Heat treatment method for improving fatigue properties of rare earth magnesium alloy and product thereof

Abstract

The present disclosure relates to the technical field of rare earth magnesium alloy heat treatment, and provides a heat treatment method for improving the fatigue performance of a rare earth magnesium alloy and a product thereof. The heat treatment method comprises: sequentially performing high-temperature homogenization treatment, rapid cooling treatment and aging treatment on the rare earth magnesium alloy; wherein the high-temperature homogenization treatment comprises: first heating the rare earth magnesium alloy from room temperature to 495-505 DEG C and keeping it for 3.5-4.5 h, and then second heating it to 515-525 DEG C and keeping it for 22-26 h. The heat treatment method for improving the fatigue performance of a rare earth magnesium alloy and the product thereof provided by the present disclosure can make the magnesium matrix of the obtained product rich in high-density stacking faults, and the inside of the crystal grains uniformly distribute a network structure, thereby achieving the effect of significantly improving the fatigue performance (for example, long-life fatigue performance) of the rare earth magnesium alloy.

Description

Technical Field

[0001] This disclosure relates to the field of heat treatment technology for rare earth magnesium alloys, and for example to a heat treatment method and product for improving the fatigue properties of rare earth magnesium alloys. Background Technology

[0002] Magnesium alloys possess numerous superior properties, including low density, high specific strength and stiffness, excellent electromagnetic shielding performance, superior vibration damping, dimensional stability, damping properties, ease of casting and machining, and sustainable recyclability. Furthermore, due to the abundance of magnesium resources, they have broad application prospects.

[0003] Currently, adding rare earth elements to magnesium alloys can significantly improve their static mechanical properties. However, the fatigue performance of magnesium alloys with added rare earth elements (i.e., rare earth magnesium alloys) remains insufficient, especially in terms of long-life fatigue. Furthermore, adding rare earth elements and zinc to magnesium alloys can form a hard, long-term packed ordered structure (LPSO) lamellar phase within the alloy, greatly improving its static mechanical properties. However, between the hard LPSO lamellar phases, there are still soft α-Mg layers with weaker mechanical properties, and due to the insufficient fatigue resistance of the soft α-Mg layer, fatigue cracks often initiate here. Just as the "weakest link" principle applies to the fatigue performance of rare earth magnesium alloys, the fatigue performance depends on the soft α-Mg layer in their microstructure. Therefore, although the hard LPSO lamellar phase can significantly improve the static mechanical properties of magnesium alloys, their fatigue performance under long-life cyclic loading remains insufficient.

[0004] Therefore, rare earth magnesium alloys cannot yet be used in critical structural components that require long-term cyclic loading, which limits their application prospects in the automotive, aerospace, and other fields. Summary of the Invention

[0005] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide a heat treatment method and product for improving the fatigue performance of rare earth magnesium alloys, so that the magnesium matrix of the obtained product is rich in high-density stacking faults and has a network structure uniformly distributed inside its grains, thereby achieving the effect of significantly improving the fatigue performance (e.g., long-life fatigue performance) of rare earth magnesium alloys.

[0006] The purpose of this disclosure is achieved through the following technical solution:

[0007] On the one hand, a heat treatment method for improving the fatigue properties of rare earth magnesium alloys is provided. The heat treatment method includes: subjecting the rare earth magnesium alloy to high-temperature homogenization treatment, rapid cooling treatment, and aging treatment in sequence; wherein, the high-temperature homogenization treatment includes: first heating the rare earth magnesium alloy from room temperature to 495-505℃ and holding it at that temperature for 3.5-4.5 hours, and then heating it a second time to 515-525℃ and holding it at that temperature for 22-26 hours.

[0008] In some examples, the high-temperature homogenization process includes: first heating the rare earth magnesium alloy from room temperature to 500°C and holding it at that temperature for 4 hours, and then heating it a second time to 520°C and holding it at that temperature for 24 hours.

[0009] It is worth noting that the heat treatment method provided in this disclosure can significantly improve the fatigue performance of the rare earth magnesium alloy, especially its long-life fatigue performance. No obvious long-period stacked ordered structure (LPSO) lamellar phases were observed in the product obtained after the heat treatment method (i.e., the resulting product). The solute elements of the rare earth magnesium alloy (e.g., rare earth elements, or rare earth elements and zinc elements) mainly form a large number of stacking faults on the basal surface of the resulting product, accompanied by some unevenly distributed prism-faceted β-nanometer precipitates. Furthermore, at the mesoscale, a special network structure is formed within the grains of the resulting product. Specifically, the high-temperature homogenization treatment enables the solute elements to be uniformly distributed in the magnesium matrix of the resulting product. Moreover, since the effect of the hard LPSO lamellars on improving the fatigue performance, especially the long-life fatigue performance, of the rare earth magnesium alloy is limited, the rapid cooling treatment avoids the excessive consumption of limited solute elements due to the formation of too many LPSO lamellar phases. In addition, the aging treatment enables the uniformly distributed solute elements to form a large number of stacking faults on the basal surface of the resulting product.

[0010] In some embodiments, the rare earth magnesium alloy is composed of the following components by mass percentage: gadolinium 14%, zinc 2.3%, zirconium 0.6%, with the balance being magnesium.

[0011] It should be noted that, in some of the above embodiments, the rare earth magnesium alloy may also be referred to as Mg-Gd-Zn-Zr rare earth magnesium alloy, and its composition may also be written as Mg-14Gd-2.3Zn-0.6Zr (wt%). In this case, the solute elements of the rare earth magnesium alloy are rare earth gadolinium and zinc.

[0012] In some embodiments, the rate of the first heating is 2.5 to 3.5 °C / min.

[0013] In some examples, the initial heating rate is 3°C / min.

[0014] In some of the above embodiments, by controlling the rate of the first heating, the rare earth magnesium alloy can be heated rapidly, thereby saving as much time as possible while ensuring the processing effect.

[0015] In some embodiments, the rate of the second heating is 1 to 1.5 °C / min.

[0016] In some examples, the rate of the second heating is 1°C / min.

[0017] In some of the above embodiments, by controlling the rate of the second heating, rapid heating can be transformed into slow heating to avoid overheating, thereby preventing changes in the properties of the rare earth magnesium alloy after the high-temperature homogenization treatment due to overheating.

[0018] In some embodiments, the rapid cooling process includes: immediately placing the rare earth magnesium alloy that has undergone the high-temperature homogenization treatment in a hot water bath to cool it to room temperature.

[0019] In some embodiments, the temperature of the hot water bath is 85–95°C.

[0020] In some examples, the temperature of the hot water bath is 90°C.

[0021] In some of the above embodiments, cooling by the hot water bath not only ensures that the material after the rapid cooling treatment has relatively good plasticity, but also prevents the material from cracking.

[0022] It should be noted that during the process of cooling the rare earth magnesium alloy that has undergone the high-temperature homogenization treatment (i.e., the treated rare earth magnesium alloy) to room temperature, since the temperature of the treated rare earth magnesium alloy is much higher than the temperature of the hot water bath, when the treated rare earth magnesium alloy is placed in the hot water bath, the hot water will first perform initial cooling on the treated rare earth magnesium alloy, and then the hot water and the initially cooled rare earth magnesium alloy will cool together to room temperature.

[0023] In some embodiments, the aging treatment includes: heating the rare earth magnesium alloy that has undergone the rapid cooling treatment to 275-285°C for a third time, then heating it to 295-305°C for a fourth time and holding it at that temperature for 46-50 hours, and finally air-cooling it to room temperature.

[0024] In some examples, the aging process includes: heating the rare earth magnesium alloy that has undergone the rapid cooling treatment to 280°C for a third time, then heating it to 300°C for a fourth time and holding it at that temperature for 48 hours, and finally air-cooling it to room temperature.

[0025] In some of the above embodiments, by controlling the temperature of the aging treatment, a large number of high-density stacking faults can be formed in the material after the aging treatment.

[0026] In some embodiments, the rate of the third heating is 2.5 to 3.5 °C / min.

[0027] In some examples, the rate of the third heating is 3°C / min.

[0028] In some of the above embodiments, by controlling the rate of the third heating, the rare earth magnesium alloy that has undergone the rapid cooling treatment can be rapidly heated, thereby saving as much time as possible while ensuring the treatment effect.

[0029] In some embodiments, the rate of the fourth heating is 1 to 1.5 °C / min.

[0030] In some examples, the rate of the fourth heating is 1°C / min.

[0031] In some of the above embodiments, by controlling the rate of the fourth heating, rapid heating can be transformed into slow heating to avoid overheating, thereby preventing changes in the properties of the rare earth magnesium alloy after the aging treatment due to overheating.

[0032] In some embodiments, prior to the high-temperature homogenization treatment, the rare earth magnesium alloy is further coated with charcoal powder.

[0033] It should be noted that the magnesium element in the rare earth magnesium alloy is chemically reactive and readily oxidizes or even burns at high temperatures. In some of the above embodiments, by covering the rare earth magnesium alloy with charcoal powder, a protective layer can be formed to isolate it from air to a certain extent, thereby protecting the magnesium element in the covered rare earth magnesium alloy from oxidation. Furthermore, since charcoal is oxyphilic under high-temperature conditions, the charcoal powder can react with oxygen in the surrounding environment (e.g., the heat treatment chamber) to consume the oxygen, thereby further protecting the magnesium element in the covered rare earth magnesium alloy from oxidation. In addition, the charcoal powder is very inexpensive, thus saving costs.

[0034] In some embodiments, the particle size of the charcoal powder is 300-350 mesh.

[0035] In some of the above embodiments, the particle size of the charcoal powder is controlled to be 300-350 mesh, which means that the charcoal powder is ultrafine charcoal powder with fine particles and small gaps between particles, which makes the formed protective layer more compact, so as to better isolate air and thus better protect the magnesium element in the covered rare earth magnesium alloy from oxidation.

[0036] On the other hand, a product prepared by the heat treatment method as described in any of the above embodiments is provided.

[0037] The beneficial effects of this disclosure are:

[0038] 1. The heat treatment method disclosed herein for improving the fatigue properties of rare earth magnesium alloys can significantly improve the fatigue properties of rare earth magnesium alloys, especially the long-life fatigue properties. No obvious LPSO lamellar phase was observed in the obtained product. The solute elements of rare earth magnesium alloys mainly form a large number of stacking faults on the basal surface of the obtained product, accompanied by some unevenly distributed prism-faced β nano-precipitates. In addition, at the mesoscale, a special network structure is formed inside the grains of the obtained product.

[0039] 2. The present invention discloses a heat treatment method for improving the fatigue performance of rare earth magnesium alloys, wherein high-temperature homogenization treatment enables solute elements to be uniformly distributed in the magnesium matrix of the resulting product.

[0040] 3. The heat treatment method disclosed herein for improving the fatigue properties of rare earth magnesium alloys can avoid the excessive consumption of limited solute elements due to the excessive formation of LPSO lamellar phases through rapid cooling treatment.

[0041] 4. A heat treatment method for improving the fatigue properties of rare earth magnesium alloys disclosed herein, wherein aging treatment enables uniformly distributed solute elements to form a large number of stacking faults on the base surface of the resulting product. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in this disclosure, the accompanying drawings used in some embodiments of this disclosure will be briefly described below. Obviously, the drawings described below are merely drawings of some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings. Furthermore, the drawings described below can be regarded as schematic diagrams and are not intended to limit the actual process of the methods involved in the embodiments of this disclosure.

[0043] Figure 1 The graph shows the relationship between fatigue life and cyclic loading stress amplitude for the product obtained in Example 1 (i.e., the rare earth magnesium alloy obtained after heat treatment by the method provided in this disclosure) and the LPSO-strengthened rare earth magnesium alloy of Comparative Example 1 (i.e., the rare earth magnesium alloy obtained after heat treatment by another method).

[0044] Figure 2The images show the nanoscale microstructure of the product obtained in Example 1 and the LPSO-strengthened rare earth magnesium alloy of Comparative Example 1; where (m) is the nanoscale microstructure of the LPSO-strengthened rare earth magnesium alloy of Comparative Example 1; and (n) is the nanoscale microstructure of the product obtained in Example 1.

[0045] Figure 3 The images shown are mesoscopic microstructures of the product obtained in Example 1; where (a) is a 200x microstructure image; (b) is a 500x microstructure image; (c) is a 1000x microstructure image; and (d) is a 2000x microstructure image. Detailed Implementation

[0046] The technical solutions in some embodiments of this disclosure will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments provided in this disclosure, all other embodiments obtained by those skilled in the art are within the scope of protection of this disclosure.

[0047] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

[0048] In describing some embodiments, the expression "A and / or B" may be used. It is readily understood that "A and / or B" includes the following three combinations: A only, B only, and a combination of A and B.

[0049] As used herein, “approximately” includes the values ​​stated and the average value within an acceptable range of deviation from the given values, wherein the acceptable range of deviation is determined by a person skilled in the art taking into account the measurement under discussion and the error associated with the measurement of the given quantity (i.e., the limitations of the measurement system).

[0050] The term "room temperature" refers to a normal temperature or ambient temperature, which is typically approximately 25°C. In some embodiments of this disclosure, the temperature range of "room temperature" can be 15–35°C.

[0051] Example 1

[0052] A heat treatment method for improving the fatigue properties of rare earth magnesium alloys, comprising:

[0053] S1. The rare earth magnesium alloy is coated with charcoal powder with a particle size of 300 mesh; wherein the rare earth magnesium alloy is a Mg-Gd-Zn-Zr rare earth magnesium alloy, and its composition is Mg-14Gd-2.3Zn-0.6Zr (wt%).

[0054] S2. The rare earth magnesium alloy obtained in S1 is heated from room temperature to 500℃ at a rate of 3℃ / min and held for 4h, and then heated to 520℃ at a rate of 1℃ / min and held for 24h.

[0055] S3. Immediately place the rare earth magnesium alloy obtained in S2 into a hot water bath at 90°C to cool to room temperature;

[0056] S4. The rare earth magnesium alloy obtained in S3 is heated to 280℃ at a rate of 3℃ / min, then heated to 300℃ at a rate of 1℃ / min and held at that temperature for 48h, and finally air-cooled to room temperature.

[0057] Example 2

[0058] A heat treatment method for improving the fatigue properties of rare earth magnesium alloys, comprising:

[0059] S1. The rare earth magnesium alloy is coated with charcoal powder with a particle size of 325 mesh; wherein, the rare earth magnesium alloy is Mg-Gd-Zn-Zr rare earth magnesium alloy, and its composition is Mg-14Gd-2.3Zn-0.6Zr (wt%).

[0060] S2. The rare earth magnesium alloy obtained in S1 is heated from room temperature to 495℃ at a rate of 2.5℃ / min and held for 3.5h, and then heated to 515℃ at a rate of 1.25℃ / min and held for 22h.

[0061] S3. Immediately place the rare earth magnesium alloy obtained in S2 into a hot water bath at 85°C to cool to room temperature;

[0062] S4. The rare earth magnesium alloy obtained in S3 is heated to 275℃ at a rate of 2.5℃ / min, then heated to 295℃ at a rate of 1.25℃ / min and held at that temperature for 46 hours, and finally air-cooled to room temperature.

[0063] Example 3

[0064] A heat treatment method for improving the fatigue properties of rare earth magnesium alloys, comprising:

[0065] S1. The rare earth magnesium alloy is coated with charcoal powder with a particle size of 350 mesh; wherein, the rare earth magnesium alloy is Mg-Gd-Zn-Zr rare earth magnesium alloy, and its composition is Mg-14Gd-2.3Zn-0.6Zr (wt%).

[0066] S2. The rare earth magnesium alloy obtained in S1 is heated from room temperature to 505℃ at a rate of 3.5℃ / min and held for 4.5h, and then heated to 525℃ at a rate of 1.5℃ / min and held for 26h.

[0067] S3. Immediately place the rare earth magnesium alloy obtained in S2 into a hot water bath at 90°C to cool to room temperature;

[0068] S4. The rare earth magnesium alloy obtained in S3 is heated to 285℃ at a rate of 3.5℃ / min, then heated to 305℃ at a rate of 1.5℃ / min and held at that temperature for 50h, and finally air-cooled to room temperature.

[0069] Compare with Example 1

[0070] The rare earth magnesium alloy strengthened by LPSO was compared with the product obtained in Example 1 (i.e., the rare earth magnesium alloy obtained after being treated by the heat treatment method provided in this disclosure). The rare earth magnesium alloy strengthened by LPSO is a rare earth magnesium alloy obtained by treating a Mg-Gd-Zn-Zr rare earth magnesium alloy by another heat treatment method. The Mg-Gd-Zn-Zr rare earth magnesium alloy used in Comparative Example 1 is the same as the Mg-Gd-Zn-Zr rare earth magnesium alloy used in Example 1, and its composition is Mg-14Gd-2.3Zn-0.6Zr (wt%).

[0071] The method for preparing the LPSO-strengthened rare earth magnesium alloy includes: heating the Mg-Gd-Zn-Zr rare earth magnesium alloy from room temperature to 500℃ at a rate of 3℃ / min and holding it at that temperature for 2h, then heating it to 520℃ at a rate of 1℃ / min and holding it at that temperature for 12h, and finally cooling it to room temperature at a rate of 1℃ / min to obtain the alloy.

[0072] Test results

[0073] To verify the effect of the heat treatment method provided in this disclosure on improving the fatigue performance of rare earth magnesium alloys, the fatigue performance and structural characteristics of the product obtained in Example 1 (i.e., the rare earth magnesium alloy obtained after treatment by the heat treatment method provided in this disclosure) were tested, and compared with the LPSO-strengthened rare earth magnesium alloy of Comparative Example 1 (i.e., the rare earth magnesium alloy obtained after treatment by another heat treatment method). The results are as follows: Figures 1-3 As shown.

[0074] It should be noted that although the chemical composition of the LPSO-strengthened rare earth magnesium alloy in Comparative Example 1 is the same as that of the product obtained in Example 1, the interior of the LPSO-strengthened rare earth magnesium alloy in Comparative Example 1 is mainly composed of LPSO lamellar phase, which is different from the interior of the product obtained in Example 1.

[0075] On the one hand, according to Figure 1 It can be seen that, for the LPSO-strengthened rare earth magnesium alloy of Comparative Example 1, the loading of 1E+09 (i.e., 1×10⁻⁹) results in a higher yield. 9No failure occurred after 10 cycles, with a maximum load of 77 MPa, and all loaded samples survived; for the product obtained in Example 1, loading 1E9 (i.e., 1 × 10⁻⁹) was performed. 9 No failures were observed after 10 cycles, with a maximum load of 115 MPa, and all loaded samples survived. Therefore, the heat treatment method provided in this disclosure can improve the long-life fatigue performance of rare earth magnesium alloys by approximately 50%.

[0076] On the other hand, since basal slip is the easiest slip system to initiate in magnesium alloys, increasing the critical shear stress for initiating basal slip is beneficial to improving the fatigue performance of magnesium alloys. Simultaneously, the LPSO lamellar phases and stacking faults distributed along the basal plane can increase the basal barrier, thereby increasing the critical shear stress for initiating basal slip. Based on this, according to Figure 2 As can be seen, in the LPSO-strengthened rare-earth magnesium alloy of Comparative Example 1, the solute elements (i.e., rare-earth gadolinium and zinc) are more concentrated, forming a thick LPSO lamellar phase and a relatively thick soft α-Mg layer. However, the basal slip within this relatively thick soft α-Mg layer is still easily initiated. In contrast, in the product obtained in Example 1, the solute elements (i.e., rare-earth gadolinium and zinc) are relatively uniformly concentrated, forming a high-density stacking fault. A thinner soft α-Mg layer exists (i.e., the thickness of the soft α-Mg layer is reduced). The initiation of basal slip within this thinner soft α-Mg layer is easily suppressed by the surrounding high-density stacking faults, thus being more conducive to improving fatigue performance.

[0077] On the other hand, according to Figure 3 It can be seen that, at the mesoscale, the product obtained in Example 1 has a network structure inside its grains. When basal slip is activated, this network structure helps to limit the dislocation slip distance, making the dislocations more evenly distributed in the network structure, reducing the degree of dislocation pile-up, and inhibiting premature fatigue cracking, thereby improving macroscopic fatigue performance.

[0078] Therefore, the heat treatment method and product for improving the fatigue performance of rare earth magnesium alloys provided in this disclosure can make the magnesium matrix of the product rich in high-density stacking faults and uniformly distributed network structure inside its grains, thereby achieving the effect of significantly improving the fatigue performance (e.g., long-life fatigue performance) of rare earth magnesium alloys.

[0079] The above description is merely a preferred embodiment of this disclosure. It should be understood that this disclosure is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this disclosure should be within the protection scope of the appended claims.

Claims

1. A heat treatment method for improving the fatigue properties of rare earth magnesium alloys, characterized in that, include: The rare earth magnesium alloy was subjected to high-temperature homogenization treatment, rapid cooling treatment and aging treatment in sequence. The high-temperature homogenization treatment includes: heating the rare earth magnesium alloy from room temperature to 495~505℃ for the first time and holding it at that temperature for 3.5~4.5h, and then heating it to 515~525℃ for the second time and holding it at that temperature for 22~26h. The rare earth magnesium alloy has the following composition by mass percentage: gadolinium 14%, zinc 2.3%, zirconium 0.6%, and magnesium 83.1%; The first heating rate is 2.5~3.5℃ / min; and / or the second heating rate is 1~1.5℃ / min.

2. The heat treatment method according to claim 1, characterized in that, The rapid cooling process includes immediately placing the rare earth magnesium alloy that has undergone the high-temperature homogenization treatment in a hot water bath to cool it to room temperature.

3. The heat treatment method according to claim 2, characterized in that, The temperature of the hot water bath is 85~95℃.

4. The heat treatment method according to claim 1, characterized in that, The aging process includes: heating the rare earth magnesium alloy that has undergone the rapid cooling treatment to 275~285℃ for the third time, then heating it to 295~305℃ for the fourth time and holding it at that temperature for 46~50 hours, and finally air cooling it to room temperature.

5. The heat treatment method according to claim 4, characterized in that, The rate of the third heating is 2.5~3.5℃ / min; and / or the rate of the fourth heating is 1~1.5℃ / min.

6. The heat treatment method according to claim 1, characterized in that, Prior to the high-temperature homogenization treatment, the process further includes covering the rare earth magnesium alloy with charcoal powder.

7. The heat treatment method according to claim 6, characterized in that, The charcoal powder has a particle size of 300-350 mesh.

8. The product obtained by the heat treatment method according to any one of claims 1 to 7.

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