High plasticity corrosion-resistant magnesium alloy and semi-solid preparation method thereof

Abstract

The application discloses a high-plasticity corrosion-resistant magnesium alloy and a semi-solid preparation method thereof. The high-plasticity corrosion-resistant magnesium alloy is prepared by a semi-solid process and contains, in percentage by mass, Al: 5.5-6.5%, Mn: 0.3-0.45%, Ca: 0.1-0.3%, Ce: 0.2-0.4%, Ba: 0.05-0.15%, and the balance of Mg and inevitable impurities, wherein the atomic ratio of Ca to Al is 0.02-0.03, and the atomic ratio of Ce to Al is 0.007-0.009. The alloy is prepared by Al 11 The complementary distribution of Ce3 and Al2Ca phases cooperatively controls the rheology of the slurry, avoids sticking, and improves corrosion resistance and high-temperature performance. Meanwhile, the adjustment of the surface of the second phase and the solid-liquid interface by Ba can realize stable filling at a high solid phase rate at a lower nozzle temperature, improve the service life of equipment, and be suitable for high-performance precision forming of complex thin-walled structural parts.

Description

Technical Field

[0001] This application belongs to the field of magnesium alloy technology, and specifically discloses a high-plasticity corrosion-resistant magnesium alloy and its semi-solid preparation method. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials currently available, have a density of only 1.74 g / cm³, approximately two-thirds that of aluminum alloys and one-quarter that of steel, making them invaluable in aerospace, transportation, and other fields. Semi-solid forming (SSM) technology, through stirring or temperature control of the alloy melt in a liquid-solid two-phase region, yields a slurry that combines the strength of solid metals with the fluidity of liquid metals. It also allows for precise control of slurry rheology and enables high-density, near-net-shape forming at relatively low temperatures. Magnesium alloys prepared using this technology possess near-spherical, non-dendritic primary phases, exhibiting good strength and plasticity, making them highly suitable for the forming and manufacturing of various magnesium alloy parts. SSM technology solves the problems of porosity defects and hot cracking caused by dendrite growth in traditional casting, as well as the poor formability of complex forging processes. It offers a range of advantages, including heat treatability, good dimensional tolerances, stable mechanical properties, excellent surface quality, adaptability to complex part fabrication, and extended die life.

[0003] However, traditional commercial magnesium alloys such as AM60 have the following problems when used in semi-solid injection molding: Firstly, commercially available particles have melting defects. Currently, commercial magnesium alloy particles are widely used as raw materials in industrial production, undergoing large-scale melting in open or semi-open crucibles before casting. This process suffers from the following technical bottlenecks: First, the large contact area between the melt and air during open melting makes oxidation and combustion more likely, resulting in numerous oxide inclusions. Second, the melt easily absorbs hydrogen and other gases during prolonged holding at high temperatures, leading to increased ingot porosity. Third, the uneven distribution of temperature and composition fields during large-scale melting easily causes macroscopic segregation and compositional fluctuations. Fourth, an oxide layer easily forms on the particle surface during casting, which is difficult to completely eliminate during subsequent semi-solid heating, becoming a source of inclusions in the finished product. These defects directly affect the mechanical properties and reliability of the final product.

[0004] Secondly, while adding more rare earth elements to commercial AM60 can improve performance to some extent, excessive rare earth elements can significantly reduce melt flowability, increase the risk of sticking, and lead to molding difficulties. This is especially true in semi-solid injection molding, where sticking can severely restrict the filling ability of complex thin-walled parts. Adding an appropriate amount of Ca can control the Ca / Al atomic ratio to preferentially form the thermally stable Al2Ca phase, thereby improving high-temperature performance, creep resistance, and flame retardancy. However, if the amount added is too high, oxides can easily form during melting or molding, increasing melt viscous resistance and inducing decreased flowability and sticking risk.

[0005] Third, when using the commonly used commercial magnesium alloy AM60 in SSM, its inherent material properties limit the full realization of the technology's advantages. Traditional alloy design does not fully consider the rheological characteristics of semi-solid injection molding, such as solid fraction control, second-phase thermal stability, and particle remelting behavior, resulting in unstable slurry rheological behavior and numerous molding defects. Furthermore, in actual semi-solid injection molding, traditional AM60 alloys suffer from high nozzle temperatures (approximately 630°C), leading to high equipment heat load and shortened lifespan. Upgrading through alloy design and process adjustments is urgently needed to improve its mechanical properties and flowability, thereby promoting its industrial development in fields such as automotive parts.

[0006] In the prior art, CN120330557A discloses a semi-solid injection-molded high-strength corrosion-resistant magnesium alloy, which is based on a high Al content and combined with Zn, RE, Ca and heat treatment for strengthening. The high Al content promotes the growth of Mg... 17 Al 12 The phase forms a continuous or near-continuous distribution, thus acting as a corrosion pathway blocking phase under certain conditions. While higher Al systems favor Mg... 17 Al 12 Phase formation occurs, but continuous or semi-continuous low-melting-point phases may cause local enrichment of liquid phase, unevenness of solid-liquid interface and instability of flow front under screw shearing, low temperature of nozzle and high speed filling conditions. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this application provides a high-plasticity corrosion-resistant magnesium alloy and its semi-solid preparation method, aiming to solve the problems of poor corrosion resistance, easy film adhesion during forming, insufficient fluidity, and poor compatibility with semi-solid processes in existing magnesium alloys.

[0008] According to one aspect of this application, a high-plasticity corrosion-resistant magnesium alloy is provided, which is prepared by a semi-solid process and comprises, by mass percentage: Al: 5.5%–6.5%, Mn: 0.3%–0.45%, Ca: 0.1%–0.3%, Ce: 0.2%–0.4%, Ba: 0.05%–0.15%, with the balance being Mg and unavoidable impurities. The atomic ratio of Ca to Al is in the range of 0.02–0.03, and the atomic ratio of Ce to Al is in the range of 0.007–0.009.

[0009] Compared with the prior art, the technical solution conceived in this application firstly designs the magnesium alloy system by limiting Al to a lower range of 5.5% to 6.5%, and by using a dual proportional constraint of Ca / Al atomic ratio of 0.02 to 0.03 and Ce / Al atomic ratio of 0.007 to 0.009, guiding the limited Al to preferentially form Al2Ca and Al2O3. 11Thermally stable phases such as Ce3, with the introduction of 0.2%–0.4% Ce element and the control of the Ce to Al atomic ratio within the range of 0.007–0.009, can introduce high-melting-point Al into the alloy. 11 The Ce3 phase allows it to participate in the regulation of rheological behavior as a stable solid phase in the semi-solid temperature range, and Ce forms CeO during corrosion. X Together with Ce(OH)₂, it embeds into the pores of the Mg(OH)₂ corrosion film, significantly improving the film's compactness and hindering the growth of Cl. - During the heating process, the high diffusion coefficient of Ba element is redistributed, which inhibits the coarsening of the second phase and improves the melt fluidity.

[0010] Furthermore, by controlling the Ca content at a relatively low level of 0.1%–0.3% and the Ca / Al atomic ratio within the range of 0.02–0.03, the formation of the Al2Ca phase enhances high-temperature performance while effectively avoiding the sticking problem caused by excessive Ca reactivity, thus achieving synergistic optimization of formability and mechanical properties. If the Ca / Al atomic ratio is too low, the Al2Ca phase will not form sufficiently, resulting in limited improvement in grain boundary pinning, high-temperature strengthening, and creep resistance. If the Ca / Al atomic ratio is too high, too many high-melting-point Ca-containing phases will easily form, increasing the oxidation tendency, leading to increased melt viscosity resistance, decreased fluidity, and increased risk of sticking.

[0011] Secondly, through composition optimization, this application can achieve stable filling of semi-solid slurry with high solids content (5% to 20%) at a lower nozzle temperature (560℃ to 580℃), which is more than 50℃ lower than the 630℃ nozzle temperature of traditional AM60 alloy, significantly reducing heat load, extending the service life of key components such as screw and barrel, and solving the problem of high nozzle temperature leading to short equipment life.

[0012] As a further preferred embodiment, the content of the impurity is less than 0.05%.

[0013] As a further preferred embodiment, the contents of Fe and Ni in the impurities are both less than 0.005%.

[0014] As a further preferred embodiment, the Ce content in the high-plasticity corrosion-resistant magnesium alloy is controlled within the range of 0.25% to 0.35%.

[0015] According to another aspect of this application, a semi-solid preparation method for the above-mentioned high-plasticity corrosion-resistant magnesium alloy is provided, comprising the following steps: S1 prepares magnesium alloy particles, ensuring that the magnesium alloy particles, by mass percentage, comprise: Al: 5.5%–6.5%, Mn: 0.3%–0.45%, Ca: 0.1%–0.3%, Ce: 0.2%–0.4%, Ba: 0.05%–0.15%, with the balance being Mg and unavoidable impurities, while ensuring that the atomic ratio of Ca to Al is in the range of 0.02–0.03, and the atomic ratio of Ce to Al is in the range of 0.007–0.009; S2 melts the magnesium alloy particles to form a semi-solid slurry, and then uses injection molding to obtain a high-plasticity, corrosion-resistant magnesium alloy specimen.

[0016] As a further preferred embodiment, step S1 specifically includes the following sub-steps: S11 places Al-10Mn, pure aluminum ingots, Mg-10Ba, Mg-30Ce, Mg-30Ca, and pure magnesium ingots into a melting container from bottom to top; S12 uses inert gas to rinse the melting container, then evacuates it and melts it, combined with mechanical stirring and ultrasonic treatment to obtain liquid magnesium alloy; S13 adjusts the temperature of the melting vessel and then casts to obtain magnesium alloy ingots; S14 cuts the magnesium alloy ingot to obtain magnesium alloy particles.

[0017] As a further preferred embodiment, in step S12, the mechanical stirring time is 5 min to 15 min, the ultrasonic treatment time is 3 min to 5 min, the ultrasonic treatment frequency is 20 kHz to 25 kHz, and the ultrasonic treatment power density is 280 W / cm² to 300 W / cm².

[0018] As a further preferred embodiment, in step S13, the temperature of the melting container is adjusted to 700℃~720℃; after casting is completed, low-frequency mechanical vibration is applied to the casting mold until the liquid magnesium alloy is completely solidified, wherein the frequency of the low-frequency mechanical vibration is 30Hz~80Hz and the acceleration is 2g~4g.

[0019] As a further preferred embodiment, in step S2, the magnesium alloy particles are heated to 600°C to 620°C to form a semi-solid slurry, wherein the solid fraction of the semi-solid slurry is 5% to 20%.

[0020] As a further preferred embodiment, in step S2, during the injection molding process, the nozzle temperature is 560℃~580℃, the barrel temperature is 620℃~635℃, the screw speed is 70rpm~130rpm, the injection speed is 1.3m / s~1.9m / s, the injection pressure is 540bar~560bar, and the injection time is 140ms~170ms.

[0021] In summary, compared with the prior art, the technical solutions conceived in this application have the following main technical advantages: At the alloy design level, this application, by limiting Al to a lower range of 5.5% to 6.5%, and through dual proportional constraints of a Ca / Al atomic ratio of 0.02 to 0.03 and a Ce / Al atomic ratio of 0.007 to 0.009, guides the preferential formation of Al2Ca and Al from the limited Al content. 11 Thermally stable phases such as Ce3, on the one hand, avoid Al 11 Insufficient Ce3 strengthening phase formation results in limited grain refinement and high-temperature stabilization. Furthermore, it's crucial to avoid forming coarse, brittle, rare-earth-rich phases, which impair plasticity and deteriorate flowability and semi-solid forming compatibility. To address this, introducing 0.2%–0.4% Ce and controlling the Ce / Al atomic ratio within the range of 0.007–0.009 generates Al... 11 The Ce3 phase remains stable within the semi-solid temperature range and can serve as a rheological behavior modulator in the slurry filling process. Simultaneously, this application introduces 0.1%–0.3% Ca and controls the atomic ratio of Ca to Al between 0.02 and 0.03, promoting the formation of a stable second phase dominated by Al2Ca in the microstructure, replacing the Mg with a large potential difference in traditional Mg-Al alloys. 17 Al 12 The brittle phase effectively weakens the driving force of galvanic corrosion. The introduction of trace amounts of Ba further optimizes the solidification behavior of the alloy; its high diffusion coefficient allows it to redistribute during heating, adsorbing onto the surface of the second phase to suppress coarsening, while simultaneously improving melt flow characteristics and reducing the tendency to stick to the film. This application achieves a balance between high-temperature strengthening effects and semi-solid forming adaptability by controlling Ca content at 0.1%–0.3% and synergistically regulating it with trace amounts of Ba.

[0022] At the raw material preparation level, this application abandons the traditional smelting method of commercial particles and adopts vacuum melting coupled with multi-field synergistic processing technology to solve the problem of melt purity from the source. Addressing the inherent defects of traditional large-pot melting that easily introduces oxide inclusions, porosity, and compositional segregation, this application eliminates oxidation reactions through vacuum melting, promotes macroscopic and microscopic homogenization of composition through the synergistic effect of mechanical stirring and ultrasonic treatment, and effectively breaks dendrites, promotes feeding, and suppresses segregation through low-frequency vibration casting, resulting in high-purity, homogeneous, and fine-structured magnesium alloy ingots, providing a high-quality raw material basis for semi-solid injection molding.

[0023] The Fe and Ni contents in the impurities are less than 0.005%, which can effectively inhibit the formation of harmful impurity phases, thereby further improving the corrosion resistance of magnesium alloys. Fe and Ni have extremely low solid solubility in magnesium (Fe < 0.005%, Ni < 0.002%). When their content exceeds the solid solution limit, they precipitate as intermetallic compounds at grain boundaries. The corrosion potential difference between these compounds and the magnesium matrix is ​​as high as hundreds of millivolts, forming a micro-cell effect in the corrosive medium and accelerating localized corrosion. This application strictly controls the Fe and Ni contents, limiting both to below 0.005%, ensuring that they are completely dissolved in the magnesium matrix or below the precipitation threshold of harmful phases. This eliminates the conditions for the formation of strong cathodic phases, making the corrosion process more uniform, effectively inhibiting pitting and intergranular corrosion, and significantly improving the service life of the alloy in harsh environments such as salt spray and humidity.

[0024] At the process adaptation level, the composition design and semi-solid injection molding window of this application work together to precisely control the nozzle temperature within the low-temperature range of 560℃ to 580℃, which is more than 50℃ lower than the 630℃ required by traditional AM60 alloys. This achieves synergistic optimization of energy saving and consumption reduction with long-distance filling, significantly reducing heat load, extending the service life of key components such as the screw and barrel, and solving the problem of high nozzle temperature leading to short equipment life. The above process parameters and alloy composition work together to form a closed-loop control path of "composition design - second phase configuration - shear rearrangement - stable filling". The significant reduction in nozzle temperature directly reduces the heat load when the melt flows through the nozzle, delays thermal wear at the nozzle, and thus extends the service life of the nozzle and screw. During rotary injection molding, although the nozzle temperature decreases, the slurry still maintains excellent thixotropic flowability under the shearing action of the screw. Solid particles are stably distributed in the filling path, which is more than 300 mm long, effectively avoiding solid-liquid separation and flow front instability. The lower nozzle temperature delays the heat exchange between the slurry and the mold cavity wall, allowing the slurry to maintain sufficient flow capacity to complete the filling of complex thin-walled structures, while significantly reducing the equipment heat load and energy consumption. Attached Figure Description

[0025] Figure 1 This is a scanning electron microscope image of the magnesium alloy obtained in Example 4 of this application; Figure 2 This is a scanning electron microscope image of the magnesium alloy prepared in Comparative Example 2 of this application; Figure 3 This is a metallographic image of the high-plasticity corrosion-resistant magnesium alloy obtained in Example 2 of this application; Figure 4 This is a metallographic image of the magnesium alloy prepared in Comparative Example 1 of this application; Figure 5This is a schematic diagram of the magnesium alloy ingot prepared according to the embodiments of this application, wherein (a) is a front view, (b) is a side view, (c) is a top view, and (d) is a three-dimensional axonometric view. Figure 6 This is a schematic diagram of the semi-solid injection molding mold used in the embodiments of this application, wherein (a) is a top view, (b) is a left view, and (c) is a right view; Figure 7 This is a schematic diagram of the semi-fluid mold used in the embodiments of this application. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0027] According to one aspect of this application, a high-plasticity, corrosion-resistant magnesium alloy is provided based on the Mg-Al-Mn ternary system by introducing three functional alloying elements: Ca, Ce, and Ba. This high-plasticity, corrosion-resistant magnesium alloy is prepared using a semi-solid process and comprises, by mass percentage: Al: 5.5%–6.5%, Mn: 0.3%–0.45%, Ca: 0.1%–0.3%, Ce: 0.2%–0.4%, Ba: 0.05%–0.15%, with the balance being Mg and unavoidable impurities. The atomic ratio of Ca to Al is controlled within the range of 0.02–0.03, and the atomic ratio of Ce to Al is controlled within the range of 0.007–0.009. The unavoidable impurities mainly originate from the raw materials and smelting process and typically include elements such as iron, silicon, copper, and nickel. Their total mass fraction is strictly limited to a low level, generally not exceeding 0.05%, and preferably controlled within 0.03%.

[0028] The high-ductility, corrosion-resistant magnesium alloy provided in this application is designed with the following composition: In the composition of magnesium alloys, besides the clearly defined main alloying components such as aluminum, manganese, calcium, cerium, and barium, the remaining components are magnesium and trace impurities that are difficult to completely avoid during the smelting process. These "unavoidable impurities" mainly originate from raw materials and the smelting process, and typically include elements such as iron, silicon, copper, and nickel. Their total mass fraction is strictly limited to a low level, generally not exceeding 0.05%, and ideally controlled within 0.03%. By implementing strict impurity control, especially limiting elements such as iron, nickel, and copper, which are highly detrimental to corrosion resistance, it is possible to effectively prevent localized electrochemical corrosion accelerated by the precipitation of impurity phases, thereby ensuring the overall corrosion resistance of the alloy.

[0029] This alloy system was intentionally designed without incorporating other common alloying elements such as strontium, yttrium, and gadolinium. This choice is primarily based on the following mechanistic considerations: First, the performance advantage of this alloy relies on the high thermal stability of the aluminum-calcium and aluminum-cerium phases as key reinforcing phases, with their morphology and distribution controlled by precisely adjusting the atomic ratio of calcium to aluminum. Introducing other alloying elements could lead to the formation of complex multi-phase complexities, interfering with the expected reactions between calcium, cerium, and aluminum, affecting the continuity and dispersion of the aluminum-calcium phase, and thus weakening its pinning effect on grain boundaries and its barrier effect against corrosion. Second, in corrosive media, the presence of multiple heterogeneous phases easily constitutes a multi-electrode system, exacerbating electrochemical inhomogeneities within the microscopic region. By controlling the types of alloying elements, the corrosion system can be maintained primarily between the magnesium matrix and a few stable phases with similar potentials, thereby reducing the interphase potential difference, lowering the driving force of galvanic corrosion, and improving the uniformity of corrosion behavior. Furthermore, simplifying alloying elements helps maintain a relatively clear and stable solidification path, avoiding the precipitation of non-equilibrium phases or component segregation. This is crucial for controlling the solid phase morphology, size, and solid fraction during semi-solid forming, and is beneficial for obtaining a uniform and fine microstructure.

[0030] This application improves the room-temperature mechanical properties of magnesium alloys by adding an appropriate proportion of dissimilar atoms to the Mg matrix to refine the grain size. Simultaneously, the second phase formed by the dissimilar elements in the Mg matrix has a very high melting point, effectively preventing grain boundary slippage and diffusion at elevated temperatures, thus providing a good pinning effect on the grain boundaries and improving the high-temperature mechanical properties of the magnesium alloy.

[0031] The composition design of this application adopts a Mg-Al-Mn-Ca-Ce-Ba alloy system. Al is dissolved in the α-Mg matrix, which has a strengthening effect and improves room temperature strength. Mn has low solid solubility in magnesium alloys, and adding an appropriate amount can reduce the hot cracking tendency of magnesium alloys. A small amount of Mn absorbs harmful impurity iron and may react with Al in the melt to form dispersed Al8Mn5 or Al 11 Manganese-containing phases such as Mn4 further enhance corrosion resistance. The Al content is controlled between 5.5% and 6.5%. If Al content is below this range, α-Mg solid solution strengthening is insufficient, and it can facilitate the formation of Al2Ca and Al2O3 from Ca and Ce. 11 Ce3 has insufficient Al source; if Al is above this range, then Mg 17 Al 12 The tendency for phase continuity is enhanced, making it easier to change the thermally stable Al2Ca and Al of this application. 11 The phase configuration is dominated by Ce3, which may increase the risk of local enrichment of liquid phase and solid-liquid separation during semi-solid heating and shearing.

[0032] The amount of Ce added was limited to 0.2%–0.4%, and the atomic ratio with Al was controlled between 0.007 and 0.009. The addition of Ce generated Al. 11 Ce3 can strongly pin moving dislocations and effectively hinder grain boundary sliding and migration at high temperatures, compared to the continuous, coarse network structure of Mg in pure Mg-Al alloys. 17 Al 12 The addition of Ce will consume Al, thereby inhibiting Mg. 17 Al 12 Phase growth and distribution. Short rod-shaped Al 11 Ce3, compared to coarse needle-like or Chinese character-shaped phases, is more likely to improve plasticity. At the same time, Ce purifies the melt and refines the grains, while Al... 11 The potential difference between Ce3 and the magnesium matrix can significantly improve the overall corrosion resistance of the alloy. However, excessive rare earth elements can significantly reduce melt fluidity, increase the risk of film adhesion, and lead to molding difficulties. Especially in semi-solid injection molding, film adhesion can severely restrict the filling capacity of complex thin-walled parts, thus requiring limitation. If the Ce / Al atomic ratio is below 0.007, then Al... 11 Insufficient Ce3 strengthening phase formation results in limited grain refinement and minimal improvement in corrosion resistance. Furthermore, if the Ce / Al atomic ratio exceeds 0.009, coarse and brittle rare earth phases are easily formed, impairing plasticity and flowability, increasing the risk of film adhesion, and reducing compatibility with semi-solid molding processes. Therefore, precisely controlling the Ce / Al atomic ratio within the range of 0.007–0.009 is crucial for balancing performance improvement and process compatibility.

[0033] Introducing 0.1%–0.3% Ca, and controlling the atomic ratio of Ca to Al between 0.02 and 0.03, will cause Ca to accumulate at the solid-liquid interface during solidification, resulting in compositional supercooling and thus refining the α-Mg grains. An appropriate amount of Ca can alter the solidification path of the alloy and the formation of the second phase, breaking down the network of Mg. 17 Al 12 This process makes the phase smaller and more dispersed, generating a new worm-like calcium-containing phase, Al2Ca, with higher thermal stability. This phase serves as the primary reinforcing phase, replacing or supplementing the original brittle phase, Mg, which has poor thermal stability. 17 Al 12 This improves the room-temperature mechanical properties, creep resistance, and flame retardancy of the new alloy. The addition of Ce allows it to combine with Al to form needle-like or short rod-like Al atoms. 11 Ce3, along with the tetragonal Al-Mn-Ce phase, further forms a thermally stable phase, which strongly refines the as-cast grains and purifies the melt.

[0034] Compared to the unstable Mg at the grain boundaries of AM60 17 Al 12The addition of Ca reinforces the grain boundaries with high-melting-point Al₂Ca. At high temperatures, these stable phases effectively pin the grain boundaries, hindering grain boundary slip and dislocation movement, thereby significantly improving high-temperature strength and creep resistance. Ca is highly reactive and preferentially oxidizes during smelting, forming a dense, well-bonded CaO composite oxide film on the melt surface. This film effectively prevents oxygen diffusion inward and magnesium vapor escape outward, thus providing flame retardancy.

[0035] However, due to Ca's extremely high reactivity, excessive Ca can easily oxidize during molding, forming oxides that may adhere to the mold surface, increasing the tendency to stick. Adding Ca reduces melt fluidity, especially at high superheat temperatures. This decreased fluidity leads to increased friction between the melt and the mold cavity walls during filling, resulting in sticking.

[0036] Secondly, this application introduces trace amounts of Ba, utilizing its surface activity in magnesium alloys to enrich at the solid-liquid interface during solidification, refining the grain structure and improving melt flowability. Simultaneously, as a low-melting-point element (melting point 727°C), Ba has a high diffusion coefficient in magnesium. The addition of Ba helps suppress the coarsening tendency of the Al2Ca phase, promotes the uniform dispersion of the second phase, and further enhances the mechanical and formability properties of the alloy. Furthermore, the synergistic effect of Ba and Ce can form finely distributed intermetallic compounds, enhancing grain boundary strengthening and improving the overall corrosion resistance of the material. As a trace interface regulating element, Ba can undergo a certain degree of redistribution during heating and solidification, tending to act on the surface of the second phase and the solid-liquid interface. Its effect is not solitary strengthening, but rather assisting in suppressing the coarsening of second phases such as Al2Ca, improving melt flow behavior, reducing the tendency of die interface adhesion, and jointly constructing a microstructure suitable for semi-solid shear rearrangement with Ca and Ce.

[0037] The design composition of this application is highly dependent on the atomic ratios of Ca / Al and Ce / Al to ensure the formation of an Al2Ca-dominated microstructure. Simultaneously, impurities such as Fe are limited, and the Ce content is rationally controlled to optimize cost and performance, achieving a 300% reduction in corrosion rate in a 3.5% NaCl solution.

[0038] Based on commercial AM60, this application controls Al at 5.5%–6.5%, Mn at 0.3%–0.45%, Ca at 0.1%–0.3%, Ce at 0.2%–0.4%, and Ba at 0.05%–0.15%. Excessive Ca and Ce will reduce fluidity. The second phase formed by Ca and Ce with Al or Mg is beneficial to improving the room temperature and high temperature mechanical properties of magnesium alloy materials. Under the premise of adding a small amount of expensive rare earth elements, the advantages of semi-solid injection molding are maximized.

[0039] Unlike the higher Al content system in the existing technology CN120330557A, this application limits Al to a lower range of 5.5% to 6.5%, and guides the limited Al to preferentially form Al2Ca and Al through dual proportional constraints of Ca / Al atomic ratio of 0.02 to 0.03 and Ce / Al atomic ratio of 0.007 to 0.009. 11 Thermally stable phases such as Ce3 reduce the degradation caused by Mg 17 Al 12 Risk of localized galvanic corrosion caused by the potential difference between the phase and the Mg matrix.

[0040] Compared with existing technologies, this application does not simply involve a change in the numerical value of Al content, but rather a holistic alteration of the Al consumption targets, second-phase configuration, grain boundary morphology, corrosion resistance pathways, and the rheological pathways of the semi-solid slurry. Higher Al systems are more prone to generating continuous or semi-continuous low-melting-point phases, which may lead to localized liquid phase enrichment and solid-liquid interface imbalance during semi-solid shearing and high-speed filling processes. This application, through the synergistic design of low Al, Ca / Al, Ce / Al, and Ba, enables the thermally stable second phase to maintain good morphological stability within the semi-solid temperature range and participate in the shear rearrangement and filling processes as a stable solid-phase framework.

[0041] Under semi-solid injection molding conditions, the above differences are substantial. While a higher Al system is advantageous for Mg... 17 Al 12 Phase formation occurs, but continuous or semi-continuous low-melting-point phases may cause localized enrichment of the liquid phase, inhomogeneity of the solid-liquid interface, and instability of the flow front under screw shearing, low-temperature nozzle, and high-speed filling conditions. This application addresses this by reducing the Al content and limiting the Ca / Al and Ce / Al atomic ratios to achieve a balance between Al₂Ca and Al₂O₃. 11 Ce3 maintains good thermal and morphological stability in the semi-solid temperature range. It can participate in grain boundary pinning and corrosion path blocking, and can also serve as a stable solid-phase skeleton in the slurry to participate in shear rearrangement.

[0042] Meanwhile, this application intentionally maintains the Mg-Al-Mn-Ca-Ce-Ba system in its composition selection, without further introducing Zn as the main strengthening element. The reason for this is that although Zn can participate in age hardening or change the corrosion film structure in some magnesium alloy systems, its addition would alter the low-melting-point liquid phase composition and heat treatment dependence in the semi-solid injection molding process. This application achieves semi-solid molding adaptation through lower Al content and Ca-Ce-Ba synergy, without relying on Zn strengthening and complex heat treatment.

[0043] Furthermore, the Fe and Ni contents in the impurities are less than 0.005%, which can effectively inhibit the formation of low-melting-point harmful phases, thereby further improving the corrosion resistance of magnesium alloys.

[0044] Furthermore, the Ce content should be controlled between 0.25% and 0.35%. Too low a Ce content will lead to the formation of Al. 11 Insufficient Ce3 strengthening phase has limited effect on improving the high-temperature performance and microstructure of the alloy; excessive Ce content easily leads to the formation of coarse, brittle rare earth phases, which not only severely impairs the alloy's plasticity and fatigue properties but also significantly deteriorates the melt's fluidity, hindering the implementation of semi-solid forming processes and causing unnecessary increases in raw material costs. Controlling the Ce content within the range of 0.25% to 0.35% ensures significant performance improvements while maintaining good processability and economic efficiency.

[0045] To address the film adhesion problem caused by excessive Ca, Ba, as a surface-active element, can reduce the surface tension of the melt, improve the filling ability, and indirectly reduce the risk of film adhesion. Ba may form a composite oxide with Ca, which can change the properties of the oxide film and reduce adhesion. Ba adsorbs on the surface of the Al2Ca phase, inhibits its coarsening, maintains a fine and dispersed distribution, and reduces mechanical seizing.

[0046] According to another aspect of this application, a semi-solid preparation method for the above-mentioned high-plasticity corrosion-resistant magnesium alloy is provided, comprising the following steps: S1 prepares magnesium alloy particles, ensuring that the magnesium alloy particles, by mass percentage, include Al: 5.5%–6.5%, Mn: 0.3%–0.45%, Ca: 0.1%–0.3%, Ce: 0.2%–0.4%, Ba: 0.05%–0.15%, with the balance being Mg and unavoidable impurities. At the same time, it is necessary to ensure that the atomic ratio of Ca to Al is within the range of 0.02–0.03. S2 first pours magnesium alloy particles into the hopper of a semi-solid injection molding machine, heats the machine to 600℃~620℃, and after reaching the target temperature, the screw starts to rotate to melt the material. The particles at the discharge port are axially conveyed forward by the screw and begin to melt to form a semi-solid slurry. Then, high-plasticity and corrosion-resistant magnesium alloy specimens are obtained through injection molding.

[0047] This application uses only a small amount of Ce for synergistic alloying, without relying on high rare earth content for strengthening, possessing excellent industrialization prospects and cost advantages. Through a semi-solid forming process, the resulting high-plasticity corrosion-resistant alloy exhibits a room temperature tensile strength of 250 MPa–270 MPa, a room temperature yield strength of 170 MPa–190 MPa, and a room temperature elongation of 11%–15%. At 150℃, the tensile strength reaches 174 MPa–226 MPa, the yield strength reaches 103 MPa–147 MPa, and the elongation reaches 15.7%–9.1%. The steady-state creep rate at 150℃ and 70 MPa can be as low as 2.1 × 10⁻⁸ s⁻¹. -1The creep strain can be controlled to a minimum of 0.34% over 100 hours; the flow length is 1385 mm; the corrosion rate is 0.2 mm / a to 0.4 mm / a, and the corrosion rate is reduced by more than 80% compared with AM60 alloy in the weight loss corrosion test.

[0048] Furthermore, step S1 specifically includes the following sub-steps: S11 places Al-10Mn, pure aluminum ingots, Mg-10Ba, Mg-30Ce, Mg-30Ca, and pure magnesium ingots in the melting container from bottom to top according to their melting points. Then, the furnace lid is closed to ensure that all sealing rings are intact and the system is completely sealed. S12 starts the mechanical pump and pre-evacuation valve to evacuate to a low vacuum state. High-purity inert gas is then introduced into the melting vessel until a certain pressure is reached, after which it is discharged. This process is repeated 2-3 times to complete the inert gas flushing pretreatment of the melting vessel. This effectively displaces and dilutes the moisture and air adsorbed on the furnace body and furnace charge surface, fundamentally avoiding the risks of "hydrogen explosion" caused by the reaction of water vapor and magnesium during subsequent heating stages, the risk of magnesium melt oxidation and combustion, and the problem of the melt absorbing a large amount of hydrogen. Then, the inlet pump is shut off, the mechanical pump and pre-evacuation valve are started, and evacuation is completed to a low vacuum state. Finally, the Roots pump is started, and evacuation is continued until... Under a high vacuum of 0.1 Pa to 1 Pa, close the pre-evacuation valve, Roots pump, and mechanical pump; insert the thermocouple into the melt, manually adjust the power, and control the temperature and holding time to ensure that the furnace charge is completely melted; then use mechanical stirring in a vacuum environment at low speed for 5-15 minutes to make the magnesium alloy composition more uniform and promote the floating and removal of hydrogen bubbles and oxide inclusions; at the same time, perform ultrasonic treatment to make the heterogeneous crystal nuclei evenly distributed through the ultrasonic cavitation effect, remove microbubbles, and avoid Ca element segregation and oxide film rupture, thereby obtaining liquid magnesium alloy; S13 adjusts the melt temperature and introduces high-purity argon gas, finally pouring it into a mold of a certain size. Immediately after casting, low-frequency mechanical vibration (parameters: frequency 50Hz, acceleration 3g) is applied to the mold until the liquid magnesium alloy completely solidifies. This, combined with ultrasonic treatment, addresses the microscopic uniformity issues within the melt, as well as the problems of feeding and segregation during macroscopic solidification, eliminating casting defects such as porosity, shrinkage, and macroscopic segregation, thereby obtaining... Figure 5 The magnesium alloy ingot shown; S14 cuts magnesium alloy ingots to obtain magnesium alloy particles.

[0049] Furthermore, in step S12, the mechanical stirring time is 5 to 15 minutes. Insufficient stirring time makes it difficult to achieve sufficient macroscopic component homogenization of the alloy melt, and the efficiency of removing dissolved gases and non-metallic inclusions will also decrease. Conversely, if the stirring time is too long, it will increase the risk of oxidation and hydrogen absorption caused by the contact between the melt and air, and continuous vigorous stirring may also re-enter the gas into the melt. The ultrasonic treatment time is 3 to 5 minutes, the ultrasonic treatment frequency is 20 kHz to 25 kHz, and the ultrasonic treatment power density is 280 W / cm² to 300 W / cm². If the ultrasonic treatment time is too short or the power is too low, the cavitation effect and acoustic flow effect will be weak, and the effect on grain refinement, degassing and homogenization of the melt will be limited. If the ultrasonic treatment is excessive or the power is too high, it may cause abnormal local temperature rise of the melt, or even cause magnesium melt splashing or erosion and wear of the ultrasonic probe. By synergistically controlling the above process parameters, it is possible to effectively achieve uniform distribution of the melt at the microscale, deep degassing, and significant refinement of the primary phase, thereby providing good melt conditions for the subsequent preparation of high-quality ingots.

[0050] Furthermore, in step S13, the temperature of the melting vessel is adjusted to 700℃~720℃. If the casting temperature is too low, the fluidity of the melt will decrease significantly, easily leading to casting defects such as incomplete pouring and cold shuts. It may also cause the pre-precipitated intermetallic compound phases to coarsen. Conversely, if the casting temperature is too high, it will exacerbate the oxidation and burning loss of the magnesium alloy melt, increase the volume shrinkage during solidification, and thus cause more severe shrinkage cavities and porosity defects in the ingot, resulting in coarse grains in the final solidified structure. Precisely controlling the casting temperature within the above range ensures that the melt has good filling ability and is also conducive to obtaining a fine-grained solidified structure.

[0051] Furthermore, in step S13, after casting is completed, low-frequency mechanical vibration is applied to the mold until the magnesium alloy ingot is completely solidified. The frequency of the low-frequency mechanical vibration is 30Hz to 80Hz, and the acceleration is 2g to 4g. If the vibration frequency or acceleration value is too low, its mechanical disturbance effect on the solidification front is limited, making it difficult to effectively break up growing dendrites, promote melt feeding, and suppress microsegregation. If the vibration parameters are set too high, it may cause melt splashing, accelerate mold wear, or even destroy the already formed fine grain structure. Applying mechanical vibration within the above parameter range can significantly refine the ingot grains, reduce casting defects, and thus improve the overall density and uniformity of mechanical properties of the ingot.

[0052] Furthermore, in step S2, the magnesium alloy particles are heated to 600℃~620℃ to form a semi-solid slurry. During this process, the target solid fraction should be controlled between 5% and 20%, and the initial melt stabilization time is recommended to be 10 to 20 minutes. If the heating temperature is insufficient or the melting time is inadequate, the solid fraction in the slurry will be too high, resulting in poor fluidity. This not only makes molding difficult but also makes the product prone to defects such as incomplete filling. If the heating temperature is too high or the melting time is too long, the solid fraction will be too low, and the slurry properties will tend to be liquid, losing the advantages of semi-solid forming in suppressing turbulence and reducing shrinkage. It is also prone to problems such as slurry component segregation and gas entrapment. Stabilizing the process parameters within this range can obtain a semi-solid slurry with optimal rheological properties, thereby ensuring that it has excellent thixotropic filling ability and stable forming quality.

[0053] Furthermore, in step S2, during the injection molding process, the nozzle temperature is 560℃~580℃, the barrel temperature is 620℃~640℃, the screw speed is 70rpm~130rpm, the injection speed is 2.2m / s~3.8m / s, the injection pressure is 540bar~560bar, and the injection time is 140ms~170ms. Injection molding trials with different molds are completed. The synergistic effect of these parameters ensures that the semi-solid slurry can fill the mold cavity in the optimal rheological state, obtaining a near-net-shape molded part with a dense structure and excellent performance. If the barrel temperature is too low or the screw speed is too slow, the viscosity of the semi-solid slurry will increase, making it difficult to completely fill the mold cavity; if the temperature is too high or the speed is too fast, it may cause the slurry to overheat, the solid content to decrease, or even flash or splashing. Insufficient injection speed or pressure will result in incomplete cavity filling, leading to defects such as underfilling or weld line defects in the product. Excessive speed or pressure, on the other hand, can easily generate turbulence and gas entrapment during filling, increasing the internal porosity of the product. Injection time must be matched with injection speed and pressure; too short a time will result in insufficient pressure holding and shrinkage compensation, easily forming shrinkage cavities; too long a time will reduce production efficiency and may cause premature solidification of the gate. Through systematic optimization of the above process parameter combinations, the rheological behavior and filling process of the semi-solid slurry can be precisely controlled, thereby achieving complete filling of complex mold cavities and ultimately obtaining high-density, high-performance near-net-shape molded parts.

[0054] Furthermore, in step S2, the first injection molding should be conducted after the semi-solid slurry has formed, followed by a 10-15 minute wait for the material to melt and stabilize before testing. Subsequent adjustments to process parameters other than temperature can be made directly for continuous testing. If the set temperature is adjusted again, the material must be allowed to stabilize for another 10-15 minutes before subsequent trial production can begin. The aforementioned process parameters and alloy composition are not independent of each other, but rather work together to affect the solid fraction, thixotropic shear state, and filling stability of the semi-solid slurry.

[0055] Stable filling can be achieved at a suitable nozzle temperature. If the nozzle temperature is too high, although the flowability will be improved in the short term, the risk of mold interface reaction, heat load and film sticking will increase; if the nozzle temperature is too low, the viscosity of the slurry will increase before entering the mold cavity, and the stability of the flow front will be insufficient.

[0056] The barrel temperature determines the degree of particle remelting and the initial solid-liquid ratio. If the barrel temperature is too low and the solid fraction is too high, Al₂Ca and Al will... 11 Although Ce3 remains stable, the apparent viscosity of the slurry is too high, making it easy for thin-walled parts to be underfilled. If the barrel temperature is too high and the solid fraction is too low, the slurry will approach a liquid state, weakening the advantages of semi-solid forming in suppressing turbulence and reducing shrinkage, while potentially amplifying liquid phase segregation.

[0057] The screw speed provides shearing and crushing, as well as spheroidizing and rearranging of solid particles. The 70 rpm to 130 rpm range matches the thermally stable second-phase configuration of this application, allowing Al₂Ca and Al₂O₃ to be processed. 11 Ce3 participates in thixotropic rearrangement without causing severe coarsening or fracture segregation. At too low a rotation speed, particle rearrangement is insufficient, while at too high a rotation speed, shear heat and localized liquid phase enrichment may lead to solid-liquid separation.

[0058] Injection speed, injection pressure, and injection time all contribute to cavity filling. Insufficient injection speed and pressure result in inadequate filling of thin-walled, long-flow molds; excessively high speeds and pressures can easily cause air entrapment, flash, or erosion of the mold interface. Insufficient injection time leads to inadequate shrinkage compensation, while excessive time may cause premature solidification of the gate area or reduced production efficiency. This application provides a stable slurry base through composition design, and then transforms it into a stable, complete, and low-defect molded part through the aforementioned injection parameter window.

[0059] Furthermore, semi-solid injection molding molds and flowable molds, such as Figure 6 , Figure 7 As shown. The barrel temperature of the semi-solid injection molding machine is set 10℃~20℃ higher than the actual temperature to compensate for system heat loss and maintain the rheological stability of the slurry. The design scheme needs to be based on the actual temperature.

[0060] In the composition system of this application, Al2Ca and Al 11 Thermally stable phases such as Ce3 can maintain good morphological stability in the semi-solid region. However, if the nozzle temperature is too low, the apparent viscosity of the slurry increases, which can easily lead to insufficient filling. If the nozzle temperature is too high, the solid fraction decreases and the reaction at the mold interface is aggravated, which in turn increases film sticking and heat load. The screw speed, injection speed, injection pressure, and injection time need to be matched together to avoid defects such as solid-liquid separation, air entrapment, flash, or underfill.

[0061] This application deeply integrates alloy system design with semi-solid injection molding technology and specific product structure to construct an integrated "material-process-structure" technical solution. Using a magnesium alloy thin-walled support as the product carrier, a temperature field distribution adapted to the alloy's melting behavior is constructed by setting zoned heating temperatures along the barrel flow path. The shear strength of the slurry during the conveying stage is optimized by adjusting the screw rotation speed to improve the morphology and distribution of solid particles. Simultaneously, the injection rate is matched according to the filling characteristics of the thin-walled structure to ensure the slurry fills the cavity in a stable flow state. The synergistic effect of these process parameters fully leverages the rheological advantages of the alloy in a semi-solid state, effectively suppressing compositional micro-region fluctuations caused by differences in particle remelting processes, ultimately producing a magnesium alloy support component with uniform microstructure, few internal defects, and stable mechanical properties.

[0062] Meanwhile, the inhibition of cathodic activity by Mn, the densification of the corrosion film by Ce, and the construction of the inert second phase by Ca significantly reduce the corrosion rate of the alloy in 3.5% NaCl solution. This technical solution deeply couples material properties with mold structure and forming process, constructing an inherent synergistic control mechanism, significantly optimizing the mechanical properties and corrosion resistance of the material, and demonstrating broad engineering application potential.

[0063] This application combines vacuum melting, ultrasonic vibration, mechanical stirring, and low-frequency vibration solidification control with semi-solid injection molding to achieve near-net-shape forming of complex components with high density, low porosity, and corrosion resistance. Through the systematic integration of multi-physics synergistic processes involving vacuum melting, mechanical stirring, ultrasonic treatment, and mechanical vibration, this application achieves precise control over the entire process of magnesium alloys from the molten state to solidification. Compared with traditional resistance furnace melting methods in protective atmospheres (such as SF6 / N2 or Ar), this process exhibits several technological advantages. Traditional resistance melting using protective gases relies mainly on forming a protective gas film on the melt surface to achieve physical isolation from air. However, this application, by establishing a high vacuum environment, fundamentally eliminates oxidation reactions and significantly reduces the number of non-metallic inclusions.

[0064] In terms of microstructure control, the combined use of mechanical stirring and ultrasonic treatment promotes macroscopic and microscopic homogenization of the alloy composition. Ultrasonic cavitation effectively breaks down primary intermetallic compounds and dendrites, causing them to disperse in the matrix as fine particles, thereby improving the material's plasticity and toughness. Simultaneously, applying mechanical vibration during alloy solidification generates periodic mechanical action on the semi-solid melt, helping to eliminate shrinkage defects at the microscale, thus improving the material's fatigue properties, elongation at fracture, and corrosion resistance.

[0065] This application focuses on the process characteristics of semi-solid injection molding, linking alloy composition design with the process window. During the alloy design stage, the entire phase transformation path from "ingot preparation → particle heating → semi-solid molding" is fully considered. The diffusion behavior of elements during particle heating, the thermal stability of the second phase at the molding temperature, and the distribution behavior between the solid and liquid phases collectively determine the rheological properties of the slurry and the microstructure and properties of the final part.

[0066] High-melting-point second phases formed during ingot solidification, such as Al₂Ca (melting point 1079°C) and Al 11 Ce3 (melting point 1200°C) remains solid at semi-solid heating temperatures (600~620°C). Its stable solid particles become the main solid component in the semi-solid slurry, directly participating in and dominating the slurry's rheological behavior. The added trace amount of Ba, due to its relatively high diffusion coefficient, can redistribute during semi-solid heating and tends to adsorb onto the Al2Ca phase surface, effectively inhibiting its coarsening and improving the overall fluidity of the melt. Through this mechanism-based integrated composition-process design, a perfect coupling between alloy properties and process window is achieved.

[0067] This application fundamentally solves the technical bottlenecks of traditional protective atmosphere smelting processes in four key aspects: material purity, compositional uniformity, microstructure density, and grain refinement. The prepared high-plasticity corrosion-resistant magnesium alloy ingots achieve synergistic improvements in static mechanical properties (including strength and plasticity), dynamic properties (such as fatigue and impact toughness), and service durability (mainly corrosion resistance), providing a high-quality raw material foundation for high-performance magnesium alloy components required in high-end equipment fields such as aerospace and transportation.

[0068] Compared to commercially available die-cast magnesium alloys, this application employs semi-solid injection molding technology. Furthermore, the technical effect of this application is not merely an improvement in strength, corrosion resistance, or flowability, but rather a comprehensive balance achieved between low nozzle temperature, stable solid fraction, low film adhesion tendency, corrosion resistance, high-temperature stability, and long-flow filling of complex thin-walled parts. This comprehensive balance arises from the combined effect of compositional and process parameters. The compositional parameters play a dominant role in the second-phase configuration and the basic rheological properties of the slurry, while the process parameters ensure that the microstructural advantages resulting from the compositional design are stably maintained during the actual injection molding process.

[0069] The excellent fluidity of semi-solid slurry allows injection molding to fill the mold cavities of complex structural parts, producing products suitable for heat dissipation / thermal conduction systems such as 3C products and new energy vehicle motor housings. Furthermore, the resulting structural parts can achieve a weight reduction of over 50% compared to traditional steel components, truly driving the development of semi-solid magnesium alloys in the automotive lightweighting field.

[0070] In addition, this technology exhibits excellent compatibility, allowing it to be combined with various processing methods. On the one hand, it can be integrated with casting processes such as vertical / horizontal continuous casting and squeeze casting; on the other hand, it can also be used in conjunction with plastic forming processes such as die forging and casting rolling. Through continuous innovation in process technology and improvement of equipment levels, and based on its low process cost, it enables planned production.

[0071] Based on the unique rheological behavior exhibited in the semi-solid temperature range, this application achieves coordinated control of parameters such as barrel zone temperature, screw speed, and injection rate. This effectively suppresses micro-compositional fluctuations during particle remelting, eliminates common defects in thin-walled parts such as flow marks, cold shuts, and air entrapment, and realizes stable filling and near-net-shape forming of complex structural parts. This technical solution not only provides a complete technical path for the application of high-performance magnesium alloys in the field of precision thin-walled components, but also demonstrates excellent prospects for industrialization due to its compositional design that does not rely on heavy rare earth elements and its good compatibility with existing semi-solid equipment.

[0072] The technical solutions provided in this application will be further described below with reference to specific embodiments.

[0073] Example 1 This application provides a high-plasticity, corrosion-resistant magnesium alloy with the following composition: 5.5 wt% Al, 0.3 wt% Mn, 0.18 wt% Ca, 0.2 wt% Ce, 0.05% Ba, and the remainder being Mg; using pure Mg ingots, pure Al ingots, Al-10Mn, Mg-30Ce, Mg-30Ca, and Mg-10Ba master alloys as raw materials, and formulating the alloy according to the weight percentage of the designed magnesium alloy composition. (1) After cleaning and preheating the surface, place pure magnesium ingots, pure aluminum ingots, Al-10Mn, Mg-30Ca, Mg-30Ce, Mg-10Ba, etc. at the bottom of the crucible according to their melting points, from bottom to top: Al-10Mn, pure aluminum ingots, Mg-10Ba, Mg-30Ce, Mg-30Ca, and pure magnesium ingots. Then close the furnace cover and ensure that all sealing rings are intact and the system is completely sealed.

[0074] (2) Start the mechanical pump, pre-extraction valve, and pump to a low vacuum state. High-purity argon gas is passed through the furnace cavity and discharged after reaching a certain pressure. Repeat this process 3 times to complete the argon gas flushing pretreatment. This can effectively drive away and dilute the moisture and air adsorbed on the furnace body and furnace charge surface, fundamentally avoiding the risk of "hydrogen explosion" caused by the reaction of water vapor and magnesium in the subsequent heating stage, the risk of magnesium liquid oxidation and combustion, and the problem of the melt absorbing a large amount of hydrogen.

[0075] (3) Close the inlet pump, start the mechanical pump and the pre-evacuation valve to evacuate to a low vacuum state, then turn on the Roots pump to evacuate to a high vacuum state of less than 1 Pa, close the pre-evacuation valve, the Roots pump and the mechanical pump; then introduce high-purity argon into the furnace cavity to the set protection pressure to form an inert protective atmosphere in the furnace; insert the thermocouple into the melt, manually adjust the power, control the temperature and holding time, so that the furnace charge is completely melted.

[0076] (4) Mechanical stirring is used to stir at low speed in a vacuum environment for 10 minutes to make the magnesium alloy composition more uniform and to promote the floating and removal of hydrogen bubbles and oxide inclusions; at the same time, ultrasonic treatment is performed for 3 minutes at a frequency of 20kHz and a power density of 300W / cm². Through the ultrasonic cavitation effect, the heterogeneous crystal nuclei are evenly distributed, and micro bubbles are removed.

[0077] (5) Adjust the melt temperature to 710℃, and pour it into a mold of a certain size under a protective atmosphere, such as... Figure 5 As shown; immediately after casting, low-frequency mechanical vibration (parameters: frequency 50Hz, acceleration 3g) is applied to the mold until the ingot is completely solidified. This, together with ultrasonic treatment, solves the microscopic uniformity problem inside the melt, as well as the feeding and segregation problems during the macroscopic solidification process, eliminating casting defects such as porosity, shrinkage porosity and macroscopic segregation.

[0078] (6) Clamp the trapezoidal magnesium alloy ingot and place it in the granulator for cutting and granulation; (7) The magnesium particles are first poured into the hopper of the semi-solid injection molding machine. The machine is heated to 610°C. After the target temperature is reached, the screw starts to rotate to melt the material. The particles at the discharge port are conveyed forward by the screw axis and begin to melt into a semi-solid slurry. (8) Set the corresponding process parameters, set the barrel temperature to 640℃, the nozzle temperature to 570℃, the screw speed to 90 rpm, the injection speed to 3.8 m / s, the injection pressure to 560 bar, and the high-speed injection time to 160 ms, and complete the injection molding trial production of magnesium alloy with different molds.

[0079] Example 2 This application provides a high-plasticity, corrosion-resistant magnesium alloy with the following composition: 6.5 wt% Al, 0.35 wt% Mn, 0.2 wt% Ca, 0.3 wt% Ce, 0.10% Ba, and the remainder being Mg; using pure Mg ingots, pure Al ingots, Al-10Mn, Mg-30Ce, Mg-30Ca, and Mg-10Ba master alloys as raw materials, and formulating the alloy according to the weight percentage of the designed magnesium alloy composition. The preparation process is the same as in Example 1.

[0080] Example 3 This application provides a high-plasticity, corrosion-resistant magnesium alloy with the following composition: 6.5 wt% Al, 0.45 wt% Mn, 0.28 wt% Ca, 0.3 wt% Ce, 0.15% Ba, and the remainder being Mg; using pure Mg ingots, pure Al ingots, Al-10Mn, Mg-30Ce, Mg-30Ca, and Mg-10Ba master alloys as raw materials, and formulating the alloy according to the weight percentage of the designed magnesium alloy composition. The preparation process is the same as in Example 1.

[0081] Example 4 This application provides a high-plasticity, corrosion-resistant magnesium alloy with the following composition: 6 wt% Al, 0.3 wt% Mn, 0.2 wt% Ca, 0.28 wt% Ce, 0.1% Ba, and the remainder being Mg. It is formulated using pure Mg ingots, pure Al ingots, Al-10Mn, Mg-30Ca, Mg-30Ce, and Mg-10Ba master alloys as raw materials, and the alloy is prepared according to the weight percentage of the designed magnesium alloy composition. (1) Melt pure magnesium ingots under a protective atmosphere, heat to 730±10℃, skim off the surface oxide slag, and obtain magnesium melt; (2) The preheated pure Al ingots, Al-10Mn, Mg-30Ca, Mg-30Ce, Mg-10Ba, etc. are added to the magnesium melt in step (1) in batches so that the added materials can fully contact and react with the magnesium melt; (3) Remove the oxide slag generated during the reaction, pass in high-purity argon gas for refining, and adjust the melt temperature to 710±10℃ to remove the suspended MgO slag and dissolved gas in the melt. After refining, remove the surface slag and cast the melt to obtain a cast magnesium alloy of a certain size.

[0082] Comparative Example 1 (AM60 Semi-Solid) Other conditions were the same as in Example 2, except that the magnesium alloy composition was selected as 6 wt% Al, 0.3 wt% Mn, and the remainder Mg, i.e., commercial AM60B. Corresponding process parameters were set: barrel temperature at 640℃, nozzle temperature at 590℃, screw speed at 90 rpm, injection speed at 3.6 m / s, injection pressure at 560 bar, and high-speed injection time at 160 ms. The injection molding trial production of the magnesium alloy support was completed.

[0083] Comparative Example 2 (AM60 Gravity) Other conditions are the same as in Example 4, except that the magnesium alloy is selected with a composition percentage of 6 wt% Al, 0.3 wt% Mn, and the remainder Mg, i.e., commercial AM60B.

[0084] Comparative Example 3 (above the atomic ratio range) Other conditions are the same as in Comparative Example 2, except that the magnesium alloy composition is selected as 6 wt% Al, 0.3 wt% Mn, 0.7 wt% Ca, 0.12 wt% Ce, 0.1% Ba, with the remainder being Mg.

[0085] Comparative Example 4 (below the atomic ratio range) Other conditions are the same as in Comparative Example 2, except that the magnesium alloy composition is selected as 6 wt% Al, 0.3 wt% Mn, 0.45 wt% Ca, 0.65 wt% Ce, 0.1% Ba, with the remainder being Mg.

[0086] Example 3 is a semi-solid forming process for the high-plasticity corrosion-resistant alloy provided in this application; Example 4 is a gravity casting process for the high-plasticity corrosion-resistant alloy provided in this application; Comparative Examples 1 and 2 are semi-solid injection molding and gravity casting processes for the commercial grade AM60B; Comparative Examples 3 and 4 are gravity casting processes for alloys with atomic ratios deviating from the limits specified in this application. Specific process parameters are shown in Table 1.

[0087] Table 1. Process parameters for Examples 1-4 and Comparative Examples 1-4

[0088] After wire cutting, the finished castings of Examples 1-4 and Comparative Examples 1-4 were subjected to mechanical property tests. Three samples were tested, and the average value was taken. The tensile test results are shown in Table 2 below. By introducing Comparative Examples 3 and 4, the adverse effects of the Ca / Al and Ce / Al atomic ratios deviating from the limits specified in this application on the alloy's strength, plasticity, and formability were further verified. As can be seen from the table, under the same preparation process parameters, Example 2 has the best tensile properties and does not exhibit mold sticking. Compared with Comparative Example 1 with the same preparation process parameters, Example 2 has better tensile properties. Compared with Example 4, which was gravity cast, Example 2 shows significant process advantages in semi-solid injection molding. The semi-solid slurry is in a laminar flow state during filling, avoiding the turbulence and air entrapment of liquid metal in gravity casting, thereby greatly reducing defects such as porosity, oxide inclusions, and shrinkage. The casting has high density and therefore better mechanical properties.

[0089] In Comparative Example 3, due to the high Ca / Al atomic ratio and the low Ce / Al atomic ratio, an excess of high-melting-point Ca phase and Al phase are easily formed in the alloy. 11Insufficient Ce3 phase formation leads to decreased fluidity and poor microstructure consistency, which is detrimental to improving plasticity and overall mechanical properties. In Comparative Example 4, due to the high Ca / Al and Ce / Al atomic ratios, coarse second phases or brittle rare-earth-rich phases are easily formed, weakening matrix continuity and increasing the tendency for crack initiation. Therefore, its overall mechanical properties are also lower than those of the embodiments in this application. It is evident that the Ca / Al and Ce / Al atomic ratio windows specified in this application play a crucial role in balancing microstructure stability, formability, and mechanical properties.

[0090] Table 2 Mechanical properties of Examples 1-4 and Comparative Examples 1-4

[0091] To further verify the stability of the high-ductility, corrosion-resistant magnesium alloy of this application under medium- and high-temperature service conditions, high-temperature tensile and creep performance tests were conducted on the samples prepared in Examples 2, 4, Comparative Example 1, and Comparative Example 2. The test results show that the alloy of this application not only exhibits a high strength-to-ductility ratio at room temperature but also maintains high strength and ductility under medium-temperature conditions, while possessing superior resistance to fatigue cracking and creep deformation. This is due to the formation of Al₂Ca and Al₂O₃ compounds in the alloy. 11 Thermally stable second phases such as Ce3 and Al-Mn-Ce can continuously pin grain boundaries and suppress dislocation climb and grain boundary slip at high temperatures, thus weakening the effect of Mg. 17 Al 12 The adverse effects of low-temperature stable phases are eliminated; the synergistic effects of vacuum melting, mechanical stirring, ultrasonic treatment and semi-solid injection molding significantly reduce porosity, inclusions and microstructure segregation, and reduce fatigue crack initiation sources. Therefore, the alloy is superior to the comparative example in terms of high-temperature strength, fatigue life and creep resistance.

[0092] Table 3. High-temperature tensile properties of Examples 1-2 and Comparative Examples 1-2 at 150°C

[0093] As shown in Table 3, at 150℃, Example 2 still maintains high tensile strength, yield strength, and elongation, and its overall performance is significantly better than that of the semi-solid AM60 comparative example 1 and the gravity-cast AM60 comparative example 2. This indicates that through the synergistic alloying of Ca, Ce, and Ba and the optimization of the semi-solid forming process, this application has formed a strengthening phase with higher thermal stability in the microstructure, effectively suppressing grain boundary softening and second-phase coarsening at high temperatures. Therefore, it still has good load-bearing capacity and deformation coordination under medium and high temperature conditions.

[0094] As shown in Table 4, Example 2 exhibits the lowest steady-state creep rate and the smallest creep strain over 100 hours, demonstrating the best creep resistance. Analysis suggests that the Al₂Ca and Al₂O₃ components in the alloy of this application... 11High-melting-point phases such as Ce3 still exhibit high thermal stability at 150°C, which can effectively pin grain boundaries and hinder dislocation movement, slow down grain boundary slip, and control the deformation process through diffusion. At the same time, the dense structure prepared by semi-solid molding reduces the possibility of defect synergistic propagation at high temperatures. Therefore, Example 2 exhibits better dimensional stability and long-term service capability under high-temperature loads.

[0095] Table 4. Creep performance of Examples 1-2 and Comparative Examples 1-2

[0096] Creep tests were conducted at 150℃ and 70MPa for 100 hours. Table 4 shows that Example 2 exhibited the lowest steady-state creep rate and the smallest creep strain after 100 hours, demonstrating the best creep resistance. Analysis suggests that the Al₂Ca and Al₂O₃ components in the alloy of this application... 11 High-melting-point phases such as Ce3 still exhibit high thermal stability at 150°C, which can effectively pin grain boundaries and hinder dislocation movement, slow down grain boundary slip, and control the deformation process through diffusion. At the same time, the dense structure prepared by semi-solid molding reduces the possibility of defect synergistic propagation at high temperatures. Therefore, Example 2 exhibits better dimensional stability and long-term service capability under high-temperature loads.

[0097] Table 5. Flow lengths of Examples and Comparative Examples 1-2

[0098] Table 5 shows the flow length results of the examples and comparative examples under the same test conditions. This application improves slurry fluidity and increases flow length through the synergistic design of alloy composition and semi-solid process. Example 2 achieved a maximum flow length of 1385 mm, which is 125 mm higher than Comparative Example 1 and 205 mm higher than Comparative Example 2, indicating that this approach is beneficial for improving the flow and filling ability of semi-solid slurry in the mold.

[0099] Scanning electron microscope images of gravity-cast magnesium alloys obtained in Example 4 and Comparative Example 2 are shown below. Figure 1 and Figure 2 As shown, in Example 4, Al-Mn-Ce phase, worm-like Al2Ca phase, and Al were newly formed. 11 Ce3 and trace amounts of dispersed Al-Ba phase. In Comparative Example 2, the AM60 alloy has a uniform and fine granular Al-Mn phase as the main reinforcing phase. Therefore, the high-plasticity corrosion-resistant magnesium alloy provided in this application can generate new reinforcing phases compared with magnesium alloys in the prior art, thereby obtaining better corrosion resistance.

[0100] Figure 3 and Figure 4Metallographic images of the semi-solid injection molded parts prepared in Example 2 and Comparative Example 1 are shown. A significant comparison of the two images reveals that, under the same process parameters, the α-Mg content of AM60 in the semi-solid structure of Comparative Example 1 is greater and more abundant than that in Example 2 (containing calcium, cerium, and barium), resulting in a higher solid fraction. Furthermore, the semi-solid structure of the calcium, cerium, and barium-containing part prepared in Example 2 is denser and more uniform than the semi-solid AM60 structure.

[0101] Examples 2, 4, Comparative Example 1, and Comparative Example 2 were cut into small squares of 10*10*3mm, drilled, and suspended in a 3.5% NaCl solution for seven days. Then, a chromic acid solution (containing 200g LCrO3 + 10g L AgNO3) was prepared, and the squares were ultrasonically cleaned in the chromic acid solution to remove corrosion products from the sample surface. The samples were then rinsed with anhydrous ethanol. The weight before and after corrosion was compared to obtain the corrosion rate, as shown in Table 6. In the semi-solid forming process, Example 2, with the best tensile properties, showed a corrosion rate reduction of over 80% compared to semi-solid AM60. In the gravity casting process, Example 4 showed a corrosion rate reduction of over 40% compared to semi-solid AM60. Therefore, the composition provided in this application has better corrosion resistance than existing technologies. Furthermore, Example 2, a high-plasticity corrosion-resistant alloy prepared by semi-solid forming, showed an 88% reduction in corrosion rate compared to gravity casting of Example 4. Therefore, the high-plasticity corrosion-resistant alloy provided in this application can achieve better corrosion resistance using a semi-solid forming process.

[0102] Regarding corrosion resistance, firstly, the dissolution of Mn significantly increases the work function of the magnesium matrix, passivates cathode activity, and reduces the driving force of electrochemical corrosion. Secondly, Ce dissolved in the α-Mg matrix undergoes a chemical reaction during corrosion to form CeO. X These products, along with Ce(OH)₂, embed themselves in the pores of the Mg(OH)₂ corrosion film, significantly improving the film's density and effectively hindering the growth of Cl₂. - Furthermore, this application promotes the formation of the more electrochemically inert Al2Ca phase by precisely controlling the Ca / Al atomic ratio between 0.02 and 0.03, replacing the Mg phase with a large potential difference from the matrix in traditional Mg-Al alloys. 17 Al 12 The brittle phase reduces the driving force of galvanic corrosion. The synergistic effect of these three layers—Mn passivating cathodic activity, Ce densifying the corrosion film, and Ca forming an inert second phase—reduces the corrosion rate of this alloy in 3.5% NaCl solution by more than 80% compared to AM60 alloy.

[0103] Table 6 Corrosion rates of Examples and Comparative Examples

[0104] This application controls the nozzle temperature of semi-solid injection molding within the range of 560℃ to 580℃, which is more than 50℃ lower than the 630℃ nozzle temperature required for traditional AM60 alloys. This optimized temperature window design not only significantly reduces the heat load of the equipment and energy consumption, but also forms a deep synergy with the semi-solid rotary injection molding process. At the lower injection temperature, the slurry maintains excellent thixotropic flowability under the shearing action of the screw rotation, and the solid particles are stably distributed during long-distance filling, effectively avoiding solid-liquid separation and flow front instability. At the same time, the lower nozzle temperature slows down the heat exchange rate between the slurry and the mold cavity wall, allowing the slurry to maintain sufficient flow capacity in a filling path of more than 300mm, ensuring the complete filling of large, complex, thin-walled structural parts. Through the above synergistic control, this application achieves energy saving and consumption reduction while successfully solving the technical problems of cold shuts and flow marks that are prone to occur during long-distance filling of large magnesium alloy components, significantly improving the molding yield and the consistency of part quality.

[0105] Adopting such Figure 6 The thin-walled bracket mold shown was subjected to a molding verification test. The alloy of this application successfully achieved complete filling of the mold cavity under the barrel temperature conditions of 560℃ to 580℃. The surface finish of the part was good, and no surface defects such as flow marks or cold shuts were observed. No film sticking phenomenon was also observed, which fully demonstrates the excellent adaptability of the alloy of this application for semi-solid forming under low temperature conditions.

[0106] This application achieves comprehensive and precise control over the entire process, from melt purity and homogeneity to solidification structure, by systematically coupling and integrating vacuum melting, mechanical stirring, ultrasonic treatment, and mechanical vibration. The resulting magnesium alloy ingots exhibit comprehensive performance unmatched by conventional processes. Parts prepared using high-quality particles possess extremely high mechanical properties, with room temperature tensile strength ranging from 250 MPa to 270 MPa, room temperature yield strength from 170 MPa to 190 MPa, and room temperature elongation from 11% to 15%. At 150°C, tensile strength reaches 174 MPa to 226 MPa, yield strength from 103 MPa to 147 MPa, and elongation from 15.7% to 9.1%. The steady-state creep rate at 150°C and 70 MPa is as low as 2.1 × 10⁻⁶. -8 s -1 The creep strain can be controlled to a minimum of 0.34% over 100 hours; the corrosion resistance rate is controlled within the range of 0.2 mm / a to 0.4 mm / a; the flow length is 1385 mm; and the overall performance indicators significantly surpass those of traditional commercial magnesium alloys.

[0107] In summary, this application has successfully developed a novel magnesium alloy material that combines high plasticity, excellent corrosion resistance, and good formability by deeply integrating alloy composition design with the semi-solid injection molding process mechanism. This alloy can achieve stable filling of high-solids slurry at relatively low nozzle temperatures, effectively solving key technical problems of traditional magnesium alloys such as high molding temperatures, severe film adhesion, and insufficient corrosion resistance during the molding process.

[0108] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0109] Furthermore, throughout this specification, the reference to "an embodiment"; "an embodiment," "an example," or similar language indicates that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. Therefore, the appearance of the phrase "in an embodiment" throughout this specification and similar language may, but not necessarily, refer to the same embodiment.

[0110] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A high-plasticity, corrosion-resistant magnesium alloy, characterized in that, The high-plasticity corrosion-resistant magnesium alloy is prepared by a semi-solid process and comprises, by mass percentage: Al: 5.5%–6.5%, Mn: 0.3%–0.45%, Ca: 0.1%–0.3%, Ce: 0.2%–0.4%, Ba: 0.05%–0.15%, with the balance being Mg and unavoidable impurities. The atomic ratio of Ca to Al is in the range of 0.02–0.03, and the atomic ratio of Ce to Al is in the range of 0.007–0.

009.

2. The high-ductility, corrosion-resistant magnesium alloy as described in claim 1, characterized in that, The content of the impurities is less than 0.05%.

3. The high-plasticity, corrosion-resistant magnesium alloy as described in claim 1, characterized in that, The contents of Fe and Ni in the impurities are both less than 0.005%.

4. The high-ductility, corrosion-resistant magnesium alloy as described in claim 1, characterized in that, The Ce content in the high-plasticity corrosion-resistant magnesium alloy is controlled within the range of 0.25% to 0.35%.

5. The semi-solid preparation method of the high-plasticity corrosion-resistant magnesium alloy according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1 prepares magnesium alloy particles, ensuring that the magnesium alloy particles, by mass percentage, comprise: Al: 5.5%–6.5%, Mn: 0.3%–0.45%, Ca: 0.1%–0.3%, Ce: 0.2%–0.4%, Ba: 0.05%–0.15%, with the balance being Mg and unavoidable impurities, while ensuring that the atomic ratio of Ca to Al is in the range of 0.02–0.03, and the atomic ratio of Ce to Al is in the range of 0.007–0.009; S2 melts the magnesium alloy particles to form a semi-solid slurry, and then uses injection molding to obtain a high-plasticity, corrosion-resistant magnesium alloy specimen.

6. The semi-solid preparation method according to claim 5, characterized in that, Step S1 specifically includes the following sub-steps: S11 places Al-10Mn, pure aluminum ingots, Mg-10Ba, Mg-30Ce, Mg-30Ca and pure magnesium ingots into a melting container from bottom to top; S12 uses inert gas to rinse the melting container, then evacuates it and melts it, combined with mechanical stirring and ultrasonic treatment to obtain liquid magnesium alloy; S13 adjusts the temperature of the melting vessel and then casts to obtain magnesium alloy ingots; S14 cuts the magnesium alloy ingot to obtain magnesium alloy particles.

7. The semi-solid preparation method according to claim 6, characterized in that, In step S12, the mechanical stirring time is 5 min to 15 min, the ultrasonic treatment time is 3 min to 5 min, the ultrasonic treatment frequency is 20 kHz to 25 kHz, and the ultrasonic treatment power density is 280 W / cm². 3 ~300w / CM 3 .

8. The semi-solid preparation method according to claim 6, characterized in that, In step S13, the temperature of the melting container is adjusted to 700℃~720℃; after casting, low-frequency mechanical vibration is applied to the casting mold until the liquid magnesium alloy is completely solidified. The frequency of the low-frequency mechanical vibration is 30Hz~80Hz and the acceleration is 2g~4g.

9. The semi-solid preparation method according to claim 5, characterized in that, In step S2, the magnesium alloy particles are heated to 600°C to 620°C to form a semi-solid slurry, wherein the solid phase of the semi-solid slurry is 5% to 20%.

10. The semi-solid preparation method according to any one of claims 5 to 9, characterized in that, In step S2, during the injection molding process, the nozzle temperature is 560℃~580℃, the barrel temperature is 620℃~640℃, the screw speed is 70rpm~130rpm, the injection speed is 2.2m / s~3.8m / s, the injection pressure is 540bar~560bar, and the injection time is 140ms~170ms.

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