A corrosion-resistant magnesium alloy with high contents of zn and al and a preparation method thereof

Abstract

The application discloses a kind of corrosion-resistant magnesium alloy based on high Zn, Al content and preparation method thereof, the magnesium alloy includes the following mass percentage components: Zn 5%~8%, Al 5%~15%, Y 0.1%~3%, Mn 0.1%~2%, the balance is Mg and inevitable impurities.The application utilizes the synergistic effect of Al and Zn, Y element, forms dispersed distribution Al2Y, Mg-Al-Y-Zn and Mg-Al-Y phase in as-cast structure, effectively refines grain and blocks corrosion propagation channel, meanwhile, the solid solution effect of Al element promotes the formation of continuous and dense composite protective film on the substrate surface.The alloy does not need complex surface treatment or heat treatment, and the hydrogen evolution corrosion rate in 3.5% NaCl solution can be as low as 0.3 mm / a.The application not only significantly improves the intrinsic corrosion resistance of high Zn, Al content corrosion-resistant magnesium alloy, but also has low cost and simple process, providing a new idea for the large-scale application of corrosion-resistant as-cast magnesium alloy.

Description

Technical Field

[0001] This invention relates to the field of metallic materials technology, and in particular to a corrosion-resistant magnesium alloy based on high Zn and Al content and its preparation method. Background Technology

[0002] Magnesium alloys, as the lightest structural metal materials currently available, possess high specific strength and excellent vibration damping properties, demonstrating enormous potential for lightweight applications in aerospace, rail transportation, automotive industry, and 3C electronics. Among the many magnesium alloy systems, Mg-Zn alloys have become an important branch of magnesium alloy research and application due to the significant solid solution strengthening effect of Zn and the low price and abundant resources of raw materials.

[0003] However, poor intrinsic corrosion resistance has always been a bottleneck restricting the large-scale application of Mg-Zn alloys. Studies have shown that high Zn content (5-9%) leads to the formation of a large number of Mg-Zn eutectic phases in the magnesium matrix. These second phases have a large potential difference with the Mg-Zn matrix, forming a dense micro-galvanic corrosion network. In the presence of Cl... - The high corrosion rate of ions in solution severely limits their application range.

[0004] To address these issues, existing technologies typically employ surface treatment techniques such as micro-arc oxidation, electroless plating, and laser cladding. While these methods can isolate corrosive media in the short term, they do not alter the intrinsic corrosion resistance of the alloy matrix. Furthermore, surface coatings are costly to manufacture, involve complex processes, and carry the risk of overall protective failure once scratched or peeling off. In recent years, a few studies have attempted to add rare earth elements to Mg-Zn alloys to improve their corrosion resistance, but these have mostly focused on heavy rare earth elements such as Gd and Nd. This not only significantly increases the production cost of the alloy but also often requires complex subsequent heat treatments (such as solution treatment and aging) or large deformation processing to be effective, which does not meet the industrialization requirements of low cost and short processing steps.

[0005] In summary, how to directly improve the intrinsic corrosion resistance of Mg-Zn alloys under as-cast conditions through reasonable composition design while maintaining low cost, thereby blocking corrosion propagation channels, is a technical problem that urgently needs to be solved in the field of magnesium alloys. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to provide a corrosion-resistant magnesium alloy with high Zn and Al content and its preparation method, which solves the serious corrosion problem caused by excessive Mg-Zn eutectic phase due to high Zn content in traditional Mg-Zn alloys.

[0007] To address the aforementioned technical problems, this invention employs the following technical solution: a corrosion-resistant magnesium alloy based on high Zn and Al content, wherein the magnesium alloy comprises the following components by mass percentage: Zn 5~8%, Al 5~15%, Y 0.1~3%, Mn 0.1~2%, with the balance being magnesium and unavoidable impurities. Thus, this alloy system is based on Mg-Zn, utilizing the synergistic effect of high Zn and Al content combined with rare earth elements Y and Mn. Even trace amounts of rare earth Y can form a dispersed Y-containing phase in the as-cast microstructure, effectively refining the grains and suppressing the continuous distribution of the Mg-Zn eutectic phase, significantly reducing the corrosion rate. Furthermore, a high content of Al is introduced, utilizing the synergistic effect of Al with Zn and Y elements to form a highly thermally stable phase in the melt; additionally, Al consumes Zn at grain boundaries, blocking corrosion propagation channels; simultaneously, the solid solution effect of Al can generate a continuous and dense composite film on the matrix surface. With the above-mentioned component combination, the magnesium alloy obtained in the as-cast state, without the need for expensive heavy rare earth elements or complex heat treatment, exhibits a hydrogen evolution corrosion rate of 0.1~0.4 mL / cm² in 3.5% NaCl solution. 2 / day (0.3~1.0 mm / a), reducing material costs and production cycle. Preferably, the magnesium alloy comprises the following components by mass percentage: Zn 5~7%, Al 6~12%, Y 0.5~2%, Mn 0.1~1%, with the balance being magnesium and unavoidable impurities. This achieves an Al / Zn ratio balance, maximally suppressing the formation of a continuous network Mg-Zn phase and promoting the formation of a denser, self-healing composite oxide film on the substrate surface, significantly improving performance in Cl... - Stability in ionic environments. More preferably, the magnesium alloy comprises the following components by mass percentage: Zn 6%, Al 6%, Y 1%, Mn 0.3%, with the balance being magnesium and unavoidable impurities.

[0008] Furthermore, the microstructure of the magnesium alloy contains dispersed γ-containing phases, mainly including Al₂Y, Mg-Al-Y-Zn, and Mg-Al-Y phases. Among these, the Al₂Y phase exhibits extremely high thermal and chemical stability, playing a role in nucleation and grain refinement during alloy solidification. The dispersed Mg-Al-Y-Zn composite phases break away from the traditional Mg... 17 Al 12 The continuous distribution of the phase at the grain boundaries alters the potential distribution at the grain boundaries, creating a more uniform microenvironment for electrochemical potential, thereby significantly reducing the risk of localized perforation corrosion.

[0009] Furthermore, the impurity content in the alloy is less than 0.02%, with the mass percentages of harmful impurities Fe, Cu, and Ni limited to: Fe ≤ 0.005%, Cu ≤ 0.005%, and Ni ≤ 0.001%, respectively. Fe, Cu, and Ni have extremely low solid solubility in magnesium alloys and their potentials are much higher than those of the magnesium matrix, making them highly susceptible to forming strong micro-cell corrosion centers. By limiting these elements to extremely low levels (ppm), the internal galvanic cell effect is weakened at its source, and together with other elements, a highly corrosion-resistant alloy system is constructed.

[0010] Another object of the present invention is to provide a method for preparing the above-mentioned corrosion-resistant magnesium alloy based on high Zn and Al content, comprising the following steps: S1: Pure aluminum, pure zinc, pure magnesium, Mg-Y master alloy and Mg-Mn master alloy are used as raw materials for component mixing. Then, pure Mg is heated to melt under a protective atmosphere. Pure aluminum, pure zinc Mg-Y master alloy and Mg-Mn master alloy are then added. After complete melting, an alloy melt is obtained.

[0011] S2: The alloy melt obtained in step S1 is stirred and kept at a constant temperature, and then cooled with water to obtain the cast magnesium alloy.

[0012] This simplifies the process, eliminates the need for expensive post-processing heat treatment or large deformation processing (such as extrusion and rolling), significantly reduces energy consumption and production costs, and is beneficial for large-scale industrial production.

[0013] Furthermore, the mass percentage of Y in the Mg-Y master alloy is 20-30%, and the mass percentage of Mn in the Mg-Mn master alloy is 10-30%; the protective atmosphere is a mixture of CO2 and SF6 in a volume ratio of 99:1.

[0014] Furthermore, the heating temperature in step S1 is 680~760℃. This ensures that Al, Zn, and the intermediate alloy are completely melted into the magnesium matrix, while also maintaining the fluidity of the melt, which is beneficial for subsequent casting.

[0015] Furthermore, the stirring method in step S2 is mechanical stirring, and the stirring time is 2-5 minutes. The holding time is 30-50 minutes; the holding process is conducive to the full reaction of solute atoms to form stable phases such as Al2Y. Slag removal is performed before stirring and during the holding process. Multi-stage slag removal effectively removes oxides and inclusions from the melt, greatly improving the purity of the alloy and reducing corrosion nuclei at the source.

[0016] Furthermore, the cooling rate of the water cooling treatment is 110~130℃ / min. In this way, the high cooling rate achieves "non-equilibrium solidification", which allows more alloying elements to dissolve in the matrix, and makes the size of the precipitated Y-containing second phase extremely fine. The second phase is also dispersed and discontinuously distributed, which inhibits the formation of coarse eutectic structure and further improves the strength and corrosion resistance of the alloy.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention is based on in-depth research on the Mg-Zn system. Through the synergistic regulation of high Al content and trace Y elements, highly thermally stable phases such as Al2Y, Mg-Al-Y-Zn, and Mg-Al-Y are formed in the as-cast microstructure. These phases effectively consume Zn elements at grain boundaries, blocking corrosion propagation channels. Simultaneously, through the solid solution effect of Al and the distribution regulation of the second phase, the alloy can form a continuous and dense composite protective film on the substrate surface during corrosion. Experiments show that the corrosion rate of the optimal composition exhibits a significant dynamic fluctuation and decreasing trend over time, demonstrating a "self-healing" characteristic that allows the film to repair itself after damage. Furthermore, the open-circuit potential remains stable, significantly reducing the hydrogen evolution corrosion rate of the alloy in 3.5% NaCl solution to 0.14 mL / cm². 2 / day (0.32 mm / a). This solves the problem of dense microgalvanic corrosion networks formed in traditional Mg-Zn alloys due to their high Zn content.

[0018] 2. This invention uses the lower-cost rare earth element Y to replace the more expensive rare earth elements such as Gd and Nd, and eliminates the need for complex solid solution treatment, aging heat treatment, or large deformation processing such as extrusion and rolling. High corrosion resistance can be achieved simply through casting. This significantly reduces raw material costs and production energy consumption, shortens the manufacturing cycle, simplifies the process, ensures good repeatability, and facilitates large-scale production. Attached Figure Description

[0019] Figure 1 The corrosion resistance of the cast magnesium alloy prepared in this invention is shown in the figures: a) average hydrogen evolution rate, b) hydrogen evolution curve over time, and c) hydrogen evolution rate over time.

[0020] Figure 2 SEM and energy dispersive spectroscopy analysis of the as-cast magnesium alloy prepared in this invention.

[0021] Figure 3 This is an optical morphology image of the cast magnesium alloy obtained by the present invention after corrosion.

[0022] Figure 4 This is an open-circuit potential diagram of the as-cast magnesium alloy prepared according to the present invention.

[0023] Figure 5The image shows the potentiodynamic polarization curve of the as-cast magnesium alloy prepared according to this invention. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to embodiments, but the scope of protection of the present invention is not limited thereto. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods; and unless otherwise specified, the materials used are commercially available.

[0025] I. Preparation method of corrosion-resistant magnesium alloys with high Zn and Al content Example 1 This example uses the following steps: (1) Ingredients: Zn 6%, Y 1%, Al 6%, Mn 0.3%, with the balance being magnesium and unavoidable impurities; Prepare the raw materials according to the above composition and weigh them after polishing them to a metallic luster. The raw materials used are high-purity magnesium (99.99%), pure aluminum (99.99%), pure zinc (99.99%), Mg-30%Y master alloy and Mg-10%Mn master alloy.

[0026] (2) Put pure magnesium into an electric resistance furnace and heat it to 680~760℃ under a protective atmosphere of CO2 and SF6 mixed gas (ratio of 99:1). After it melts, perform the first slag removal treatment. Then put in pure Zn, pure Al and Mg-Y and Mg-Mn master alloys and wait for them to melt completely to obtain a magnesium alloy melt with uniform composition.

[0027] (3) The magnesium alloy melt obtained in step (2) is subjected to a second slag removal treatment, and then mechanically stirred for 2 to 5 minutes. It is then kept at 680 to 760°C for 30 to 50 minutes. During the heat preservation process, the alloy melt is subjected to a third slag removal treatment when the heat preservation time is 20 to 30 minutes. After the heat preservation is completed, it is placed in water to cool to room temperature. The cooling rate is controlled at 110 to 130°C / min to obtain the cast magnesium alloy.

[0028] The component allocation of Examples 2-4 and Comparative Examples 1-6 is shown in Table 1, and the other steps are the same as in Example 1.

[0029] Table 1 II. Performance Verification 1. The cast magnesium alloys of Examples 1-4 and Comparative Examples 1-6 were placed in a 3.5% NaCl solution for corrosion performance testing at room temperature. The average hydrogen evolution corrosion rate over 9 days was recorded using the water displacement method. Before corrosion testing, the sample surface is usually ground and polished. The main purpose of this process is to reduce surface roughness, improve surface uniformity, remove oxide layers and other contaminants, ensure consistency of samples under experimental conditions, and reduce errors caused by surface irregularities, thereby obtaining more accurate and reliable experimental data. The same applies below. The results are as follows: Figure 1 As shown.

[0030] from Figure 1 As shown in a, with the contents of other components remaining constant, the hydrogen evolution corrosion rate of the as-cast magnesium alloy shows a trend of "first decreasing and then increasing" with the increase of Al addition, and the total amount of hydrogen evolution also shows a trend of "first decreasing and then increasing" with the increase of Al addition. Figure 1 c) When the Al addition amount was 6% (Example 1), the hydrogen evolution corrosion rate of the as-cast magnesium alloy was the lowest, at 0.14 mL / cm. 2 / day (0.32 mm / a). Compared to Comparative Example 1 (5.39 mL / cm²), 2 In Example 1, the corrosion rate was significantly reduced. This is because Al can form dispersed particles such as Al2Y, Mg-Al-Y-Zn, and Mg-Al-Y phases in the magnesium matrix, increasing the matrix potential and refining the grains. Furthermore, Al can discretize and spheroidize Zn-rich phases at grain boundaries, hindering corrosion propagation pathways. However, as the Al content increases, the corrosion rate of the as-cast magnesium alloy slightly increases; for example, the corrosion rate of the alloy in Example 4 increased to 0.42 mL / cm². 2 / day (0.96 mm / a), this is because as the amount of Al added increases, a large amount of network Mg is introduced. 17 Al 12 The hard and brittle phase actually accelerates corrosion.

[0031] Furthermore, from Figure 1 The corrosion rate curves in Figure b show that the corrosion rates of Examples 1-4, which exhibit excellent corrosion resistance, show a significant dynamic increase and decrease over time, with overall values ​​being relatively low. This indicates that the alloy composition has a "self-healing" effect on the corrosion film. In contrast, the hydrogen evolution rate curves of Comparative Examples 1-6 show an almost gradually increasing trend. This is because the corrosion film formed by this alloy composition is easily affected by Cl. - Ion damage, and it cannot heal itself.

[0032] 2. The microstructure of the cast magnesium alloys of Examples 1, 4 and Comparative Example 1 was observed using a scanning electron microscope, and the results are as follows: Figure 2 As shown.

[0033] from Figure 2 It can be seen that in the ZW61+0.5Al alloy (Comparative Example 1), a large number of high-potential MgZn phases were formed. Figure 2 The presence of point "A" and Mg-Zn solid solution significantly accelerates the corrosion of the alloy. When the appropriate amount of Al added is controlled, a dispersed Mg-Zn-Al second phase is obtained in the ZW61+6Al alloy (Example 1), which mitigates corrosion from the alloy microstructure perspective. Furthermore, the introduction of a small amount of Y forms second phases such as Al2Y. This is because Al2Y is the most thermodynamically stable high-temperature second phase, playing a role in nucleation and grain refinement during alloy solidification. However, due to the low total Y addition and rapid cooling rate, the volume fraction of most Y-containing second phases is small, making them difficult to capture in spot scan analysis. Nevertheless, this dispersed high-potential phase disrupts the continuous path of corrosion propagation and alters the potential distribution at grain boundaries, thereby significantly reducing the risk of localized perforation corrosion. In the ZW61+15Al alloy (Example 4), with the increase of Al, a large amount of Mg-Al-Zn phase (…) is introduced. Figure 2 The high-potential second phase is distributed in a network on the magnesium alloy matrix, thus increasing the corrosion rate of the alloy.

[0034] The surface scanning results show that Al transforms from a "solid solution → second phase" state with increasing Al content in the alloy. Zn mainly forms the Mg-Al-Zn phase with Al, so Al and Zn exhibit some similarity in their distribution. Y and Mn primarily combine with Al to form Al2Y or Al8Mn5 phases, therefore, with increasing Al content, these two elements tend to aggregate towards the second phase particles.

[0035] 3. The cast magnesium alloys from Examples 1-4 and Comparative Examples 1-6 were immersed in a 3.5% NaCl solution for 9 days. After the immersion, the corrosion on the surface of the magnesium alloys was observed, and the results were as follows: Figure 3 As shown.

[0036] from Figure 3 It can be seen that after the cast magnesium alloy of Example 1 was immersed in 3.5% NaCl solution for 9 days, its surface corrosion was uniform, and some areas were not damaged by corrosion, and these areas were evenly distributed. However, for the alloy of Comparative Example 1 with low Al content, obvious corrosion pits appeared on its surface, and a large amount of white corrosion products were present. For the alloy of Example 4 with high Al content, more obvious corrosion pits also gradually appeared on its surface, which is consistent with the hydrogen evolution data.

[0037] 4. The cast magnesium alloys prepared in Examples 1-3 and Comparative Examples 1 and 3 were subjected to open circuit potential tests. The open circuit potential test is the electrostatic potential at which the anodic dissolution and cathodic reduction reach dynamic equilibrium when the external current is 0. The more positive the value and the more it shifts positively over time, the faster the surface passivation film is formed and the more complete it is, and the better the corrosion resistance of the corresponding magnesium alloy. Conversely, a negative potential and a continuous negative shift indicate that the film layer is broken, the active area is expanded, and corrosion is accelerated.

[0038] like Figure 4 As shown, the initial open-circuit potentials of Comparative Example 1 and Example 3 were -1.66 V and -1.65 V, respectively, and both showed a significant positive shift in open-circuit potential with prolonged immersion time, indicating that a protective corrosion film was gradually forming. However, both examples experienced a sudden drop in open-circuit potential / destruction of the corrosion film at immersion times of 21 min and 26 min, respectively. While Comparative Example 3 and Example 2 did not exhibit this phenomenon during the open-circuit potential test period, their open-circuit potentials remained relatively low, generally between -1.64 V and -1.61 V. The open-circuit potential of Example 1 generally remained between -1.61 V and -1.60 V during the open-circuit potential test period and was relatively stable, indicating that the cast magnesium alloy of the present invention has good corrosion resistance. The above results indicate that when the ZW61 alloy contains too little or too much Al, the corrosion film on the metal surface is easily destroyed by Cl. - Intrusion damage, while appropriately increasing or decreasing the Al content will cause the corrosion film potential to shift negatively, it can improve the stability of the film. When the Al content is adjusted to a suitable ratio (ZW61+6Al), the corrosion film has a relatively stable corrosion potential, which is consistent with the above hydrogen evolution results.

[0039] 5. After immersing the magnesium alloys prepared in Examples 1-2 and Comparative Examples 1 and 3 in a 3.5% NaCl solution for 1 hour, potentiodynamic polarization curves were tested. The potentiodynamic polarization curve test involved applying a continuously varying potential scan to the working electrode, recording the corresponding current response, and fitting the experimentally measured data to obtain the corrosion potential and corrosion current density of the alloy. A more positive corrosion potential and a lower corrosion current density indicate a slower dissolution rate and better corrosion resistance of the magnesium alloy. The experimental results are as follows: Figure 5 As shown in the figure, the corresponding fitting data results are shown in Table 2.

[0040] Table 2 from Figure 5 As can be seen from Table 2, compared to Comparative Examples 1 and 3, Example 1 has the most positive corrosion potential and the lowest corrosion current density, with a corrosion potential of -1.37 V and a corrosion current density of 1.76 × 10⁻⁶ V. -5 A / cm 2The corrosion current densities of comparative examples 1 and 3 were 2.42 × 10⁻⁶, respectively. -4 A / cm 2 and 5.53×10 -5 A / cm 2 The corrosion potentials were -1.48 V and -1.42 V, respectively, both relatively low, demonstrating the excellent effect of Al addition on improving the corrosion resistance of the magnesium alloy in this system. Conversely, excessively high or low Al content would increase the corrosion current density and negatively shift the corrosion potential. This indicates that the as-cast magnesium alloy of this invention possesses good corrosion resistance.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A corrosion-resistant magnesium alloy based on high Zn and Al content, characterized in that, The magnesium alloy comprises the following components by mass percentage: Zn 5%~8%, Al 5%~15%, Y 0.1%~3%, Mn 0.1%~2%, with the balance being magnesium and unavoidable impurities.

2. The corrosion-resistant magnesium alloy based on high Zn and Al content according to claim 1, characterized in that, The magnesium alloy comprises the following components by mass percentage: Zn 5%~7%, Al 6%~12%, Y 0.5%~2%, Mn 0.1%~1%, with the balance being magnesium and unavoidable impurities.

3. The corrosion-resistant magnesium alloy based on high Zn and Al content according to claim 1, characterized in that, The magnesium alloy, in its as-cast state, exhibits a hydrogen evolution corrosion rate of 0.1–0.4 mL / cm² in a 3.5% NaCl solution. 2 / day.

4. The corrosion-resistant magnesium alloy based on high Zn and Al content according to claim 1, characterized in that, The microstructure of the magnesium alloy contains diffusely distributed Y-containing phases, including Al2Y, Mg-Al-Y-Zn, and Mg-Al-Y phases.

5. The corrosion-resistant magnesium alloy based on high Zn and Al content according to claim 1, characterized in that, The impurity content in the alloy is less than 0.02%, and the mass percentage of harmful impurities Fe, Cu and Ni is limited to: Fe≤0.005%, Cu≤0.005% and Ni≤0.001%, respectively.

6. A method for preparing a corrosion-resistant magnesium alloy with high Zn and Al content as described in claim 1, characterized in that, Includes the following steps: S1: Pure aluminum, pure zinc, pure magnesium, Mg-Y master alloy and Mg-Mn master alloy are used as raw materials for composition and feeding. Then, pure Mg is heated to melt under a protective atmosphere. Then, the polished pure aluminum, pure zinc Mg-Y master alloy and Mg-Mn master alloy are added. After complete melting, the alloy melt is obtained. S2: The alloy melt obtained in step S1 is stirred and kept at a constant temperature, and then cooled with water to obtain the cast magnesium alloy.

7. The method for preparing corrosion-resistant magnesium alloys based on high Zn and Al content according to claim 6, characterized in that, The mass percentage of Y in the Mg-Y master alloy is 20-30%, and the mass percentage of Mn in the Mg-Mn master alloy is 10-30%; the protective atmosphere is a mixture of CO2 and SF6 in a volume ratio of 99:

1.

8. The method for preparing corrosion-resistant magnesium alloys based on high Zn and Al content according to claim 6, characterized in that, The heating temperature in step S1 is 680~760℃.

9. The method for preparing corrosion-resistant magnesium alloys based on high Zn and Al content according to claim 6, characterized in that, The stirring method described in step S2 is mechanical stirring, and the stirring time is 2 to 5 minutes; the heat preservation time is 30 to 50 minutes; and slag removal is performed before stirring and during heat preservation.

10. The method for preparing corrosion-resistant magnesium alloys based on high Zn and Al content according to claim 6, characterized in that, The cooling rate in the water cooling process is 110~130℃ / min.

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