Heat treatment method of Mg-Zn-Y-Nd series alloy

Abstract

The invention discloses a heat treatment method for Mg-Zn-Y-Nd series alloys, and belongs to the technical field of magnesium alloy heat treatment. The heat treatment method of the Mg-Zn-Y-Nd series alloy comprises the following steps that the Mg-Zn-Y-Nd alloy is subjected to solution treatment, and a magnesium alloy subjected to solution treatment is obtained; and the magnesium alloy subjected to solution treatment is placed in a quenching medium to be subjected to quenching treatment, then aging treatment is conducted, and the Mg-Zn-Y-Nd alloy subjected to heat treatment is obtained. And after aging treatment, the precipitation of the second phase obtains optimized size, morphology and distribution, so that the aging strengthening effect is exerted as much as possible, the strength and ductility of the alloy are further improved, and a guarantee is provided for subsequent thermal machining of the alloy. After heat treatment, the strength and plasticity of the Mg-Zn-Y-Nd alloy are improved at the same time, the yield strength, tensile strength, ductility, microhardness and the like of the alloy are all improved, and the mechanical performance of the alloy is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment of magnesium alloys, in particular to a heat treatment method for Mg-Zn-Y-Nd series alloys. Background Art

[0002] Magnesium has attracted much attention due to its excellent properties such as good damping, high specific strength, strong impact resistance, good heat dissipation, and good electromagnetic shielding. It has been widely used in aerospace, automobile, 3C electronics and other industries. In addition, magnesium's low density (1.7-2.0g / cm 3 ), elastic modulus similar to human bone (41-45GPa), biodegradable absorbability and relatively good biocompatibility also make it a candidate material for biomedical implants with great research value. However, the relatively low ductility and strength of cast magnesium alloys hinder their widespread application, so there is a need to improve their mechanical properties.

[0003] Alloying is one of the most convenient ways to improve mechanical properties. Elements such as zinc, aluminum, and rare earth (RE) have been used to develop new magnesium alloys. In recent years, Mg-Zn-Y-Nd series alloys have been developed as new rare earth magnesium alloys. The addition of Zn, Y, and Nd elements to the alloy can form W-Mg3Zn3Y2, Mg 41 Nd5 and Mg 24 Phases such as Y5 can achieve strengthening effects through grain refinement and second phase strengthening. However, cast alloys cannot directly play a strengthening effect, and it is necessary to further induce the formation of these strengthening phases during the heat treatment process to achieve a strengthening effect. On the other hand, the cast alloy structure is coarse, and the alloy is often accompanied by casting defects such as holes. It is necessary to improve the structure morphology and distribution through heat treatment to improve its mechanical properties. In order to facilitate the subsequent thermomechanical deformation of Mg-Zn-Y-Nd series alloys such as extrusion and rolling, the material needs to have a good match between strength and plasticity. If the plasticity of the material is poor, hot cracking problems are prone to occur. If the strength is low, it may lead to a weak deformation strengthening effect. Therefore, how to achieve a better balance between the strength and plasticity of the blank before hot extrusion is an important consideration for the thermomechanical processing of magnesium alloys.

[0004] In the current existing technology, there is no in-depth research on the heat treatment method of Mg-Zn-Y-Nd series alloys. Therefore, it is urgent to develop a heat treatment process that can effectively improve the microstructure distribution and mechanical properties of Mg-Zn-Y-Nd series alloys, so as to more effectively eliminate the internal stress and work hardening of Mg-Zn-Y-Nd series alloys and prepare for further mechanical processing of the alloys. Summary of the invention

[0005] The purpose of the present invention is to provide a heat treatment method for Mg-Zn-Y-Nd series alloys to solve the above-mentioned problems in the background technology. After the heat treatment of the present invention, the strength and plasticity of the Mg-Zn-Y-Nd alloy are improved at the same time, and the yield strength, tensile strength, elongation and microhardness of the alloy are all improved, effectively improving the mechanical properties of the alloy.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention is to provide a heat treatment method for Mg-Zn-Y-Nd series alloys, comprising the following steps:

[0008] Performing a solid solution treatment on the Mg-Zn-Y-Nd alloy to obtain a solid solution treated magnesium alloy;

[0009] The solution treated magnesium alloy is placed in a quenching medium, quenched, and then subjected to aging treatment to obtain a heat treated Mg-Zn-Y-Nd alloy.

[0010] Preferably, the solution treatment is carried out at a temperature of 490-550° C. and for a time of 2-4 hours.

[0011] Preferably, the quenching medium is water.

[0012] Preferably, in the quenching treatment, the water temperature is 0°C and the quenching time is 50-80s / cm·kg.

[0013] The quenching time (unit s / cm·kg) of the present invention is related to the thickness and weight of the solution treated magnesium alloy. The cm in the unit of quenching time refers to the thickness of the thickest part of the solution treated magnesium alloy, and kg refers to the weight of the solution treated magnesium alloy.

[0014] Preferably, the aging treatment is carried out at a temperature of 200-240°C and for a time of 12-24 hours.

[0015] Preferably, the Mg-Zn-Y-Nd alloy comprises the following chemical components in percentage by mass: Zn 3.5-6.0wt%, Y 0.2-1.2wt%, Nd 0.2-1.0wt%, and the balance being Mg and unavoidable impurities.

[0016] Preferably, the Mg-Zn-Y-Nd alloy is obtained by smelting and casting industrial pure magnesium ingots, industrial pure zinc ingots, Mg-25.0wt% Y master alloy and Mg-25.0wt% Nd master alloy as raw materials.

[0017] The second technical solution of the present invention is to provide a heat-treated Mg-Zn-Y-Nd alloy prepared according to the above-mentioned heat treatment method.

[0018] The beneficial technical effects of the present invention are as follows:

[0019] In the heat treatment process defined in the present invention, in addition to the precipitation of the traditional strengthening phase W-Mg3Zn3Y2, the Mg 41 Nd5 phase and Mg 24 The formation of Y5 phase and the aging precipitation effect are obvious.

[0020] In the solution treatment stage, the alloying elements in the Mg-Zn-Y-Nd alloy of the present invention are fully dissolved into the matrix, the solubility of the alloy is improved, and the dissolution of the brittle eutectic structure is accelerated. After the aging treatment, the second phase is fully precipitated, so that the aging strengthening effect is exerted as much as possible, the strength and ductility of the alloy are further improved, and the subsequent thermomechanical processing of the alloy is guaranteed.

[0021] After the heat treatment of the present invention, the strength and plasticity of the Mg-Zn-Y-Nd alloy are improved at the same time, and the yield strength, tensile strength, elongation and microhardness of the alloy are all improved, thereby effectively improving the mechanical properties of the alloy.

[0022] The heat treatment process of the present invention is simple, easy to operate and highly efficient. The microstructure of the Mg-Zn-Y-Nd alloy is regulated by heat treatment, and the mechanical properties of the obtained alloy are effectively improved, which provides a guarantee for the application and further processing of the cast Mg-Zn-Y-Nd alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 This is the SEM image of the cast Mg-Zn-Y-Nd alloy.

[0025] Figure 2 The SEM images of the products of Comparative Examples 1-2 are shown in Figure 1. (a) is the SEM image of Comparative Example 1, and (b) is the SEM image of Comparative Example 2.

[0026] Figure 3 The SEM images of the products of Examples 1 to 5 are shown in Figures 1 to 5. (a) is the SEM image of Example 1, (b) is the SEM image of Example 2, (c) is the SEM image of Example 3, (d) is the SEM image of Example 4, and (e) is the SEM image of Example 5.

[0027] Figure 4This is the TEM image of the product of Example 1.

[0028] Figure 5 The tensile stress-strain curves are those of the cast Mg-Zn-Y-Nd alloy, the comparative examples 1-2 and the examples 1-5. DETAILED DESCRIPTION

[0029] Now, various exemplary embodiments of the present invention are described in detail, and this detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present invention. It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention.

[0030] In addition, for the numerical range in the present invention, it is understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0031] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention pertains. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention.

[0032] The words “include,” “including,” “have,” “contain,” etc. used in the present invention are open-ended terms, meaning including but not limited to.

[0033] The cast Mg-Zn-Y-Nd alloy in the present invention is made of industrial pure magnesium ingots, industrial pure zinc ingots, Mg-25.0wt% Y master alloy and Mg-25.0wt% Nd master alloy as raw materials, and is smelted and cast. The alloy casting process selects a metal mold casting process to obtain the cast Mg-Zn-Y-Nd alloy. The cast Mg-Zn-Y-Nd alloy is composed of the following chemical components in mass percentage: Zn 4.0wt%, Y 0.5wt%, Nd 0.5wt%, and the remainder is Mg and unavoidable impurities. The cast Mg-Zn-Y-Nd alloy is surface polished to remove the surface oxide layer to observe its microstructure morphology, such as Figure 1 As shown. According to the measurement, the microhardness of the cast Mg-Zn-Y-Nd alloy is 57.2HV 0.1 , the tensile strength is 201.49MPa, the yield strength is 113.31MPa, and the elongation is 7.25%.

[0034] All raw materials used in the following examples and comparative examples of the present invention are commercially available products.

[0035] Example 1

[0036] A heat treatment method for a cast Mg-Zn-Y-Nd alloy comprises the following steps:

[0037] (1) After the surface oxide layer of the cast Mg-Zn-Y-Nd alloy is removed by surface grinding, the cast Mg-Zn-Y-Nd alloy is placed in a heat treatment furnace at 500° C. and kept at this temperature for 4 h to obtain a solution-treated magnesium alloy;

[0038] (2) taking the solution treated magnesium alloy out of the heat treatment furnace and immediately transferring it to ice water at 0° C. for quenching for 60 s / cm·kg to obtain a quenched magnesium alloy;

[0039] (3) The quenched magnesium alloy is placed in a heat treatment furnace at 200° C., aged for 12 h, and then naturally cooled in an air environment to obtain a heat-treated Mg-Zn-Y-Nd alloy.

[0040] The microhardness of the magnesium alloy obtained in this embodiment is measured to be 70.5 HV 0.1 , the tensile strength is 228.19MPa, the yield strength is 130.71MPa, and the elongation is 13.53%.

[0041] Compared with the cast Mg-Zn-Y-Nd alloy, the microhardness of the product of Example 1 increased from 57.2 HV 0.1 Increased to 70.5HV 0.1 , an increase of nearly 23.3%; the tensile strength also increased from 7.25% to 13.25%, an increase of 82.76%.

[0042] Figure 4 This is the TEM image of the product of Example 1.

[0043] like Figure 4 As shown, after the heat treatment of Example 1, the alloy has dispersed granular second phase.

[0044] Example 2

[0045] A heat treatment method for a cast Mg-Zn-Y-Nd alloy comprises the following steps:

[0046] (1) After the surface oxide layer of the cast Mg-Zn-Y-Nd alloy is removed by surface grinding, the cast Mg-Zn-Y-Nd alloy is placed in a heat treatment furnace at 500° C. and kept at this temperature for 4 h to obtain a solution-treated magnesium alloy;

[0047] (2) taking the solution treated magnesium alloy out of the heat treatment furnace and immediately transferring it to ice water at 0° C. for quenching for 60 s / cm·kg to obtain a quenched magnesium alloy;

[0048] (3) The quenched magnesium alloy is placed in a heat treatment furnace at 240° C., aged for 12 h, and then naturally cooled in an air environment to obtain a heat-treated Mg-Zn-Y-Nd alloy.

[0049] The microhardness of the magnesium alloy obtained in this embodiment is measured to be 70.0 HV 0.1 , the tensile strength is 228.19MPa, the yield strength is 119.37MPa, and the elongation is 11.95%.

[0050] Example 3

[0051] A heat treatment method for a cast Mg-Zn-Y-Nd alloy comprises the following steps:

[0052] (1) After the surface oxide layer of the cast Mg-Zn-Y-Nd alloy is removed by surface grinding, the cast Mg-Zn-Y-Nd alloy is placed in a heat treatment furnace at 535° C. and kept at this temperature for 4 h to obtain a solution-treated magnesium alloy;

[0053] (2) taking the solution treated magnesium alloy out of the heat treatment furnace and immediately transferring it to ice water at 0° C. for quenching for 60 s / cm·kg to obtain a quenched magnesium alloy;

[0054] (3) The quenched magnesium alloy is placed in a heat treatment furnace at 200° C., subjected to aging treatment for 24 h, and then placed in an air environment for natural cooling to obtain a heat-treated Mg-Zn-Y-Nd alloy.

[0055] The microhardness of the magnesium alloy obtained in this embodiment is measured to be 66.5 HV 0.1 , the tensile strength is 225.01MPa, the yield strength is 131.32MPa, and the elongation is 13.11%.

[0056] Example 4

[0057] A heat treatment method for a cast Mg-Zn-Y-Nd alloy comprises the following steps:

[0058] (1) After the surface oxide layer of the cast Mg-Zn-Y-Nd alloy is removed by surface grinding, the cast Mg-Zn-Y-Nd alloy is placed in a heat treatment furnace at 550° C. and kept at this temperature for 4 h to obtain a solution-treated magnesium alloy;

[0059] (2) taking the solution treated magnesium alloy out of the heat treatment furnace and immediately transferring it to ice water at 0° C. for quenching for 60 s / cm·kg to obtain a quenched magnesium alloy;

[0060] (3) The quenched magnesium alloy is placed in a heat treatment furnace at 240° C. for aging treatment for 4 h, and then placed in an air environment for natural cooling to obtain a heat-treated Mg-Zn-Y-Nd alloy.

[0061] The microhardness of the magnesium alloy obtained in this embodiment is measured to be 68.9 HV 0.1 , the tensile strength is 224.36MPa, the yield strength is 138.21MPa, and the elongation is 13.63%.

[0062] Example 5

[0063] A heat treatment method for a cast Mg-Zn-Y-Nd alloy comprises the following steps:

[0064] (1) After the surface oxide layer of the cast Mg-Zn-Y-Nd alloy is removed by surface grinding, the cast Mg-Zn-Y-Nd alloy is placed in a heat treatment furnace at 550° C. and kept at this temperature for 4 h to obtain a solution-treated magnesium alloy;

[0065] (2) taking the solution treated magnesium alloy out of the heat treatment furnace and immediately transferring it to ice water at 0° C. for quenching for 60 s / cm·kg to obtain a quenched magnesium alloy;

[0066] (3) The quenched magnesium alloy is placed in a heat treatment furnace at 200° C., aged for 12 h, and then naturally cooled in an air environment to obtain a heat-treated Mg-Zn-Y-Nd alloy.

[0067] The microhardness of the magnesium alloy obtained in this embodiment is measured to be 68.4 HV 0.1 , the tensile strength is 224.44MPa, the yield strength is 135.34MPa, and the elongation is 11.69%.

[0068] Comparative Example 1

[0069] The only difference from Example 1 is that the aging treatment in step (3) is omitted, and the quenched magnesium alloy after quenching in step (2) is directly used as the final product.

[0070] The microhardness of the magnesium alloy obtained in this comparative example is measured to be 59.7 HV 0.1 , the tensile strength is 191.42MPa, the yield strength is 102.82MPa, and the elongation is 5.23%.

[0071] Comparative Example 2

[0072] The only difference from Example 3 is that the aging treatment in step (3) is omitted, and the quenched magnesium alloy after quenching in step (2) is directly used as the final product.

[0073] The microhardness of the magnesium alloy obtained in this comparative example is measured to be 64.3HV 0.1 , the tensile strength is 180.13MPa, the yield strength is 87.99MPa, and the elongation is 6.51%.

[0074] Figure 1 This is the SEM image of the cast Mg-Zn-Y-Nd alloy.

[0075] Figure 2 The SEM images of the products of Comparative Examples 1-2 are shown in Figure 1. (a) is the SEM image of Comparative Example 1, and (b) is the SEM image of Comparative Example 2.

[0076] Figure 3 The SEM images of the products of Examples 1 to 5 are shown in Figures 1 to 5. (a) is the SEM image of Example 1, (b) is the SEM image of Example 2, (c) is the SEM image of Example 3, (d) is the SEM image of Example 4, and (e) is the SEM image of Example 5.

[0077] Depend on Figure 2 It can be seen that the equiaxed grains in each comparative example are coarsened, the second phase is distributed along the grain boundary, and the second phase is transformed into a continuous distribution.

[0078] Depend on Figure 3 It can be seen that the grain size and the volume fraction of the second phase in each embodiment increase, the precipitation amount of the second phase increases, and the second phase is semi-continuously distributed along the grain boundary in the form of a eutectic structure.

[0079] Combination Figure 1 , 3 -4 It can be seen that the heat treatment of the cast Mg-Zn-Y-Nd alloy promotes the dissolution of Nd and Y elements in the alloy and strengthens the Mg 24 Y5 phase and Mg 41 Nd5 precipitates. Moreover, after the heat treatment of Examples 1-5, the strength and plasticity of the Mg-Zn-Y-Nd alloy are improved at the same time, and the room temperature yield strength, tensile strength, elongation and microhardness of the alloy are all improved, indicating that the heat treatment effectively improves the mechanical properties of the alloy.

[0080] Effect Example 1

[0081] The room temperature tensile properties of the prepared samples were tested. The test results are shown in Figure 5 .

[0082] Figure 5 The tensile stress-strain curves are those of the cast Mg-Zn-Y-Nd alloy, the comparative examples 1-2 and the examples 1-5.

[0083] Depend on Figure 5It can be seen that after the heat treatment of the present invention, the plasticity of the casting alloy can be increased by nearly 1 times. In contrast, the plasticity and tensile strength of the product of Comparative Example 1-2 are lower than those of the cast Mg-Zn-Y-Nd alloy, and the yield strength is not significantly improved, that is, the mechanical properties of the Mg-Zn-Y-Nd alloy after solid solution are reduced.

[0084] Generally, aging treatment is usually used to promote the precipitation of the second phase. Due to the precipitation of the second phase, the pinning on the grain boundary will be more dense, and the plasticity of the alloy should be reduced in theory; however, the plasticity of the product of the present invention has been greatly improved, which is exactly the opposite of theoretical expectations. This may be because the present invention adjusts the preparation parameters to regulate the microstructure, so that the second phase in the prepared Mg-Zn-Y-Nd alloy is distributed in a dispersed manner, and this microstructure is more conducive to improving plasticity.

[0085] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A heat treatment method for Mg-Zn-Y-Nd series alloy, characterized in that: The following steps are involved: Performing a solid solution treatment on the Mg-Zn-Y-Nd alloy to obtain a solid solution treated magnesium alloy; The solution treated magnesium alloy is placed in a quenching medium, quenched, and then subjected to aging treatment to obtain a heat treated Mg-Zn-Y-Nd alloy.

2. The heat treatment method according to claim 1, characterized in that The temperature of the solution treatment is 490-550° C. and the time is 2-4 hours.

3. The heat treatment method according to claim 1, characterized in that The quenching medium is water.

4. The heat treatment method according to claim 3, characterized in that: In the quenching treatment, the water temperature is 0° C. and the quenching time is 50-80 s / cm·kg.

5. The heat treatment method according to claim 1, characterized in that: The aging treatment is carried out at a temperature of 200-240° C. and for a time of 12-24 hours.

6. The heat treatment method according to claim 1, characterized in that: The Mg-Zn-Y-Nd alloy includes the following chemical components in mass percentage: Zn 3.5-6.0wt%, Y 0.2-1.2wt%, Nd 0.2-1.0wt%, and the balance is Mg and inevitable impurities.

7. A heat-treated Mg-Zn-Y-Nd alloy prepared according to the heat treatment method according to any one of claims 1 to 6.

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