized water at 90℃ for sealing for 20 minutes. After sealing, rinse it with deionized water and blow it dry.
[0039] Example 2: The only difference between this example and Example 1 is that, by mass percentage, the Si content is 0.05% and the Fe content is 0.03%, while the rest of the formulation and preparation method are the same as in Example 1.
[0040] Example 3: The only difference between this example and Example 1 is that, by mass percentage, the Si content is 0.2% and the Fe content is 0.1%, while the rest of the formulation and preparation method are the same as in Example 1.
[0041] Example 4: The only difference between this example and Example 1 is that, by mass percentage, the content of Mg is 0.4%, the content of Mn is 0.33%, and the mass ratio of Mg to Mn is 1.2:1. The rest of the formulation and preparation method are the same as in Example 1.
[0042] Example 5: The only difference between this example and Example 1 is that, by mass percentage, the content of Mg is 0.6%, the content of Mn is 0.4%, the mass ratio of Mg to Mn is 1.5:1, and the rest of the formulation and preparation method are the same as in Example 1.
[0043] Example 6: The only difference between this example and Example 1 is that the Cu content is 0.02% by mass percentage, while the rest of the formulation and preparation method are the same as in Example 1.
[0044] Example 7: The only difference between this example and Example 1 is that the Cu content is 0.04% by mass percentage, while the rest of the formulation and preparation method are the same as in Example 1.
[0045] Example 8: The only difference between this example and Example 1 is that the content of Sr-Ti composite refining agent is 0.05% by mass percentage, the mass ratio of Sr to Ti is 1:2, and the rest of the formulation and preparation method are the same as in Example 1.
[0046] Example 9: The only difference between this example and Example 1 is that, by mass percentage, the content of Sr-Ti composite refining agent is 0.15%, the mass ratio of Sr to Ti is 1:5, and the rest of the formulation and preparation method are the same as in Example 1.
[0047] Example 10: The only difference between this example and Example 1 is that in the argon refining, degassing and slag removal step, the argon gas inlet pressure is 0.2 MPa, the flow rate is 10 L / min, the rotor speed is 400 r / min, and the refining time is 8 min. The rest of the formula composition and preparation method are the same as in Example 1.
[0048] Example 11: The only difference between this example and Example 1 is that in the low-pressure die casting process, the filling pressure is 0.02 MPa, the filling time is 3 s, the holding pressure is 0.05 MPa, the holding time is 5 s, the injection temperature of the alloy melt is 680℃, and the mold temperature is 200℃. The rest of the formula composition and preparation method are the same as in Example 1.
[0049] Example 12: The only difference between this example and Example 1 is that in the anodizing process, the electrolyte temperature is 18°C and the current density is 1.0 A / dm³. 2 The oxidation time was 30 min, and the rest of the formulation and preparation method were the same as in Example 1.
[0050] Comparative Example 1: The only difference between this comparative example and Example 1 is that the Sr-Ti composite refining agent is not added to the formulation, while the rest of the formulation composition and preparation method are the same as those in Example 1.
[0051] Comparative Example 2: This comparative example uses a conventional aluminum-silicon die-cast aluminum alloy in the prior art. By mass percentage, its composition is: Si 8%, Fe 0.8%, with the balance being Al and unavoidable impurities.
[0052] Its preparation method includes the following steps:
[0053] Melting: Weigh the raw materials according to the above proportions, put them into a medium-frequency induction melting furnace, heat them to 760℃ to completely melt them, and obtain the alloy melt.
[0054] Refining: Argon gas is introduced into the alloy melt for 5 minutes to refine it, and after standing for 10 minutes, the scum is skimmed off.
[0055] Die casting: The conventional high-pressure die casting process is adopted, with an injection temperature of 700℃ and a mold temperature of 180℃ to obtain the die casting blank.
[0056] Pretreatment: The die-cast blanks are degreased and alkaline washed sequentially. Degreasing is done with an organic solvent, and alkaline washing is done with a 10% sodium hydroxide solution at a temperature of 60℃ for 5 minutes.
[0057] Anodizing treatment: using 180 g / L sulfuric acid electrolyte, at a temperature of 20℃, and a current density of 1.5 A / dm³. 2 The oxidation time is 30 minutes, and a lead plate is used as the cathode.
[0058] Sealing treatment: Seal the holes with room temperature deionized water for 10 minutes, then remove and blow dry.
[0059] Comparative Example 3: The only difference between this comparative example and Example 1 is that the mass ratio of Sr to Ti in the Sr-Ti composite refining agent is 1:1. The rest of the formulation and preparation method are the same as in Example 1.
[0060] Comparative Example 4: The only difference between this comparative example and Example 1 is that the water mist cooling and quenching step after low-pressure die casting is omitted, and the die-cast blank is directly air-cooled to room temperature. The rest of the formula composition and preparation method are the same as those in Example 1.
[0061] Test method:
[0062] Grain size grade: The microstructure of the die-cast blank was observed using a metallographic microscope and evaluated in accordance with GB / T6394-2017 "Method for determination of average grain size of metals".
[0063] Iron-rich phase size: The average size of the iron-rich phase in the metallographic structure was measured using image analysis. More than 50 iron-rich phase particles were measured for each sample, and the average value was taken.
[0064] Oxide film color difference: The CIELab* value of the oxide film surface is measured using a colorimeter, and the color difference ΔE between the oxide film and the standard white board is calculated. The smaller the ΔE, the more uniform the color.
[0065] Number of pinholes: The oxide film surface was observed using a stereomicroscope, and the number of pinholes was counted per 100 cm. 2 The number of pinholes within the area.
[0066] Film adhesion: Tested according to GB / T9286-1998 "Cross-cut test for paint and varnish film". The adhesion level is divided into 0-5, with 0 being the best and 5 being the worst.
[0067] Surface gloss: The gloss value at 60° on the oxide film surface is measured using a gloss meter. The higher the value, the better the gloss.
[0068] Test results:
[0069] The performance test results of each embodiment and comparative example are shown in Table 1.
[0070] Table 1 Performance test results of each embodiment and comparative example
[0071] Sample number Grain size grade Average size of iron-rich phase (μm) Color difference ΔE <![CDATA[Number of pinholes (pcs / 100 cm 2 )]]> Adhesion rating 60° gloss Example 1 Level 7 2.1 0.32 0 Level 0 89 Example 2 Level 7 1.8 0.28 0 Level 0 91 Example 3 Level 7 2.5 0.38 1 Level 0 86 Example 4 Level 7 2.2 0.35 0 Level 0 88 Example 5 Level 7 2.0 0.30 0 Level 0 90 Example 6 Level 7 2.1 0.33 0 Level 0 88 Example 7 Level 7 2.2 0.34 0 Level 0 87 Example 8 Level 6 2.8 0.42 2 Level 0 84 Example 9 Level 8 1.9 0.29 0 Level 0 90 Example 10 Level 7 2.3 0.36 1 Level 0 87 Example 11 Level 7 2.4 0.37 1 Level 0 86 Example 12 Level 7 2.1 0.35 0 Level 0 88 Comparative Example 1 Level 3 8.7 2.15 28 Level 2 62 Comparative Example 2 Level 2 15.3 4.82 76 Level 4 45 Comparative Example 3 Level 4 7.2 1.87 22 Level 1 67 Comparative Example 4 Level 5 6.5 1.63 19 Level 1 71
[0072] Results analysis:
[0073] All performance indicators of Examples 1-12 are significantly better than those of Comparative Examples 1-4. Among them, Example 1 is the best example, with a grain size of grade 7, an average iron-rich phase size of only 2.1 μm, a color difference ΔE as low as 0.32, no pinholes on the surface, a film adhesion grade of 0, and a gloss of 89 at 60°, exhibiting the best overall performance.
[0074] Examples 2-9, by adjusting the content and ratio of each component within the formulation range defined by this invention, all achieved good anodizing quality, demonstrating that the formulation of this invention has a wide applicability and good robustness. Examples 2 and 9, by further reducing the Si and Fe content or increasing the Sr-Ti composite refining agent content, further reduced the size of the iron-rich phase and slightly improved the color difference and gloss indicators. Examples 3 and 8, near the upper limit of the component content, showed a slight decrease in performance but were still far superior to the comparative examples.
[0075] Examples 10-12 show that by adjusting the key process parameters within the range of preparation process parameters defined in this invention, all performance indicators remained at a high level, indicating that the preparation method of this invention has good process stability and repeatability.
[0076] Comparative Example 1, without the addition of Sr-Ti composite grain refiner, showed coarse matrix grains (only level 3), with an average iron-rich phase size of 8.7 μm. This resulted in a significant increase in color difference and pinhole number after anodizing, and a decrease in film adhesion to level 2. This fully demonstrates the key role of Sr-Ti composite grain refiner in refining grains and eliminating impurity phase segregation.
[0077] Comparative Example 2 uses a conventional high-silicon, high-iron die-cast aluminum alloy formulation and preparation process. Its grain size is only level 2, the average size of the iron-rich phase is as high as 15.3 μm, the color difference ΔE after anodizing reaches 4.82, and the number of pinholes is 76 / 100cm. 2 The film adhesion was only level 4 and the gloss was poor, which is in stark contrast to the technical solution of the present invention. This fully demonstrates the significant technical progress brought about by the present invention through the combination of low silicon and low iron formulation design, composite refinement and special preparation process.
[0078] Comparative Example 3 adjusted the mass ratio of Sr-Ti composite grain refiner to 1:1, which exceeded the 1:(2-5) range specified in this invention. This caused the synergistic grain refinement effect of Sr and Ti to disappear, the grain refinement effect to drop significantly, the size of the iron-rich phase to increase to 7.2 μm, and the quality of anodic oxidation to decrease significantly. This proves that the Sr-Ti mass ratio specified in this invention is the key parameter for obtaining a good grain refinement effect.
[0079] Comparative Example 4 omitted the water mist cooling quenching step. During the cooling process, the iron-rich phase grew to an average size of 6.5 μm, and the grains coarsened to level 5. This resulted in increased color difference, increased number of pinholes, and decreased gloss after anodizing. This fully demonstrates the important role of the water mist cooling quenching step in inhibiting the growth of the iron-rich phase and further refining the microstructure.
[0080] In summary, this invention, through a low-silicon, low-iron formulation design, the addition of a specific mass ratio of Sr-Ti composite refining agent, and an optimized preparation process, reduces the generation of harmful impurity phases at the source, eliminates impurity phase segregation, significantly reduces casting defects, and ultimately obtains a uniform, dense, color-different, pinhole-free, highly adhesive, and glossy anodic oxide film. This solves a long-standing technical problem in the prior art and achieves unexpected technical results.
Claims
1. A high-quality anodized die-cast aluminum alloy formulation, characterized in that, The die-cast aluminum alloy formulation comprises, by weight percentage: Si≤0.3%, Fe≤0.15%, Mg0.3%-0.8%, Mn0.2%-0.5%, Cu0.01%-0.05%, Sr-Ti composite refining agent0.05%-0.15%, balance being Al and unavoidable impurities; The mass ratio of Sr to Ti in the Sr-Ti composite refining agent is 1:(2-5); The preparation process of the high-quality anodized die-cast aluminum alloy formulation includes the following steps: The alloy raw materials are smelted according to the specified proportions to obtain an alloy melt; Argon gas is introduced into the alloy melt for refining, degassing, and slag removal. The alloy melt that has undergone the refining, degassing and slag removal treatment is subjected to low-pressure die casting to obtain a die casting blank; The die-cast blank is pretreated; The pretreated die-cast blanks are then subjected to anodizing.
2. The high-quality anodized die-cast aluminum alloy formulation according to claim 1, characterized in that, By mass percentage, the die-cast aluminum alloy formulation contains 0.05%-0.2% Si and 0.03%-0.1% Fe. The content of any single impurity among the unavoidable impurities is ≤0.02%; The pretreatment includes alkaline washing and acid washing for membrane removal. The alkaline washing uses a sodium hydroxide solution with a mass fraction of 5%-8%, and the acid washing uses a nitric acid solution with a mass fraction of 10%-15%.
3. The high-quality anodized die-cast aluminum alloy formulation according to claim 1, characterized in that, The Sr-Ti composite refining agent is added in the form of an Al-Sr-Ti master alloy, wherein the mass fraction of Sr in the Al-Sr-Ti master alloy is 5%-10% and the mass fraction of Ti is 15%-25%. The Al-Sr-Ti master alloy is added at a temperature of 720℃-750℃. After addition, it is stirred at a speed of 200-300r / min for 3-5min. After standing for 10-15min, argon gas is introduced for refining, degassing and slag removal.
4. The high-quality anodized die-cast aluminum alloy formulation according to claim 1, characterized in that, The refining, degassing, and slag removal treatment of the alloy melt by introducing argon gas is carried out using a rotary jetting device. The argon gas is introduced at a pressure of 0.2-0.4 MPa and a flow rate of 10-15 L / min. The rotor speed of the rotary jetting device is 400-600 r / min, and the refining time is 8-12 min. After refining, let the alloy melt stand for 15-20 minutes and skim off the surface slag.
5. The high-quality anodized die-cast aluminum alloy formulation according to claim 1, characterized in that, The process parameters for low-pressure die casting include: The filling pressure is 0.02-0.05 MPa, the filling time is 3-6 s, the holding pressure is 0.05-0.08 MPa, and the holding time is 5-10 s. The injection temperature of the alloy melt is 680℃-710℃, the mold temperature is 200℃-250℃, and a release agent containing zirconium fluoride is sprayed onto the surface of the mold.
6. The high-quality anodized die-cast aluminum alloy formulation according to claim 1, characterized in that, The pretreatment of the die-cast blank includes mechanical polishing, degreasing and brightening steps in sequence; The degreasing process uses a weak alkaline solution containing surfactants at a temperature of 50℃-60℃ for 3-5 minutes. The light emission process uses a mixed acid solution of nitric acid and phosphoric acid with a volume ratio of 1:1, at room temperature, for 1-2 minutes.
7. The high-quality anodized die-cast aluminum alloy formulation according to claim 1, characterized in that, The electrolyte used in the anodic oxidation process contains 150-180 g / L of sulfuric acid, 5-10 g / L of oxalic acid, and 3-8 g / L of glycerol. The anodizing treatment is performed at a temperature of 18℃-22℃ and a current density of 1.0-1.5A / dm³. 2 The oxidation time is 30-45 minutes, and a lead plate is used as the cathode.
8. The high-quality anodized die-cast aluminum alloy formulation according to claim 1, characterized in that, The die-cast aluminum alloy formula contains 0.4%-0.6% Mg and 0.3%-0.4% Mn by mass percentage, and the mass ratio of Mg to Mn is (1.2-1.5):
1. The anodizing process is followed by a sealing process, which uses deionized water at a temperature of 85℃-95℃ and a sealing time of 15-25 minutes.
9. The high-quality anodized die-cast aluminum alloy formulation according to claim 5, characterized in that, After the low-pressure die casting is formed, the process also includes a water mist cooling and quenching step on the die casting blank. The cooling rate of the water mist cooling and quenching is 15℃ / s-25℃ / s, and after cooling to 150℃-200℃, it is air-cooled to room temperature. The grain size grade of the die-cast blank is 6-8, and the size of the iron-rich phase in the microstructure of the die-cast blank is ≤5μm.
10. The high-quality anodized die-cast aluminum alloy formulation according to claim 7, characterized in that, The Cu content in the die-cast aluminum alloy formulation is 0.02%-0.04% by mass percentage; The anodizing process employs a stepped voltage ramping method, with an initial voltage of 10V, ramping up to the operating voltage at a rate of 2V / min, wherein the operating voltage is 12V-15V. After oxidation at the operating voltage for 20-30 minutes, the voltage is reduced to 8V at a rate of 1V / min and maintained for 5-10 minutes.