Background
With the increasing environmental issues, industrial lightweight is receiving more and more attention. Magnesium alloys play a crucial role in industrial lightweight applications as the lightest metallic structural material. The magnesium alloy not only has good energy-saving and emission-reducing characteristics, but also is a green engineering material easy to recycle, and becomes a preferred material in lightweight design in the fields of aerospace, transportation and the like.
However, the crystal structure of magnesium is a close-packed hexagonal structure, and independent sliding systems are few, so that the plasticity of the alloy is poor, the deformation processing at room temperature is difficult, and the development and application of the alloy are severely restricted, so that the research and development of high-plasticity magnesium alloys are the primary direction of the development of the magnesium alloys. At present, rare earth elements Gd, Nd and Y are mainly added to prepare the high-plasticity wrought magnesium alloy material commonly used for preparing the high-plasticity wrought magnesium alloy material, the variety of the elements is multiple, the price of the rare earth elements is high, resources are limited, the high-plasticity wrought magnesium alloy material has certain limitations in industrial mass production, large-size section production is difficult, and meanwhile, the high-plasticity wrought magnesium alloy material is also seriously influenced in light weight effect due to the fact that high-content rare earth element Gd is generally added to the high-plasticity wrought magnesium alloy at present, and the specific gravity is large and the content is high. Based on the results, the applicant develops 'low-cost high-performance Mg-Al-Mn magnesium alloy and a preparation method thereof' (CN 2016101998527) as a scientific research result, and the research result is advanced in stages; although the mechanical properties such as strength, toughness and formability are superior to those of the traditional commercial magnesium alloy AZ31, the requirements of 3C product shells, leisure article bearing structures, aerospace parts and the like on high ductility and yield strength cannot be met.
In view of the above, the research on rare earth-free magnesium alloy with low cost and high plasticity is a problem to be solved by those skilled in the art.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a low-cost high-plasticity wrought magnesium alloy, solve the problem that the ductility and yield strength of the wrought magnesium alloy cannot meet the requirements of a bearing structure, aerospace parts and the like, and avoid the use of rare earth elements to meet the requirement of low cost.
In order to solve the technical problems, the invention adopts the following technical scheme: the magnesium alloy mainly comprises Mg, Mn and low-content Al, and the mass percentage of each component is as follows: 0.5-4.0%, Al: 0.1 to 0.5%, and the balance of magnesium and inevitable impurities. The preparation method comprises the following steps:
1) taking a pure magnesium ingot, a pure aluminum ingot and a magnesium-manganese intermediate alloy as raw materials, mechanically polishing (removing a surface oxide layer), and batching according to the components;
2) preheating pure magnesium, pure aluminum and magnesium-manganese intermediate alloy at 300 ℃ for 30-40 min, then placing a pure magnesium ingot in a resistance furnace, and adding SF (sulfur hexafluoride) with a volume ratio of 1:996And CO2The magnesium-manganese intermediate alloy and the pure aluminum ingot are added into the completely melted magnesium melt after the temperature of the magnesium melt is raised to 720 ℃ and stabilized, and when the temperature is raised to 700-740 ℃, the alloy is poured into a preheating furnace after heat preservation for 10minCooling the magnesium alloy ingot in a mold at the temperature of 300 ℃ to obtain a magnesium alloy ingot;
3) machining the magnesium alloy ingot obtained in the step 2) to a specified size to obtain a magnesium alloy extrusion blank;
4) preheating the magnesium alloy extrusion blank obtained in the step 3) at 200-300 ℃ for 1.5-3.0 h by using an extrusion die, then carrying out hot extrusion on the magnesium alloy extrusion blank at 200-300 ℃ to obtain a magnesium alloy rod, and air-cooling the magnesium alloy rod to room temperature to obtain the low-cost high-plastic deformation magnesium alloy. The extrusion ratio in the hot extrusion is more than or equal to 25: 1, the extrusion speed is 0.5-30 m/min.
By adopting the method, the content of the Al element is obviously reduced, so that Al and Mn all form a compound which is not dissolved in a Mg matrix; and the Mn-Al content of the Mg-Mn-Al alloy is controlled to be lower than 5 wt.%, the maximum element solid solution amount in the alloy matrix is controlled to be lower than 2 wt.%, the deformation resistance among crystal lattices is very low, the forming capability is better, and the preparation of the deformed section bar at lower temperature and higher deformation speed is facilitated. Therefore, extrusion can be carried out at a lower temperature (200-300 ℃, preferably 200-240 ℃) to effectively prevent abnormal growth of recrystallized grains, so that the finished alloy material is promoted to form a fine grain structure. Furthermore, the formed deformation material has finer and more uniform microstructure and better plasticity by performing larger plastic deformation at a lower temperature, and the prepared magnesium alloy material has high plasticity.
Compared with the prior art, the Mg-Mn-Al disclosed by the invention has the following beneficial effects:
firstly, the invention carries out deep research on a Mg-Mn-Al ternary system, and finds that when the content of Al element is obviously reduced and the content of the components is 0.5-4.0% of Mn, 0.1-0.50% of Al, and the balance of magnesium and inevitable impurities, the lower content of Al can react with Mn to form a nano-scale Al-Mn phase, and simultaneously, the nano-scale Al-Mn phase does not form solid solution nor Mg17Al12Eutectic phase, the lattice distortion can be reduced by reducing the solid solution amount of Al, the lattice resistance is reduced, and further deformation is facilitated; the absence of eutectic phase can reduce grain boundary precipitation and improve the dispersion strengthening effect of the second phase; the eutectic phase has a low melting point and is also detrimental to the high temperature properties of the alloy, thereby reducing the melting pointAnd a few eutectic phases exist, so that the high-temperature resistance of the alloy is improved.
Secondly, reducing the content of Al element to ensure that Al and Mn all form a compound and do not form solid solution in a Mg matrix; and the solid solubility of Mn element in Mg matrix is low, so that the composition segregation is difficult to generate to cause the uneven composition of the cast ingot, and the homogenization heat treatment process is not needed before extrusion. The alloy has low Mn-Al content (the total content is lower than 5 wt.%), the maximum element solid solution amount in the alloy matrix is lower than 2 wt.%, the deformation resistance among crystal lattices is very low, and the alloy has good forming capability and is beneficial to realizing low-temperature high-speed deformation. In the alloy system, Mn-Al elements are conventional elements, the alloying degree is low, after the Mn-Al alloy is added into magnesium, Mn and Al elements form an Al-Mn phase, and the surplus Mn element forms a simple substance Mn phase, namely an Al-Mn phase and a simple substance Mn second phase exist. In the extrusion process, the two phases can promote recrystallization nucleation, generate fine recrystallization grains, weaken texture and improve the plasticity of the alloy.
Thirdly, the invention creatively proposes that the abnormal growth of recrystallized grains can be effectively prevented by extrusion at a lower temperature of 200-300 ℃ on the basis of an Mg-Mn-Al ternary system, so that the finished alloy material is promoted to form a fine grain structure. Furthermore, the large plastic deformation is carried out at a low temperature, the microstructure of the formed deformed material is fine and uniform, the deformed material has good plasticity, and the prepared magnesium alloy material has high plasticity, so that unexpected technical effects are achieved; meanwhile, the low-temperature high-speed deformation is beneficial to saving energy, improving the production efficiency and reducing the production cost.
In addition, the raw materials of magnesium, manganese and aluminum are conventional elements, the price is low, the preparation process is simple, the preparation efficiency is high, the energy is saved, large block materials are easy to produce, the solid solution treatment is not needed, and the magnesium, manganese and aluminum can be directly used.
In conclusion, the invention creatively realizes the remarkable improvement of the elongation, the yield strength and the strength of the Mg-Mn-Al magnesium alloy material by remarkably reducing the content of the Al element and by extruding at lower temperature and adjusting the process; the magnesium alloy material has plasticity far superior to that of the prior similar high-plasticity magnesium alloy, and simultaneously has greatly improved yield strength. The elongation percentage reaches 23.4-34.2%, the yield strength can reach 207-278 MPa, and the steel plate is suitable for 3C product shells, leisure articles bearing structures, aerospace parts and the like, and has a good industrialization prospect. Therefore, the unexpected technical effect is achieved technically.
Detailed Description
The present invention will be described in further detail with reference to examples.
It should be noted that, in the following examples, the purity of the commercially pure magnesium and the purity of the commercially pure aluminum are both 99% or more; the magnesium-manganese master alloy is added in the form of Mg-5 Mn. The smelting and the pouring steps are carried out under the protection gas, and the protection gas adopts SF with the volume ratio of 1:996And CO2The mixed gas of (1). The percentages referred to in the examples are percentages by mass.
Example 1
1) Taking a pure magnesium ingot, a pure aluminum ingot and a magnesium-manganese intermediate alloy as raw materials, mechanically polishing, and adding a polishing agent according to the proportion of Mn: 1.0%, Al: 0.3 percent of magnesium and the balance of inevitable impurities by mass percentage;
2) preheating pure magnesium, pure aluminum and magnesium-manganese intermediate alloy at 300 ℃ for 30min, then placing a pure magnesium ingot in a resistance furnace, and adding SF (sulfur hexafluoride) with the volume ratio of 1:996And CO2The magnesium alloy ingot is completely melted under the protection of the mixed gas, after the temperature of the magnesium melt is raised to 720 ℃ and stabilized, the magnesium-manganese intermediate alloy and the pure aluminum ingot are added into the completely melted magnesium melt, when the temperature is raised to 720 ℃, the alloy is poured into a mold preheated to 300 ℃ after heat preservation is carried out for 10min, and a magnesium alloy ingot is obtained after cooling;
3) machining the magnesium alloy ingot obtained in the step 2) to a specified size to obtain a magnesium alloy extrusion blank;
4) preheating the magnesium alloy extrusion blank obtained in the step 3) at 240 ℃ for 1.5h by using an extrusion die, and then carrying out hot extrusion on the magnesium alloy extrusion blank at 240 ℃, wherein the extrusion ratio is 25: 1, extruding at the speed of 15m/min to obtain a magnesium alloy rod, and air-cooling the magnesium alloy rod to room temperature to obtain the low-cost high-plastic deformation magnesium alloy.
Example 2
1) Taking a pure magnesium ingot, a pure aluminum ingot and a magnesium-manganese intermediate alloy as raw materials, mechanically polishing, and adding a polishing agent according to the proportion of Mn: 0.5%, Al: 0.5 percent of magnesium and the balance of inevitable impurities by mass percentage;
2) preheating pure magnesium, pure aluminum and magnesium-manganese intermediate alloy at 300 ℃ for 30min, then placing a pure magnesium ingot in a resistance furnace, and adding SF (sulfur hexafluoride) with the volume ratio of 1:996And CO2The magnesium alloy ingot is completely melted under the protection of the mixed gas, after the temperature of the magnesium melt is raised to 720 ℃ and stabilized, the magnesium-manganese intermediate alloy and the pure aluminum ingot are added into the completely melted magnesium melt, when the temperature is raised to 700 ℃, the alloy is poured into a mold preheated to 300 ℃ after heat preservation is carried out for 10min, and a magnesium alloy ingot is obtained after cooling;
3) machining the magnesium alloy ingot obtained in the step 2) to a specified size to obtain a magnesium alloy extrusion blank;
4) preheating the magnesium alloy extrusion blank obtained in the step 3) at 200 ℃ for 1.5h by using an extrusion die, then carrying out hot extrusion on the magnesium alloy extrusion blank at 200 ℃ with an extrusion ratio of 30:1 and an extrusion speed of 25m/min to obtain a magnesium alloy rod, and carrying out air cooling on the magnesium alloy rod to room temperature to obtain the low-cost high-plasticity deformation magnesium alloy.
Example 3
1) Taking a pure magnesium ingot, a pure aluminum ingot and a magnesium-manganese intermediate alloy as raw materials, mechanically polishing, and adding a polishing agent according to the proportion of Mn: 0.5%, Al: 0.1 percent of magnesium and the balance of inevitable impurities by mass percentage;
2) preheating pure magnesium, pure aluminum and magnesium-manganese intermediate alloy at 300 ℃ for 30min, then placing a pure magnesium ingot in a resistance furnace, and adding SF (sulfur hexafluoride) with the volume ratio of 1:996And CO2The magnesium alloy ingot is completely melted under the protection of the mixed gas, after the temperature of the magnesium melt is raised to 720 ℃ and stabilized, the magnesium-manganese intermediate alloy and the pure aluminum ingot are added into the completely melted magnesium melt, when the temperature is raised to 720 ℃, the alloy is poured into a mold preheated to 300 ℃ after heat preservation is carried out for 10min, and a magnesium alloy ingot is obtained after cooling;
3) machining the magnesium alloy ingot obtained in the step 2) to a specified size to obtain a magnesium alloy extrusion blank;
4) preheating the magnesium alloy extrusion blank obtained in the step 3) at 200 ℃ for 1.5h by using an extrusion die, and then carrying out hot extrusion on the magnesium alloy extrusion blank at 200 ℃, wherein the extrusion ratio is 30:1, extruding at the speed of 30m/min to obtain a magnesium alloy rod, and air-cooling the magnesium alloy rod to room temperature to obtain the low-cost high-plastic deformation magnesium alloy.
Example 4
1) Taking a pure magnesium ingot, a pure aluminum ingot and a magnesium-manganese intermediate alloy as raw materials, mechanically polishing, and adding a polishing agent according to the proportion of Mn: 2.0%, Al: 0.5 percent of magnesium and the balance of inevitable impurities by mass percentage;
2) preheating pure magnesium, pure aluminum and magnesium-manganese intermediate alloy at 300 ℃ for 30min, then placing a pure magnesium ingot in a resistance furnace, and adding SF (sulfur hexafluoride) with the volume ratio of 1:996And CO2The magnesium alloy ingot is completely melted under the protection of the mixed gas, after the temperature of the magnesium melt is raised to 720 ℃ and stabilized, the magnesium-manganese intermediate alloy and the pure aluminum ingot are added into the completely melted magnesium melt, when the temperature is raised to 720 ℃, the alloy is poured into a mold preheated to 300 ℃ after heat preservation is carried out for 10min, and a magnesium alloy ingot is obtained after cooling;
3) machining the magnesium alloy ingot obtained in the step 2) to a specified size to obtain a magnesium alloy extrusion blank;
4) preheating the magnesium alloy extrusion blank obtained in the step 3) at 280 ℃ for 2.0h by using an extrusion die, then carrying out hot extrusion on the magnesium alloy extrusion blank at 280 ℃ with an extrusion ratio of 40:1 and an extrusion speed of 10m/min to obtain a magnesium alloy rod, and carrying out air cooling on the magnesium alloy rod to room temperature to obtain the low-cost high-plasticity deformation magnesium alloy.
Example 5
1) Taking a pure magnesium ingot, a pure aluminum ingot and a magnesium-manganese intermediate alloy as raw materials, mechanically polishing, and adding a polishing agent according to the proportion of Mn: 3.0%, Al: 0.5 percent of magnesium and the balance of inevitable impurities by mass percentage;
2) preheating pure magnesium, pure aluminum and magnesium-manganese intermediate alloy at 300 ℃ for 30min, and then placing a pure magnesium ingot in a resistance furnaceIn a volume ratio of 1:99 of SF6And CO2The magnesium alloy ingot is completely melted under the protection of the mixed gas, after the temperature of the magnesium melt is raised to 720 ℃ and stabilized, the magnesium-manganese intermediate alloy and the pure aluminum ingot are added into the completely melted magnesium melt, when the temperature is raised to 740 ℃, the alloy is poured into a mold preheated to 300 ℃ after heat preservation is carried out for 10min, and a magnesium alloy ingot is obtained after cooling;
3) machining the magnesium alloy ingot obtained in the step 2) to a specified size to obtain a magnesium alloy extrusion blank;
4) preheating the magnesium alloy extrusion blank obtained in the step 3) at 280 ℃ for 2.0h by using an extrusion die, then carrying out hot extrusion on the magnesium alloy extrusion blank at 280 ℃ with an extrusion ratio of 80:1 and an extrusion speed of 10m/min to obtain a magnesium alloy rod, and carrying out air cooling on the magnesium alloy rod to room temperature to obtain the low-cost high-plasticity deformation magnesium alloy.
Second, performance verification
The magnesium alloys prepared in examples 1 to 5 were tested using a tensile specimen designed according to the GB/T228.1: 2010 standard at a tensile rate of 1.5 mm/s, and the results are shown in Table 1.
TABLE 1
Examples
|
Mn
|
Al
|
Mg
|
Tensile strength (MPa)
|
Yield strength (MPa)
|
Extension ofRate of change
|
Example 1
|
1.0%
|
0.3%
|
Balance of
|
248
|
240
|
31%
|
Example 2
|
0.5%
|
0.5%
|
Balance of
|
288
|
278
|
23.4%
|
Example 3
|
0.5%
|
0.1%
|
Balance of
|
244
|
227
|
30.3%
|
Example 4
|
2.0%
|
0.5%
|
Balance of
|
253
|
244
|
27%
|
Example 5
|
3.0%
|
0.5%
|
Balance of
|
215
|
207
|
34.2% |
As can be seen from the table 1, the elongation of the Mg-Al-Mn magnesium alloy material prepared by the invention can reach 23.4-34.2%, the yield strength can reach 207-278 MPa, and compared with the similar products, the magnesium alloy material has the advantages that the plasticity is far better than that of the existing high-plasticity magnesium alloy, and the yield strength is greatly improved. The method is suitable for 3C product shells, leisure articles bearing structures, aerospace parts and the like, and has good industrialization prospects.
The above description is only exemplary of the present invention and should not be taken as limiting, and any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.