Aging treatment method of Mg-Gd-Zr alloy

Abstract

This invention discloses an aging treatment method for Mg-Gd-Zr alloys, comprising the following steps: providing an extruded Mg-Gd-Zr alloy; aging the extruded Mg-Gd-Zr alloy at 220-230℃ for 6-8 hours under a pulsed magnetic field, followed by cooling to obtain an aged Mg-Gd-Zr alloy; wherein the pulsed magnetic field has a current of 1-5A, a frequency of 12-16Hz, and a duty cycle of 45-55%. This invention ages the extruded Mg-Gd-Zr alloy under pulsed magnetic field conditions, significantly enhancing the alloy's strength and ductility through the synergistic effect of electromagnetic force and Joule heating. The shorter aging time of this invention helps improve processing efficiency and reduce aging treatment costs.

Description

Technical Field

[0001] This invention relates to an aging treatment method for Mg-Gd-Zr alloys, and more particularly to an aging treatment method for Mg-Gd-Zr alloys assisted by a pulsed magnetic field, belonging to the field of heat treatment of non-ferrous metal materials. Background Technology

[0002] Mg-Gd-Zr alloys are typical age-hardening alloys. The phase is its main strengthening phase, belonging to the lamellar {11} The 0} cylindrical phase generally has three orientations and is perpendicular to the (0001) basal plane, which significantly hinders basal plane slip and strengthens the alloy (see: F. Zhang, Y. Wang, Y. Duan, K. Wang, Y. Wang, W. Zhang, J. Hu, Precipitation processes during the peak-aged and over-aged stages in an Mg-Gd-Y-Zr alloy, Journal of Alloys and Compounds[J] 788 (2019) 541-548.

[12] J.-F. Nie, Precipitation and Hardening in Magnesium Alloys, Metall. Mater.Trans. A[J] 43(11) (2012) 3891-3939.). The aging strengthening effect of Mg-Gd-Zr alloy depends not only on Variations in phase size and dispersion are also closely related to their distribution. You et al. (see: C. You, C. Liu, Y. Wan, B. Tang, B. Wang, Y. Gao, X. Han, Dislocations-induced precipitates and their effect on mechanical properties of Mg-Gd-Y-Zr alloy, J. Magnes. Alloy[J] 7(3)(2019) 414-418.) induced precipitates in Mg-9.5Gd-3.8Y-0.6Zr(wt%) alloys. The phases are preferentially distributed along only one orientation on the dislocation line array, and Compared to the normal case where the phases are triangularly distributed on the cylindrical surface, the hindering effect on dislocations is weakened, while the alloy's strength and plasticity are improved. Therefore, when... When the phase distribution changes from a triaxial network to a biaxial or even uniaxial distribution, i.e., once the network distribution is destroyed, the strengthening effect of the alloy decreases, but good plasticity can be retained. Therefore, existing aging treatment methods are difficult to simultaneously strengthen or improve the tensile strength and elongation of Mg-Gd-Zr alloys.

[0003] Currently, pulsed magnetic fields are applied during the solidification process of Mg-7Zn alloys to refine the solidification microstructure, increase the volume fraction of the MgZn phase, and improve the alloy's mechanical properties and corrosion resistance (see: L. Zhang, PH Hu, Q. Zhou, W. Zhan, F. Jin, Effects of pulsed magnetic field on microstructure, mechanical properties and bio-corrosion behavior of Mg-7Zn alloy, Materials Letters[J].193 (2017) 224-227.). The Lorentz force generated by the pulsed magnetic field promotes basal slip, leading to localized plastic deformation of the alloy (see: Currently, there are no reports of applying pulsed magnetic field technology to the aging treatment of Mg-Gd-Zr alloys. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide an aging treatment method for Mg-Gd-Zr alloys, so as to improve the tensile strength and elongation of Mg-Gd-Zr alloys.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] An aging treatment method for Mg-Gd-Zr alloys includes the following steps:

[0007] S1. Provides extruded Mg-Gd-Zr alloys;

[0008] S2. The extruded Mg-Gd-Zr alloy is aged at 220-230℃ for 6-8 hours under a pulsed magnetic field, and then cooled to obtain the aged Mg-Gd-Zr alloy.

[0009] The pulsed magnetic field has a current of 1-5A, a frequency of 12-16Hz, and a duty cycle of 45-55%.

[0010] Furthermore, the preparation method of extruded Mg-Gd-Zr alloy includes the following steps: preheating the cast Mg-Gd-Zr alloy to 385-395℃ and then extruding it to obtain the alloy; wherein, during the extrusion process, the extrusion speed is 0.2-0.6 mm / s, the temperature of the extrusion cylinder is 430-440℃, the temperature of the extrusion die is 295-305℃, and the extrusion ratio is 8-12, preferably 10.

[0011] Optionally, the extruded Mg-Gd-Zr alloy is in plate form with a thickness of 23-29 mm and a width of 155-175 mm.

[0012] Furthermore, the Mg-Gd-Zr alloy is a Mg-Gd-Y-Nd-Zr alloy, preferably a Mg-8Gd-4Y-1Nd-0.5Zr alloy.

[0013] Further, in S2, the extruded Mg-Gd-Zr alloy is aged at 222-228℃ for 6.5-7h under a pulsed magnetic field.

[0014] Furthermore, in S2, the current of the pulsed magnetic field is 2-4A, and even further, it is 2.5-3.5A.

[0015] Furthermore, in S2, the frequency of the pulsed magnetic field is 13-15 Hz, and the duty cycle is 48-52%.

[0016] Furthermore, in S2, the magnetic induction intensity of the pulsed magnetic field is 0.45-2.5T, and even further, it is 0.6-2.2T.

[0017] Furthermore, in S2, the tensile strength of the aged Mg-Gd-Zr alloy is ≥305MPa, further 306-321MPa; the elongation is ≥5%, further 5.2-6.8%.

[0018] Furthermore, in S2, the hardness of the Mg-Gd-Zr alloy after aging treatment is ≥105HV.

[0019] Furthermore, in S2, the aged Mg-Gd-Zr alloy contains serrated grain boundaries.

[0020] This invention reveals that aging extruded Mg-Gd-Zr alloys under pulsed magnetic field conditions can improve both tensile strength and elongation (i.e., ductility). This is likely because the pulsed magnetic field accelerates solute atom diffusion through the synergistic effect of electromagnetic force and Joule heating, causing the strengthening phase to precipitate directionally in the matrix. Grain boundaries change from straight to serrated, which not only increases strength but also provides more space for dislocation movement and coordination, thus synergistically improving both strength and ductility. Conversely, aging extruded Mg-Gd-Zr alloys without an external pulsed magnetic field, while improving tensile strength to some extent, leads to a decrease in elongation.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The present invention performs aging treatment on extruded Mg-Gd-Zr alloy under pulsed magnetic field treatment conditions. Through the synergistic effect of electromagnetic force and Joule heat, the tensile strength and ductility of the alloy are significantly enhanced.

[0023] (2) The present invention has a shorter processing time, which helps to improve processing efficiency and reduce processing costs. Attached Figure Description

[0024] Figure 1 The image shows a TEM image of the Mg-Gd-Zr alloy after aging treatment in Example 2. Figure 1 a is a TEM image of a grain boundary at a certain point. Figure 1 b is a TEM image of the grain boundary at another location. Figure 1 c is a TEM image (magnified view) of the interior of the grain. Figure 1 d is a TEM image of the interior of the grain.

[0025] Figure 2 The image shows a TEM image of the aging-treated Mg-Gd-Zr alloy obtained in Comparative Example 1. Figure 2 a is a TEM image of a grain boundary at a certain point. Figure 2 b is a TEM image of the grain boundary at another location. Figure 2 c is a TEM image of the interior of the grain. Figure 2 d is a TEM image (enlarged view) of the interior of the grain.

[0026] Figure 3 The images show the microstructure of the extruded Mg-Gd-Zr alloy described in Example 1, as well as the aged Mg-Gd-Zr alloys obtained in Examples 1-3 and Comparative Example 1, after tensile fracture. Figure 3 Image a shows the microstructure of the fracture surface of the extruded Mg-Gd-Zr alloy after tensile fracture. Figure 3b is a microstructure of the fracture surface of the aging-treated Mg-Gd-Zr alloy obtained in Comparative Example 1 after tensile fracture. Figure 3 c is a microstructure of the fracture surface of the aging-treated Mg-Gd-Zr alloy obtained in Example 1 after tensile fracture. Figure 3 d is a microstructure of the fracture surface of the aging-treated Mg-Gd-Zr alloy obtained in Example 2 after tensile fracture. Figure 3 e is a microscopic morphology image of the fracture surface of the aging-treated Mg-Gd-Zr alloy obtained in Example 3 after tensile fracture.

[0027] Figure 4 The image shows the optical microstructure of the extruded Mg-Gd-Zr alloy obtained in Example 1. Figure 4 a is an optical microstructure diagram with a scale bar of 50m; Figure 4 b is an optical microstructure diagram with a scale bar of 2 μm. Detailed Implementation

[0028] The present invention will be described in detail below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0029] Example 1

[0030] In this embodiment, the aging treatment method for Mg-Gd-Zr alloy includes the following steps:

[0031] S1. The as-cast Mg-Gd-Zr alloy is preheated to 389℃ and then extruded to obtain an extruded Mg-Gd-Zr alloy (plate shape, 26mm thick and 165mm wide). During extrusion, the extrusion speed is 0.4mm / s, the extrusion cylinder temperature is 435℃, the extrusion die temperature is 300℃, and the extrusion ratio is 10. The Mg-Gd-Zr alloy is a Mg-8Gd-4Y-1Nd-0.5Zr alloy.

[0032] The extruded Mg-Gd-Zr alloy was tested and found to have a tensile strength (UTS) of 293.4 MPa and an elongation of 4.1%.

[0033] Depend on Figure 4 As can be seen from a, the extruded Mg-Gd-Zr alloy has equiaxed grains, which are fine and have an average size of about 3 μm; Figure 4 As shown in b, the extruded Mg-Gd-Zr alloy contains a large number of irregular Mg5RE precipitates (RE is a rare earth element), which will hinder the further improvement of the alloy strength after aging.

[0034] S2. The extruded Mg-Gd-Zr alloy is aged at 225°C for 6 hours under a pulsed magnetic field, and then cooled to obtain the aged Mg-Gd-Zr alloy.

[0035] The pulsed magnetic field has a current of 1A, a magnetic induction intensity of 0.49T, a frequency of 14Hz, and a duty cycle of 50%.

[0036] Testing revealed that the tensile strength of the aged Mg-Gd-Zr alloy was 307.9 MPa, but the elongation increased to 5.3%. The tensile strength and elongation were measured using an Instron 8802 electro-hydraulic servo mechanical testing machine (USA).

[0037] Example 2

[0038] Repeat Example 1, except that in S2, the current of the pulsed magnetic field is 3A, the magnetic induction intensity is 1.47T, and the aging treatment time is 10h.

[0039] Testing revealed that the tensile strength of the aged Mg-Gd-Zr alloy was 321 MPa, but the elongation increased to 5.4%.

[0040] Figure 1 This is a TEM image of the Mg-Gd-Zr alloy after aging treatment in Example 2. Figure 1 As can be seen from ab, after aging treatment under pulsed magnetic field conditions, the alloy grain boundaries exhibit a distinct serrated structure; from Figure 1 It is evident that the size of the internal grain-strengthening phase is significantly increased, indicating that this treatment effectively enhances the directional precipitation ability of the strengthening phase. The pulsed magnetic field, through the synergistic effect of electromagnetic force and Joule heating, accelerates the diffusion of solute atoms, enabling the directional precipitation of the strengthening phase within the matrix. A possible reason is that in magnesium-gadolinium-yttrium (Mg-Gd-Y) alloys, the main alloying element gadolinium (Gd) is a ferromagnetic material. When a pulsed magnetic field is applied, the Lorentz force acts on the dissolved atoms, providing a directional driving force for their migration. The pulsed magnetic field causes the alloy's strengthening phase to form a strong distribution along a single precipitation direction, while exhibiting a weak distribution in the other two directions. This optimized distribution pattern not only ensures improved alloy strength but also provides more space for dislocation movement and coordination, thereby synergistically improving the alloy's strength and ductility.

[0041] Example 3

[0042] Repeat Example 1, except that in S2, the current of the pulsed magnetic field is 5A, the magnetic induction intensity is 2.45T, and the aging treatment time is 8h.

[0043] Testing revealed that the tensile strength of the aged Mg-Gd-Zr alloy was 318.9 MPa, but the elongation increased to 6.6%.

[0044] Comparative Example 1

[0045] Repeat Example 1, except that in S2, the aging treatment is carried out at 225°C for 12 hours under no pulsed magnetic field conditions.

[0046] Testing revealed that the tensile strength of the Mg-Gd-Zr alloy after aging treatment was 320.2 MPa, but the elongation decreased to 3.9%.

[0047] Figure 2 The TEM image shows the Mg-Gd-Zr alloy after aging treatment obtained in Comparative Example 1, as shown below. Figure 2 As shown in Figure a, coarse rare earth enriched phases are distributed along the alloy grain boundaries, which are linear; as... Figure 2 b to Figure 2 As shown in d, the strengthening phase inside the grain exhibits a fine and uniform dotted distribution.

[0048] After the conventional aging process compared to Example 1, the strengthening phase will move along [ 100]、[10 0] and [0] 10] Crystalline precipitation, these crystallines correspond to the three slip directions of the slip plane [ 20]、[1 10] and [2] [0] They are perpendicular to each other. This structure significantly restricts dislocation movement induced by slip planes, thereby promoting twinning and crack initiation. While this process increases the alloy's strength, it also reduces its ductility.

[0049] Figure 3 The figures show the microstructure of the fracture surface of the extruded Mg-Gd-Zr alloy described in Example 1, as well as the aged Mg-Gd-Zr alloys obtained in Examples 1-3 and Comparative Example 1 after tensile fracture. As can be seen from the figures, the fracture surface of the extruded Mg-Gd-Zr alloy exhibits numerous irregular protrusions and depressions, and sparse dimples. Figure 3 a). After the conventional aging process described in Comparative Example 1, Figure 3 b. Fine cleavage planes are visible, indicating a decrease in plasticity. After the aging treatment described in Examples 1-3, the fracture surface of the aging-treated Mg-Gd-Zr alloy has deeper dimples, see [reference]. Figure 3 Of particular note is that after the aging treatment described in Example 3, the fracture dimples of the alloy reached their minimum and deepest, resulting in the highest elongation of the alloy aged by this treatment, reaching 6.6%. It is evident that, compared to the conventional aging treatment described in Comparative Example 1, the aging treatment method of the present invention more readily forms a fracture structure conducive to improved plasticity.

[0050] The comparison shows that, compared with traditional aging treatment, the aging treatment of the present invention under pulsed magnetic field conditions can achieve synergistic enhancement of the strength and plasticity of Mg-Gd-Zr alloy, and the aging treatment time is shorter.

[0051] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

Claims

1. An aging treatment method of a Mg-Gd-Zr alloy, characterized by, Includes the following steps: S1. Provides extruded Mg-Gd-Zr alloys; S2. The extruded Mg-Gd-Zr alloy is aged at 220-230℃ for 6-8 hours under a pulsed magnetic field, and then cooled to obtain the aged Mg-Gd-Zr alloy. The pulsed magnetic field has a current of 1-5A, a frequency of 12-16Hz, and a duty cycle of 45-55%.

2. The method of claim 1, wherein The preparation method of extruded Mg-Gd-Zr alloy includes the following steps: preheating the cast Mg-Gd-Zr alloy to 385-395℃ and then extruding it to obtain the alloy; wherein, during the extrusion process, the extrusion speed is 0.2-0.6 mm / s, the temperature of the extrusion cylinder is 430-440℃, the temperature of the extrusion die is 295-305℃, and the extrusion ratio is 8-12.

3. The method of claim 1, wherein the aging treatment is performed at a temperature of 150 to 250°C for 1 to 100 hours. The Mg-Gd-Zr alloy is a Mg-Gd-Y-Nd-Zr alloy, preferably a Mg-8Gd-4Y-1Nd-0.5Zr alloy.

4. The method of aging according to any one of claims 1 to 3, characterized in that, In S2, the extruded Mg-Gd-Zr alloy is aged at 222-228℃ for 6.5-7 hours under a pulsed magnetic field.

5. The method of aging according to any one of claims 1 to 3, wherein In S2, the current in the pulsed magnetic field is 2-4A.

6. The method of aging according to any one of claims 1 to 3, wherein In S2, the magnetic induction intensity of the pulsed magnetic field is 0.45-2.5T.

7. The method of aging according to any one of claims 1 to 3, wherein In S2, the frequency of the pulsed magnetic field is 13-15Hz, and the duty cycle is 48-52%.

8. The time-sensitive processing method according to any one of claims 1-3, characterized in that, In S2, the tensile strength of the aged Mg-Gd-Zr alloy is ≥305MPa and the elongation is ≥5%.

9. The time-sensitive processing method according to any one of claims 1-3, characterized in that, In S2, the hardness of the aged Mg-Gd-Zr alloy is ≥105HV.

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