A rare earth magnesium alloy with a low coefficient of thermal expansion

Abstract

This invention discloses a rare-earth magnesium alloy with a low coefficient of thermal expansion. The rare-earth magnesium alloy has a composition of Mg-RE-M, where RE is one or more of Ce, Dy, Er, Gd, Ho, La, Sm, Y, Yb, Pr, Tm, Sc, and Nd, and M is one or more of Sr, Ca, Li, Ag, Zn, Al, Sn, Cu, Zr, Si, Ti, and Hf; the total RE content is 0.02 wt.%~7.0 wt.%, and the total M content is 0.5 wt.%~13.0 wt.%; the coefficient of thermal expansion of the rare-earth magnesium alloy is ≤25×10⁻⁶. ‑6 / K. This solves the problems of process defects and mechanical property deterioration caused by the difficulty in melting high-melting-point rare earth intermetallic compounds and their large coefficient of thermal expansion during rapid melting and solidification in additive manufacturing, powder metallurgy, and precision casting.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal material processing and metallurgical engineering, and particularly to a rare earth magnesium alloy with a low coefficient of thermal expansion. Background Technology

[0002] Rare-earth magnesium alloys, with their extremely low density, excellent corrosion resistance, specific strength, and high-temperature stability, have become core materials for lightweight, high-performance components in aerospace, rail transportation, and precision electronics, effectively meeting the stringent requirements of high-end equipment for structural weight reduction, service reliability, and adaptability to extreme operating conditions. However, the magnesium matrix has a close-packed hexagonal lattice structure, and the solid solubility of rare-earth elements in magnesium at room temperature is extremely low. Rare-earth magnesium alloys prepared by conventional processes contain a large number of micron-sized high-melting-point rare-earth intermetallic compounds, such as Mg5Gd and Mg... 12 Ce, Mg 24 Y5, etc. These compounds have melting points much higher than the magnesium matrix, and during rapid melting and solidification processes such as additive manufacturing, powder metallurgy, and precision casting, they easily induce a series of process defects and severely degrade alloy properties. Specifically, these intermetallic compounds are difficult to completely melt during rapid melting and solidification, easily becoming nucleation sites for unfused materials and porosity defects, significantly reducing component density and even causing matrix cracking; unmelted particles disrupt the spreading and fluidity of the alloy melt, and due to the poor liquid fluidity of magnesium alloys themselves, problems such as poor interlayer bonding and low forming accuracy are exacerbated during the preparation process; in addition, the large difference in thermal expansion coefficients between rare earth intermetallic compounds and the magnesium matrix easily leads to severe stress concentration at the phase interface during rapid cooling, becoming a source of microcrack initiation and significantly reducing the impact toughness of the component; simultaneously, the rapid solidification rate of magnesium alloys makes it easy for rare earth metals to agglomerate and segregate, failing to achieve uniform dispersion, thus losing the grain refinement effect and causing alloy performance fluctuations, making it difficult to meet the performance consistency requirements of high-end equipment.

[0003] In addition to the aforementioned problems, due to the high coefficient of thermal expansion of the magnesium matrix, the rapid heating and cooling thermal cycles in additive manufacturing, powder metallurgy, and precision casting processes easily induce enormous residual stresses, significantly increasing the risk of interlayer cracking and severely impairing the mechanical properties of the components. Therefore, effectively suppressing the formation of high-melting-point rare-earth intermetallic compounds or controlling their size and quantity within a manageable range, while simultaneously improving melt surface tension, wettability, and fluidity, suppressing molten pool turbulence, reducing spatter and keyhole defects, and thus improving the forming quality, microstructure uniformity, and interfacial compatibility of magnesium alloys, and effectively reducing the coefficient of thermal expansion of the alloy by controlling the matrix lattice to reduce stress concentration and solidification cracking tendency at the phase interface, are pressing technical challenges in the field of rare-earth magnesium alloys. Summary of the Invention

[0004] The purpose of this invention is to provide a rare-earth magnesium alloy with a low coefficient of thermal expansion. This is achieved by introducing one or more elements from Sr, Ca, Li, Ag, Zn, Al, Sn, Cu, Zr, Si, Ti, and Hf, and controlling their total content to be 0.5 wt.%~13.0 wt.%, thereby increasing the solid solubility of rare earth elements in the magnesium matrix and reducing the alloy's coefficient of thermal expansion to ≤25 × 10⁻⁶. -6 / K solves the problems of process defects and mechanical property deterioration caused by the difficulty in melting high-melting-point rare earth intermetallic compounds and their large thermal expansion coefficient during rapid melting and solidification processes in additive manufacturing, powder metallurgy, and precision casting.

[0005] To solve the above technical problems, embodiments of the present invention provide a rare earth magnesium alloy with a low coefficient of thermal expansion. The rare earth magnesium alloy has a composition of Mg-RE-M, where RE is one or more of Ce, Dy, Er, Gd, Ho, La, Sm, Y, Yb, Pr, Tm, Sc and Nd, and M is one or more of Sr, Ca, Li, Ag, Zn, Al, Sn, Cu, Zr, Si, Ti and Hf. The total content of RE is 0.02 wt.%~7.0 wt.%, the total content of M is 0.5 wt.%~13.0 wt.%, and the content of Mg is 80 wt.%~99.48 wt.%; the coefficient of thermal expansion of the rare earth magnesium alloy is ≤25×10⁻⁶. -6 / K.

[0006] Furthermore, the rare earth elements in the rare earth magnesium alloy exist in a fully dissolved state or in a dissolved state coexisting with finely dispersed intermetallic compounds. When rare earth intermetallic compounds are present, the size of the intermetallic compounds is <0.8 μm, the average area fraction is ≤0.5%, and any 1 mm... 2 Within the alloy region, the quantity of the intermetallic compound varies by no more than 10%.

[0007] Furthermore, when the rare earth magnesium alloy is detected by differential scanning calorimetry, no endothermic melting peak of rare earth intermetallic compounds is observed in the temperature range of 450℃ to 850℃.

[0008] Further, the RE is one or more of Gd, Y, Yb, Nd and Ce, and the total RE content is 0.1 wt.% to 4.5 wt.%.

[0009] Furthermore, M includes one or more of Sr, Ca, Li, and Ag.

[0010] Furthermore, the Sr content is 0.001 wt.% ~ 0.05 wt.%, the Ca content is 0.01 wt.% ~ 2 wt.%, the Li content is 0.01 wt.% ~ 2 wt.%, and the Ag content is 0.02 wt.% ~ 2 wt.%.

[0011] Furthermore, M includes one or more of Zn, Al, Sn, and Cu.

[0012] Furthermore, the Zn content is 0.01 wt.% ~ 7 wt.%, the Al content is 0.1 wt.% ~ 9.5 wt.%, the Sn content is 0.002 wt.% ~ 0.5 wt.%, and the Cu content is 0.005 wt.% ~ 0.03 wt.%.

[0013] Furthermore, M includes one or more of Zr, Si, Ti, and Hf.

[0014] Furthermore, the Zr content is 0.01 wt.% ~ 1.5 wt.%, the Si content is 0.01 wt.% ~ 0.5 wt.%, the Ti content is 0.01 wt.% ~ 0.5 wt.%, and the Hf content is 0.01 wt.% ~ 0.3 wt.%.

[0015] The above-described technical solutions of the embodiments of the present invention have the following beneficial technical effects: 1. By introducing solid solution regulating elements such as Sr, Ca, Li, and Ag, and utilizing their preferential solid solution in the magnesium matrix to change the local lattice distortion energy and electronic distribution state, the solid solubility limit and site stability of rare earth elements in magnesium are significantly improved. This allows the rare earth elements in the alloy to exist in a fully solid solution state or as fine, dispersed intermetallic compounds with a size of less than 0.8 μm and an area fraction of no more than 0.5%. Furthermore, DSC detection shows no endothermic melting peaks of high-melting-point rare earth intermetallic compounds in the 450~850℃ range. This effectively solves the problem that micron-sized high-melting-point compounds in conventional rare earth magnesium alloys are difficult to dissolve and easily become unfused and porosity nuclei. It also significantly reduces process defects in additive manufacturing, powder metallurgy, and precision casting processes, and improves the density and crack resistance of components. 2. By introducing one or more low-melting-point eutectic forming elements from Zn, Al, Sn, and Cu, these elements form a multi-element low-melting-point eutectic structure or dispersed phase with rare earth elements, improving the surface tension, wettability, and fluidity of the melt. This promotes faster and more uniform melting of rare earth elements, avoiding local enrichment of rare earth elements and the resulting poor spreading and interlayer bonding defects. At the same time, the grain refinement and microalloying effects synergistically improve the forming accuracy and process stability of the alloy, solving problems such as splashing, keyholes, and interlayer cracking that occur during rapid melting and solidification of magnesium alloys due to their poor liquid fluidity. This improves the forming quality and mechanical property consistency of the components. 3. By introducing one or more lattice and phase structure regulating elements from Zr, Si, Ti, and Hf, and utilizing atomic solid solution, lattice constant fine-tuning, and the formation of low-expansion dispersed phases, the overall thermal expansion coefficient of the alloy was significantly reduced to ≤25×10⁻⁶. -6 / K effectively alleviates the interfacial stress concentration problem caused by the mismatch between the high thermal expansion coefficient of the magnesium matrix and the "rapid cooling" thermal cycle processes such as additive manufacturing and powder metallurgy. It reduces the tendency of thermal stress concentration and solidification crack initiation, solves the problem of microcracks and toughness deterioration caused by the large difference in the thermal expansion coefficient of the phase interface in conventional rare earth magnesium alloys during rapid cooling, and improves the service reliability and dimensional stability of components under extreme working conditions. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of the invention.

[0017] This invention provides a rare-earth magnesium alloy with a low coefficient of thermal expansion. The rare-earth magnesium alloy has a composition of Mg-RE-M, where RE is one or more of Ce, Dy, Er, Gd, Ho, La, Sm, Y, Yb, Pr, Tm, Sc, and Nd, and M is one or more of Sr, Ca, Li, Ag, Zn, Al, Sn, Cu, Zr, Si, Ti, and Hf. The total content of RE is 0.02 wt.%~7.0 wt.%, the total content of M is 0.5 wt.%~13.0 wt.%, and Mg is 80 wt.%~99.48 wt.%. The coefficient of thermal expansion of this rare-earth magnesium alloy is ≤25 × 10⁻⁶. -6 / K.

[0018] The aforementioned rare-earth magnesium alloy with a low coefficient of thermal expansion is represented by the alloying system Mg-RE-M. Mg, as the matrix element, is the main component of the alloy, giving it its lightweight properties. RE represents one or more rare-earth elements selected from Ce, Dy, Er, Gd, Ho, La, Sm, Y, Yb, Pr, Tm, Sc, and Nd. These rare-earth elements significantly refine the grain size, strengthen the magnesium matrix, and improve its high-temperature stability. M represents one or more alloying elements selected from Sr, Ca, Li, Ag, Zn, Al, Sn, Cu, Zr, Si, Ti, and Hf. These elements respectively play multiple roles, such as improving the solid solubility of rare-earth elements, enhancing melt flowability, and regulating lattice thermal expansion behavior. Through the synergistic effect of these three components, the alloy exhibits a low coefficient of thermal expansion on a macroscopic scale, making it suitable for rapid thermal cycling processes such as additive manufacturing, powder metallurgy, and precision casting.

[0019] The rare earth elements (REs) encompass various common members of the lanthanides, as well as Sc and Y, including Ce, Dy, Er, Gd, Ho, La, Sm, Y, Yb, Pr, Tm, Sc, and Nd. These rare earth elements possess certain solid solution strengthening potential in magnesium and can form metastable phases through subsequent aging treatment, resulting in precipitation strengthening effects. The total RE content is limited to 0.02 wt.% to 7.0 wt.%, a range established based on two considerations: firstly, a content of not less than 0.02 wt.% ensures that rare earths exert basic grain refinement and strengthening effects; secondly, a content not exceeding 7.0 wt.% avoids the precipitation of large amounts of high-melting-point rare earth intermetallic compounds due to solid solution saturation caused by excessive rare earths, thereby reducing the tendency to induce process defects such as unmelted particles, porosity, and cracks during rapid solidification. Within this content range, rare earth elements can exist in a relatively efficient solid solution state, providing a microstructure basis for achieving a low coefficient of thermal expansion.

[0020] Among them, there are 13 M elements, which can be divided into three categories: The first category is rare earth solid solution regulating elements, including Sr, Ca, Li, and Ag. They preferentially dissolve in the magnesium matrix, changing the local lattice distortion energy and electronic distribution state, thereby improving the solid solution limit and site stability of rare earth atoms in magnesium. The second category is low-melting-point eutectic formation and melt fluidity improvement elements, including Zn, Al, Sn, and Cu. They can form multi-element low-melting-point eutectic structures or dispersed phases with rare earth elements, improving melt surface tension, wettability, and fluidity, promoting rapid and uniform melting of rare earth elements, and avoiding local enrichment. The third category is lattice and phase structure regulating elements, including Zr, Si, Ti, and Hf. They significantly reduce the overall thermal expansion coefficient of the alloy through solid solution strengthening, lattice constant fine-tuning, and the formation of low-expansion dispersed phases. The total M content is limited to 0.5 wt.% to 13.0 wt.%, which ensures that the above-mentioned elements can perform their respective functions, while avoiding damage to the lightweight properties of the magnesium matrix or the introduction of unnecessary brittle phases due to excessive addition.

[0021] Conventional magnesium matrices have a relatively high coefficient of thermal expansion. Under the rapid heating and cooling cycles of additive manufacturing, powder metallurgy, and precision casting processes, they are highly susceptible to inducing significant residual stress, thus greatly increasing the risk of interlaminar cracking and severely impairing the mechanical properties of the components. Alloys, however, have a coefficient of thermal expansion ≤25×10⁻⁶. -6 / K, by controlling the overall thermal expansion coefficient of the alloy within the above range, can effectively alleviate the mismatch between the high thermal expansion coefficient of the magnesium matrix and the rapid thermal cycling process, reduce stress concentration at the phase interface, and suppress the tendency of thermal stress concentration and solidification crack initiation.

[0022] This invention constructs a multi-component synergistic alloy system by combining a Mg matrix with specific types and amounts of rare earth elements (RE) and metal elements (M). The appropriate addition of RE elements provides the alloy with the potential for solid solution strengthening and age hardening; solid solution regulating elements such as Sr, Ca, Li, and Ag improve the solid solubility of rare earth elements in magnesium and suppress the coarse precipitation of high-melting-point intermetallic compounds; elements such as Zn, Al, Sn, and Cu improve the melt's fluidity and formability, reducing the sensitivity to process defects during rapid melting and solidification; and lattice regulating elements such as Zr, Si, Ti, and Hf adjust the thermal expansion behavior of the matrix at the atomic scale, reducing the overall thermal expansion coefficient of the alloy to no more than 25 × 10⁻⁶. -6 / K. These components work together to give the alloy the advantages of lightweight magnesium alloys while also providing a low coefficient of thermal expansion. This allows it to adapt to the rapid thermal cycling conditions in advanced manufacturing processes such as additive manufacturing, powder metallurgy, and precision casting, reducing defects such as cracks, lack of fusion, and porosity caused by thermal stress. This provides a rare earth magnesium alloy material with stronger process adaptability and lower cracking tendency for aerospace, rail transportation, precision electronics, and other fields.

[0023] Specifically, in rare-earth magnesium alloys with low thermal expansion coefficients, rare earth elements exist in a fully dissolved state or in a dissolved state coexisting with finely dispersed intermetallic compounds; when rare earth intermetallic compounds are present, the size of the intermetallic compounds is <0.8μm, the average area fraction is ≤0.5%, and any 1mm 2 Within the alloy region, the dispersion of the number of intermetallic compounds does not exceed 10%.

[0024] Rare earth elements can exist in magnesium alloys in two states. The first is the fully dissolved state, where rare earth atoms are completely integrated into the close-packed hexagonal lattice of the magnesium matrix, existing in the form of substitutional atoms. No independent rare earth intermetallic compound phases exist in the alloy matrix. In this state, the strengthening effect of rare earth elements mainly comes from the lattice distortion and dislocation movement hindrance caused by solid solution. The second state is a coexistence of the solid solution state and fine, dispersed intermetallic compounds. Most rare earth atoms remain dissolved in the magnesium matrix, but a very small number combine with magnesium or other alloying elements to form nanoscale or submicron-sized intermetallic compound particles. These particles are uniformly dispersed within the grains or at grain boundaries. The fully dissolved state is the ideal state, but the presence of a small amount of dispersed compounds is permissible. As long as their size and quantity are strictly controlled within a specific range, they will not adversely affect the rapid melting process; on the contrary, they may further improve mechanical properties through second-phase strengthening.

[0025] When rare earth intermetallic compounds are unavoidably present in the alloy, this invention requires that the size of these compounds be less than 0.8 micrometers. While the melting point of intermetallic compounds smaller than 0.8 micrometers may still be higher than that of the magnesium matrix, their actual melting temperature is significantly reduced during rapid melting processes such as additive manufacturing and powder metallurgy due to particle curvature and volume effects. This allows them to completely melt or achieve compositional homogenization with the surrounding matrix within a very short heating time, thus preventing unfused particles from becoming nucleation sites for pores or cracks. In contrast, micrometer-sized high-melting-point rare earth intermetallic compounds formed in conventional processes are difficult to completely melt during rapid melting, becoming a major source of process defects.

[0026] The average area fraction of rare earth intermetallic compounds in the alloy does not exceed 0.5%. Area fraction is an important indicator for measuring the overall content of the second phase. The 0.5% limit means that the volume proportion of rare earth intermetallic compounds in the alloy is extremely low, and the vast majority of rare earth atoms still exist in solid solution form in the magnesium matrix. This low area fraction ensures that the alloy has a uniform composition distribution and microstructure on a macroscopic scale, avoiding problems such as reduced melt fluidity, poor spreading, and thermal stress concentration at phase interfaces caused by the presence of a large number of high-melting-point phases. At the same time, the very small amount of dispersed fine compounds can act as heterogeneous nucleation cores to promote grain refinement, thereby improving the alloy strength without compromising processing performance.

[0027] Within any 1 square millimeter of the alloy, the dispersion of intermetallic compounds does not exceed 10%. This means that the compound particles are highly uniformly distributed in space, without local agglomeration or segregation. In conventional rare-earth magnesium alloys, rare-earth intermetallic compounds are prone to agglomeration and segregation during rapid solidification, failing to achieve a uniform and dispersed distribution. This results in a loss of grain refinement and fluctuations in alloy properties. Rare-earth elements can distribute more uniformly during solidification, and the small amount of intermetallic compounds formed also exhibits uniform dispersion. This uniformity requirement ensures consistent properties on a macroscopic scale; regardless of where the sample is taken from, its mechanical properties, thermal expansion behavior, and melting characteristics during rapid solidification are highly consistent.

[0028] By controlling the rare earth elements in rare earth magnesium alloys to be in a fully dissolved state or in a dissolved state coexisting with fine, dispersed intermetallic compounds with a size less than 0.8 micrometers, an area fraction not exceeding 0.5%, and a quantity dispersion range not exceeding 10%, this invention effectively solves the problem that micron-sized high-melting-point rare earth intermetallic compounds in conventional rare earth magnesium alloys are difficult to completely dissolve during rapid solidification. This avoids unfused particles becoming nucleation sites for defects such as pores and cracks, while also eliminating performance inhomogeneities caused by compound agglomeration and segregation. These strictly controlled dispersed phases have small differences in thermal expansion coefficients with the magnesium matrix and good interfacial compatibility. They are less prone to severe stress concentration during rapid cooling, thus significantly reducing the sensitivity to microcrack initiation. This enables the alloy to obtain high-density, high-uniformity formed parts in advanced processes such as additive manufacturing, powder metallurgy, and precision casting, and provides a microstructure basis for achieving low thermal expansion coefficients and excellent mechanical properties.

[0029] Specifically, when rare-earth magnesium alloys with low thermal expansion coefficients are tested using differential scanning calorimetry (DSC), no endothermic melting peaks of rare-earth intermetallic compounds are observed in the temperature range of 450℃ to 850℃. When using this method to test rare-earth magnesium alloys, the focus should be on whether endothermic melting peaks appear in the 450℃ to 850℃ temperature range. The selection of this temperature range has clear technical significance: high-melting-point rare-earth intermetallic compounds (such as Mg5Gd, Mg...) formed in conventional rare-earth magnesium alloys... 12 Ce, Mg 24 The melting or phase transformation temperatures of Y5 and other rare earth metals usually fall within this range. Therefore, the presence or absence of an endothermic peak in this range directly reflects the presence of detectable amounts of high-melting-point rare earth metal intermetallic compounds in the alloy.

[0030] When no endothermic melting peak of rare earth intermetallic compounds appears in the alloy within the temperature range of 450℃ to 850℃, it indicates that the rare earth elements in the alloy do not exist in the conventional form of high-melting-point intermetallic compounds with significant thermal effects. In conjunction with the microstructure control requirements of this invention, this detection result means that rare earth elements in the alloy mainly exist in two states: either completely integrated into the magnesium matrix lattice in a fully solid solution state, with melting or dissolution behavior consistent with the magnesium matrix, and no independent endothermic peaks are generated in the characteristic temperature range; or they exist in the form of extremely fine dispersed intermetallic compounds. Due to the particle size reaching the nanometer or submicrometer scale, their melting point is significantly reduced, and the melting endothermic peak may shift out of the 450℃ to 850℃ range, or the extremely small quantity results in a thermal effect that is too weak to be detected by differential scanning calorimetry. Therefore, this detection characteristic is an important macroscopic characterization method for verifying the high rare earth solid solubility and effective suppression of intermetallic compounds achieved by this invention.

[0031] The absence of endothermic melting peaks in rare earth intermetallic compounds directly proves the absence of a second phase with significant thermal effects capable of melting within the 450℃ to 850℃ range in the alloy. During rapid heating processes such as additive manufacturing, powder metallurgy, and precision casting, no unmelted high-melting-point particles remain in the alloy. In conventional rare earth magnesium alloys, micron-sized intermetallic compounds, due to their melting points being much higher than the magnesium matrix, are difficult to completely melt during rapid solidification. Residual unmelted particles not only become nucleation sites for pores and incomplete fusion defects but also disrupt the flow continuity of the melt. However, in the alloy of this invention, all components melt simultaneously when heated to the melting or sintering temperature, forming a homogeneous melt, thus avoiding the aforementioned problems and providing a thermodynamic basis for obtaining high-density, low-defect-rate formed parts.

[0032] The absence of an endothermic melting peak in the 450℃ to 850℃ range is a hallmark of the multi-element alloying design of this invention. The solid solution limit of rare earth elements in magnesium is increased by introducing solid solution regulating elements such as Sr, Ca, Li, and Ag; the uniform integration of rare earth elements with the matrix is ​​promoted by introducing elements such as Zn, Al, Sn, and Cu; and the lattice thermal stability is regulated by introducing elements such as Zr, Si, Ti, and Hf. These synergistic effects prevent rare earth elements from precipitating as coarse, high-melting-point intermetallic compounds. Therefore, this detection characteristic can serve as a non-destructive, macroscopic detection method for rapidly determining whether an alloy meets its design objectives. It allows for preliminary assessment of the rare earth occurrence state without relying on complex quantitative microstructure analysis, and has significant practical value for alloy quality control and process adaptability evaluation.

[0033] By employing differential scanning calorimetry to detect the endothermic melting peak of rare earth intermetallic compounds in the temperature range of 450℃ to 850℃, this invention provides a macroscopic thermal analysis basis for verifying the existence of rare earths in a fully dissolved or extremely fine dispersed state. This characteristic confirms that there are no high-melting-point rare earth intermetallic compounds with significant thermal effects that can melt in this temperature range in the alloy. This ensures that all components can melt synchronously and uniformly during rapid solidification processes such as additive manufacturing, powder metallurgy, and precision casting, avoiding unmelted particles becoming nucleation sites for defects such as pores, lack of fusion, and cracks. At the same time, it ensures that the fluidity and spreadability of the melt are not affected by the residual solid phase, providing key thermophysical conditions for obtaining high-density, uniformly structured, and stable formed parts, and further supporting the realization of the alloy's overall low coefficient of thermal expansion and excellent mechanical properties.

[0034] Specifically, RE is one or more of Gd, Y, Yb, Nd, and Ce, with a total RE content of 0.1 wt.% to 4.5 wt.%. The rare earth elements are further preferably one or more of Gd, Y, Yb, Nd, and Ce as the rare earth components of the alloy, based on the relatively high solid solubility limits and significant age-hardening responses of these elements in the magnesium matrix. Gd and Y are recognized as highly efficient strengthening elements in magnesium alloys, capable of forming metastable phases with magnesium and producing significant precipitation strengthening effects during aging. Simultaneously, their effect on lattice distortion in the magnesium matrix is ​​relatively mild, and they are less likely to induce brittle phases. Yb exhibits unique solid solution behavior in magnesium, effectively refining grains and improving corrosion resistance. Nd and Ce are light rare earth elements with moderate diffusion rates in magnesium, capable of forming thermally stable precipitates, and are relatively inexpensive. The above five elements can achieve a good synergistic effect between solid solution strengthening and precipitation strengthening. Compared with other rare earth elements, they are more likely to achieve high solid solubility under conventional smelting and rapid solidification conditions, thereby more effectively suppressing the formation of high melting point coarse intermetallic compounds.

[0035] When multiple rare earth elements from the above five categories are added in combination, synergistic effects may occur between different rare earth elements. For example, when Gd and Y are added in combination, their solid solution behavior in magnesium promotes each other, forming a more complex precipitation sequence, delaying the decomposition of supersaturated solid solutions, and thus improving the high-temperature stability of the alloy. When Nd and Ce are combined with Gd or Y, the combination of light and heavy rare earth elements can optimize the morphology and distribution of precipitates and reduce the tendency of coarse phases to agglomerate at grain boundaries. The addition of Yb helps to improve the corrosion resistance of the alloy. By rationally selecting and combining these preferred rare earth elements, multi-element synergistic strengthening can be achieved without increasing the total content, further improving the mechanical properties and thermal stability of the alloy, while maintaining a low coefficient of thermal expansion and good adaptability to rapid melting and solidification processes.

[0036] The lower limit is raised to 0.1 wt.% because below this content, the effects of rare earth elements on grain refinement, solid solution strengthening, and high-temperature stability improvement in magnesium alloys are not significant enough to fully realize the technical value of rare earth addition. The upper limit is lowered to 4.5 wt.% because when the total rare earth content exceeds 4.5 wt.%, even with the solid solution control elements of this invention, the solid solubility of rare earths in the magnesium matrix may still tend to saturate. Some rare earth atoms will inevitably precipitate in the form of intermetallic compounds, and the size and quantity of the precipitated phases may exceed the controllable range, thereby increasing the risk of defects such as incomplete fusion and porosity during rapid solidification. Therefore, 0.1 wt.% to 4.5 wt.% is a preferred range that balances strengthening effect and process adaptability.

[0037] In one embodiment of the present invention, M includes one or more of Sr, Ca, Li, and Ag. The Sr content is 0.001 wt.% to 0.05 wt.%, the Ca content is 0.01 wt.% to 2 wt.%, the Li content is 0.01 wt.% to 2 wt.%, and the Ag content is 0.02 wt.% to 2 wt.%.

[0038] In this embodiment, Sr, Ca, Li, and Ag are defined as rare earth solid solution regulating elements. These elements have atomic radii and electronic structures similar to or specific to magnesium, enabling them to preferentially dissolve in the magnesium matrix and occupy specific positions in the magnesium lattice, thereby altering the local lattice distortion energy and electronic distribution state of the magnesium matrix. This change in the lattice environment directly affects the occupancy stability and migration behavior of rare earth solute atoms in the matrix: on the one hand, the lattice expansion or contraction caused by the solid solution regulating elements can provide more favorable solid solution positions for rare earth atoms, reducing the thermodynamic driving force for their segregation and precipitation; on the other hand, these elements may form short-range ordered interatomic interactions with rare earth atoms, delaying the diffusion and precipitation of rare earths during solidification and cooling. Through the above mechanism, Sr, Ca, Li, and Ag can effectively improve the solid solubility limit and site stability of target rare earth solute atoms in the magnesium matrix, and inhibit the premature precipitation of rare earth atoms during solidification to form coarse high-melting-point intermetallic compounds, thus laying the foundation for achieving full solid solution or extremely fine dispersion distribution of rare earths in subsequent rapid melting and solidification processes.

[0039] This embodiment specifies the exact content ranges for Sr, Ca, Li, and Ag. The Sr content is 0.001 wt.% to 0.05 wt.%, which is considered a trace addition. This is because Sr has extremely low solid solubility in magnesium, and excessive addition can easily form a brittle Mg-Sr binary phase, which would impair the alloy's plasticity. However, trace amounts of Sr can strongly adsorb at grain boundaries and phase interfaces, altering interfacial energy and suppressing the grain boundary segregation of rare earth elements. The Ca content is 0.01 wt.% to 2 wt.%. Ca is a commonly used flame-retardant and grain-refining element in magnesium alloys. Within this range, it can significantly refine the grains and improve the high-temperature strength of the alloy. Simultaneously, Ca has a strong affinity for rare earth elements, forming stable composite compounds and reducing the tendency for rare earth elements to precipitate individually. The Li content ranges from 0.01 wt.% to 2 wt.%. Li can reduce the axial ratio of the close-packed hexagonal lattice of magnesium, improving the plastic deformation ability of the matrix. Simultaneously, the atomic size of Li differs significantly from that of magnesium, and its solid solution causes significant lattice distortion, thereby enhancing the lattice capacity for rare earth atomic solid solutions. The Ag content ranges from 0.02 wt.% to 2 wt.%. Ag has high solid solubility in magnesium, enabling it to form multi-element solid solutions with rare earth elements. Through electronic effects, it enhances the bonding strength between rare earth elements and the matrix, delaying the precipitation of rare earth elements. The lower limits of these element contents ensure the effective functioning of each element, while the upper limits avoid the negative effects of excessive addition, such as the precipitation of brittle phases, increased density, or increased cost.

[0040] By introducing one or more of Sr, Ca, Li, and Ag and strictly controlling their content within the aforementioned range, this invention achieves precise regulation of the lattice environment of the magnesium matrix, thereby significantly improving the solid solution limit and site stability of rare earth elements in magnesium. These solid solution regulating elements, through preferential solid solution alteration of local lattice distortion energy and electron distribution, effectively suppress the premature precipitation of rare earth atoms during solidification to form coarse, high-melting-point intermetallic compounds, allowing rare earth elements in the alloy to exist in a fully solid-solid state or a dispersed state with extremely small sizes. Simultaneously, the trace addition of these elements also brings additional beneficial effects such as grain refinement, improved flame retardancy, and enhanced plasticity, synergistically enhancing the process stability of the alloy in rapid melting and solidification processes such as additive manufacturing, powder metallurgy, and precision casting. This reduces defects such as incomplete fusion, porosity, and cracks caused by rare earth segregation and compound precipitation, providing crucial microstructure guarantees for achieving the alloy's low coefficient of thermal expansion and excellent mechanical properties.

[0041] In one embodiment of the present invention, M includes one or more of Zn, Al, Sn, and Cu. The Zn content is 0.01 wt.% to 7 wt.%, the Al content is 0.1 wt.% to 9.5 wt.%, the Sn content is 0.002 wt.% to 0.5 wt.%, and the Cu content is 0.005 wt.% to 0.03 wt.%.

[0042] In this embodiment, Zn, Al, Sn, and Cu are defined as elements that form low-melting-point eutectics and improve melt flowability. These elements share the common characteristic of forming multi-element low-melting-point eutectic structures or dispersed phases with magnesium and rare earth elements, thereby significantly reducing the liquidus temperature and solidification range of the alloy. In rapid melting and solidification processes such as additive manufacturing, powder metallurgy, and precision casting, a lower melting point and a wider eutectic reaction range mean that the alloy can achieve complete melting more quickly upon heating, and the superheat of the melt is easier to control, effectively reducing the risk of unmelted particle residue. These elements can improve the surface tension, wettability, and flowability of the melt: reduced surface tension helps the melt spread on a solid substrate or solidified layer, reducing spheroidization and discontinuous melt channels; increased wettability enhances the interfacial bonding strength between the melt and the solid phase, reducing interlayer incomplete fusion defects; improved flowability allows the melt to fully fill the tiny voids in the molten pool before rapid solidification, suppressing the formation of porosity and keyholes. The synergistic effect of Zn, Al, Sn, and Cu promotes faster and more uniform melting of rare earth elements, avoiding local enrichment of rare earth elements, thereby significantly improving the forming quality and process stability of the alloy in the rapid melting and solidification process.

[0043] This embodiment specifies the content ranges for Zn, Al, Sn, and Cu. The Zn content is 0.01 wt.% to 7 wt.%. Zn is one of the most commonly used alloying elements in magnesium alloys. Within this range, it can form a Mg-Zn eutectic structure with magnesium, significantly refining the grains. Simultaneously, Zn has a strong affinity for rare earth elements, forming fine rare earth-zinc compounds, further suppressing the precipitation of coarse rare earth phases. Too low a Zn content results in insignificant effects, while too high a content easily leads to the formation of coarse brittle Mg-Zn phases. The Al content is 0.1 wt.% to 9.5 wt.%. Al can significantly improve the strength and casting performance of magnesium alloys, forming Al-RE compounds with rare earth elements. These compounds typically have high thermal stability and fine size, which is beneficial for dispersion strengthening. Controlling the Al content above 0.1 wt.% ensures the strengthening effect, while not exceeding 9.5 wt.% avoids the formation of excessive Mg. 17 Al 12Brittle phases. The Sn content ranges from 0.002 wt.% to 0.5 wt.%. Sn is a surface-active element; even trace amounts can significantly reduce the surface tension of the melt and improve its wettability to the solid matrix. Sn also forms the Mg2Sn phase with magnesium, exhibiting good high-temperature stability. Extremely low Sn content (0.002 wt.%) is sufficient to function, while the upper limit of 0.5 wt.% avoids increased density and precipitation of brittle phases. The Cu content ranges from 0.005 wt.% to 0.03 wt.%. Cu can form a eutectic structure with magnesium, refining the grains and improving the alloy's corrosion resistance. However, Cu has limited solid solubility in magnesium, and excessive addition will reduce corrosion resistance; therefore, it is controlled within extremely small amounts. The lower limits of these elements ensure the activation of their respective functions, while the upper limits avoid negative effects such as brittle phase formation, increased density, or decreased corrosion resistance. The elements can also form composite eutectic structures, further optimizing the overall flow characteristics of the melt.

[0044] By introducing one or more of Zn, Al, Sn, and Cu and strictly controlling their content within the aforementioned range, the physicochemical properties of rare earth magnesium alloys during rapid melting and solidification were significantly improved. These elements, by forming a multi-element low-melting-point eutectic structure or dispersed phase with magnesium and rare earths, effectively reduced the alloy's liquidus temperature and solidification range, promoting rapid and uniform melting of rare earth elements during heating and avoiding localized enrichment of rare earths and the resulting compositional segregation. Simultaneously, by reducing melt surface tension, improving wettability and fluidity, they significantly suppressed turbulent flow, splashing, and keyhole defects in the molten pool, reducing problems such as poor interlayer bonding and low forming accuracy. Furthermore, these trace elements also have a micro-alloying effect, refining grains and improving casting performance, synergistically enhancing the mechanical properties and process stability of components. This enables the alloy to obtain high-density, uniformly structured, and consistently performing formed parts in advanced processes such as additive manufacturing, powder metallurgy, and precision casting, providing a crucial melt processing foundation for achieving a low coefficient of thermal expansion and excellent strength-toughness matching.

[0045] In one embodiment of the present invention, M includes one or more of Zr, Si, Ti, and Hf. The Zr content is 0.01 wt.% to 1.5 wt.%, the Si content is 0.01 wt.% to 0.5 wt.%, the Ti content is 0.01 wt.% to 0.5 wt.%, and the Hf content is 0.01 wt.% to 0.3 wt.%.

[0046] In this embodiment, Zr, Si, Ti, and Hf are defined as lattice and phase structure regulating elements. These elements have different atomic sizes and crystal structure characteristics than magnesium, and can enter the magnesium matrix lattice through solid solution or form fine dispersed phases, thereby adjusting the lattice constant and thermal vibration behavior of the magnesium matrix at the atomic scale. Specifically, when these elements exist in solid solution form, they cause local distortion of the magnesium lattice, changing the bonding strength between atoms and the thermal vibration frequency, thus affecting the degree of lattice expansion with increasing temperature; when they exist in dispersed phase form (such as forming Zr particles, Mg2Si, Ti, or Hf intermetallic compounds, etc.), these dispersed phases themselves usually have a low coefficient of thermal expansion, and their uniform distribution in the matrix can constrain the free expansion of the magnesium matrix, producing a pinning effect, thereby effectively reducing the overall coefficient of thermal expansion of the alloy. More importantly, the segregation or precipitation of these elements at grain boundaries and phase interfaces can improve the high-temperature thermal stability of the interface, reduce interfacial slip and stress accumulation caused by drastic temperature changes during rapid heating and cooling cycles, thereby fundamentally suppressing the tendency of thermal stress concentration and solidification crack initiation.

[0047] This embodiment specifies the content ranges for Zr, Si, Ti, and Hf. The Zr content is 0.01 wt.% to 1.5 wt.%. Zr is the most effective grain refiner in magnesium alloys. During solidification, Zr particles form heterogeneous nucleation sites, significantly refining the grains. Simultaneously, Zr can form a solid solution with magnesium, slightly altering the lattice constant and reducing the coefficient of thermal expansion. When the Zr content is below 0.01 wt.%, the refining effect is not significant; when it is above 1.5 wt.%, large Zr particles easily aggregate, impairing mechanical properties. The Si content is 0.01 wt.% to 0.5 wt.%. Si forms the high-melting-point, low-thermal-expansion Mg2Si phase with magnesium. This phase has excellent thermal stability and high-temperature strength, and its uniform distribution in the matrix effectively suppresses the thermal expansion behavior of the magnesium matrix. Controlling the Si content above 0.01 wt.% ensures the formation of Mg2Si, while not exceeding 0.5 wt.% prevents the Mg2Si phase from coarsening and becoming a brittle crack initiation point. The Ti content ranges from 0.01 wt.% to 0.5 wt.%. Ti has extremely low solid solubility in magnesium and mainly exists as fine elemental or compound particles. These particles have extremely high melting points and extremely low coefficients of thermal expansion, making them effective inhibitors of thermal expansion. Ti particles can also act as nucleation sites for heterogeneous formation, refining grain size. Too low a Ti content results in insufficient particle quantity, while too high a content leads to agglomeration. The Hf content ranges from 0.01 wt.% to 0.3 wt.%. Hf belongs to the same group as Ti and has similar but stronger lattice control capabilities. It can form stable intermetallic compounds with magnesium, significantly improving the high-temperature thermal stability of grain boundaries and inhibiting grain boundary slip and thermal expansion at high temperatures. Furthermore, Hf can be effective with a lower addition amount than Ti; excessive addition leads to excessive cost and may introduce brittleness. The lower limits of these element contents ensure the activation of their respective functions, while the upper limits avoid negative effects such as particle agglomeration, increased cost, or decreased plasticity. The elements can also work synergistically; for example, the combined addition of Zr and Ti can form a finer and more uniform dispersed particle distribution, further optimizing the thermal expansion inhibition effect.

[0048] By introducing one or more of Zr, Si, Ti, and Hf and strictly controlling their content within the aforementioned range, this invention successfully reduced the overall thermal expansion coefficient of the alloy to no higher than 25 × 10⁻⁶. -6The target of / K is to significantly suppress the inherent high thermal expansion behavior of the magnesium matrix through multiple mechanisms, including solid solution strengthening causing fine-tuning of the lattice constant, forming a pinning effect from a low-expansion dispersed phase, and stabilizing grain boundaries and phase interfaces. This technical effect directly alleviates the mismatch between magnesium alloys and rapid heating and cooling thermal cycling processes such as additive manufacturing, powder metallurgy, and precision casting: during the rapid heating stage, the low thermal expansion characteristics of the alloy reduce the accumulation of compressive stress caused by rapid volume expansion; during the rapid cooling stage, the low thermal expansion characteristics reduce the thermal mismatch stress between the matrix and the strengthening phase, effectively suppressing the initiation of microcracks at the phase interface; throughout the entire thermal cycle, the overall level of residual stress is significantly reduced, thereby reducing thermal stress concentration and the tendency for solidification cracking. Ultimately, the forming accuracy, dimensional stability, and service reliability of the alloy are significantly improved, providing a magnesium alloy material with low thermal expansion characteristics, excellent adaptability to rapid melting and solidification processes, and good mechanical properties for high-end lightweight components in aerospace, rail transportation, and other fields.

[0049] Below, this invention prepares rare earth magnesium alloys of different compositions using a vacuum induction melting method, and performs compositional analysis, microstructure characterization, DSC thermal analysis, and thermal expansion coefficient testing on each alloy. Simultaneously, using each alloy as raw material, selective laser melting (SLM) and powder metallurgy experiments were conducted. The area fractions of defects such as incomplete fusion, porosity, and cracks in each formed part were compared and statistically analyzed, and the mechanical properties were also analyzed and statistically summarized. The alloy sample, finished part preparation, and testing methods are as follows: Alloy sample preparation: High-purity magnesium (99.99%), pure zinc (99.9%), pure aluminum (99.9%), and intermediate alloys such as Mg-RE, Mg-Zr, Mg-Si, and Al-Ti were used as raw materials, weighed and batched according to the designed composition. Melting was carried out in a vacuum induction furnace at a temperature of 700–800℃, with argon protection throughout to prevent oxidation and combustion. After refining, the melt was used to prepare the alloy through processes such as gravity casting, gas atomization powdering, single-roller extreme cooling belt spinning, and rotating electrode powdering.

[0050] Microstructure characterization of alloy samples: Polished cross-sections of each alloy were observed using field emission scanning electron microscopy (FE-SEM), and the chemical composition of intermetallic compounds was determined using energy dispersive spectroscopy (EDS). The maximum size, average size, and area fraction of rare-earth intermetallic compounds were quantitatively analyzed using Image-Pro Plus image analysis software.

[0051] Method for testing the dispersion of the number of second phases per unit area in the alloy: Observation was performed using field emission scanning electron microscopy (FE-SEM) in backscattered electron (BSE) mode. Five different fields of view were randomly selected, each with an area of ​​0.1 mm × 0.1 mm (i.e., 0.01 mm²). 2High-resolution photomicrographs (≥5000×) were taken. Using Image-Pro Plus or Nano Measurer image analysis software, the second-phase particles in each photograph were automatically identified and manually counted. The total number of second-phase particles in each field of view was recorded. The maximum number of second-phase particles (N) across the five fields of view was calculated. max ) and minimum value (N) min The dispersion amplitude (D) of the number of second phases per unit area is calculated using the following formula: D = (N max - N min ) / N avg .

[0052] Thermal analysis of alloy samples: Differential scanning calorimetry (DSC) was performed under an argon atmosphere at a heating rate of 10℃ / min. The detection range was 25℃~900℃. The focus was on observing whether endothermic melting peaks of rare earth intermetallic compounds appeared in the 450℃~850℃ range to determine the occurrence state of rare earths.

[0053] Additive manufacturing preparation test: Using the alloy powders obtained in the various examples and comparative examples as raw materials, forming tests were conducted on a selective laser melting (SLM) device. The laser power was 150W~250W; the scanning speed was 600~1000mm / s; the layer thickness was 30μm; and the scanning spacing was 0.1mm. The substrate was preheated to 150℃~200℃. Powder metallurgy preparation test: Using the powders obtained in the various examples and comparative examples as raw materials, dense bulk samples were prepared by cold isostatic pressing under a pressure of 300MPa~400MPa, followed by vacuum sintering at 500℃~580℃ for 2h~4h.

[0054] Forming quality: After SLM and powder metallurgy forming, the cross-section and longitudinal section are observed by SEM, and non-destructive testing and Image-Pro Plus software are used to count the area fraction of defects such as incomplete fusion, porosity, and cracks.

[0055] Thermal expansion coefficient test: Using a thermomechanical analyzer (TMA) or thermal dilatometer, under argon protection, the sample was heated from room temperature to 400℃ at a heating rate of 5℃ / min. The change in sample length was recorded, and the average linear expansion coefficient in the range of 30-200℃ was calculated.

[0056] Mechanical property testing of finished products: Standard plate-shaped tensile specimens (refer to GB / T 228.1-2021) were cut from SLM formed parts and powder metallurgy sintered parts along the forming direction. Tensile tests were carried out at room temperature using a universal testing machine with the clamp displacement rate set to 1 mm / min. At least 3 valid specimens were tested for each component and the average value was taken to calculate the tensile strength and elongation after fracture.

[0057] Comparative Example 1 The alloy was precisely formulated according to mass percentages, with M element at Zn: 5.8%, Zr: 0.55%, and no rare earth elements added; Mg was 93.65%. High-purity magnesium, pure zinc, and a Mg-Zr master alloy were selected as raw materials. Melting was carried out in a vacuum induction furnace at 730℃ under argon protection throughout the process. After refining the melt, it was atomized into powder with a particle size of 15μm~53μm. SEM, EDS, and DSC analyses were performed on the powder to quantitatively analyze the size and area fraction of intermetallic compounds, detect the presence of endothermic peaks of rare earth intermetallic compounds in the 450℃~850℃ range, and test the coefficient of thermal expansion. SLM forming was used, with process parameters consistent with Example 1 for comparison, and the forming quality and mechanical properties of the finished parts were tested.

[0058] Comparative Example 2 The alloy was precisely formulated according to mass percentages, with M elements comprising Al: 2.8%, Zn: 0.8%, and Mn: 0.3%, without any rare earth elements, and Mg: 96.1%. High-purity magnesium, pure aluminum, pure zinc, and an Al-Mn master alloy were selected as raw materials. The alloy was vacuum induction melted at 710℃ under argon protection, and then refined and atomized into powder. The powder was analyzed by SEM, EDS, and DSC to statistically analyze the intermetallic compound characteristics and thermal effects, and the coefficient of thermal expansion was tested. SLM forming was used, with process parameters consistent with Example 2, to prepare dense bulk samples. Defect statistics and mechanical property tests were performed on the finished parts.

[0059] Comparative Example 3 The alloy was precisely formulated according to mass percentages, with RE being Y: 3.8% and Nd: 2.5%; M being Hf: 1.2% and Zr: 0.3%, but no synergistic optimization treatment was performed on thermal expansion regulating elements such as Hf and Zr (Hf content exceeds the preferred range of this invention), and Mg being 92.2%. High-purity magnesium and corresponding intermediate alloys were selected as raw materials, and vacuum induction melting was carried out at 750°C under argon protection. After refining, the powder was atomized into powder. The powder was analyzed by SEM, EDS, and DSC to test the coefficient of thermal expansion. Powder metallurgy was employed, with parameters consistent with Example 3, and the finished parts were inspected for defects and mechanical properties.

[0060] Comparative Example 4 The alloy was precisely formulated according to mass percentages, with RE being Y: 5.8%; M being Zn: 5.2% and Zr: 0.5%, but no synergistic optimization treatment was performed on thermal expansion regulating elements such as Zr; Mg was 88.5%. High-purity magnesium and corresponding intermediate alloys were selected as raw materials, and vacuum induction melting was carried out at 760℃ under argon protection. After refining, the powder was atomized into powder. The powder was analyzed by SEM, EDS, and DSC to test the coefficient of thermal expansion. SLM forming was used, with process parameters consistent with Example 4, to prepare finished parts, and their defect rate and mechanical properties were tested.

[0061] Example 1 The alloy was precisely formulated according to mass percentages, with the following composition: Y 0.02%, Sr 0.001%, Zn 0.01%, Al 0.1%, Zr 0.01%, Si 0.01%, Ca 0.369%, and Mg 99.48%. The raw materials used were high-purity magnesium (99.99%), Mg-Y master alloy, Mg-Sr master alloy, pure zinc, pure aluminum, Mg-Zr master alloy, Mg-Si master alloy, and pure calcium. Melting was carried out in a vacuum induction furnace at 720℃, with argon protection throughout to prevent oxidation and combustion. After refining, the melt was atomized into spherical powder with a particle size distribution of 15μm~53μm, suitable for laser powder bed melting processes. The alloy powder was observed using field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS), and the size and area fraction of intermetallic compounds were quantitatively analyzed using Image-Pro Plus software. Differential scanning calorimetry (DSC) was also performed to detect the presence of endothermic peaks in the 450℃–850℃ range for rare-earth intermetallic compounds. The coefficient of thermal expansion of the powder was measured using a thermomechanical analyzer. The powder was then used for forming tests on an SLM device, and the forming quality and mechanical properties of the finished parts were assessed.

[0062] Example 2 The alloy was precisely formulated according to mass percentages, with the following composition: Gd 7%, Ca 2.0%, Zn 3.5%, Al 3.7%, Zr 1.5%, Si 0.5%, Ti 0.5%, Hf 0.3%, and Mg 81%. High-purity magnesium, pure aluminum, pure zinc, Mg-Gd master alloy, pure calcium, Mg-Zr, Mg-Si, Mg-Ti, and Mg-Hf master alloys were selected as raw materials. Melting was carried out in a vacuum induction furnace at 740℃ under argon protection. After refining the melt, it was atomized into powder with a particle size of 15μm~53μm. SEM, EDS, and DSC analyses were performed on the powder to detect intermetallic compound characteristics and thermal effects at 450℃~850℃, and the coefficient of thermal expansion was measured. SLM forming was used with a laser power of 180W, a scanning speed of 900mm / s, a layer thickness of 30μm, and a scanning spacing of 0.1mm. The substrate was preheated to 180℃, and the finished parts were subjected to defect statistics and mechanical property testing.

[0063] Example 3 The alloy was precisely formulated according to mass percentages, with the alloy composition being Nd 3.5%, Li 1.5%, Zn 3.5%, Al 4.5%, Zr 0.8%, Si 0.25%, Ti 0.25%, Hf 0.15%, and Mg 85.5%. High-purity magnesium, Mg-Nd, pure lithium, pure zinc, pure aluminum, Mg-Zr, Mg-Si, Mg-Ti, and Mg-Hf master alloys were selected as raw materials. Vacuum induction melting was performed at 730℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed using SEM, EDS, and DSC to statistically analyze the size, area fraction, and thermal effect of intermetallic compounds, and the coefficient of thermal expansion was tested. A powder metallurgy process was employed: cold isostatic pressing at 350MPa, followed by vacuum sintering at 560℃ for 3 hours to prepare dense bulk samples. Defect statistics and mechanical property tests were performed on the finished parts.

[0064] Example 4 The alloy was precisely formulated according to mass percentages, with the alloy composition being Y 6.5%, Ag 1.5%, Zn 7.0%, Al 0.1%, Zr 0.01%, Si 0.01%, and Mg 84.88%. High-purity magnesium, Mg-Y, pure silver, pure zinc, pure aluminum, Mg-Zr, and Mg-Si master alloys were selected as raw materials. Vacuum induction melting was performed at 750℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed using SEM, EDS, and DSC, and the coefficient of thermal expansion was tested. SLM forming was employed with a laser power of 220W, a scanning speed of 600mm / s, a layer thickness of 30μm, and a scanning spacing of 0.1mm. The substrate was preheated to 200℃. Defects and mechanical properties of the finished parts were inspected.

[0065] Example 5 The alloy was precisely formulated according to mass percentages, with the following composition: Y 0.5%, Nd 0.5%, Sr 0.001%, Ca 0.01%, Li 2.0%, Ag 0.02%, Zn 0.01%, Al 9.5%, Zr 0.01%, and Mg 87.45%. High-purity magnesium, Mg-Y, Mg-Nd, Mg-Sr, Mg-Ca, pure lithium, pure silver, pure zinc, pure aluminum, and Mg-Zr master alloys were selected as raw materials. Vacuum induction melting was performed at 710℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed using SEM, EDS, and DSC, and the coefficient of thermal expansion was tested. Powder metallurgy was employed: cold isostatic pressing at 300MPa, vacuum sintering at 540℃ for 4 hours to prepare finished parts, and the defect rate and mechanical properties were tested.

[0066] Example 6 The alloy was precisely formulated according to mass percentages, with the following composition: Ce 4.5%, Sr 0.05%, Ca 2.0%, Li 0.01%, Ag 2.0%, Zn 0.01%, Al 0.1%, Sn 0.5%, Cu 0.03%, Zr 1.5%, Si 0.5%, Ti 0.5%, Hf 0.3%, and Mg 88%. High-purity magnesium, Mg-Ce, Mg-Sr, pure calcium, pure lithium, pure silver, pure zinc, pure aluminum, pure tin, pure copper, Mg-Zr, Mg-Si, Mg-Ti, and Mg-Hf master alloys were selected as raw materials. Vacuum induction melting was performed at 740℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed by SEM, EDS, and DSC, and the coefficient of thermal expansion was measured. SLM forming was used with a laser power of 210W, a scanning speed of 700mm / s, a layer thickness of 30μm, and a scanning spacing of 0.1mm. The substrate was preheated to 180℃, and the finished parts were subjected to defect statistics and mechanical property testing.

[0067] Example 7 The alloy was precisely formulated according to mass percentages, with the following M and RE compositions: Y 2.5%, Sr 0.025%, Ca 1.0%, Li 1.0%, Ag 1.0%, Zn 3.5%, Al 4.8%, Sn 0.25%, Cu 0.015%, Zr 0.75%, Si 0.25%, Ti 0.01%, and Hf 0.01%. High-purity magnesium, Mg-Y, Mg-Sr, pure calcium, pure lithium, pure silver, pure zinc, pure aluminum, pure tin, pure copper, Mg-Zr, Mg-Si, Mg-Ti, and Mg-Hf master alloys were selected as raw materials. Vacuum induction melting was performed at 730℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed using SEM, EDS, and DSC to determine the occurrence state of rare earth elements and to measure their coefficients of thermal expansion. The powder metallurgy process was used: cold isostatic pressing at 350MPa and vacuum sintering at 550℃ for 3h to prepare finished parts, and their defect rate and mechanical properties were tested.

[0068] Example 8 The alloy was precisely formulated according to mass percentages, with M and RE compositions of Sm 1.5, Ca 0.5, Zn 4.5, Al 3.5, Zr 0.5, and Sn 0.15. High-purity magnesium, Mg-Sm, pure calcium, pure zinc, pure aluminum, Mg-Zr, and pure tin master alloys were selected as raw materials. Vacuum induction melting was performed at 720℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed using SEM, EDS, and DSC to test the coefficient of thermal expansion. SLM forming was employed with a laser power of 190W, a scanning speed of 850mm / s, a layer thickness of 30μm, and a scanning spacing of 0.1mm. The substrate was preheated to 180℃. Defect and mechanical property testing was then performed on the finished parts.

[0069] Example 9 The alloy was precisely formulated according to mass percentages, with M and RE compositions of Yb 0.8%, Li 0.2%, Zn 6.0%, Al 5.5%, Zr 1.2%, and Cu 0.008%. High-purity magnesium, Mg-Yb, pure lithium, pure zinc, pure aluminum, Mg-Zr, and pure copper master alloys were selected as raw materials. Vacuum induction melting was performed at 730℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed using SEM, EDS, and DSC to test the coefficient of thermal expansion. SLM forming was employed with a laser power of 210W, a scanning speed of 700mm / s, a layer thickness of 30μm, and a scanning spacing of 0.1mm. The substrate was preheated to 180℃. Defect and mechanical property testing was then performed on the finished parts.

[0070] Example 10 The alloy was precisely formulated according to mass percentages, with M and RE compositions of La 1.8%, Sr 0.01%, Zn 2.5%, Al 2.5%, Zr 0.3%, Si 0.1%, and Ti 0.1%. High-purity magnesium, Mg-La, Mg-Sr, pure zinc, pure aluminum, Mg-Zr, Mg-Si, and Mg-Ti master alloys were selected as raw materials. Vacuum induction melting was performed at 710℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed using SEM, EDS, and DSC, and the coefficient of thermal expansion was tested. Powder metallurgy was employed: cold isostatic pressing at 300MPa, followed by vacuum sintering at 530℃ for 4 hours to prepare finished parts, and their defect rate and mechanical properties were tested.

[0071] Example 11 The alloy was precisely formulated according to mass percentages, with M and RE compositions of Er 0.9g, Ag 0.5g, Zn 1.5g, Al 1.5g, Zr 0.2g, Ti 0.05g, and Hf 0.05g. High-purity magnesium, Mg-Er, pure silver, pure zinc, pure aluminum, Mg-Zr, Mg-Ti, and Mg-Hf master alloys were selected as raw materials. Vacuum induction melting was performed at 720℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed using SEM, EDS, and DSC to test the coefficient of thermal expansion. SLM forming was employed with a laser power of 200W, a scanning speed of 700mm / s, a layer thickness of 30μm, and a scanning spacing of 0.1mm. The substrate was preheated to 180℃ to obtain finished parts, which were then subjected to defect and mechanical property testing.

[0072] Example 12 The alloy was precisely formulated according to mass percentages, with M and RE compositions of Dy 2.5%, Ca 0.8%, Zn 5.0%, Al 5.0%, Zr 1.0%, Sn 0.08%, and Cu 0.02%. High-purity magnesium, Mg-Dy, pure calcium, pure zinc, pure aluminum, Mg-Zr, pure tin, and pure copper master alloys were selected as raw materials. Vacuum induction melting was performed at 735℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed using SEM, EDS, and DSC to statistically analyze the size, area fraction, and thermal effects of intermetallic compounds, and to test the coefficient of thermal expansion. SLM forming was employed with a laser power of 200W, a scanning speed of 800mm / s, a layer thickness of 30μm, and a scanning spacing of 0.1mm. The substrate was preheated to 180℃ to obtain finished parts, which were then subjected to defect statistics and mechanical property testing.

[0073] Example 13 The alloy was precisely formulated according to mass percentages, with M and RE compositions of Ho 1.8%, Sr 0.01%, Ca 0.5%, Li 0.5%, Ag 0.5%, Zn 2.0%, Al 2.0%, and Zr 0.4%. High-purity magnesium, Mg-Ho, Mg-Sr, pure calcium, pure lithium, pure silver, pure zinc, pure aluminum, and Mg-Zr master alloys were selected as raw materials. Vacuum induction melting was performed at 715℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed using SEM, EDS, and DSC, and the coefficient of thermal expansion was tested. Powder metallurgy was employed: cold isostatic pressing at 320MPa, vacuum sintering at 540℃ for 3.5h, to prepare finished parts, and the defect rate and mechanical properties were tested.

[0074] Example 14 The alloy was precisely formulated according to mass percentages, with M and RE compositions of Pr 1.2%, Li 1.5%, Zn 4.0%, Al 4.0%, and Zr 0.6%. High-purity magnesium, Mg-Pr, pure lithium, pure zinc, pure aluminum, and Mg-Zr master alloys were selected as raw materials. Vacuum induction melting was performed at 725℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed using SEM, EDS, and DSC to test the coefficient of thermal expansion. SLM forming was employed with a laser power of 205W, a scanning speed of 780mm / s, a layer thickness of 30μm, and a scanning spacing of 0.1mm. The substrate was preheated to 180℃ to obtain finished parts, which were then subjected to defect and mechanical property testing.

[0075] Example 15 The alloy was precisely formulated by mass percentage, with M and RE compositions of Tm 0.5%, Ag 1.5%, Zn 2.5%, Al 6.5%, and Zr 0.9%. High-purity magnesium, Mg-Tm, pure silver, pure zinc, pure aluminum, and Mg-Zr master alloys were selected as raw materials. The alloy was vacuum induction melted at 730℃ under argon protection, and then refined and atomized into powder. The powder was analyzed by SEM, EDS, and DSC, and the coefficient of thermal expansion was tested. Powder metallurgy was employed: cold isostatic pressing at 350MPa, followed by vacuum sintering at 550℃ for 3 hours to obtain finished parts, and the defect rate and mechanical properties were tested.

[0076] Example 16 The alloy was precisely formulated according to mass percentages, with M and RE compositions of Sc 0.3%, Ca 1.2%, Zn 3.0%, Al 3.0%, and Zr 0.5%. High-purity magnesium, Mg-Sc, pure calcium, pure zinc, pure aluminum, and Mg-Zr master alloys were selected as raw materials. Vacuum induction melting was performed at 710℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed using FE-SEM, EDS, and DSC to test the coefficient of thermal expansion. SLM forming was employed with a laser power of 185W, a scanning speed of 880mm / s, a layer thickness of 30μm, and a scanning spacing of 0.1mm. The substrate was preheated to 180℃ to obtain finished parts, which were then subjected to defect and mechanical property testing.

[0077] Example 17 The alloy was precisely formulated according to mass percentages, with the following M and RE compositions: Gd 0.1%, Sr 0.005%, Ca 0.1%, Li 0.1%, Ag 0.1%, Zn 0.1%, Al 0.5%, Sn 0.002%, Cu 0.005%, Zr 0.05%, Si 0.05%, Ti 0.05%, and Hf 0.01%. High-purity magnesium and corresponding intermediate alloys and pure metals were selected as raw materials. The alloy was vacuum induction melted at 720℃ under argon protection, and then refined and atomized into powder. The powder was analyzed using FE-SEM, EDS, and DSC, and the coefficient of thermal expansion was tested. A powder metallurgy process was employed: cold isostatic pressing at 300MPa, followed by vacuum sintering at 530℃ for 4 hours to prepare finished parts, and their defect rate and mechanical properties were tested.

[0078] Example 18 The alloy composition was precisely formulated according to mass percentages, with M and RE components of Gd 3.5%, Ce 3.5%, Ca 0.3%, Zn 0.5%, Al 0.8%, Zr 0.2%, and Si 0.1%. High-purity magnesium, Mg-Gd, Mg-Ce, pure calcium, pure zinc, pure aluminum, Mg-Zr, and Mg-Si master alloys were selected as raw materials. Vacuum induction melting was performed at 730℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed using SEM, EDS, and DSC to test the coefficient of thermal expansion. SLM forming was employed with a laser power of 200W, a scanning speed of 800mm / s, a layer thickness of 30μm, and a scanning spacing of 0.1mm. The substrate was preheated to 180℃ to obtain finished parts, which were then subjected to defect statistics and mechanical property testing.

[0079] Example 19 The alloy composition was precisely formulated by mass percentage, with M and RE components of Nd 0.8%, Y 0.8%, Sr 0.005%, Zn 2.0%, Al 2.5%, Zr 0.4%, and Sn 0.05%. High-purity magnesium, Mg-Nd, Mg-Y, Mg-Sr, pure zinc, pure aluminum, Mg-Zr, and pure tin master alloys were selected as raw materials. Vacuum induction melting was performed at 720℃ under argon protection, followed by refining and gas atomization powdering. The powder was analyzed by SEM, EDS, and DSC, and the coefficient of thermal expansion was tested. Powder metallurgy was employed: cold isostatic pressing at 320MPa, vacuum sintering at 540℃ for 3.5h, to prepare finished parts, and the defect rate and mechanical properties were tested.

[0080] Example 20 The alloy composition was precisely formulated by mass percentage, with M and RE components of Y 1.2%, Sr 0.02%, Ca 0.8%, Li 0.8%, Ag 0.8%, Zn 2.5%, Al 3.0%, and Zr 0.6%. High-purity magnesium, Mg-Y, Mg-Sr, pure calcium, pure lithium, pure silver, pure zinc, pure aluminum, and Mg-Zr master alloys were selected as raw materials. Vacuum induction melting was performed at 725℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed by SEM, EDS, and DSC to test the coefficient of thermal expansion. SLM forming was used with a laser power of 205W, a scanning speed of 780mm / s, a layer thickness of 30μm, and a scanning spacing of 0.1mm. The substrate was preheated to 180℃ to obtain finished parts, which were then subjected to defect and mechanical property testing.

[0081] Example 21 The alloy was precisely formulated according to mass percentages, with M and RE compositions of Ce 0.2%, Li 0.05%, Zn 0.05%, Al 0.2%, Zr 0.03%, Si 0.02%, and Ca 1.0%. High-purity magnesium, Mg-Ce, pure lithium, pure zinc, pure aluminum, Mg-Zr, Mg-Si master alloys, and pure calcium were selected as raw materials. The alloy was vacuum induction melted at 710℃ under argon protection, and then refined and atomized into powder. The powder was analyzed by SEM, EDS, and DSC, and the coefficient of thermal expansion was tested. A powder metallurgy process was employed: cold isostatic pressing at 350MPa, followed by vacuum sintering at 550℃ for 3 hours to prepare finished parts, and the defect rate and mechanical properties were tested.

[0082] Example 22 The alloy was precisely formulated according to mass percentages, with the following M and RE compositions: Y 0.8%, Nd 0.8%, Gd 0.8%, Ce 0.8%, Sr 0.008%, Ca 0.3%, Li 0.3%, Ag 0.3%, Zn 1.0%, Al 1.5%, Sn 0.03%, Cu 0.01%, Zr 0.2%, Si 0.1%, Ti 0.1%, and Hf 0.05%. High-purity magnesium and corresponding intermediate alloys and pure metals were selected as raw materials. Vacuum induction melting was performed at 730℃ under argon protection, followed by refining and gas atomization to form powder. The powder was analyzed using FE-SEM, EDS, and DSC to test the coefficient of thermal expansion. SLM forming was employed with a laser power of 190W, a scanning speed of 850mm / s, a layer thickness of 30μm, and a scanning spacing of 0.1mm. The substrate was preheated to 180℃ to obtain finished parts, which were then subjected to defect and mechanical property testing.

[0083] Table 1 As can be seen from the experimental results of the various embodiments and comparative examples in Table 1, after adopting the scheme of the present invention, the maximum size of the intermetallic compounds in the microstructure of each embodiment is less than 0.7 μm and the area fraction is less than 0.32%. DSC analysis shows that there are no endothermic peaks of rare earth intermetallic compounds in the 450–850℃ range, and the coefficients of thermal expansion are all <25×10. -6The concentration of rare earth elements in magnesium is significantly lower than that in the comparative example. This indicates that by introducing solid solution regulating elements such as Sr, Ca, Li, and Ag, and low-melting-point intermetallic compound forming elements such as Zn, Al, Sn, and Cu, this invention effectively breaks through the solid solubility limit of rare earth elements in the magnesium matrix and inhibits the formation of high-melting-point rare earth intermetallic compounds. Simultaneously, lattice regulating elements such as Zr, Si, Ti, and Hf successfully reduce the thermal expansion coefficient of the alloy, alleviating interfacial stress concentration under rapid thermal cycling. Furthermore, the defect area fraction in additive manufacturing and powder metallurgy finished parts is 0.08% to 0.25%, the tensile strength reaches 210 to 350 MPa, and the elongation is 4% to 16.0%, all significantly better than the comparative example. In summary, the magnesium alloy system with high rare earth solid solubility, low thermal expansion coefficient, and controllable microstructure provided by this invention can be widely adapted to advanced manufacturing processes such as additive manufacturing, powder metallurgy, and precision casting, meeting the stringent application requirements for lightweight and high-strength materials in aerospace, rail transportation, and precision electronics fields.

[0084] The embodiments of the present invention aim to protect a rare earth magnesium alloy with a low coefficient of thermal expansion, and have the following effects: 1. By introducing solid solution regulating elements such as Sr, Ca, Li, and Ag, and utilizing their preferential solid solution in the magnesium matrix to change the local lattice distortion energy and electronic distribution state, the solid solubility limit and site stability of rare earth elements in magnesium are significantly improved. This allows the rare earth elements in the alloy to exist in a fully solid solution state or as fine, dispersed intermetallic compounds with a size of less than 0.8 μm and an area fraction of no more than 0.5%. Furthermore, DSC detection shows no endothermic melting peaks of high-melting-point rare earth intermetallic compounds in the 450~850℃ range. This effectively solves the problem that micron-sized high-melting-point compounds in conventional rare earth magnesium alloys are difficult to dissolve and easily become unfused and porosity nuclei. It also significantly reduces process defects in additive manufacturing, powder metallurgy, and precision casting processes, and improves the density and crack resistance of components. 2. By introducing one or more low-melting-point eutectic forming elements from Zn, Al, Sn, and Cu, these elements form a multi-element low-melting-point eutectic structure or dispersed phase with rare earth elements, improving the surface tension, wettability, and fluidity of the melt. This promotes faster and more uniform melting of rare earth elements, avoiding local enrichment of rare earth elements and the resulting poor spreading and interlayer bonding defects. At the same time, the grain refinement and microalloying effects synergistically improve the forming accuracy and process stability of the alloy, solving problems such as splashing, keyholes, and interlayer cracking that occur during rapid melting and solidification of magnesium alloys due to their poor liquid fluidity. This improves the forming quality and mechanical property consistency of the components. 3. By introducing one or more lattice and phase structure regulating elements from Zr, Si, Ti, and Hf, and utilizing atomic solid solution, lattice constant fine-tuning, and the formation of low-expansion dispersed phases, the overall thermal expansion coefficient of the alloy was significantly reduced to ≤25×10⁻⁶. -6 / K effectively alleviates the interfacial stress concentration problem caused by the mismatch between the high thermal expansion coefficient of the magnesium matrix and the "rapid cooling" thermal cycle processes such as additive manufacturing and powder metallurgy. It reduces the tendency of thermal stress concentration and solidification crack initiation, solves the problem of microcracks and toughness deterioration caused by the large difference in the thermal expansion coefficient of the phase interface in conventional rare earth magnesium alloys during rapid cooling, and improves the service reliability and dimensional stability of components under extreme working conditions.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A rare-earth magnesium alloy with a low coefficient of thermal expansion, characterized in that, The rare earth magnesium alloy has a composition of Mg-RE-M, where RE is one or more of Ce, Dy, Er, Gd, Ho, La, Sm, Y, Yb, Pr, Tm, Sc and Nd, and M is one or more of Sr, Ca, Li, Ag, Zn, Al, Sn, Cu, Zr, Si, Ti and Hf; The total content of RE is 0.02 wt.%~7.0 wt.%, the total content of M is 0.5 wt.%~13.0 wt.%, and the content of Mg is 80 wt.%~99.48 wt.%; the coefficient of thermal expansion of the rare earth magnesium alloy is ≤25×10⁻⁶. -6 / K.

2. The rare earth magnesium alloy with a low coefficient of thermal expansion according to claim 1, characterized in that, The rare earth elements in the rare earth magnesium alloy exist in a fully dissolved state or in a dissolved state coexisting with fine, dispersed intermetallic compounds. When rare earth intermetallic compounds are present, the size of the intermetallic compounds is <0.8 μm, the average area fraction is ≤0.5%, and any 1 mm... 2 Within the alloy region, the quantity of the intermetallic compound varies by no more than 10%.

3. The rare earth magnesium alloy with a low coefficient of thermal expansion according to claim 1, characterized in that, When the rare earth magnesium alloy was detected by differential scanning calorimetry, no endothermic melting peak of rare earth intermetallic compounds was observed in the temperature range of 450℃ to 850℃.

4. The rare earth magnesium alloy with a low coefficient of thermal expansion according to claim 1, characterized in that, The RE is one or more of Gd, Y, Yb, Nd and Ce, and the total RE content is 0.1 wt.% to 4.5 wt.%.

5. The rare earth magnesium alloy with a low coefficient of thermal expansion according to any one of claims 1-4, characterized in that, The M includes one or more of Sr, Ca, Li and Ag.

6. The rare earth magnesium alloy with a low coefficient of thermal expansion according to claim 5, characterized in that, The Sr content is 0.001 wt.% ~ 0.05 wt.%, the Ca content is 0.01 wt.% ~ 2 wt.%, the Li content is 0.01 wt.% ~ 2 wt.%, and the Ag content is 0.02 wt.% ~ 2 wt.%.

7. The rare-earth magnesium alloy with a low coefficient of thermal expansion according to any one of claims 1-4, characterized in that, The M includes one or more of Zn, Al, Sn, and Cu.

8. The rare earth magnesium alloy with a low coefficient of thermal expansion according to claim 7, characterized in that, The Zn content is 0.01 wt.% ~ 7 wt.%, the Al content is 0.1 wt.% ~ 9.5 wt.%, the Sn content is 0.002 wt.% ~ 0.5 wt.%, and the Cu content is 0.005 wt.% ~ 0.03 wt.%.

9. The rare-earth magnesium alloy with a low coefficient of thermal expansion according to any one of claims 1-4, characterized in that, The M includes one or more of Zr, Si, Ti, and Hf.

10. The rare earth magnesium alloy with a low coefficient of thermal expansion according to claim 9, characterized in that, The Zr content is 0.01 wt.% ~ 1.5 wt.%, the Si content is 0.01 wt.% ~ 0.5 wt.%, the Ti content is 0.01 wt.% ~ 0.5 wt.%, and the Hf content is 0.01 wt.% ~ 0.3 wt.%.

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