CN115627399B - Low-rare-earth high-strength Mg 98.5 Y 1 Zn 0.5 Preparation method of magnesium alloy - Google Patents

Abstract

The invention discloses a low rare earth high strength Mg _98.5 Y ₁ Zn _0.5 A preparation method of magnesium alloy, belonging to the technical field of high-strength magnesium alloy preparation; the method comprises the following steps: according to Mg _98.5 Y ₁ Zn _0.5 Preparing pure magnesium, pure zinc and Mg-30Y intermediate alloy from alloy components; sequentially adding pure zinc and Mg-30Y intermediate alloy into the melted magnesium ingot for refining and pouring; carrying out solution treatment on the casting piece obtained by casting, wherein the temperature of the solution treatment is 530-550 ℃; performing forward extrusion on the test piece subjected to solution treatment; the extrusion temperature of the forward extrusion is 380-420 ℃; the extrusion speed is 0.3-0.5mm/s, the extrusion ratio is 23-26:1, and the extrusion angle is 30-40 degrees; the low rare earth high strength Mg prepared by the invention _98.5 Y ₁ Zn _0.5 The comprehensive performance index of the toughness level of the magnesium alloy is obviously improved; meanwhile, the cost of the rare earth magnesium alloy is reduced.

Description

Preparation method of low rare earth high strength Mg98.5Y1Zn0.5 magnesium alloy

Technical field

The invention belongs to the technical field of high-strength magnesium alloy preparation and relates to a preparation method of low rare earth high-strength Mg _98.5 Y ₁ Zn _0.5 magnesium alloy.

Background technique

With the depletion of energy, there is an increasing demand for lightweighting in aviation, aerospace, automobiles and other fields. As the lightest structural material, magnesium alloy has high specific strength, high specific stiffness, good electrical conductivity, electromagnetic shielding, It has always been highly anticipated due to its advantages such as ease of processing and forming. However, with the development of science and technology, higher requirements have been placed on the performance of materials. The application of magnesium alloys has been seriously restricted due to its low absolute strength, low plasticity, and poor high-temperature performance.

Through the unremitting efforts of researchers, a series of high-performance magnesium alloys have been developed, especially rare earth magnesium alloys, such as WE43 developed abroad, Mg-Gd-Y series magnesium alloys developed domestically, etc., all of which have excellent mechanical properties. performance. In particular, the extruded WE43 magnesium alloy has an elongation of more than 20%, but its tensile strength is low, only about 225MPa. In addition, the tensile strength of the high-strength cast Mg-14Gd-3Y-1.8Zn-0.5Zr magnesium alloy developed by Song Zhang et al. can reach 366MPa, but its elongation is extremely low, only 2.8%, but its rare earth content is as high as 17% . Currently, in the process of developing magnesium alloys, reducing the use of rare earths while ensuring high strength and high plasticity is still a hot topic.

Adding Zn element to the Mg-Re system can form a Long Period Stacking Ordered (LPSO) special structure, in which the rare earths Gd and Y are mainly added. However, compared to Y, Gd has a larger relative atomic mass and cannot meet the need for lightweighting. There are many structures of LPSO, among which 18R-LPSO and 14H-LPSO are the most common. 18R-LPSO is a massive structure with high strength and hardness. It is a hard and brittle phase, which can easily cause stress concentration during the stress process, leading to the formation of micro-cracks and adversely affecting the structure; 14H-LPSO is a A stacked layered structure with high strength and good toughness is an advantageous structure. 18R-LPSO can generally be formed in the cast state, while 14H-LPSO can only be formed through solid phase transformation. During the heat treatment process, when the temperature is lower than 500°C, the treatment time is long, which easily causes grain growth, and the transformation of 18R-LPSO to 14H-LPSO is incomplete; when the temperature is higher than 500°C, it is easy to cause alloy burning.

Forward extrusion is a common method to improve the mechanical properties of magnesium alloys. A large number of fine dynamic recrystallized grains can be obtained through positive extrusion, which can also improve the structure, reduce shrinkage, porosity, and dense structure to a certain extent. At present, forward extrusion is mainly concentrated in the range of 300°C to 400°C. When the extrusion temperature is lower than 250°C, forward extrusion can easily lead to cracking of the workpiece during the extrusion process, and will also form a large amount of internal stress, resulting in reduced plasticity.

Contents of the invention

The present invention overcomes the shortcomings of the prior art and proposes a preparation method of low rare earth and high strength Mg _98.5 Y ₁ Zn _0.5 magnesium alloy. In order to achieve the above objects, the present invention is achieved through the following technical solutions.

A preparation method of low rare earth high strength Mg _98.5 Y ₁ Zn _0.5 magnesium alloy, including the following steps:

1) Prepare pure magnesium, pure zinc and Mg-30Y master alloy according to the Mg _98.5 Y ₁ Zn _0.5 alloy composition;

2) Add pure zinc and Mg-30Y master alloy to the molten magnesium ingot in sequence for refining and pouring;

3) Perform solution treatment on the cast parts obtained by casting. The temperature of solution treatment is 530-550℃;

4) Perform forward extrusion on the solution-treated specimen; the extrusion temperature of forward extrusion is 380°C~420°C; the extrusion speed is 0.3-0.5mm/s, the extrusion ratio is 23~26:1, and Angle 30°~40°.

Preferably, the extrusion temperature of forward extrusion is 400°C; the extrusion speed is 0.4mm/s, the extrusion ratio is 25:1, and the extrusion angle is 30°.

Preferably, the refining is to wait until the furnace temperature is maintained at 780°C for 15 minutes, then turn off the power, wait until the temperature drops to 750°C, peel off the slag on the surface of the molten liquid, and perform refining; after that, evenly spread the covering After adding the agent, close the furnace lid and keep the furnace at 750°C for 20 minutes.

Preferably, the pouring is performed by holding the temperature at 750°C for 20 minutes, then pouring the magnesium alloy melt into the preheated mold after slag removal; after the mold temperature naturally cools to room temperature, the sample is taken out of the mold. A casting rod with a diameter of Ø80mm was obtained.

Preferably, the poured casting and dry magnesium oxide powder are wrapped in tin foil and compacted, and then placed in a ceramic pot; then the ceramic pot is wrapped with tin foil, and finally the ceramic pot is placed in an iron can. Magnesium oxide powder is filled around the ceramic jar and compacted, and then the wrapped specimen is placed in a heat treatment furnace for solid solution treatment.

Preferably, the solution treatment temperature is 530°C; the solution is kept for 10 hours, and then cooled to room temperature in the furnace.

Preferably, the forward extrusion is to heat the heat treatment furnace to the extrusion temperature. After the temperature reaches the solution-treated specimen, put it into the furnace and keep it warm for 1 hour; after the mold reaches the extrusion temperature, try When the specimen reaches the holding time, disconnect the power supply and place the specimen into the mold for extrusion.

The beneficial effects produced by the present invention compared with the existing technology are:

This invention uses low rare earth and solid solution at high temperature for a short time to convert more 18R-LPSO into 14H-LPSO. At the same time, it overcomes the problems of incomplete conversion and grain growth, and then obtains a large number of fine dynamics through high-temperature forward extrusion. Recrystallize the grains, reduce internal stress, and improve the plasticity of the alloy, thus obtaining a low rare earth and high strength Mg _98.5 Y ₁ Zn _0.5 magnesium alloy. The extrusion temperature of the low rare earth high strength Mg _98.5 Y ₁ Zn _0.5 magnesium alloy prepared by the present invention is controlled at 400°C, the tensile strength is 330.6MPa, and the elongation is 12.8%; the comprehensive performance index characterizing the strength and toughness level of the magnesium alloy is significant. improve. At the same time, the rare earth metal used in the Mg _98.5 Y ₁ Zn _0.5 magnesium alloy of the present invention is significantly reduced, which reduces the cost of the magnesium alloy.

Description of drawings

Figure 1 is the microstructure diagram of solid solution Mg _98.5 Y ₁ Zn _0.5 alloy OM.

Figure 2 is a schematic diagram of the forward extrusion process; where: 1-punch die; 2-gasket; 3-concave die; 4-sample before extrusion; 5-sample after extrusion; the thickness of the sample before extrusion is 30mm , the diameter is 40mm; the diameter of the sample after extrusion is 8mm.

Figure 3 is the room temperature tensile stress-strain curve of extruded Mg _98.5 Y ₁ Zn _0.5 alloy under different extrusion parameters.

Figure 4 is the SEM microstructure of the extruded Mg _98.5 Y ₁ Zn _0.5 alloy under different extrusion parameters; the extrusion temperatures of (a), (c), and (e) are 380°C, 400°C, and 420°C respectively. ℃; (b), (d), and (f) are enlarged views of area 1 in figure (a), area 2 in figure (c), and area 3 in figure (e), respectively.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clear, the present invention will be further described in detail with reference to the embodiments and drawings. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit the present invention. The technical solution of the present invention will be described in detail below with reference to the embodiments and drawings, but the scope of protection is not limited by this.

Example 1

Design of alloy components: This embodiment uses magnesium ingots with a purity of 99.99 wt%, Mg-30Y master alloy, zinc with a purity of 99.99 wt%, as well as covering agents and refining agents. A total of 1500g is smelted at one time, including 1303.8g of Mg, 19.5g of Zn, 176.7g of Mg-30Y master alloy, a small amount of covering agent and refining agent, and the composition of the Mg _98.5 Y ₁ Zn _0.5 alloy is shown in Table 1.

Step 1. Alloy smelting

Before smelting, the raw materials, molds, stirring rods, and slag removal rods need to be preheated. The molds, stirring rods, and slag removal rods are all made of steel. In order to facilitate the demoulding of the casting and prevent the introduction of impurities, they need to be sprayed off the inner wall of the mold. Mold agent, polish the mold before spraying; in order to prevent the oxide layer on the surface of the stirring rod and slag removal rod from falling off and bringing in impurities during use, it is necessary to apply protective coating on the surface of the stirring rod and slag removal rod. The coating used is talc powder, To make a mixed solution of sodium silicate and water, first heat the stirring rod and scraping rod to 400°C, then evenly apply paint on the surface, keep it warm, wait until the paint is dry, and then apply the paint again, repeat 3 to 4 times, the purpose is Make the paint stick firmly to the surface of the stirring rod and slag scraping rod. In order to facilitate the addition of raw materials and reduce the introduction of impurities, pure magnesium, pure zinc, and Mg-30Y master alloy need to be cut into blocks of appropriate size and the oxide film impurities on the surface must be polished with sandpaper.

1) Melting magnesium ingot

When the temperature of the resistance furnace rises to 500°C, add the preheated pure magnesium ingot into the crucible, and evenly sprinkle the preheated covering agent on its surface. At the same time, start to introduce argon gas into the furnace for gas protection. Since Mg easily reacts with O ₂ , N ₂ and water vapor in the air at high temperatures, this embodiment uses a covering agent + argon gas protection method for protection. When the resistance furnace temperature rises to 720°C, start holding it at constant temperature for 20 minutes to ensure that the magnesium ingot can be completely melted.

2) Add zinc

After the magnesium ingot is completely melted, open the furnace cover to remove the slag, then add the preheated pure zinc, evenly sprinkle the covering agent, close the furnace cover and start to heat up to 780°C.

3) Add Mg-30Y master alloy

When the temperature rises to 780°C, open the furnace and remove the slag, add the preheated Mg-30Y master alloy according to the test requirements, stir and sprinkle the covering agent, close the furnace lid, and wait for the furnace temperature to rise to 780°C and then keep it warm for 15 minutes.

4) Refining

After the furnace temperature is maintained at 780°C for 15 minutes, turn off the power, wait until the temperature drops to 750°C, peel off the slag on the surface of the melt, and proceed with refining. Finally, evenly sprinkle the covering agent, close the furnace lid, and keep the furnace at 750°C for 20 minutes.

5) Pouring

After holding at 750 °C for 20 min, the magnesium alloy melt was poured into the preheated mold (200 °C) after slag removal. After the mold temperature naturally cools to room temperature, the sample is taken out of the mold to obtain a casting rod with a diameter of Ø80mm.

Step 2. Solid solution treatment

1) Cut the cast rod into a Ø40×30mm cylinder with a wire EDM machine, and use emery cloth to remove the oxide layer on the surface;

2) Place the magnesium oxide powder in a drying oven and dry it at 200°C for 2 hours to prevent water vapor from being introduced during subsequent heat treatment;

3) After the magnesium oxide powder is dried, wrap the cut casting rod and magnesium oxide powder with tin foil and compact it, then place it in a ceramic jar, fill it with magnesium oxide powder and compact it, and then place it outside the ceramic jar Wrap it with tin foil, and finally put the ceramic pot in the iron can, fill it with magnesium oxide powder around the ceramic pot and compact it, cover the top of the iron can with tin foil and poke a few small holes for ventilation. . The reason why the heat-treated parts are tightly wrapped with magnesium oxide powder is to prevent air and water vapor from entering, and to make the heating even and prevent the parts from being burned if the temperature is too high;

4) Put the wrapped parts into the heat treatment furnace, raise the temperature to 530℃ with the furnace, keep it warm for 10 hours, and then cool to room temperature with the furnace;

5) Wait for the furnace to cool to room temperature, take out the parts and clean them, use sandpaper to polish the surface oxide layer, and the OM diagram after solution treatment is shown in Figure 1.

Step 3. Positive extrusion

1) After installing the mold, use a resistance furnace to heat the grinding tool to the extrusion temperature;

2) While heating the mold, heat the heat treatment furnace to the extrusion temperature of 380°C. When the temperature reaches the temperature, quickly put the solution-treated parts into the furnace and keep them warm for 1 hour;

3) When the mold reaches the extrusion temperature and the heat-treated parts reach the holding time, disconnect the power supply, quickly place the extrusion parts into the mold, and place the gasket and extrusion rod;

4) After placing the extruded parts, extrusion is carried out at an extrusion speed of 0.4mm/s, an extrusion ratio of 25:1, and an extrusion angle of 30°;

5) After the extrusion is completed, take out the extrusion part and air-cool it to room temperature to obtain a slender extrusion rod with a diameter of Ø8mm. The forward extrusion process is shown in Figure 2. The diameter of the punch 1 used is 38mm, and the thickness of the gasket 2 is 10mm.

Example 2

The method and materials of this embodiment are the same as those of Example 1, except that the extrusion temperature is 400°C.

Example 3

The method and materials of this embodiment are the same as those of Example 1, except that the extrusion temperature is 420°C.

Performance experimental results of the magnesium alloy prepared in Examples 1-3:

Examples 1-3 used three extrusion temperatures. The smelting process and solution treatment process used in the three methods all adopted the process described above. The difference was the extrusion temperature. Examples 1-3 adopted 380°C respectively. The extrusion was carried out at ℃, 400℃ and 420℃, the extrusion speed was 0.4mm/s, the extrusion angle was 30 ^° , and the extrusion ratio was 25:1. When extruded at 380°C, the tensile strength is 339.5MPa and the elongation is 7.5%; when extruded at 400°C, the tensile strength is 330.6MPa and the elongation is 12.8%; when extruded at 420°C, the tensile strength is 339.5MPa and the elongation is 7.5%. The tensile strength is 231.7MPa and the elongation is 17.6%. The room temperature tensile stress-strain curve, tensile strength and elongation of the alloy are shown in Figure 3 and Table 2.

When extruded at 380°C, the highest tensile strength reaches 339.5MPa, but the elongation is the lowest, 7.5%; when extruded at 420°C, the tensile strength is the lowest, 231.7MPa, but the elongation is the highest, 17.6%. According to the strong plastic product (strong plastic product is a comprehensive performance index that characterizes the strength and toughness level of metal materials, that is, tensile strength * elongation), 400°C has the best comprehensive performance, followed by 420°C, and 380°C is the lowest.

As the extrusion temperature increases, its strength gradually decreases, but its plasticity increases significantly. This is because as the extrusion temperature increases, the more complete the dynamic recrystallization occurs, the greater the number of recrystallizations, and the recrystallized grains are particularly fine. It can achieve fine grain strengthening, which can not only improve the strength but also improve the plasticity. However, as the extrusion temperature increases, the recrystallized grains gradually grow, resulting in a decrease in strength, as shown in Figure 4.

The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be concluded that the specific embodiments of the present invention are limited to this. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the premise of the present invention, Below, several simple deductions or substitutions can be made, which should all be deemed to belong to the patent protection scope of the present invention as determined by the submitted claims.

Claims (5)

1. A method for preparing low rare earth high strength Mg _98.5 Y ₁ Zn _0.5 magnesium alloy, which is characterized by comprising the following steps: 1) Prepare pure magnesium, pure zinc and Mg-30Y master alloy according to the Mg _98.5 Y ₁ Zn _0.5 alloy composition; 2) Add pure zinc and Mg-30Y master alloy to the molten magnesium ingot in sequence for refining and pouring; 3) Perform solution treatment on the cast parts obtained by pouring. The temperature of solution treatment is 530°C; keep it warm for 10 hours, and then cool to room temperature in the furnace; 4) The specimen after solution treatment is subjected to forward extrusion; the extrusion temperature of forward extrusion is 400°C; the extrusion speed is 0.4mm/s, the extrusion ratio is 25:1, and the extrusion angle is 30°. 2. The preparation method of a low rare earth high strength Mg _98.5 Y ₁ Zn _0.5 magnesium alloy according to claim 1, characterized in that the refining is to wait until the furnace temperature is maintained at 780° C. for 15 minutes, and then disconnect the power supply. , wait until the temperature drops to 750°C, peel off the slag on the surface of the molten liquid, and perform refining; then, evenly sprinkle the covering agent, close the furnace cover, and keep the furnace temperature at 750°C for 20 minutes. 3. The preparation method of a low rare earth high-strength Mg _98.5 Y ₁ Zn _0.5 magnesium alloy according to claim 1, characterized in that the pouring is maintained at 750° C. for 20 minutes, and the magnesium is removed after slag removal. The alloy melt is poured into the preheated mold; after the mold temperature naturally cools to room temperature, the sample is taken out of the mold to obtain a pouring rod with a diameter of Ø80mm. 4. The preparation method of a low rare earth high strength Mg _98.5 Y ₁ Zn _0.5 magnesium alloy according to claim 1, characterized in that the cast piece obtained by casting and the dry magnesium oxide powder are wrapped together in tin foil and compacted , then put it into the ceramic pot; then wrap the outside of the ceramic pot with tin foil, and finally put the ceramic pot into the iron pot, fill the surroundings of the ceramic pot with magnesium oxide powder and compact it, and then place the wrapped test piece into a heat treatment furnace for solution treatment. 5. The preparation method of a low rare earth high strength Mg _98.5 Y ₁ Zn _0.5 magnesium alloy according to claim 1, characterized in that the forward extrusion is to heat the heat treatment furnace to the extrusion temperature, and wait until the temperature reaches Finally, put the solution-treated specimen into the furnace and keep it warm for 1 hour; when the mold reaches the extrusion temperature and the specimen reaches the holding time, turn off the power supply and put the specimen into the mold for extrusion.