Method for improving strength and plasticity of low-alloying Mg-Y-based rare earth magnesium alloy

Abstract

The invention belongs to the technical field of magnesium alloys, and discloses a method for improving the strength and plasticity of a low-alloying Mg-Y-based rare earth magnesium alloy. The method comprises the following steps: 1) according to a target alloy, dividing a precursor alloy into a low-temperature high-quality precursor alloy and a high-temperature low-quality precursor alloy; melting the low-temperature high-quality precursor alloy and the high-temperature low-quality precursor alloy respectively to obtain a low-temperature high-quality melt and a high-temperature low-quality melt; the target alloy is a magnesium alloy containing Mg and Y; the liquidus temperature difference between the low-temperature high-quality precursor alloy and the high-temperature low-quality precursor alloy is 50-80 DEG C; and 2) respectively reducing the low-temperature high-quality melt and the high-temperature low-quality melt to respective liquidus temperature + (5-40) DEG C, then uniformly mixing the high-temperature low-quality melt and the low-temperature high-quality melt, and carrying out casting molding to obtain a casting blank. The method further comprises the step that the casting blank is subjected to hot rolling forming. According to the method, the strength and plasticity of the magnesium alloy are remarkably improved, and the effect is more remarkable especially under low alloying.

Description

Technical Field

[0001] The invention relates to the technical field of magnesium alloy processing, and in particular to a method for improving the strength and plasticity of a low-alloyed Mg-Y based rare earth magnesium alloy. Background Art

[0002] As the lightest metal material, magnesium alloy is being widely used in transportation and other fields. However, the mechanical properties of ordinary magnesium alloys, especially the strength properties, are relatively poor, which has largely hindered the further expansion of the application range of magnesium alloys. Alloying with heavy rare earth elements such as Y, Gd, and Nd is an effective method to improve the strength and toughness of magnesium alloys, but the content is often high and the cost is high.

[0003] Chinese invention patent application CN 104928549 B discloses a high-strength and high-elastic modulus cast magnesium rare earth alloy and a preparation method thereof, wherein the rare earth content in the cast magnesium rare earth alloy is: Gd: 8-14wt.%, Y: 2-6wt.%. Chinese invention patent CN116219243A discloses an ultra-high-strength rare earth magnesium alloy, wherein the mass percentage composition of the rare earth is: Gd: 12.8-13.4%. The above high-strength rare earth magnesium alloys all contain ≥10% (mass ratio, the same throughout) of heavy rare earth. Low-alloyed rare earth magnesium alloys are cheap, but their mechanical properties are poor and difficult to meet actual needs. Therefore, it is particularly important to develop a method for improving the strength and plasticity of low-alloyed rare earth magnesium alloys.

[0004] Among all rare earth elements, the important role of Y (yttrium) is particularly eye-catching. The solubility of Y in Mg can reach up to 13.9wt% (574℃), and the solubility decreases rapidly with the decrease of temperature, and is basically zero at room temperature. Therefore, Y can produce excellent strengthening effect in magnesium alloys, which is specifically manifested in that Mg-Y based alloys show both solid solution and aging strengthening effects during the decomposition of supersaturated solid solution. Therefore, Y is considered to be the most effective element to improve the mechanical properties of magnesium alloys.

[0005] Mg-Y based alloy products are often first formed by casting, and then the alloy properties are further improved by deformation heat treatment to meet production needs. Although magnesium alloy structural parts with complex shapes and large specifications can be obtained by casting, especially gravity casting processes such as sand casting and metal mold casting. However, products formed by gravity casting are prone to casting defects such as component segregation, coarse grains, coarsening of the second phase, and difficult-to-remove oxide inclusions, which are difficult to meet the industry's high performance requirements for materials. For magnesium alloys containing rare earths, Zr-based alloying is an effective way to achieve their refinement. However, the addition of Zr will introduce new elements, and Zr is easy to settle, with low utilization rate, and requires a large amount of addition, which makes the composition of the alloy more complex on the one hand, and significantly increases the cost at the same time. How to achieve efficient refinement of rare earth magnesium alloys, especially low-content alloy grains, is very critical to improving their performance and product quality.

[0006] In response to this problem, Chinese invention patent CN116790926B discloses the use of controlled diffusion process to prepare non-dendritic structure of magnesium-aluminum alloy. Forced convection can form fine non-dendrites and refine grains, which is conducive to eliminating hot cracking and segregation, has good shrinkage compensation, and can even eliminate risers to achieve near-net solidification forming. This technology does not change the target composition, and has a more prominent effect on the regulation and control of microstructure refinement, and has a more significant effect on the grain refinement of magnesium alloys containing Al. However, for rare earth magnesium alloys, especially those with low alloying content, its refinement effect is still unclear.

[0007] In order to achieve high strength and toughness of rare earth magnesium alloys, further solid-state plastic deformation of the cast ingot is a common path. Chinese invention patent application CN117187652A discloses a method for simultaneously improving the yield strength and elongation of high-alloyed Mg-Gd-Y rare earth magnesium alloys. The process consists of four parts: alloy melting and casting, two-stage homogenization annealing, hot rolling and aging treatment. In actual production, the casting and deformation processes of magnesium alloys are often not isolated, but combined and complement each other. In terms of technology, a casting process is often used to first produce a blank with complex shape and high dimensional accuracy, and then it is further processed into a finished product of the required shape and size through a deformation process. This combination can give full play to the advantages of casting and deformation processes and improve the quality and performance of magnesium alloy parts.

[0008] The quality of deformed magnesium alloy products is often closely related to the quality of the ingot. The chemical composition, organizational uniformity, internal defects (such as pores, inclusions), etc. of the ingot will significantly affect the quality and performance of the deformed magnesium alloy. Ingots with poor organizational uniformity are prone to stress concentration and cracking during extrusion, rolling or forging, and pores and inclusions will become the source of crack initiation during the deformation process of magnesium alloys. Ingots with coarse grain size or coarse second phase size are prone to work hardening. These hardened areas will increase the deformation resistance of the material and make the deformation process more difficult. Therefore, in order to obtain high-performance deformable magnesium alloys, it is necessary to strictly control its organizational structure during the ingot preparation stage, and to prepare ingots with fewer casting defects, fine grains and uniform organization by optimizing the casting process parameters.

[0009] Especially in the case of low alloying, how to effectively exert the strengthening effect of alloying elements can not only reduce the consumption of expensive metals, but also is critical for the development of low-cost, high-performance rare earth magnesium alloys and their products. In order to solve the above problems, the present invention proposes a method for significantly improving strength and plasticity by coordinated treatment of controlled diffusion solidification and rolling for low-alloyed Mg-Y-based alloys. The present invention first prepares a magnesium alloy ingot by controlled diffusion solidification technology, mixes and solidifies two precursor alloy melts with significant differences in composition and temperature into a target component alloy, and prepares an alloy ingot with significantly refined grain size and high solid solubility, and then prepares a Mg-Y-based alloy sheet with excellent strength and plasticity by rolling forming. Summary of the invention

[0010] In order to overcome the shortcomings and deficiencies of the prior art, the purpose of the present invention is to provide a method for improving the strength and plasticity of low-alloyed Mg-Y-based rare earth magnesium alloys. The most significant difference between the present invention and the traditional process is that the present invention uses controlled diffusion solidification technology to prepare alloy ingots with significantly refined grain size and high solid solubility, and then prepares Mg-Y-based alloy plates with excellent strength and plasticity through rolling forming. The method of the present invention is simple, low-cost, and can significantly improve the strength and plasticity of the alloy.

[0011] The purpose of the present invention is achieved through the following technical solutions:

[0012] A preparation method for improving the strength and plasticity of a low-alloyed Mg-Y based rare earth magnesium alloy comprises the following steps:

[0013] 1) Pioneer alloy smelting: according to the target alloy, the pioneer alloy is divided into a low-temperature high-quality pioneer alloy and a high-temperature low-quality pioneer alloy; the low-temperature high-quality pioneer alloy and the high-temperature low-quality pioneer alloy are melted respectively to obtain a low-temperature high-quality melt and a high-temperature low-quality melt; the target alloy is a magnesium alloy containing Mg and Y; the liquidus temperature difference between the low-temperature high-quality pioneer alloy and the high-temperature low-quality pioneer alloy is 50-80° C.; the low-temperature high-quality melt is Mg-25Y;

[0014] 2) The low-temperature high-quality melt and the high-temperature low-quality melt are respectively lowered to their respective liquidus temperatures + (5-40)°C, and then the high-temperature low-quality melt and the low-temperature high-quality melt are uniformly mixed, cast and molded to obtain a casting.

[0015] The method further comprises: 3) hot rolling the ingot.

[0016] The hot rolling forming is specifically as follows: preheating the ingot to 400-500°C and then hot rolling; during the hot rolling process, the pressing amount of each pass is 8%-12%, and after each rolling pass, the heat is kept for 8-12 minutes before the next rolling pass; after the total pressing amount reaches 80%-85%, water quenching is performed to obtain the Mg-Y based alloy plate.

[0017] The preheating holding time is 10 to 20 minutes and the holding temperature is 400 to 500°C.

[0018] The target alloy is a magnesium alloy containing Mg and Y. When the target alloy is a magnesium alloy of Mg and Y, the Y content is 1.5-2.5%, and the percentage is the mass percentage; when the target alloy is a magnesium alloy of Mg, Y and other doping elements, the Y content is 1.5-7.5% (preferably 1.5-2.5%), and the content of other doping elements is 0.5-3.5% (0.5-1.5%), and the percentage is the mass percentage.

[0019] The other doping element is Zn.

[0020] When the target alloy is a magnesium alloy of Mg and Y, the high-temperature low-quality melt is pure magnesium;

[0021] When the target alloy is a magnesium alloy of Mg, Y and other doping elements, the high-temperature low-mass melt is Mg-other doping elements, composed of pure magnesium and other doping element metals. When the other doping element is Zn, the high-temperature low-mass melt is a Mg-Zn alloy, and the Zn content is determined according to the target alloy composition.

[0022] The melting in step 1) is carried out under a protective atmosphere, such as 99% CO 2+ 1%SF 6 protective atmosphere.

[0023] In step 2), the low-temperature high-quality melt and the high-temperature low-quality melt are respectively reduced to their respective liquidus temperatures + (5 to 40)°C, preferably to their respective liquidus temperatures + (5 to 15)°C.

[0024] The uniform mixing in step 2) refers to adding the high-temperature low-mass melt to the low-temperature high-mass melt for mixing; adding the high-temperature low-mass melt to the low-temperature high-mass melt and stirring to mix (eg, stirring time is 10 to 60 seconds).

[0025] In step 1), the melting temperature is 690-720° C. After melting, the melt is kept at a temperature for 20-30 minutes, the scum on the surface of the melt is removed, and a refining and impurity removal treatment is performed.

[0026] The refining and impurity removal treatment specifically includes blowing high-purity argon gas into the alloy melt for refining and slag removal, followed by standing and heat preservation at 690-720°C; the time for blowing argon for refining and impurity removal is 3-6 minutes, and the time for standing and heat preservation is 10-20 minutes.

[0027] The casting in step 2) refers to casting into a metal mold preheated at 190-210°C and naturally cooling and solidifying.

[0028] Combined with the solidification characteristics of magnesium alloy in the controlled diffusion process, the basic principle of the present invention to achieve a significant improvement in the strength and plasticity of rolled low-alloyed Mg-Y based alloy sheets is as follows:

[0029] Solidification characteristics of magnesium alloy in controlled diffusion process: The controlled diffusion solidification technology used in the present invention is to mix two precursor alloy melts with significantly different compositions and temperatures into a target composition melt, and after casting, a magnesium alloy casting with significantly refined grain size and high solid solubility is obtained. The significant refinement of grain size mainly benefits from the two-stage nucleation mechanism unique to the controlled diffusion solidification technology, which provides a large number of nucleation sites. The high solid solubility is mainly attributed to the fact that the mass diffusion rate is lower than the thermal diffusion rate during the controlled diffusion solidification process. When the two precursor alloys are mixed, the high-temperature melt undergoes the first burst of nucleation due to the quenching effect of the low-temperature melt, thereby generating a large number of free nuclei in the mixed melt. After mixing, the temperature of the high-temperature melt decreases and the temperature of the low-temperature melt increases, and the thermal diffusion and mass diffusion processes begin to be established. The temperature of the mixed melt begins to rise, and the thermal diffusion stops when the temperature of the mixed melt reaches the highest point, but the mass diffusion continues, which easily causes a large number of solute atoms to be dissolved in the magnesium matrix without time to precipitate, and the solid solubility of the magnesium matrix is ​​increased. The existence of heat diffusion and mass diffusion makes it easy to form stronger energy and more significant composition fluctuations in the melt, which promotes the second burst nucleation of the high-temperature melt solute micro-region at a large undercooling after the completion of heat diffusion and mass diffusion, and grows towards the low-temperature and high-concentration area. The advancement direction of the solid / liquid interface is opposite to the solute diffusion direction. Under the control of this reverse diffusion mode, the influence of composition undercooling is small, and the primary phase is more inclined to equiaxed growth, which ultimately achieves a significant refinement of the grain size of the Mg-Y-based alloy.

[0030] Principle of improving strong plasticity: Due to the significant refinement of the grain size of the ingot, the grain boundary content increases accordingly. The grain boundary has a stronger ability to hinder dislocations during rolling, which in turn generates high-density dislocations, thereby promoting the transformation of grains into long strip-shaped substructures during deformation. In addition, due to the increase in the solid solubility of solute atoms after controlled diffusion solidification treatment, a large number of Y atoms are dissolved into the magnesium matrix, which will cause the stacking fault energy to be reduced, thereby inducing the generation of a large number of deformation twins. Under the interaction of dislocations and dislocations, dislocations and twins, and twins and twins, the deformed grains are significantly refined through the dynamic recrystallization mechanism. In the further continuous rolling process, new geometrically necessary dislocations and deformation twins are generated inside the fine dynamically recrystallized grains. Geometrically necessary dislocations and tensile twins have the ability to coordinate deformation, which can avoid premature fracture and failure of magnesium alloys, and ultimately promote a significant improvement in the plasticity of magnesium alloy sheets. In addition, deformation twins also play a role in dividing grains, and their ability to hinder dislocation deformation is equivalent to that of large-angle grain boundaries. According to the Hall-Petch formula (σ s =σ 0 +kd -1 / 2 ), further division of fine grains can promote a significant increase in strength.

[0031] In particular, the present invention achieves a significant improvement in strength and plasticity by regulating the low-alloyed Mg-Y-based alloy sheet through controlled diffusion solidification and rolling synergistic treatment. On the one hand, it is attributed to the fact that controlled diffusion solidification can provide a low-alloyed Mg-Y-based alloy with a finer grain size of the original ingot compared to ordinary solidification, and it is easier to form fine dynamic recrystallized grains in the subsequent rolling process. On the other hand, it is attributed to the fact that controlled diffusion solidification gives the Mg-Y-based alloy ingot a higher solid solubility, reduces the stacking fault energy of the Mg-Y-based alloy, and provides a large number of deformation twins for the subsequent rolling process. The deformation twins can not only promote the further refinement of the deformed grain size, but also coordinate the deformation to provide good plasticity for the Mg-Y-based alloy sheet. However, in comparison, the grain size refinement effect of the high-alloyed Mg-Y-based alloy after controlled diffusion solidification is not as good as that of the low-alloyed Mg-Y-based alloy, and the mechanical properties of the subsequent rolling process are only increased in strength, and the plasticity loss is large. The improvement effect of the mechanical properties of the high-alloyed Mg-Y-based alloy after controlled diffusion solidification and rolling synergistic treatment is far less than that of the low-alloyed Mg-Y-based alloy.

[0032] Compared with the prior art, the present invention has the following outstanding advantages and beneficial effects:

[0033] (1) The method of the present invention of coordinated treatment of controlled diffusion solidification and rolling significantly improves the strength and plasticity of the alloy, especially under low alloying conditions.

[0034] (2) The present invention provides a preparation method for low-alloyed rare earth magnesium alloys that has simple process equipment requirements and can significantly improve the strength and plasticity of the alloy, which can effectively broaden the application range of low-cost low-alloyed rare earth magnesium alloys.

[0035] (3) The low-alloyed Mg-Y-based alloy ingot prepared by controlled diffusion solidification in the present invention has a grain size refinement rate of >90% compared to conventional casting, and a large amount of rare earth elements are dissolved in the magnesium matrix, which promotes the ingot to increase its strength by >300% without losing plasticity.

[0036] (4) The present invention uses controlled diffusion solidification and rolling to coordinately regulate the microstructure of low-alloyed Mg-Y-based alloys, and obtains magnesium alloy sheets with significantly refined grain size, significantly increased dislocation density, and a large number of deformation twins. Compared with conventional casting and rolling, its strength is further improved by more than 120%, and its plasticity is further improved by more than 30%. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The optical microstructure of the Mg-2Y alloy prepared by conventional casting in Comparative Example 1;

[0038] Figure 2XRD pattern and lattice constants of Mg-2Y alloy prepared by conventional casting in Comparative Example 1;

[0039] Figure 3 The optical microstructure of the Mg-2Y alloy prepared by mixing pure magnesium and Mg-25Y alloy in a ratio of 11.5:1 at a superheat of 20 to 40° C. by controlled diffusion solidification;

[0040] Figure 4 XRD pattern and lattice constant of Mg-2Y alloy prepared by mixing pure magnesium and Mg-25Y alloy in a ratio of 11.5:1 at a superheat of 20 to 40° C. under controlled diffusion solidification;

[0041] Figure 5 The optical microstructure of the Mg-2Y alloy prepared by mixing pure magnesium and Mg-25Y alloy in a ratio of 11.5:1 at a superheat of 5 to 15°C by controlled diffusion solidification;

[0042] Figure 6 The XRD spectrum and lattice constants of the Mg-2Y alloy prepared by mixing pure magnesium and Mg-25Y alloy in a ratio of 11.5:1 at a superheat of 5 to 15°C through controlled diffusion solidification. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below in conjunction with specific examples, but the embodiments of the present invention are not limited thereto. In the embodiments of the present invention, the total content of impurity elements in the target alloy is ≤0.1%, except for Y or Y and Zn content, and the balance is Mg.

[0044] The impurity elements Fe≤0.02%, Al≤0.01%, and Si≤0.01% among the impurity elements.

[0045] Comparative Example 1: Preparation of low alloyed Mg-Y binary alloy sheet by conventional casting followed by rolling

[0046] The specific steps and process parameters are as follows:

[0047] (1) Melting: According to the target alloy composition, the mixing ratio of pure magnesium and Mg-25Y alloy is determined, and the required raw materials are calculated and weighed; first, pure magnesium is added to the resistance furnace, and after it is fully melted, the Mg-25Y alloy is added, and the melting temperature is 700-720°C. After all the raw materials are melted, they are quickly stirred and allowed to stand for 20-30 minutes to ensure that the melt is fully mixed; after standing, the scum on the surface of the melt is removed, and high-purity argon gas is blown into the alloy melt for refining and slag removal, followed by standing and holding; the time for argon blowing, refining and impurity removal is 3-6 minutes, and the time for standing and holding is 10-20 minutes.

[0048] (2) Casting: The melt in step (1) is cast into a metal mold preheated to 200° C., and naturally cooled and solidified to obtain a low-alloyed Mg-Y alloy ingot, and then samples are taken from the casting for analysis.

[0049] (3) Hot rolling: preheat the solidified ingot to 400-500℃ and keep it warm for 10-20min to fully heat the ingot; then carry out hot rolling, with the pressing amount of each pass being 8%-12%, and keep it warm for 8-12min after each rolling pass before rolling the next pass. When the total pressing amount reaches 80%-85%, quickly water quench it to obtain a low-alloyed Mg-Y binary alloy plate. Finally, take samples from the rolled plate for analysis.

[0050] The target alloy is a low alloyed Mg-Y based alloy, i.e., Mg-(1.5-2.5)Y alloy (the percentage of Y is 1.5-2.5%); the low alloyed Mg-Y binary alloy in this comparative example is preferably Mg-2Y alloy. Preferably, the rolling temperature in step (3) in this comparative example is 400°C, the pressing amount is 10%, the holding time is 10 minutes, and the total pressing amount is 80%.

[0051] In order to characterize the microstructure and performance characteristics of the above alloys, the microstructure of the alloys was observed using an optical microscope. The alloy phase composition was identified using an X-ray diffractometer. The tensile curve was obtained using an electronic universal material testing machine. The mechanical properties test method is described as follows.

[0052] According to GB / T228-2010, the test samples were processed into dumbbell shapes by wire cutting, and the surface was polished with 1000-grit sandpaper to eliminate the influence of cutting defects on the experimental results. Then the mechanical properties were tested on a universal testing machine. In this test, each group of alloys was tested 3 times at a tensile speed of 0.5mm / min and room temperature (25°C), and the stress-strain curve was recorded to obtain performance data, and the average value was taken as the final test data.

[0053] According to GB / T 228.1 standard, image and data processing are performed to remove the displacement of the sliding part of the clamping section. The gauge length of the sample is 25mm, and the elongation δ is calculated according to the following formula:

[0054]

[0055] Where, δ is the elongation, %; l 0 is the gauge length of the specimen, mm; l 1 It is the length of the gauge part of the specimen after breaking, in mm.

[0056] The Mg-2Y alloy prepared under the preferred conditions in Comparative Example 1 was tested. The test showed that the low alloyed Mg-2Y alloy ingot prepared by conventional casting had all columnar grains. Figure 1As shown. According to statistics, its average grain size is about 4734μm. Its yield strength and tensile strength are 12.9 and 75.5MPa respectively, and its elongation is 10.8%. The magnesium matrix lattice constant of the conventional casting ingot was further tested by XRD. The results show that a=0.32076nm, c=0.52080nm, as shown Figure 2 After rolling, the yield strength and tensile strength of the Mg-2Y alloy are 85.5 and 186.5 MPa, respectively, and the elongation is 14.2%.

[0057] Figure 1 The optical microstructure of the Mg-2Y alloy prepared by conventional casting in Comparative Example 1;

[0058] Figure 2 The XRD spectrum and lattice constants of the Mg-2Y alloy prepared by conventional casting in Comparative Example 1.

[0059] To further illustrate the implementation effect of the present invention, the present invention is described below in conjunction with Examples 1 and 2.

[0060] Example 1: Synergistic preparation of low alloyed Mg-Y binary alloy sheet by high superheat controlled diffusion solidification and rolling

[0061] The target alloy of this embodiment is preferably Mg-2Y alloy, and the raw materials for preparing the alloy are the same as those in Comparative Example 1, namely pure Mg and Mg-25Y alloy. Different from Comparative Example 1, the smelting and casting method is different: two precursor alloys are melted separately and then mixed and cast to obtain Mg-2Y alloy ingot.

[0062] The specific steps and process parameters are as follows:

[0063] (1) Precursor alloy smelting: according to the target alloy composition, the mixing ratio of pure magnesium and Mg-25Y alloy is determined, and the required precursor alloy is calculated and weighed; the two groups of weighed precursor alloys, pure magnesium and Mg-25Y alloy, are melted in two resistance furnaces (the melting temperature is 700°C), respectively, and then allowed to stand and be kept warm for 20 to 30 minutes to obtain a high-temperature pure magnesium melt and a low-temperature Mg-25Y alloy melt; the scum on the surface of the melted alloy melt is removed, and high-purity argon gas is blown into the alloy melt for refining and slag removal, and then allowed to stand and be kept warm; the time for argon blowing for refining and impurity removal is 3 to 6 minutes, and the time for standing and being kept warm is 10 to 20 minutes.

[0064] (2) Melt mixing and casting: The two precursor alloy melts in step (1) are cooled to 20 to 40°C above their liquidus temperatures (20°C on the liquidus has the same effect as 40°C on the liquidus); the high-temperature pure magnesium melt is poured into the low-temperature Mg-25Y melt for mixing and stirring for 10 to 60 seconds; the mixed melt is then rapidly cast into a metal mold, and naturally cooled and solidified to obtain a low-alloyed Mg-Y binary alloy ingot.

[0065] (3) Hot rolling: preheat the solidified ingot to 400-500°C and keep it for 10-20 min (the holding time here has no effect on the product) to allow the ingot to be fully heated; then hot rolling is performed, with the pressing amount of each pass being 8%-12%. After each rolling pass, the next rolling pass is performed after keeping it for 8-12 min. When the total pressing amount reaches 80%-85%, it is quickly water quenched to obtain a low-alloyed Mg-Y binary alloy plate.

[0066] The target alloy is a low alloyed Mg-Y binary alloy, specifically a Mg-(1.5-2.5)Y alloy; preferably, the low alloyed Mg-Y binary alloy of this embodiment is a Mg-2Y alloy. The mass ratio of pure magnesium melt to Mg-25Y alloy melt is 12.5:1-10.5:1. Preferably, the low alloyed Mg-Y based alloy is a Mg-2Y alloy, and the mass ratio of pure magnesium melt to Mg-25Y master alloy melt is 11.5:1.

[0067] In step (2), the liquidus temperatures of pure magnesium and Mg-25Y alloy are 650 and 577° C. respectively. Pure magnesium and Mg-25Y alloy are cooled to 20-40° C. above their liquidus temperatures and then mixed, i.e., pure magnesium melt is cooled to 670-690° C. and Mg-25Y alloy melt is cooled to 597-617° C. and then mixed. Preferably, in step (3) of this embodiment, the rolling temperature is 400° C., the pressing amount is 10%, the holding time is 10 min, and the total pressing amount is 80%.

[0068] The microstructure characteristics of the Mg-2Y alloy prepared under the preferred conditions of this embodiment were observed and analyzed. The results show that the grains of the ingot prepared in this embodiment are no longer columnar, but are mainly composed of columnar crystals, including a small amount of columnar crystals at the edges, such as Figure 3 As shown. At this time, the average grain size of the ingot is about 1480μm. The yield strength and tensile strength are about 42.2 and 96.4MPa respectively, and the elongation is about 12.3%. The magnesium matrix lattice constant of the ingot obtained by high superheat controlled diffusion solidification was further tested by XRD. The results show that a=0.32112nm, c=0.52118nm, as shown Figure 4As shown in Figure 1, compared with comparative example 1, the grain size of the ingot is refined by 68.7%, and the yield strength is greatly increased by 227.1% without loss of plasticity. At the same time, the increase in lattice constant also indicates that the solid solubility has increased.

[0069] The Mg-2Y alloy prepared under the preferred conditions of this embodiment has a yield strength of 114.9 MPa, a tensile strength of 192.5 MPa, and an elongation of 13.9% after rolling. Compared with comparative example 1, the yield strength is increased by 34.4%, the tensile strength is only increased by 3.2%, and the plasticity is slightly decreased.

[0070] Figure 3 The optical microstructure of the Mg-2Y alloy prepared by mixing pure magnesium and Mg-25Y alloy in a ratio of 11.5:1 at a superheat of 20 to 40° C. by controlled diffusion solidification;

[0071] Figure 4 The XRD spectrum and lattice constants of the Mg-2Y alloy prepared by mixing pure magnesium and Mg-25Y alloy in a ratio of 11.5:1 at a superheat of 20 to 40° C. by controlled diffusion solidification.

[0072] Example 2: Synergistic preparation of low alloyed Mg-Y binary alloy sheet by low superheat controlled diffusion solidification and rolling

[0073] The difference between this embodiment and embodiment 1 is that the controlled diffusion solidification is reduced, that is, the two precursor alloy melts are cooled to 5 to 15°C above their liquidus temperatures before mixing. The specific steps and process parameters are as follows:

[0074] (1) Precursor alloy smelting: according to the target alloy composition, the mixing ratio of pure magnesium and Mg-25Y alloy is determined, and the required precursor alloy is calculated and weighed; the two weighed groups of precursor alloys are melted in two resistance furnaces respectively, and kept at a temperature of 20 to 30 minutes to obtain a high-temperature pure magnesium melt and a low-temperature Mg-25Y alloy melt; the scum on the surface of the melt is removed from the melt, and high-purity argon gas is blown into the alloy melt for refining and slag removal, followed by keeping the melt at a temperature of 10 to 20 minutes; the time for blowing argon for refining and impurity removal is 3 to 6 minutes, and the time for keeping at a temperature of 10 to 20 minutes.

[0075] (2) Melt mixing and casting: The two precursor alloy melts in step (1) are cooled to 5 to 15°C above their liquidus temperatures respectively, and the high-temperature pure magnesium melt is poured into the lower-temperature Mg-25Y melt for mixing and stirring for 10 to 60 seconds; the mixed melt is then quickly cast into a metal mold, and naturally cooled and solidified to obtain a low-alloyed Mg-Y binary alloy ingot.

[0076] (3) Hot rolling: preheat the solidified ingot to 400-500°C and keep it warm for 10-20 minutes to allow the ingot to be fully heated; then perform hot rolling, with the pressing amount of each pass being 8%-12%. After each rolling pass, keep it warm for 8-12 minutes before performing the next rolling pass. When the total pressing amount reaches 80%-85%, quickly water quench it to obtain a low-alloyed Mg-Y binary alloy plate.

[0077] The target alloy is a low alloyed Mg-Y binary alloy, specifically a Mg-(1.5-2.5)Y alloy; preferably, the low alloyed Mg-Y binary alloy of this embodiment is a Mg-2Y alloy. Preferably, the low alloyed Mg-Y based alloy of this embodiment is a Mg-2Y alloy, and the mass ratio of the pure magnesium melt to the Mg-25Y master alloy melt is 11.5:1.

[0078] In step (2), the liquidus temperatures of pure magnesium and Mg-25Y alloy are 650°C and 577°C, respectively. The two precursor alloy melts are cooled to 5-15°C above their liquidus temperatures and then mixed, i.e., the pure magnesium melt is cooled to 655-665°C and the Mg-25Y alloy melt is cooled to 582-592°C and then mixed. Preferably, the rolling temperature of step (3) is 400°C, the pressing amount is 10%, the holding time is 10 minutes, and the total pressing amount is 80%.

[0079] The microstructure characteristics of the alloy prepared under the preferred conditions of this embodiment were observed and analyzed. The results showed that compared with Comparative Example 1, the grains of the ingot obtained in this embodiment were all equiaxed grains, and the grain size was greatly refined. At this time, the average grain size was about 198 μm. Figure 5 The yield strength and tensile strength of the ingot are about 53.2 and 142.5 MPa respectively, and the elongation is about 14.9%. The lattice constants of the magnesium matrix in the cast state of this embodiment are calculated to be a = 0.32138 nm, c = 0.52154 nm, as shown in FIG. Figure 6 Compared with comparative example 1, the grain size of the ingot is significantly refined, and the solid solubility is increased. The yield strength is greatly increased by 312.4%, the tensile strength is greatly increased by 88.7%, and the elongation is also increased by 38.0%.

[0080] The Mg-2Y alloy prepared under the preferred conditions of this embodiment has a yield strength and a tensile strength of approximately 188.6 and 229.5 MPa, respectively, and an elongation of 18.5% after rolling. Compared with Comparative Example 1, the yield strength is increased by 120.5%, the tensile strength is increased by 23.1%, and the elongation is increased by 30.3%. This embodiment obtains a Mg-2Y alloy ingot with significantly refined grain size and high solid solubility, and then obtains a Mg-2Y alloy plate with excellent strength-ductility matching after rolling.

[0081] Figure 5 The optical microstructure of the Mg-2Y alloy prepared by mixing pure magnesium and Mg-25Y alloy in a ratio of 11.5:1 at a superheat of 5 to 15°C by controlled diffusion solidification;

[0082] Figure 6 The XRD spectrum and lattice constants of the Mg-2Y alloy prepared by mixing pure magnesium and Mg-25Y alloy in a ratio of 11.5:1 at a superheat of 5 to 15°C through controlled diffusion solidification.

[0083] To further illustrate the implementation effect of the present invention, the process flow and implementation effect are explained below by taking low-alloyed Mg-Y-Zn alloy as an example based on comparative examples and embodiments.

[0084] Comparative Example 2: Preparation of low alloyed Mg-Y-Zn alloy by conventional casting followed by rolling

[0085] The specific steps and process parameters are as follows:

[0086] (1) Melting: Pure magnesium, Mg-25Y master alloy and pure Zn are used as raw materials. The mixing ratio of the raw materials is determined according to the target alloy composition, and the required raw materials are calculated and weighed. First, pure magnesium is added to the resistance furnace, and after it is fully melted, Mg-25Y alloy and pure Zn are added. The melting temperature is 700-720°C. After all the raw materials are melted, they are quickly stirred and allowed to stand for 20-30 minutes to ensure that the melt is fully mixed. After standing, the scum on the surface of the melt is removed, and high-purity argon gas is blown into the alloy melt for refining and slag removal, followed by standing and holding. The time for blowing argon for refining and impurity removal is 3-6 minutes, and the time for standing and holding is 10-20 minutes.

[0087] (2) Casting: The melt in step (1) is cast into a metal mold preheated to 200° C., and naturally cooled and solidified to obtain a low-alloyed Mg-Y-Zn alloy ingot. Finally, samples are taken from the casting for analysis.

[0088] (3) Hot rolling: preheat the solidified ingot to 400-500℃ and keep it warm for 10-20min to fully heat the ingot; then carry out hot rolling, with the pressing amount of each pass being 8%-12%, and keep it warm for 8-12min after each rolling pass before rolling the next pass. When the total pressing amount reaches 80%-85%, quickly water quench it to obtain a low-alloyed Mg-Y-Zn alloy plate. Finally, take samples from the rolled plate for analysis.

[0089] The low alloyed Mg-Y-Zn alloy is Mg-(1.5-2.5)Y-(0.5-1.5)Zn alloy; preferably, the low alloyed Mg-Y-Zn alloy is Mg-2Y-1Zn alloy. Preferably, in step (3), the rolling temperature is 400°C, the pressing amount each time is 10%, the holding time is 10 minutes, and the total pressing amount is 80%.

[0090] The average grain size of the low alloyed Mg-2Y-1Zn alloy prepared by conventional casting is about 3650μm. Its yield strength and tensile strength are 16.7 and 76.6MPa respectively, and the elongation is 9.5%. The magnesium matrix lattice constant of the conventional casting ingot was further tested, a = 0.32081nm, c = 0.52085nm. After rolling treatment, the yield strength and tensile strength of the Mg-2Y-1Zn alloy are 92.3 and 188.3MPa respectively, and the elongation is 13.9%.

[0091] Example 3: Synergistic preparation of low alloyed Mg-Y-Zn alloy plates by high superheat controlled diffusion solidification and rolling

[0092] The raw materials for preparing the alloy in this embodiment are pure Mg, Mg-25Y alloy and pure Zn respectively.

[0093] The specific steps and process parameters are as follows:

[0094] (1) Precursor alloy smelting: Mg-xZn (x% represents the mass percentage of Zn) alloy is used as a high-temperature low-mass melt, and Mg-25Y is used as a low-temperature high-quality melt; wherein Mg-xZn is obtained by mixing pure magnesium and pure zinc; according to the target alloy composition, the mixing ratio of Mg-xZn alloy and Mg-25Y alloy is determined, and the required precursor alloy is calculated and weighed; the two weighed groups of precursor alloys are melted in two resistance furnaces respectively, and allowed to stand and be kept warm for 20 to 30 minutes to obtain a high-temperature Mg-xZn alloy melt and a low-temperature Mg-25Y alloy melt; the scum on the surface of the melt is removed from the melt, and high-purity argon gas is blown into the alloy melt for refining and slag removal, followed by standing and keeping warm; the time for blowing argon for refining and impurity removal is 3 to 6 minutes, and the time for standing and keeping warm is 10 to 20 minutes.

[0095] (2) Melt mixing and casting: The two precursor alloy melts in step (1) are cooled to 20 to 40°C above their liquidus temperatures respectively, and the high-temperature Mg-xZn alloy melt is poured into the lower-temperature Mg-25Y melt for mixing and stirring for 10 to 60 seconds; the mixed melt is then rapidly cast into a metal mold, and naturally cooled and solidified to obtain a low-alloyed Mg-Y-Zn alloy ingot.

[0096] (3) Hot rolling: preheat the solidified ingot to 400-500°C and keep it warm for 10-20 minutes to fully heat the ingot; then perform hot rolling, with the pressing amount of each pass being 8%-12%. After each rolling pass, keep it warm for 8-12 minutes before performing the next rolling pass. When the total pressing amount reaches 80%-85%, quickly water quench it to obtain a low-alloyed Mg-Y-Zn alloy plate.

[0097] The target alloy is a low alloy Mg-Y-Zn alloy (the percentage of Y is z%, the percentage of Zn is y%), specifically Mg-(1.5-2.5)Y-(0.5-1.5)Zn alloy. In Mg-xZn, x=(1.06-1.11)y, and the percentage of Zn is x%.

[0098] Preferably, the low alloyed Mg-Y-Zn alloy is a Mg-2Y-1Zn alloy; Mg-xZn is Mg-1.1Zn. Preferably, the low alloyed Mg-Y-Zn alloy is a Mg-2Y-1Zn alloy, and the mass ratio of the Mg-1.1Zn melt to the Mg-25Y master alloy melt is 10:1. In step (2), the liquidus temperatures of the two precursor alloys Mg-1.1Zn and Mg-25Y are 647 and 577°C, respectively, and the two precursor alloy melts are cooled to 20 to 40°C above their liquidus temperatures, that is, the Mg-1.1Zn melt is cooled to 667 to 687°C, and the Mg-25Y alloy melt is cooled to 597 to 617°C. Preferably, in step (3), the rolling temperature is 400°C, the pressing amount each time is 10%, the holding time is 10 minutes, and the total pressing amount is 80%.

[0099] The microstructural characteristics of the alloy prepared under the preferred conditions of this embodiment were observed and analyzed. The results show that the average grain size of the ingot obtained in this embodiment is about 1360μm, the yield strength and tensile strength are about 40.4 and 94.3MPa respectively, and the elongation is about 11.4%. The magnesium matrix lattice constant of the ingot obtained by high superheat controlled diffusion solidification was further tested by XRD, and the results showed that a=0.32092nm, c=0.52102nm. Compared with comparative example 2, the grain size of the ingot was refined by 62.7%, and the yield strength was greatly improved by 141.9% without plastic loss. At the same time, the increase in lattice constant also indicates that the solid solubility has increased.

[0100] After rolling, the alloy prepared under the preferred conditions of this embodiment has a yield strength of 104.3 MPa, a tensile strength of 189.5 MPa, and an elongation of 12.4%. Compared with Comparative Example 1, the yield strength is only increased by 13.0%, the tensile strength is only increased by 0.6%, and the plasticity is slightly decreased.

[0101] Example 4: Synergistic preparation of low alloyed Mg-Y-Zn alloy plate by low superheat controlled diffusion solidification and rolling

[0102] The difference between this embodiment and embodiment 3 is that the two precursor alloy melts are cooled to 5-15°C above their liquidus temperature before mixing. The specific steps and process parameters are as follows:

[0103] (1) Precursor alloy smelting: Mg-xZn (x% represents the content of Zn) alloy is used as a high-temperature low-quality melt, and Mg-25Y is used as a low-temperature high-quality melt, wherein Mg-xZn is obtained by mixing pure magnesium and pure zinc; according to the target alloy composition, the mixing ratio of Mg-xZn alloy and Mg-25Y alloy is determined, and the required precursor alloy is calculated and weighed; the two weighed groups of precursor alloys are melted in two resistance furnaces respectively, and the melts are kept at a temperature of 20 to 30 minutes to obtain a high-temperature Mg-xZn alloy melt and a low-temperature Mg-25Y alloy melt; the scum on the surface of the melt is removed from the melt, and high-purity argon gas is blown into the melt for refining and slag removal, followed by keeping the melt at a temperature of 10 to 20 minutes. The time for blowing argon for refining and impurity removal is 3 to 6 minutes, and the time for keeping the melt at a temperature of 10 to 20 minutes.

[0104] (2) Melt mixing and casting: The two precursor alloy melts in step (1) are cooled to 5 to 15°C above their liquidus temperatures respectively, and the high-temperature Mg-xZn alloy melt is poured into a crucible containing a lower-temperature Mg-25Y melt, and mixed and stirred for 10 to 60 seconds; the mixed melt is then quickly cast into a metal mold, and naturally cooled and solidified to obtain a low-alloyed Mg-Y-Zn alloy ingot.

[0105] (3) Hot rolling treatment: preheat the solidified ingot to 400-500°C and keep it warm for 10-20 minutes to allow the ingot to be fully heated; then hot rolling treatment is carried out, with the reduction amount of each pass being 8%-12%. After each rolling pass, the next rolling pass is carried out after keeping warm for 8-12 minutes. When the total reduction amount reaches 80%-85%, it is quickly water quenched to obtain a low-alloyed Mg-Y-Zn alloy plate.

[0106] The target alloy is a low alloy Mg-Y-Zn alloy (the percentage of Y is z%, the percentage of Zn is y%), specifically Mg-(1.5-2.5)Y-(0.5-1.5)Zn alloy. In Mg-xZn, x=(1.06-1.11)y, and the percentage of Zn is x%.

[0107] Preferably, the low alloyed Mg-Y-Zn alloy is a Mg-2Y-1Zn alloy; Mg-xZn is Mg-1.1Zn. Preferably, the low alloyed Mg-Y-Zn alloy is a Mg-2Y-1Zn alloy, and the mass ratio of the Mg-1.1Zn melt to the Mg-25Y master alloy melt is 10:1. In step (2), the liquidus temperatures of the two precursor alloys Mg-1.1Zn and Mg-25Y are 647 and 577°C, respectively, and the two precursor alloy melts are cooled to 5 to 15°C above their liquidus temperatures, that is, the Mg-1.1Zn melt is cooled to 652 to 662°C, and the Mg-25Y alloy melt is cooled to 582 to 592°C. Preferably, the rolling temperature in step (3) is 400°C, the pressing amount each time is 10%, the holding time is 10 minutes, and the total pressing amount is 80%.

[0108] The microstructural characteristics of the Mg-2Y-1Zn alloy prepared under the preferred conditions of this embodiment were observed and analyzed. The results show that compared with Comparative Example 2, the grain size of this embodiment is greatly refined, and the average grain size is about 184μm at this time. The yield strength and tensile strength of the ingot are approximately 60.4 and 145.3MPa, respectively, and the elongation is about 13.5%. The lattice constants of the magnesium matrix in the cast state of this embodiment were calculated and found to be a=0.321225nm, c=0.52138nm. Compared with Comparative Example 1, the grain size of the ingot is significantly refined, and the solid solubility is increased. The yield strength is greatly improved by 261.7%, the tensile strength is greatly improved by 89.7%, and the elongation is also improved by 42.1%.

[0109] The alloy prepared under the preferred conditions of this embodiment has a yield strength and tensile strength of approximately 164.3 and 203.6 MPa, respectively, and an elongation of 14.2% after rolling. Compared with Comparative Example 1, the yield strength is increased by 78.0%, the tensile strength is only increased by 8.1%, and the elongation is only increased by 2.2%. Compared with Example 2, since Zn alloying is compounded on the basis of Mg-2Y alloy, even if the added content is low, the improvement in strength and plasticity is not as good as that of the Mg-2Y binary alloy plate prepared by controlled diffusion solidification and rolling.

[0110] In order to better illustrate that compared with high alloying, the mechanical properties of low alloying Mg-Y based alloys are more significantly improved after controlled diffusion solidification and rolling synergistic treatment, the present invention further prepares high alloying Mg-Y based alloy plates by controlled diffusion solidification and rolling synergistic treatment, and tests its structure and mechanical properties as a comparative illustration.

[0111] Comparative Example 3: Preparation of high alloyed Mg-Y binary alloy sheet by conventional casting followed by rolling

[0112] The specific steps and process parameters are as follows:

[0113] (1) Melting: Pure magnesium and Mg-25Y alloy are used as raw materials. According to the target alloy composition, the required raw materials are calculated and weighed. First, pure magnesium is added to an electric resistance furnace. After it is fully melted, Mg-25Y alloy is added. The melting temperature is 700 - 720 °C. After all the raw materials are melted, they are quickly stirred and kept warm for 20 - 30 min to ensure full mixing of the melt. After standing, the dross on the surface of the melt is removed, and high-purity argon gas is blown into the alloy melt for refining and slag removal treatment, followed by standing and heat preservation. The time for argon blowing and refining is 3 - 6 min, and the standing and heat preservation time is 10 - 20 min.

[0114] (2) Casting: The melt in step (1) is cast into a metal mold preheated to 200 °C, and it is naturally cooled and solidified to form a highly alloyed Mg-Y binary alloy. Finally, samples are taken from the casting for analysis.

[0115] (3) Hot rolling forming: The solidified ingot is preheated to 450 - 550 °C and kept warm for 10 - 20 min to fully heat the ingot. Subsequently, hot rolling is carried out. The reduction per pass is 8% - 12%. After each pass of rolling, it is kept warm for 8 - 12 min and then the next pass of rolling is carried out. After the total reduction reaches 80% - 85%, it is quickly water quenched to obtain a highly alloyed Mg-Y binary alloy sheet. Finally, samples are taken from the rolled sheet for analysis.

[0116] The target alloy of this comparative example is a highly alloyed Mg-Y binary alloy, specifically Mg-(4 - 7)Y alloy; preferably, the highly alloyed Mg-Y binary alloy is Mg-5Y alloy. Preferably, in step (3), the rolling temperature is 450 °C, the reduction per pass is 10%, the heat preservation time is 10 min, and the total reduction is 80%.

[0117] After testing, under the preferred conditions, the average grain size of the highly alloyed Mg-5Y alloy ingot prepared by conventional casting is about 991 μm. Its yield strength and tensile strength are 39.4 and 111.2 MPa respectively, and the elongation is 7.28%. The lattice constants of the magnesium matrix of the ingot obtained by conventional casting under the preferred conditions are further tested, a = 0.32157 nm, c = 0.52115 nm. After rolling treatment, the yield strength and tensile strength of the Mg-5Y alloy are 124.7 and 240.5 MPa respectively, and the elongation is 8.6%.

[0118] Example 5: Preparation of highly alloyed Mg-Y binary alloy sheet by synergistic low superheat controlled diffusion solidification and rolling

[0119] After relevant verification of Examples 2 and 4, it is shown that the grain size refinement of the Mg-2Y ingot prepared by low superheat controlled diffusion solidification is the most significant, and the solid solubility is the highest. Based on this, when comparing the high-alloyed Mg-Y binary alloy, only low superheat controlled diffusion solidification and rolling are used to synergistically prepare the high-alloyed Mg-Y binary alloy plate, and the high superheat situation is no longer repeated. Low superheat controlled diffusion solidification means that the two precursor alloy melts are cooled to 5 to 15°C above their liquidus temperature and then mixed. The specific steps and process parameters are as follows:

[0120] (1) Precursor alloy smelting: pure magnesium and Mg-25Y alloy are used as two precursor alloys, the mixing ratio of pure magnesium and Mg-25Y alloy is determined according to the target and gold, and the required precursor alloy is calculated and weighed; the two groups of weighed precursor alloys are melted in two resistance furnaces respectively, the melting temperature is 700-710°C, and then they are kept at room temperature for 20-30 minutes to obtain high-temperature pure magnesium melt and low-temperature Mg-25Y alloy melt; the scum on the surface of the melt is removed from the melt, high-purity argon gas is blown into the alloy melt for refining and slag removal, and then the melt is kept at room temperature; the time for blowing argon for refining and impurity removal is 3-6 minutes, and the time for standing and keeping at room temperature is 10-20 minutes.

[0121] (2) Melt mixing and casting: The two precursor alloy melts in step (1) are cooled to 5 to 15°C above their liquidus temperatures, respectively, and the high-temperature pure magnesium melt is poured into the lower-temperature Mg-25Y melt for mixing and stirring for 10 to 60 seconds; the mixed melt is then quickly cast into a metal mold, and naturally cooled and solidified to obtain a low-alloyed Mg-Y based alloy ingot.

[0122] (3) Hot rolling: preheat the solidified ingot to 400-500°C and keep it warm for 10-20 minutes to allow the ingot to be fully heated; then perform hot rolling, with the pressing amount of each pass being 8%-12%. After each rolling pass, keep it warm for 8-12 minutes before performing the next rolling pass. When the total pressing amount reaches 80%-85%, quickly water quench it to obtain a low-alloyed Mg-Y based alloy sheet.

[0123] The target alloy of this embodiment is a high alloyed Mg-Y binary alloy, specifically a Mg-(4.5-7.5)Y alloy. Preferably, the high alloyed Mg-Y binary alloy is a Mg-5Y alloy, and the mass ratio of the pure magnesium melt to the Mg-25Y master alloy melt is 4:1.

[0124] In step (2), the liquidus temperatures of the two precursor alloys, pure magnesium and Mg-25Y alloy, are 650 and 577° C., respectively. The two precursor alloy melts are cooled to 5 to 15° C. above their liquidus temperatures and then mixed, i.e., the pure magnesium melt is cooled to 655 to 665° C. and the Mg-25Y alloy melt is cooled to 582 to 592° C. and then mixed. Preferably, in step (3), the rolling temperature is 450° C., the pressing amount each time is 10%, the holding time is 10 min, and the total pressing amount is 80%.

[0125] The microstructural characteristics of the alloy prepared under the preferred conditions of this embodiment were observed and analyzed. The results show that compared with Comparative Example 3, the average grain size of the ingot obtained in this embodiment is about 132μm, and the grain size is greatly refined. At this time, the yield strength and tensile strength are about 86.9 and 139.3MPa, respectively, and the elongation is about 6.56%. The lattice constants of the magnesium matrix in the cast state of this embodiment were calculated and found to be a=0.32172nm, c=0.52203nm. Compared with Comparative Example 3, the grain size of the ingot is significantly refined, and the solid solubility is increased. At the same time, the yield strength of the ingot is increased by 121.0%, the tensile strength is increased by 25.3%, but the plasticity is lost by 9.9%. It can be seen from this that the high-alloyed Mg-Y binary alloy prepared by controlled diffusion solidification is not as good as the low-alloyed Mg-Y binary alloy in terms of mechanical property improvement.

[0126] The alloy prepared under the preferred conditions of this embodiment, after rolling treatment, has a yield strength and tensile strength of 180.8 and 281.4 MPa, respectively, and an elongation of 8.1%. Compared with Comparative Example 3, the yield strength is increased by 45.0%, and the tensile strength is only increased by 17.0%. The elongation is reduced, with a loss of 5.8%. It can be seen that the high-alloyed Mg-Y binary alloy sheet prepared by controlled diffusion solidification and rolling does not break the inverse relationship between strength and plasticity like low alloying; and the strength improvement is far less than that of low alloying.

[0127] Comparative Example 4: Preparation of high alloyed Mg-Y-Zn alloy sheet by conventional casting followed by rolling

[0128] The specific steps and process parameters are as follows:

[0129] (1) Melting: Pure magnesium, Mg-25Y master alloy and pure Zn are used as raw materials. The mixing ratio of the raw materials is determined according to the target alloy composition, and the required raw materials are calculated and weighed. Pure magnesium is first added to a resistance furnace, and after it is fully melted, Mg-25Y alloy and pure Zn are added. The melting temperature is 700-720°C. After all the raw materials are melted, they are quickly stirred and allowed to stand for 20-30 minutes to ensure that the melt is fully mixed. After standing, the scum on the surface of the melt is removed, and high-purity argon gas is blown into the alloy melt for refining and slag removal, followed by standing and holding. The time for blowing argon for refining and impurity removal is 3-6 minutes, and the time for standing and holding is 10-20 minutes.

[0130] (2) Casting: The melt in step (1) is cast into a metal mold preheated to 200° C., and naturally cooled and solidified to obtain a highly alloyed Mg-Y-Zn alloy. Finally, samples are taken from the casting for analysis.

[0131] (3) Hot rolling: Preheat the solidified ingot to 400-500℃ and keep it warm for 10-20 minutes to fully heat the ingot. Then carry out hot rolling, with the pressing amount of each pass being 8%-12%. Keep it warm for 8-12 minutes after each rolling pass before rolling the next pass. When the total pressing amount reaches 80%-85%, quickly water quench it to obtain a low-alloyed Mg-Y based alloy plate. Finally, take samples from the rolled plate for analysis.

[0132] The target alloy is a high alloyed Mg-Y-Zn alloy, specifically a Mg-(4-7)Y-(1.5-3.5)Zn alloy; preferably, the high alloyed Mg-Y-Zn alloy is a Mg-5Y-2Zn alloy. Preferably, in step (3), the rolling temperature is 450°C, the pressing amount each time is 10%, the holding time is 10 minutes, and the total pressing amount is 80%.

[0133] After testing, the average grain size of the Mg-5Y-2Zn alloy ingot prepared by conventional casting under the preferred conditions is about 903μm. Its yield strength and tensile strength are 46.6 and 133.1MPa respectively, and the elongation is 11.6%. The magnesium matrix lattice constant of the ingot obtained by conventional casting under the preferred conditions was further tested, a=0.32155nm, c=0.52109nm. However, after rolling treatment, the alloy sheet cracked; the main reason for this is that the plastic deformation ability of the high-alloyed Mg-Y-Zn ingot prepared by conventional casting is poor.

[0134] Example 6: Synergistic preparation of high alloyed Mg-Y-Zn alloy plate by low superheat controlled diffusion solidification and rolling

[0135] The low superheat controlled diffusion solidification of this embodiment is that the two precursor alloy melts are cooled to 5-15°C above their liquidus temperature and then mixed. The specific steps and process parameters are as follows:

[0136] (1) Precursor alloy smelting: Mg-2.5Zn alloy is used as a high-temperature low-quality melt, and Mg-25Y is used as a low-temperature high-quality melt, wherein Mg-2.5Zn is obtained by mixing pure magnesium and pure zinc; the mixing ratio of the Mg-2.5Zn alloy and the Mg-25Y alloy is determined according to the target alloy composition, and the required precursor alloy is calculated and weighed; the two weighed groups of precursor alloys are melted in two resistance furnaces respectively at a melting temperature of 700°C, and are kept at a temperature of 20 to 30 minutes to obtain a high-temperature Mg-2.5Zn alloy melt and a low-temperature Mg-25Y alloy melt; the scum on the surface of the melt is removed from the melt, and high-purity argon gas is blown into the alloy melt for refining and slag removal, followed by keeping the melt at a temperature of 10 to 20 minutes. The time for blowing argon for refining and impurity removal is 3 to 6 minutes, and the time for keeping the melt at a temperature of 10 to 20 minutes.

[0137] (2) Melt mixing and casting: The two precursor alloy melts in step (1) are cooled to 5 to 15°C above their liquidus temperatures, respectively, and the high-temperature Mg-2.5Zn alloy melt is poured into the low-temperature Mg-25Y melt for mixing and stirring for 10 to 60 seconds; the mixed melt is then rapidly cast into a metal mold, and naturally cooled and solidified to obtain a highly alloyed Mg-Y-Zn alloy ingot.

[0138] (3) Hot rolling: preheat the solidified ingot to 400-500°C and keep it warm for 10-20 minutes to allow the ingot to be fully heated; then hot rolling is performed, with the pressing amount of each pass being 8%-12%. After each rolling pass, the next rolling pass is performed after keeping warm for 8-12 minutes. When the total pressing amount reaches 80%-85%, it is quickly water quenched to obtain a high-alloyed Mg-Y-Zn alloy plate.

[0139] The target alloy is a high alloyed Mg-Y-Zn alloy, specifically a Mg-(4.5-7.5)Y-(1.5-3.5)Zn alloy. Preferably, the high alloyed Mg-Y-Zn alloy is a Mg-5Y-2Zn alloy (Y is 5%, Zn is 2%); the Zn content in Mg-2.5Zn is 2.5%. Preferably, the high alloyed Mg-Y-Zn alloy is a Mg-5Y-2Zn alloy, and the mass ratio of the Mg-2.5Zn melt to the Mg-25Y master alloy melt is 4:1.

[0140] In step (2), the liquidus temperatures of the two precursor alloys Mg-2.5Zn and Mg-25Y are 643° C. and 577° C., respectively, and the two precursor alloy melts are cooled to 5-15° C. above their liquidus temperatures, i.e., the Mg-2.5Zn melt is cooled to 648-658° C., and the Mg-25Y melt is cooled to 582-592° C. Preferably, in step (3), the rolling temperature is 450° C., the pressing amount each time is 10%, the holding time is 10 min, and the total pressing amount is 80%.

[0141] The microstructural characteristics of the alloy prepared under the preferred conditions of this embodiment were observed and analyzed. The results show that compared with Comparative Example 4, the average grain size of the ingot obtained in this embodiment is about 64μm, the yield strength and tensile strength are about 101.7 and 184.2MPa respectively, and the elongation is about 14.9%. The lattice constants of the magnesium matrix in the cast state of this embodiment were calculated and found to be a=0.32176nm, c=0.522214nm. Compared with Comparative Example 4, the grain size of the ingot is significantly refined, while the solid solubility is increased, and the strength and plasticity are significantly improved. After rolling treatment, the alloy plate did not crack, but an alloy plate of better quality was obtained; the main reason for this is that the controlled diffusion solidification improves the performance of the high-alloyed Mg-Y-Zn alloy ingot.

[0142] In order to better compare and illustrate the differences in the processes and effects of the comparative examples and the embodiments, the experimental parameters and performance data are summarized in Tables 1 to 3. The present invention prepares Mg-Y-based alloy plates by controlled diffusion solidification and rolling synergistic treatment. Controlled diffusion solidification improves the performance of rolled plates by improving the performance of Mg-Y-based alloy ingots and reducing casting defects. In particular, the low-alloyed Mg-Y-based alloy prepared by low-superheat controlled diffusion solidification and rolling synergistic treatment has the best performance. Compared with the low-alloyed Mg-Y-based alloy prepared by conventional casting and rolling, it achieves a significant improvement in strength and plasticity while refining the structure.

[0143] Table 1 Experimental parameters of comparative examples and embodiments

[0144]

[0145] Table 2 Performance of various as-cast alloy microstructure parameters in comparative examples and embodiments

[0146]

[0147]

[0148] Note: The improvement is calculated for the same target alloy under the same conditions.

[0149] Table 3 Properties of various rolled alloys in comparative examples and embodiments

[0150]

[0151] Note: The improvement is calculated for the same target alloy under the same conditions.

[0152] The implementation methods of the present invention are not limited to the embodiments described, and any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention.

Claims

1. A method for improving the strength and plasticity of a low-alloyed Mg-Y based rare earth magnesium alloy, characterized in that: The steps include: 1) Pioneer alloy smelting: according to the target alloy, the pioneer alloy is divided into a low-temperature high-quality pioneer alloy and a high-temperature low-quality pioneer alloy; the low-temperature high-quality pioneer alloy and the high-temperature low-quality pioneer alloy are melted respectively to obtain a low-temperature high-quality melt and a high-temperature low-quality melt; the target alloy is a magnesium alloy containing Mg and Y; the liquidus temperature difference between the low-temperature high-quality pioneer alloy and the high-temperature low-quality pioneer alloy is 50-80° C.; the low-temperature high-quality melt is Mg-25Y; 2) The low-temperature high-quality melt and the high-temperature low-quality melt are respectively lowered to their respective liquidus temperatures + (5-40)°C, and then the high-temperature low-quality melt and the low-temperature high-quality melt are uniformly mixed, cast and molded to obtain a casting.

2. The method for improving the strength and plasticity of low-alloyed Mg-Y based rare earth magnesium alloy according to claim 1, characterized in that: The method further comprises: 3) hot rolling the ingot.

3. The method for improving the strength and plasticity of low-alloyed Mg-Y based rare earth magnesium alloy according to claim 2, characterized in that: The hot rolling forming is specifically as follows: preheating the ingot to a temperature of 400-500° C., and then hot rolling; during the hot rolling process, the pressing amount per pass is 8%-12%, and after each rolling pass, the ingot is kept warm for 8-12 minutes before the next rolling pass is performed; after the total pressing amount reaches 80%-85%, the ingot is water quenched to obtain a Mg-Y based alloy plate.

4. The method for improving the strength and plasticity of low alloyed Mg-Y based rare earth magnesium alloy according to claim 1, characterized in that: The target alloy is a magnesium alloy containing Mg and Y. When the target alloy is a magnesium alloy of Mg and Y, the Y content is 1.5-2.5%, and the percentage is the mass percentage; when the target alloy is a magnesium alloy of Mg, Y and other doping elements, the Y content is 1.5-7.5%, and the content of other doping elements is 0.5-3.5%, and the percentage is the mass percentage.

5. The method for improving the strength and plasticity of low alloyed Mg-Y based rare earth magnesium alloy according to claim 4, characterized in that: When the target alloy is a magnesium alloy of Mg, Y and other doping elements, the Y content is 1.5-2.5%, and the content of other doping elements is 0.5-1.5%.

6. The method for improving the strength and plasticity of low alloyed Mg-Y based rare earth magnesium alloy according to claim 4, characterized in that: When the target alloy is a magnesium alloy of Mg and Y, the high-temperature low-quality melt is pure magnesium; When the target alloy is a magnesium alloy of Mg, Y and other doping elements, the high-temperature low-quality melt is Mg-other doping elements, which is composed of pure magnesium and other doping element metals.

7. The method for improving the strength and plasticity of low alloyed Mg-Y based rare earth magnesium alloy according to claim 6, characterized in that: When the other doping element is Zn, the high-temperature low-quality melt is a Mg-Zn alloy, and the content of Zn is determined according to the target alloy composition and component content.

8. The method for improving the strength and plasticity of low alloyed Mg-Y based rare earth magnesium alloy according to claim 1, characterized in that: In step 2), the low-temperature high-quality melt and the high-temperature low-quality melt are respectively reduced to their respective liquidus temperatures + (5-15)°C; The uniform mixing in step 2) refers to adding a high-temperature low-quality melt into a low-temperature high-quality melt for mixing.

9. The method for improving the strength and plasticity of low alloyed Mg-Y based rare earth magnesium alloy according to claim 1, characterized in that: The melting in step 1) is carried out under a protective atmosphere; In step 1), the melting temperature is 690-720° C. After melting, the melt is kept at a temperature of 20-30 minutes to remove scum on the surface of the melt and to perform refining and impurity removal treatment; The casting in step 2) refers to casting into a metal mold preheated at 190-210°C and naturally cooling and solidifying; The total content of impurity elements in the target alloy is ≤0.1%; among the impurity elements, the impurity elements Fe are ≤0.02%, Al is ≤0.01%, and Si is ≤0.01%.

10. The method for improving the strength and plasticity of low alloyed Mg-Y based rare earth magnesium alloy according to claim 9, characterized in that: The refining and impurity removal treatment specifically comprises blowing high-purity argon gas into the alloy melt for refining and slag removal, followed by standing and heat preservation at 690-720°C; the time for blowing argon for refining and impurity removal is 3-6 minutes, and the time for standing and heat preservation at 690-720°C is 10-20 minutes.

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