Semi-solid recovery method for rare earth magnesium alloy

Abstract

The invention discloses a rare earth magnesium alloy semi-solid recovery method, which relates to the technical field of magnesium alloy recovery, and comprises four steps of reclaimed material preparation, vacuum hot pressing, semi-solid heating and thixotropic extrusion. By adopting vacuum hot pressing and semi-solid thixotropic extrusion technologies, the problems of serious oxidation and combustion of the rare earth magnesium alloy in traditional liquid recovery are avoided, and environmental pollution and resource waste are avoided; through vacuum hot pressing, high-temperature oxidation of the recycled material in the hot pressing process is avoided while the density of the vacuum hot pressing blank is ensured; by adopting semi-solid thixotropic extrusion, liquid phase flow in the forming process is promoted, an original interface between cuttings is eliminated, new metallurgical bonding is formed again, and the interface bonding force between the cuttings is greatly improved.

Description

Technical Field

[0001] This invention relates to the technical field of magnesium alloy recycling, and specifically to a semi-solid recycling method for rare earth magnesium alloys. Background Technology

[0002] Magnesium alloys are currently among the lowest density metallic structural materials used in practical applications, finding increasingly widespread use in the automotive, aerospace, and communications electronics industries. However, magnesium lacks allotropic transformations, and most alloying elements have low solid solubility, resulting in a lack of effective strengthening phases and consequently, poor mechanical properties in magnesium alloys. Rare earth elements possess unique valence electron structures, and some heavy rare earth elements exhibit high solid solubility in magnesium, enabling them to form effective strengthening phases and demonstrating significant age-hardening properties. This can substantially improve the room-temperature and high-temperature mechanical properties of magnesium alloys.

[0003] Therefore, the research on high-performance rare earth magnesium alloys has become an important direction for the development of magnesium alloys.

[0004] With the increasing application of magnesium alloys, their recycling technology will become an important factor affecting the development of the magnesium alloy industry. Currently, there are two main types of technologies for recycling magnesium alloy waste: liquid recycling and solid recycling.

[0005] Traditional liquid recycling involves remelting magnesium alloy process waste, scrap, or end-of-life parts, followed by refining to obtain cast billets or formed parts. While the liquid recycling process for magnesium alloy waste based on melting is relatively mature and has been applied in actual industrial production, it still has some drawbacks: the remelting process requires the addition of covering agents, refining agents, or other atmospheres for special protection, resulting in high costs and the generation of harmful gases, exacerbating environmental pollution; furthermore, magnesium alloys are highly susceptible to oxidation and burn-off, leading to low recycling rates, with a utilization rate of less than 55% from waste to finished materials. Solid recycling, on the other hand, involves pre-treating magnesium alloy scraps or offcuts through cleaning and crushing, followed by plastic deformation processes such as extrusion, rolling, or repeated plastic processing to obtain denser blocks or profiles.

[0006] Solid-state recycling technology eliminates the need to remelt waste materials, directly turning chips or scraps into profiles. The process is simple, easy to implement, low-cost, energy-saving, and has a high recycling rate. However, when using solid-state recycling, it is difficult to form a good metallurgical bond between the chip interfaces, which has an adverse effect on mechanical properties.

[0007] Therefore, developing a new method for recycling rare earth magnesium alloys is of great significance. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a semi-solid recycling method for rare earth magnesium alloys. By subjecting rare earth magnesium alloy chips to vacuum hot pressing and semi-solid thixotropic extrusion, the high density of the recycled rare earth magnesium alloy is ensured, the original interfaces are eliminated, and a metallurgical bond is formed, thus achieving safe and efficient recycling of rare earth magnesium alloys.

[0009] To achieve the above objectives, the technical solution of the present invention is: a semi-solid recycling method for rare earth magnesium alloys, comprising the following steps:

[0010] Step 1: Preparation of recycled materials: After the rare earth magnesium alloy recycled materials are mixed evenly, they are weighed;

[0011] Step 2: Vacuum hot pressing: A certain weight of rare earth magnesium alloy recycled material is placed into a vacuum hot pressing chamber, vacuum is drawn, heating and pressure are applied, and the pressure is maintained at a certain temperature for a certain time to obtain a vacuum hot pressing billet.

[0012] Step 3: Semi-solid heating: Transfer the vacuum hot-pressed billet to a heating furnace with a protective atmosphere, heat it to the semi-solid temperature range, and hold it at that temperature for a certain time to obtain a semi-solid billet containing a certain volume fraction of liquid phase.

[0013] Step 4: Thixotropic extrusion: The semi-solid heated billet is transferred to an extruder and thixotropically extruded at a certain extrusion ratio to obtain semi-solid recycled rare earth magnesium alloy material.

[0014] Preferably, in the recycling material preparation process, the rare earth magnesium alloy recycled material used is a Mg-Gd-Y series alloy, wherein the Gd element content is 6-12wt% and the Y element content is 2-4wt%.

[0015] Preferably, in the recycling material preparation process, the rare earth magnesium alloy recycled material used is in the form of chips obtained from cutting.

[0016] Preferably, in the vacuum hot pressing process, the heating temperature is 350-450℃, the applied pressure is 200-300MPa, and the holding time is 10-20min.

[0017] Preferably, in the semi-solid heating process, the protective atmosphere is an argon protective atmosphere.

[0018] Preferably, in the semi-solid heating process, the semi-solid heating temperature is 580–620°C, and the semi-solid holding time is 5–15 min.

[0019] Preferably, in the semi-solid heating process, the liquid phase volume fraction in the semi-solid billet is 40-60%.

[0020] Preferably, in the thixotropic extrusion process, the extrusion ratio is 4:1 to 8:1.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) By adopting vacuum hot pressing and semi-solid thixotropic extrusion technology, this invention avoids the problem of severe oxidation and combustion of rare earth magnesium alloys in traditional liquid recycling, thus avoiding environmental pollution and resource waste.

[0023] (2) The present invention ensures the density of vacuum hot-pressed blanks while avoiding high-temperature oxidation of recycled materials during the hot-pressing process by vacuum hot pressing.

[0024] (3) By adopting semi-solid thixotropic extrusion, the present invention promotes the flow of liquid phase during the forming process, eliminates the original interface between chips, and re-forms a new metallurgical bond, which greatly improves the interfacial bonding force between chips. Detailed Implementation

[0025] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0026] The present invention provides a semi-solid recycling method for rare earth magnesium alloys, comprising the following steps:

[0027] Step 1: Preparation of recycled material: Mix the Mg-(6~12wt%)Gd-(2~4wt%)Y rare earth magnesium alloy scrap recycled material evenly and then weigh it;

[0028] Step 2: Vacuum hot pressing: A certain weight of rare earth magnesium alloy recycled material is placed into a vacuum hot pressing chamber, vacuum is drawn, and then heated and pressure is applied to 200-300 MPa. The pressure is maintained at 350-450℃ for 10-20 minutes to obtain a vacuum hot pressing billet.

[0029] Step 3: Semi-solid heating: Transfer the vacuum hot-pressed billet to a heating furnace with an argon protective atmosphere, heat it to a semi-solid temperature range of 580-620℃, and hold it for 5-15 minutes to obtain a semi-solid billet containing 40-60% liquid phase by volume.

[0030] Step 4: Thixotropic extrusion: The semi-solid heated billet is transferred to an extruder and thixotropically extruded at an extrusion ratio of 4:1 to 8:1 to obtain semi-solid recycled rare earth magnesium alloy material.

[0031] The present invention will now be described in detail with reference to the embodiments. The embodiments are based on the technical solutions of the present invention and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0032] Example 1

[0033] A semi-solid recycling method for rare earth magnesium alloys includes the following steps:

[0034] Step 1: Preparation of recycled materials: Mix the Mg-6wt%Gd-2wt%Y rare earth magnesium alloy scrap recycled materials evenly and then weigh them;

[0035] Step 2: Vacuum hot pressing: A certain weight of rare earth magnesium alloy recycled material is placed into a vacuum hot pressing chamber, vacuum is drawn, and then heated and pressure is applied to 200MPa. The pressure is held at 350℃ for 10 minutes to obtain a vacuum hot pressing billet.

[0036] Step 3: Semi-solid heating: Transfer the vacuum hot-pressed billet to a heating furnace with an argon protective atmosphere, heat it to the semi-solid temperature range of 580℃, and hold it for 5 minutes to obtain a semi-solid billet containing 40% volume fraction liquid phase.

[0037] Step 4: Thixotropic extrusion: The semi-solid heated billet is transferred to an extruder and thixotropically extruded at an extrusion ratio of 4:1 to obtain semi-solid recycled rare earth magnesium alloy material.

[0038] Characterization showed that the semi-solid recycled rare earth magnesium alloy material obtained in this embodiment had a density of 98.5%, a room temperature tensile strength of 325 MPa, and an elongation of 12%.

[0039] Example 2

[0040] A semi-solid recycling method for rare earth magnesium alloys includes the following steps:

[0041] Step 1: Preparation of recycled materials: Mix the Mg-12wt%Gd-4wt%Y rare earth magnesium alloy scrap recycled materials evenly and then weigh them;

[0042] Step 2: Vacuum hot pressing: A certain weight of rare earth magnesium alloy recycled material is placed into a vacuum hot pressing chamber, vacuum is drawn, and then heated and pressure is applied to 300MPa. The pressure is held at 450℃ for 20 minutes to obtain a vacuum hot pressing billet.

[0043] Step 3: Semi-solid heating: Transfer the vacuum hot-pressed billet to a heating furnace with argon as a protective atmosphere, heat it to the semi-solid temperature range of 620℃, and hold it for 15 minutes to obtain a semi-solid billet containing 60% volume fraction liquid phase.

[0044] Step 4: Thixotropic extrusion: The semi-solid heated billet is transferred to an extruder and thixotropically extruded at an extrusion ratio of 8:1 to obtain semi-solid recycled rare earth magnesium alloy material.

[0045] Characterization showed that the semi-solid recycled rare earth magnesium alloy material obtained in this embodiment had a density of 98.9%, a room temperature tensile strength of 358 MPa, and an elongation of 10%.

[0046] Example 3

[0047] A semi-solid recycling method for rare earth magnesium alloys includes the following steps:

[0048] Step 1: Preparation of recycled materials: Mix the Mg-9wt%Gd-3wt%Y rare earth magnesium alloy scrap recycled materials evenly and then weigh them;

[0049] Step 2: Vacuum hot pressing: A certain weight of rare earth magnesium alloy recycled material is placed into a vacuum hot pressing chamber, vacuum is drawn, and then heated and pressure is applied to 250MPa. The pressure is held at 400℃ for 15 minutes to obtain a vacuum hot pressing billet.

[0050] Step 3: Semi-solid heating: Transfer the vacuum hot-pressed billet to a heating furnace with argon as a protective atmosphere, heat it to the semi-solid temperature range of 600℃, and hold it for 10 minutes to obtain a semi-solid billet containing 50% liquid phase by volume.

[0051] Step 4: Thixotropic extrusion: The semi-solid heated billet is transferred to an extruder and thixotropically extruded at an extrusion ratio of 6:1 to obtain semi-solid recycled rare earth magnesium alloy material.

[0052] Characterization showed that the semi-solid recycled rare earth magnesium alloy material obtained in this example had a density of 98.7%, a room temperature tensile strength of 346 MPa, and an elongation of 10%.

[0053] Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or equivalent to the scope of this invention are included in this invention.

Claims

1. A method for semi-solid recycling of rare earth magnesium alloys, characterized in that: Includes the following steps: Step 1: Preparation of recycled materials: After the rare earth magnesium alloy recycled materials are mixed evenly, they are weighed; Step 2: Vacuum hot pressing: A certain weight of rare earth magnesium alloy recycled material is placed into a vacuum hot pressing chamber, vacuum is drawn, heating and pressure are applied, and the pressure is maintained at a certain temperature for a certain time to obtain a vacuum hot pressing billet. Step 3: Semi-solid heating: Transfer the vacuum hot-pressed billet to a heating furnace with a protective atmosphere, heat it to the semi-solid temperature range, and hold it at that temperature for a certain time to obtain a semi-solid billet containing a certain volume fraction of liquid phase. Step 4: Thixotropic extrusion: The semi-solid heated billet is transferred to an extruder and thixotropically extruded at a certain extrusion ratio to obtain semi-solid recycled rare earth magnesium alloy material.

2. The method for semi-solid recycling of rare earth magnesium alloys according to claim 1, characterized in that: In the recycling process, the rare earth magnesium alloy recycled material used is a Mg-Gd-Y series alloy, in which the Gd element content is 6-12wt% and the Y element content is 2-4wt%.

3. The method for semi-solid recycling of rare earth magnesium alloys according to claim 1, characterized in that: In the recycling material preparation process, the rare earth magnesium alloy recycled material used is in the form of chips obtained from cutting.

4. The method for semi-solid recycling of rare earth magnesium alloys according to claim 1, characterized in that: In the vacuum hot pressing process, the heating temperature is 350-450℃, the applied pressure is 200-300MPa, and the holding time is 10-20min.

5. The method for semi-solid recycling of rare earth magnesium alloys according to claim 1, characterized in that: In the semi-solid heating process, the protective atmosphere is argon.

6. The method for semi-solid recycling of rare earth magnesium alloys according to claim 1, characterized in that: In the semi-solid heating process, the semi-solid heating temperature is 580-620℃, and the semi-solid holding time is 5-15 minutes.

7. The method for semi-solid recycling of rare earth magnesium alloys according to claim 1, characterized in that: In the semi-solid heating process, the liquid phase volume fraction in the semi-solid billet is 40-60%.

8. The method for semi-solid recycling of rare earth magnesium alloys according to claim 1, characterized in that: In the thixotropic extrusion process, the extrusion ratio is 4:1 to 8:1.