Heat treatment method for regulating and controlling performance of soluble rare earth magnesium alloy

Abstract

According to the heat treatment method for regulating and controlling the performance of the soluble rare earth magnesium alloy, a two-stage solid solution and three-stage cooling method is adopted, it is ensured that alloy elements are dissolved in a matrix as many as possible, and meanwhile the problems of thermal stress, coarse grains and the like are solved. According to the two-stage solid solution heat treatment mode, the solid solution effect of rare earth elements such as Gd and Y in the alloy can be remarkably regulated and controlled, then the number, form and distribution of subsequent precipitated phases are remarkably influenced, and the alloy performance can be regulated and controlled within a large range. Precipitation of solid solution elements in the cooling process is effectively restrained through the two-section rapid cooling process, meanwhile, thermal stress in cast ingots can be effectively reduced through the slow cooling process, and the subsequent material extrusion difficulty is reduced. And the two-stage aging method combining pre-aging and aging can remarkably shorten the time required for the alloy to reach the peak aging, and the production efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation and processing of metal materials, and particularly relates to a heat treatment method for regulating the properties of soluble rare earth magnesium alloys. Background Art

[0002] The core of shale oil and gas exploitation is the horizontal well staged fracturing technology, and downhole plugging tools are the core equipment of the horizontal well staged fracturing technology. Traditional plugging tools are processed from materials such as alloy steel and cast iron. After fracturing, it is necessary to drill and grind them into debris several kilometers deep underground and discharge them back into the wellbore to achieve unobstructed wellbore for oil and gas production. Magnesium alloys have the characteristics of low density, high specific strength, and poor corrosion resistance (i.e., good corrosion performance). Soluble plugging tools (such as bridge plugs, ball seats, etc.) developed with them can be corroded and dissolved under the action of backflow fluid and formation water after construction, without the need for drilling and grinding construction, saving time and cost, and avoiding the risk of sticking and jamming at the same time.

[0003] The distribution areas of oil and gas resources are different and the burial depths vary, resulting in significant differences in the service environments (such as temperature, pressure, salinity, etc.) of soluble tools, which greatly affects the dissolution rate of the tools and further affects the plugging reliability of the tools. Based on this, soluble materials with different properties need to be developed for different operating conditions. The conventional method of developing new materials by changing alloy components has led to a sharp increase in the cost of soluble tools. Using heat treatment methods to regulate the properties of soluble alloys has become a new research idea.

[0004] In the past, the heat treatment of soluble rare earth magnesium alloys used a method of one-stage solution treatment followed by air cooling. The range of regulating material properties by this heat treatment method is small. High-strength soluble magnesium alloys mostly contain elements such as Gd, Y, Zn, Ni, and Cu. Wei et al. started from the aspect of composition ratio, increased the Zn content, and decreased the Gd and Y contents, which could effectively improve the alloy properties within a certain range. However, this method has a small change in composition and a small corresponding change in material properties (Materials Characterization, 2020, 169: 110670). Chen Fan et al. from Central South University studied the influence of aging on property regulation in high-strength magnesium alloys and found that a single heat treatment step is not ideal for regulating alloy properties. For example, the elongation rate in the T4 state can reach 18%, while the elongation rate in the T6 state is only 0.5%. Although the material strength has increased, its comprehensive performance shows a downward trend, which is not an ideal regulation method (The Chinese Journal of Nonferrous Metals, http: / / kns.cnki.net / kcms / detail / 43.1238.TG.20230518.1715.006.html). Summary of the Invention

[0005] The object of the present invention is to provide a heat treatment method for regulating the properties of a soluble rare earth magnesium alloy, so as to overcome the above-mentioned technical problems existing in the prior art.

[0006] To this end, the technical solution provided by the present invention is as follows: A heat treatment method for regulating the properties of a soluble rare earth magnesium alloy, comprising the following steps: Step 1) performing two-stage solution treatment on the soluble rare earth magnesium alloy; Step 2) adopting three-stage cooling, wherein the cooling rate of the first stage is not less than that of the third stage, and the cooling rate of the second stage is less than that of the third stage; Step 3) extruding into a bar after cooling, and after extrusion, performing pre-aging on the bar, and then performing aging. In step 1), the first-stage solution temperature of the two-stage solution treatment is 450-485°C, and the solution time is 15-40 h.

[0007] In step 1), the second-stage solution temperature of the two-stage solution treatment is 500-535°C, and the solution time is 10-30 h.

[0008] In step 2), the cooling rate of the first stage is 70-150°C / s, and the cooling temperature range is from the second-stage solution temperature of 500-535°C to 350-380°C.

[0009] In step 2), the cooling rate of the second stage is 0.5-3°C / s, and the cooling temperature range is from the first-stage cooling termination temperature of 350-380°C to 290-330°C.

[0010] In step 2), the cooling rate of the third stage is 50-100°C / s, and the cooling temperature range is from the second-stage cooling termination temperature of 290-330°C to room temperature.

[0011] In step 3), the pre-aging temperature is 100-150°C, and the pre-aging time is 1-3 h.

[0012] In step 3), the aging temperature is 150-250°C, and the aging time is 30-80 h.

[0013] The soluble rare earth magnesium alloy contains Mg3RE and Mg5RE phases.

[0014] The soluble rare earth magnesium alloy is a Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy.

[0015] The beneficial effects of the present invention are: The heat treatment method for regulating the properties of the soluble rare earth magnesium alloy provided by the present invention adopts a two-stage solution treatment and a three-stage cooling method to ensure that as many alloying elements as possible are dissolved in the matrix, while also avoiding problems such as thermal stress and coarse grains.

[0016] Through the two-stage solution heat treatment method of the present invention, the solution effect of rare earth elements such as Gd and Y in the alloy can be significantly regulated, thereby significantly affecting the quantity, morphology and distribution of the subsequent precipitated phases, and the properties of the alloy can be regulated within a large range. The two-stage rapid cooling process effectively inhibits the precipitation of the solution elements during the cooling process, while the slow cooling process can effectively reduce the thermal stress in the ingot and reduce the difficulty of subsequent material extrusion. The two-stage aging method combining pre-aging and aging can significantly shorten the time required for the alloy to reach peak aging and improve production efficiency.

[0017] The process of the present invention is simple and only requires a heat treatment furnace to complete, without excessive upfront investment in equipment, and it also has important reference significance for soluble magnesium alloys of other systems. Brief Description of the Drawings

[0018] Figure 1 are the metallographic diagram and scanning electron microscope pictures of the heat-treated soluble magnesium alloy in Example 2 (a, d) of the present invention; Figure 2 are the metallographic diagram and scanning electron microscope pictures of the heat-treated soluble magnesium alloy in Example 3 (b, e) of the present invention; Figure 3 are the metallographic diagram and scanning electron microscope pictures of the heat-treated soluble magnesium alloy in Example 4 (c, f) of the present invention; Figure 4 are the transmission electron microscope pictures of the heat-treated soluble magnesium alloy in Example 2 (a, b) of the present invention; Figure 5 are the transmission electron microscope pictures of the heat-treated soluble magnesium alloy in Example 3 (c, d) of the present invention; Figure 6 are the transmission electron microscope pictures of the heat-treated soluble magnesium alloy in Example 4 (e, f) of the present invention. Detailed Embodiments

[0019] The following specific embodiments illustrate the implementation manners of the present invention, and those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0020] Reference is now made to the accompanying drawings to describe exemplary embodiments of the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely, and to fully convey the scope of the present invention to those skilled in the art. The terms in the exemplary embodiments shown in the drawings are not limitations on the present invention.

[0021] Unless otherwise specified, the terms used herein (including scientific and technical terms) have the ordinary meaning understood by those skilled in the art. Additionally, it can be understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant fields, and should not be understood in an idealized or overly formal sense.

[0022] Example 1 The present invention provides a heat treatment method for regulating the properties of soluble rare earth magnesium alloys, comprising the following steps: Step 1) Perform a two-stage solution treatment on the soluble rare earth magnesium alloy; Step 2) Adopt a three-stage cooling, wherein the cooling rate of the first stage is not less than that of the third stage, and the cooling rate of the second stage is less than that of the third stage; Step 3) After cooling, extrude into bars. After extrusion, perform pre-aging on the bars, and then perform aging. Among them, in step 1), the first-stage solution temperature of the two-stage solution treatment is 450 - 485 °C, and the solution time is 15 - 40 h.

[0023] In step 1), the second-stage solution temperature of the two-stage solution treatment is 500 - 535 °C, and the solution time is 10 - 30 h.

[0024] In step 2), the cooling rate of the first stage is 70 - 150 °C / s, and the cooling temperature range is from the second-stage solution temperature of 500 - 535 °C to 350 - 380 °C.

[0025] In step 2), the cooling rate of the second stage is 0.5 - 3 °C / s, and the cooling temperature range is from the termination temperature of the first-stage cooling of 350 - 380 °C to 290 - 330 °C.

[0026] In step 2), the cooling rate of the third stage is 50 - 100 °C / s, and the cooling temperature range is from the termination temperature of the second-stage cooling of 290 - 330 °C to room temperature.

[0027] In step 3), the pre-aging temperature is 100 - 150 °C, and the pre-aging time is 1 - 3 h.

[0028] In step 3), the aging temperature is 150 - 250 °C, and the aging time is 30 - 80 h.

[0029] The present invention adopts a two-stage solution treatment and a three-stage cooling method to ensure that as many alloying elements as possible are dissolved in the matrix, while also avoiding problems such as thermal stress and grain coarsening. Among them, through the two-stage solution heat treatment method, the solution effect of rare earth elements such as Gd and Y in the alloy can be significantly regulated, and then the quantity, morphology and distribution of the subsequent precipitated phases are significantly affected, and the alloy properties can be regulated within a large range. The precipitation of solution elements during the cooling process is effectively inhibited through the two-stage rapid cooling process, while the slow cooling process can effectively reduce the thermal stress in the ingot and reduce the difficulty of subsequent material extrusion. The two-stage aging method combining pre-aging and aging can significantly shorten the time required for the alloy to reach peak aging and improve production efficiency.

[0030] Example 2 The present invention provides a heat treatment method for regulating the properties of soluble rare earth magnesium alloys. Taking the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy as an example, the specific process is as follows: First, heat the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy ingot to 470 °C and hold for 18 h, and then heat it to 520 °C and hold for 12 h. Cool it to 370 °C by water cooling, with a cooling rate of about 100 °C / s, then cool it to 300 °C by air cooling, with a cooling rate of about 0.5 °C / s, and finally cool it to room temperature by water cooling, with a cooling rate of about 70 °C / s. After cooling, extrude it into a bar. After extrusion, pre-age the bar at 100 °C for 1 h, and then age it at 200 °C for 54 h. The mechanical properties and dissolution rate of the alloy are shown in Table 1. As can be seen from Figure 1 (a, d), under this solution treatment process of the alloy, various second phases have been largely re-dissolved into the magnesium matrix, and the second phases are no longer continuous. The largely re-dissolved second phases will provide potential for the precipitation of phases during the aging process. At the same time, the discontinuously distributed second phases will have a large contact area between the matrix and the corrosive medium during the corrosion process, accelerating the corrosion rate.

[0031] Example 3 The present invention provides a heat treatment method for regulating the properties of soluble rare earth magnesium alloys. Taking the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy as an example, the specific process is as follows: First, heat the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy ingot to 470 °C and hold for 24 h, then heat it to 500 °C and hold for 24 h. Cool it to 370 °C by water cooling with a cooling rate of about 120 °C / s, then cool it to 290 °C by air cooling with a cooling rate of about 1 °C / s, and finally cool it to room temperature by water cooling with a cooling rate of about 90 °C / s. After cooling, extrude it into a rod. After extrusion, pre-age the rod at 100 °C for 2 h, and then age it at 200 °C for 40 h. The mechanical properties and dissolution rate of the alloy are shown in Table 1. As can be seen from Figure 2 (b, e), continuous secondary phases and independent secondary phases are distributed in the alloy. After aging, the secondary phases that are not dissolved into the matrix (mainly LPSO phase) and the β' phase precipitated during the aging process jointly provide strength, while the continuous secondary phases will hinder the contact between the corrosive medium and the magnesium matrix, slightly reducing the corrosion rate.

[0032] Example 4 The present invention provides a heat treatment method for regulating the properties of soluble rare earth magnesium alloys. Taking the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy as an example, the specific process is as follows: First, heat the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy ingot to 470 °C and hold for 30 h, then heat it to 520 °C and hold for 24 h. Cool it to 380 °C by water cooling with a cooling rate of about 80 °C / s, then cool it to 310 °C by air cooling with a cooling rate of about 1 °C / s, and finally cool it to room temperature by water cooling with a cooling rate of about 70 °C / s. After cooling, extrude it into a rod. After extrusion, pre-age the rod at 100 °C for 1 h, and then age it at 200 °C for 61 h. The mechanical properties and dissolution rate of the alloy are shown in Table 1. As can be seen from Figure 3 (c, f), the secondary phases show a large-area continuous distribution, resulting in insufficient aging precipitation potential and low strength of the alloy. And the large-area continuous secondary phases will more significantly hinder the contact between the corrosive medium and the magnesium matrix, greatly reducing the corrosion rate.

[0033] Example 5 The present invention provides a heat treatment method for regulating the properties of soluble rare earth magnesium alloys. Taking the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy as an example, the specific process is as follows: First, heat the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy ingot to 480 °C and hold for 20 h, then heat it to 525 °C and hold for 18 h. Cool it to 370 °C by water cooling with a cooling rate of about 100 °C / s, then cool it to 320 °C by air cooling with a cooling rate of about 0.5 °C / s, and finally cool it to room temperature by water cooling with a cooling rate of about 100 °C / s. After cooling, extrude it into bars. After extrusion, pre-age the bars at 100 °C for 2 h, and then age at 200 °C for 65 h. The mechanical properties and dissolution rate are shown in Table 1.

[0034] Comparative Example 1 Take the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy as an example.

[0035] First, heat the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy ingot to 520 °C and hold for 24 h. Cool it to room temperature by air cooling with a cooling rate of about 0.5 °C / s. After cooling, extrude it into bars. After extrusion, age the bars at 200 °C for 54 h. The mechanical properties and dissolution rate are shown in Table 1.

[0036] Comparative Example 2 Take the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy as an example.

[0037] First, heat the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy ingot to 520 °C and hold for 24 h. Cool it to room temperature by a combination of air cooling and water cooling with a cooling rate of about 30 °C / s. After cooling, extrude it into bars. After extrusion, age the bars at 200 °C for 46 h. The mechanical properties and dissolution rate are shown in Table 1.

[0038] Comparative Example 3 Take the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy as an example.

[0039] First, heat the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu-0.8Ni alloy ingot to 520 °C and hold for 24 h. Cool it to room temperature by water cooling with a cooling rate of about 80 °C / s. After cooling, perform extrusion, and the material fractures in the extrusion cylinder during the extrusion process.

[0040] Table 1 Mechanical and dissolution property parameters of soluble magnesium alloys (Corrosion rate was tested in 3% KCl solution at 93 °C)

[0041] It can be seen from the experimental results that the properties of the alloy can be adjusted within a large range by the heat treatment method of the present invention. As shown in Table 1, for the soluble rare earth magnesium alloys obtained in Examples 2-5, the yield strength of the material can be adjusted between 349 and 378 MPa, the tensile strength can be adjusted between 401 and 436 MPa, the elongation can be adjusted between 3% and 8%, and the corrosion rate can be adjusted between 35 and 63 mg / cm 2 / h. Among them, the adjustment range of 80% of the corrosion rate is particularly important, indicating that alloy materials with low corrosion rates can be selected in high-temperature and high salinity environments to ensure the reliability of tools during construction. Otherwise, alloy tools with high corrosion rates can be selected.

[0042] Figures 1 - 6 The alloy microstructure diagrams shown indicate from a microscopic perspective that the heat treatment process directly affects the type, quantity, and distribution of the precipitated phases, and thus affects the macroscopic properties of the material. For example, Figure 4 (a), Figure 5 (c) Figure 6 (e) show that there are obvious differences in the quantity and distribution of the precipitated phases in the material, which is due to the significant differences in the solution and aging processes, which significantly affect the precipitation of precipitated phases such as β-phase and β'-phase. Among them, the solution in Example 2 is the most complete, Figure 4 and the precipitated phases in (a) are diffusely distributed. The solution in Example 4 is incomplete, so it can be seen from Figure 6 (e) that there are continuous distributions of a large number of precipitated phases.

[0043] Comparative Examples 1-2 show that the properties of the materials obtained by using one-stage solution and aging treatment means are similar. The yield strength is 325-332 MPa, the tensile strength is 400-417 MPa, the elongation is 6.5%-7%, and the corrosion rate is 31-33 mg / cm2 / h. It can be seen from Comparative Example 3 that too fast a cooling rate results in the existence of thermal stress in the material, and the material fractures during the extrusion process.

[0044] The above examples are only illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. Any design identical or similar to the present invention falls within the protection scope of the present invention.

Claims

1. A heat treatment method for regulating the properties of soluble rare earth magnesium alloys, characterized in that: It includes the following steps: Step 1) Perform two-stage solution treatment on the soluble rare earth magnesium alloy; Step 2) Adopt three-stage cooling, wherein the cooling rate of the first stage is not less than that of the third stage, and the cooling rate of the second stage is less than that of the third stage; Step 3) After cooling, extrude it into a rod. After extrusion, perform pre-aging on the rod and then perform aging.

2. The heat treatment method for regulating the properties of a soluble rare earth magnesium alloy according to claim 1, characterized in that: In Step 1), the solution temperature of the first stage of the two-stage solution treatment is 450 - 485 °C, and the solution time is 15 - 40 h.

3. A heat treatment method for regulating the properties of a soluble rare earth magnesium alloy according to claim 1, characterized in that: In Step 1), the solution temperature of the second stage of the two-stage solution treatment is 500 - 535 °C, and the solution time is 10 - 30 h.

4. A heat treatment method for regulating the properties of a soluble rare earth magnesium alloy according to claim 1, characterized in that: In Step 2), the cooling rate of the first stage is 70 - 150 °C / s, and the cooling temperature range is from the solution temperature of the second stage 500 - 535 °C to 350 - 380 °C.

5. The heat treatment method for regulating the properties of a soluble rare earth magnesium alloy according to claim 1, characterized in that: In Step 2), the cooling rate of the second stage is 0.5 - 3 °C / s, and the cooling temperature range is from the termination temperature of the first stage cooling 350 - 380 °C to 290 - 330 °C.

6. The heat treatment method for regulating the properties of a soluble rare earth magnesium alloy according to claim 1, characterized in that: In Step 2), the cooling rate of the third stage is 50 - 100 °C / s, and the cooling temperature range is from the termination temperature of the second stage cooling 290 - 330 °C to room temperature.

7. A heat treatment method for regulating the properties of a soluble rare earth magnesium alloy according to claim 1, characterized in that: In Step 3), the pre-aging temperature is 100 - 150 °C, and the pre-aging time is 1 - 3 h.

8. A heat treatment method for regulating the properties of a soluble rare earth magnesium alloy according to claim 1, characterized in that: In Step 3), the aging temperature is 150 - 250 °C, and the aging time is 30 - 80 h.

9. A heat treatment method for regulating the properties of a soluble rare earth magnesium alloy according to any one of claims 1-8, characterized in that: The soluble rare earth magnesium alloy contains Mg3RE and Mg5RE phases.

Images