CN115141948A - High-strength and high-toughness die-casting magnesium alloy - Google Patents
High-strength and high-toughness die-casting magnesium alloy Download PDFInfo
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- 229910000861 Mg alloy Inorganic materials 0.000 title claims abstract description 59
- 238000004512 die casting Methods 0.000 title claims abstract description 53
- 239000011777 magnesium Substances 0.000 claims abstract description 51
- 239000012535 impurity Substances 0.000 claims abstract description 14
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 10
- 229910045601 alloy Inorganic materials 0.000 claims description 54
- 239000000956 alloy Substances 0.000 claims description 54
- 229910052749 magnesium Inorganic materials 0.000 claims description 35
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 30
- 238000010438 heat treatment Methods 0.000 claims description 30
- 239000002994 raw material Substances 0.000 claims description 23
- 238000000034 method Methods 0.000 claims description 16
- 238000007670 refining Methods 0.000 claims description 15
- 230000001681 protective effect Effects 0.000 claims description 14
- 239000000155 melt Substances 0.000 claims description 13
- 230000008569 process Effects 0.000 claims description 12
- 238000003723 Smelting Methods 0.000 claims description 6
- 238000002347 injection Methods 0.000 claims description 6
- 239000007924 injection Substances 0.000 claims description 6
- 238000005266 casting Methods 0.000 claims description 4
- 238000001816 cooling Methods 0.000 claims description 3
- 238000002156 mixing Methods 0.000 claims description 3
- 238000003825 pressing Methods 0.000 claims description 3
- 238000003756 stirring Methods 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 abstract description 7
- 239000007789 gas Substances 0.000 description 15
- 230000000694 effects Effects 0.000 description 8
- 238000006243 chemical reaction Methods 0.000 description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 7
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 6
- 239000001301 oxygen Substances 0.000 description 6
- 229910052760 oxygen Inorganic materials 0.000 description 6
- 229910003023 Mg-Al Inorganic materials 0.000 description 5
- 230000003647 oxidation Effects 0.000 description 5
- 238000007254 oxidation reaction Methods 0.000 description 5
- 238000005275 alloying Methods 0.000 description 4
- 230000004888 barrier function Effects 0.000 description 4
- 230000008859 change Effects 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- 229910000882 Ca alloy Inorganic materials 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 3
- 239000000395 magnesium oxide Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000011159 matrix material Substances 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- 230000002829 reductive effect Effects 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- 230000007812 deficiency Effects 0.000 description 2
- 238000004880 explosion Methods 0.000 description 2
- 238000009472 formulation Methods 0.000 description 2
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000007769 metal material Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 244000241872 Lycium chinense Species 0.000 description 1
- 235000015468 Lycium chinense Nutrition 0.000 description 1
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- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000013016 damping Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 235000013399 edible fruits Nutrition 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- -1 i.e. Substances 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/02—Making non-ferrous alloys by melting
- C22C1/03—Making non-ferrous alloys by melting using master alloys
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
- B22D17/14—Machines with evacuated die cavity
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/06—Making non-ferrous alloys with the use of special agents for refining or deoxidising
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/02—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working in inert or controlled atmosphere or vacuum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/06—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of magnesium or alloys based thereon
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Abstract
The invention discloses a high-strength and high-toughness die-casting magnesium alloy which is characterized by comprising the following elements in percentage by mass: 9.5 to 10.4 percent of Al, 1.0 to 3.0 percent of Ca, 0.1 to 0.6 percent of Mn, 0.01 to 0.3 percent of Sr and the balance of Mg and impurity elements. The invention can obtain the die-casting magnesium alloy with high ductility and high strength and toughness at room temperature, and has simple production operation and lower cost.
Description
Technical Field
The invention relates to the technical field of metal material processing, in particular to a high-strength and high-toughness die-casting magnesium alloy.
Background
The magnesium and the magnesium alloy have low density, high specific strength and specific stiffness, high damping and shock-absorbing performance, excellent heat conduction and electromagnetic shielding performance, good casting and machining process performance and rich resource support, become one of the most potential metal materials, and have wide application prospects in the fields of ground vehicles, aerospace, 3C products and the like.
The magnesium alloy is prepared by adopting a die-casting mode, so that the process is simpler, the cost is lower, and the application is more common. There is data indicating that about 90% of the cast magnesium alloys are die cast magnesium alloys, but the die cast magnesium alloys have relatively low performance. Therefore, the academic engineering community strives to obtain low-cost high-performance die-cast magnesium alloy. As a die-casting magnesium alloy system which is most widely applied, the comprehensive mechanical properties of commercial AZ91D and AM60 die-casting alloys can not meet the service requirements under partial working conditions. To improve the properties of Mg-Al alloys, alloying and heat treatment can be used. Ca element is used as an effective grain refining element, and can form a second phase stable at room temperature when added into Mg-Al series alloy, thereby improving the performance of the alloy. The Sr element obviously improves the form, quantity and distribution of a matrix and a secondary phase of the alloy, and the addition of the Sr element can improve the deficiency of the performance of the Mg-Al-Ca alloy in all aspects. Therefore, in the conventional pressed magnesium alloy, it is generally considered to add the above elements to improve the properties of the magnesium alloy. Meanwhile, the heat treatment of the die-casting magnesium alloy is an important means for improving the performance of die-casting parts. For Mg-Al-Ca alloys, conventional T6 and T5 heat treatment is usually used to improve their performance. However, the tensile strength and elongation performance of the conventional die-casting magnesium alloy at room temperature are still limited, and the conventional die-casting magnesium alloy is difficult to improve and cannot be applied to occasions with higher requirement on ductility.
CN108118226 discloses a high thermal conductivity, corrosion resistant, heat resistant die-cast magnesium alloy and a manufacturing method thereof, CN110195181B discloses a die-cast magnesium alloy with high temperature heat resistance and a manufacturing method thereof; can obtain the die-casting magnesium alloy with better overall performance, but the plastic extensibility of the die-casting magnesium alloy is still poorer. In general, the tensile strength at room temperature hardly exceeds 290 MPa, and the elongation (elongation) hardly exceeds 8%. To obtain higher performance magnesium alloys, more complicated processes and formulations are generally required, and the production cost is higher.
Therefore, how to provide a die-cast magnesium alloy with better room temperature ductility to reduce the production cost of high-performance magnesium alloys is a problem to be considered and solved by those skilled in the art.
Disclosure of Invention
Aiming at the defects of the prior art, the technical problems to be solved by the invention are as follows: how to provide a high-strength and high-toughness die-casting magnesium alloy with better ductility at room temperature so as to reduce the production cost of the high-performance magnesium alloy.
The technical scheme adopted by the invention is as follows:
the high-strength and high-toughness die-casting magnesium alloy is characterized by comprising the following elements in percentage by mass: 9.5 to 10.4 percent of Al, 1.0 to 3.0 percent of Ca, 0.1 to 0.6 percent of Mn, 0.01 to 0.3 percent of Sr, and the balance of Mg and impurity elements.
The magnesium alloy of the scheme consists of Al, ca, mn, sr, mg and impurities in a specific proportion, and belongs to die-casting Mg-Al series alloy. Wherein, impurity elements refer to inevitable impurity elements introduced from raw materials for preparing the alloy during the process of preparing the alloy, i.e., metal or nonmetal elements which are present in the metal but are not intentionally added or retained. The addition of Mn can improve the alloy strength and improve the anti-rust performance. Ca element is used as an effective grain refining element, and can form a second phase stable at room temperature when added into Mg-Al series alloy, and the original Mg in the Mg-Al series alloy 17 Al 12 Phase is highly heat-stabilized C36- (Mg, al) 2 Ca phase, C15-Al 2 Ca phase and C14-Mg 2 The Ca phase is substituted, and the high thermal stability of the alloy is improved. The Sr element obviously improves the form, quantity and distribution of a matrix and a secondary phase of the alloy, and the addition of the Sr element can improve the deficiency of the performance of the Mg-Al-Ca alloy in all aspects. In the formula of the magnesium alloy, the content of Al is 9.5-10.4%, and the alloy performance is adversely affected by overhigh content of Al; the low content of aluminum can reduce the fluidity of the alloy, further affect the castability of the alloy and reduce the ductility of the alloy. Meanwhile, the Sr content in the formula is 0.01-0.3%, if the Sr content is less than 0.01%, the effect of the component is difficult to achieve, but if the Sr content is more than 0.3%, the alpha-Mg matrix is seriously coarsened, and due to Al 4 Formation of Sr phaseAnd the consumption of Sr atoms, the alloy is excessively deteriorated, thus reducing the ductility of the alloy.
Preferably, the mass percentage of inevitable impurity elements is 0% to 0.15%. The influence of impurities on the performance can be better avoided.
Further, the percentage content of each element is as follows: 10% of Al, 3% of Ca, 0.3% of Mn, 0.1% of Sr and the balance of Mg and impurity elements.
Tests show that the product performance effect can be better due to the optimized proportion content.
Further, the preparation method comprises the following steps:
s1, preparing raw materials according to the mass proportion of each element of the magnesium alloy;
s2, mixing the raw materials in the step S1, and then smelting to obtain a melt;
s3, carrying out vacuum die-casting by using the melt in the step S2 to obtain a die-casting piece;
and S4, carrying out isothermal heat treatment on the die casting in the step S3 to obtain the high-strength and high-toughness die-casting magnesium alloy.
Therefore, the operation is reduced, the processing is convenient, and the cost is low. The fourth step is to carry out isothermal heat treatment after the temperature of the die casting piece at the room temperature is raised again, so that the ductility of the magnesium alloy at the room temperature can be effectively improved and promoted, and the vacuum die casting magnesium alloy with low cost and high strength and toughness is obtained.
Preferably, step S1 is specifically: taking pure Mg, pure Al, mg-Ca intermediate alloy, mg-Mn intermediate alloy and Mg-Sr intermediate alloy according to selected mass percentage to prepare raw materials.
Thus, some of the components are added as master alloys to facilitate the addition of certain alloying elements that have relatively high melting points and are not readily soluble or readily oxidizable or volatile, in order to more accurately control the composition. In addition, the intermediate alloy is used as furnace charge, so that the overheating of a melt can be avoided, the smelting time is shortened, and the melting loss is reduced.
Preferably, the raw material configured in step S1 is preheated before step S2, specifically: preheating the pure Mg, the pure Al, the Mg-Ca intermediate alloy, the Mg-Mn intermediate alloy and the Mg-Sr intermediate alloy in the step S1 at 100-200 ℃ for 5-12h.
In this way, preheating is performed to remove moisture from the raw material. This is because magnesium reacts very strongly with water, magnesium oxide is formed by the reaction and releases a large amount of heat, the formed hydrogen gas is rapidly combined with ambient oxygen to form water, and the water is rapidly vaporized and expanded by heating, resulting in explosion.
Preferably, step S2 specifically includes:
(1) Heating the pure magnesium melt to 650-780 ℃ by adopting a solvent-free refining method, and sequentially adding the weighed rest raw materials in the step S1 into the middle upper part of the magnesium melt by using a feeding tool;
(2) Stirring for 5-30 min to make the raw materials flow fully in the magnesium melt and react;
(3) Keeping the temperature and standing for 30-120 minutes to ensure that the raw materials react in the magnesium melt, thereby achieving the purpose of standing and refining.
Therefore, better refining effect can be obtained, and subsequent die casting is facilitated.
Preferably, the refining is carried out under a protective gas, wherein the protective gas is SF 6 And CO 2 Mixed gas of (1), flow rate of protective gas SF 6 ：0.01-1.0L/min；CO 2 ：0.1-30L/min。
Wherein, the protection and the refining of the melt are very important in the process of smelting the magnesium alloy. Magnesium and its alloys are chemically active and prone to reactions with surrounding media such as oxygen, nitrogen, water vapor, etc., which can cause loss of magnesium melt and even safety issues. Magnesium has a higher affinity for oxygen than aluminum, and an oxide film formed on the surface of the melt is less porous, resulting in further oxidation of the magnesium melt. When the temperature is lower, the oxidation rate is lower, but when the temperature reaches 500 ℃, the oxidation rate is accelerated to exceed 650 ℃, the oxidation rate is increased sharply, the melt is oxidized violently when meeting oxygen to burn, the generated MgO has good heat insulation, so that the heat generated by the reaction cannot be diffused in time, the combustion reaction is further promoted, and the temperature rises sharply until the magnesium melt explodes. Under the same conditions, the reaction of magnesium with water is more violent than the reaction of magnesium with oxygen, the reaction of magnesium with water generates magnesium oxide and releases a large amount of heat, and the generated hydrogen gas can generate magnesium oxideRapidly combined with ambient oxygen to produce water which is rapidly vaporized and expanded by heating, resulting in explosion. In addition, nitrogen also reacts with magnesium, although more slowly than the first two, but produces Mg 3 N 2 Neither the reaction of magnesium with nitrogen nor the evaporation of magnesium can be prevented. Therefore, magnesium and magnesium alloy must be protected by magnesium melt in the smelting process, and a continuous compact protective film is formed on the surface of the magnesium liquid to prevent oxidation and combustion of the magnesium melt.
Preferably, the process parameters when the melt is used for vacuum die casting in step S3 are as follows: degree of vacuum 50 kPa, casting temperature: 685 ℃, mold temperature: and (3) performing high-injection speed at 200 ℃:6.0 m/s, slow pressing speed: 0.2 m/s and injection time: 4s, cooling time: and 5s.
Preferably, the intermediate temperature heat treatment in step S4 specifically includes: keeping the die casting at 380-480 ℃ for 12-36h; the pressure of the protective gas applied in the process is 180-220 MPa. The shielding gas may be the same as the refining shielding gas.
The isothermal heat treatment can improve the appearance of a second phase in the alloy and promote phase change, so that the performance of the alloy is improved. Specifically, based on the unique formulation and preparation process of the present application, a large amount of continuous network (Mg, al) can be generated at grain boundaries in alloy die castings before isothermal heat treatment 2 A Ca phase. Then, in the isothermal heat treatment process, the morphology of the second phase in the die casting can be obviously changed again, and the die casting is continuously reticular (Mg, al) 2 The Ca phase gradually separates and rounds off and is converted into Al 2 A Ca phase, and a rod-like and spherical phase appear in the crystal. Specifically, under the action of high temperature of 380-480 deg.C and pressure of 180-220 MPa, the continuous reticular second phase distributed at grain boundary can be partially dissolved, and the reticular continuous distributed (Mg, al) 2 The Ca phase becomes dispersed granular Al 2 The volume fraction and size of the Ca phase and the second phase are greatly reduced. After the isothermal heat treatment in the state of the long-time duration and the high pressure, the granular Al is obtained 2 The Ca phase is very stable, does not disappear along with the temperature reduction after treatment, can be pinned at the crystal boundary, and reduces the dislocation movement in the crystal grainsThe ability to resist. Reticular continuous distribution (Mg, al) before treatment 2 Ca has stronger barrier capability relative to dislocation slip, and is more easy to cause stress concentration, thus leading to premature failure of the material in the deformation process, and the elongation and tensile strength of the as-cast alloy are lower. And the second phase of the alloy after isothermal heat treatment is in discontinuous distribution, and the alloy keeps a certain barrier effect of dislocation slip, but the barrier effect is not too large, stress concentration caused by too strong barrier ability is avoided, and the material can keep better plasticity. Therefore, after the alloy is subjected to the isothermal heat treatment, the elongation and the tensile strength of the alloy are greatly improved.
Further, the intermediate temperature heat treatment in step S4 specifically includes: keeping the die casting at 430 ℃ for 24h; the treatment was carried out under an applied protective gas pressure of 200 MPa. The effect can be made better.
Compared with the prior art, the invention has the following beneficial effects:
1. the low-cost high-toughness vacuum die-casting magnesium alloy disclosed by the embodiment of the invention is realized by coupling alloying and isothermal heat treatment. The magnesium alloy with low cost is obtained through magnesium alloy alloying and isothermal heat treatment, and simultaneously has the mechanical properties of high strength and high elongation, and can meet the application requirements of various industrial fields.
2. Compared with published invention patents and documents, the vacuum die-casting Mg-Al-Ca-Mn-Sr magnesium alloy prepared by the embodiment of the invention has better comprehensive mechanical properties after isothermal treatment, the tensile strength at room temperature is 297-328 MPa, the yield strength is 171-177 MPa, the elongation (elongation) is 9.9-12.6%, and the performance indexes are obviously better than those of commercial AZ91 and AM60 alloys.
3. The experimental equipment required by the invention is easy to obtain, and other equipment is not required to be added.
In conclusion, the invention can obtain the high-strength and high-toughness die-casting magnesium alloy with better ductility at room temperature, and has simple production operation and lower cost.
Drawings
FIG. 1 is an SEM of a preferred embodiment die casting alloy: a and c in the as-cast state and b and d after heat treatment.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments.
The specific implementation mode is as follows:
the high-strength and high-toughness die-casting magnesium alloy is characterized by comprising the following elements in percentage by mass: 9.5 to 10.4 percent of Al, 1.0 to 3.0 percent of Ca, 0.1 to 0.6 percent of Mn, 0.01 to 0.3 percent of Sr, and the balance of Mg and impurity elements. Wherein, the mass percent of the inevitable impurity elements is 0 to 0.15 percent. The influence of impurities on the performance can be better avoided.
The magnesium alloy is prepared according to the following steps:
s1, preparing raw materials according to the mass proportion of each element of the magnesium alloy;
s2, mixing the raw materials in the step S1, and then smelting to obtain a melt;
s3, performing vacuum die-casting by using the melt in the step S2 to obtain a die-casting piece;
and S4, carrying out isothermal heat treatment on the die casting in the step S3 to obtain the high-strength and high-toughness die-casting magnesium alloy.
Wherein, the step S1 specifically comprises the following steps: taking pure Mg, pure Al, mg-Ca intermediate alloy, mg-Mn intermediate alloy and Mg-Sr intermediate alloy according to selected mass percentage to prepare raw materials.
Wherein, the raw material configured in the step S1 is preheated before the step S2, specifically: preheating the pure Mg, the pure Al, the Mg-Ca intermediate alloy, the Mg-Mn intermediate alloy and the Mg-Sr intermediate alloy in the step S1 at 100-200 ℃ for 5-12h.
Wherein, step S2 specifically includes:
(1) Heating the pure magnesium melt to 650-780 ℃ by adopting a solvent-free refining method, and sequentially adding the weighed rest raw materials in the step S1 into the middle upper part of the magnesium melt by using a feeding tool;
(2) Stirring for 5-30 min to make the raw material flow fully in the magnesium melt and react;
(3) Keeping the temperature and standing for 30-120 minutes to enable the raw materials to react in the magnesium melt, thereby achieving the purpose of standing and refining.
In step S2, refining under protective gas, wherein the protective gas is SF 6 And CO 2 Mixed gas of (1), flow rate of protective gas SF 6 ：0.01-1.0L/min；CO 2 ：0.1-30L/min。
Wherein, the technological parameters when the melt is used for vacuum die casting in the step S3 are as follows: degree of vacuum 50 kPa, casting temperature: 685 ℃, mold temperature: and (3) performing high-injection speed at 200 ℃:6.0 m/s, slow pressing speed: 0.2 m/s, injection time: 4s, cooling time: and 5s.
The medium temperature heat treatment in step S4 specifically includes: keeping the die casting at 380-480 ℃ for 12-36h; the pressure of the protective gas applied in the process is 180-220 MPa. The shielding gas is the same as the refining shielding gas.
In order to better prove the effect of the invention, the applicant adjusts the material formulas and the preparation process parameters of each step in the limited range based on the above specific embodiments to obtain a series of magnesium alloy die castings, forms a series of examples, and then detects the mechanical properties of the magnesium alloy die castings before and after the isothermal heat treatment step. Specific experimental part data are as follows.
| Fruit of Chinese wolfberry Applying for medical instruments Example (b) | Al content Quantity of （wt.% ） | Ca contains Quantity of （wt.% ） | Mn content Quantity of （wt.% ） | Sr content Measurement of （wt.% ） | Isothermal heat treatment Temperature/time （℃/h） | Tensile strength at room temperature Change before and after degree （MPa） | Room temperature yield strength Change before and after degree （MPa） | Elongation at room temperature Rate front and back variation Formation (%) |
| 1 | 9.9 | 1.1 | 0.4 | 0.1 | 430/24 | 227/297 | 150/171 | 6.0/9.9 |
| 2 | 10.4 | 2.1 | 0.3 | 0.1 | 430/24 | 210/317 | 157/175 | 3.2/11.5 |
| 3 | 10.1 | 2.9 | 0.3 | 0.1 | 430/24 | 208/328 | 162/177 | 2.7/12.6 |
| 4 | 9.5 | 2.9 | 0.6 | 0.2 | 430/24 | 206/309 | 164/175 | 2.8/10.7 |
| 5 | 9.8 | 2.7 | 0.1 | 0.3 | 430/24 | 202/301 | 158/172 | 2.4/10.1 |
| 6 | 10.2 | 2.8 | 0.4 | 0.1 | 430/24 | 205/312 | 160/171 | 2.6/11.1 |
As can be seen from the above test results. After isothermal treatment, the vacuum die-casting Mg-Al-Ca-Mn-Sr magnesium alloy prepared by the invention has excellent comprehensive mechanical properties, the room-temperature tensile strength is 297-328 MPa, the yield strength is 171-177 MPa, the elongation (elongation) is 9.9-12.6%, and the performance index is obviously superior to that of commercial AZ91 and AM60 alloys.
From the above test results, it can be seen that the performance of example 3 is the best, and fig. 1 is an SEM photograph of the best example die casting alloy: a and c in the as-cast state and b and d after heat treatment. The change of the structure of the alloy before and after heat treatment can be clearly seen from the figure, and the structure of the alloy structure is changed from a continuous net shape to a separated and rounded particle shape, so that the heat treatment effect of the scheme of the application can be shown.
Claims (10)
1. The high-strength and high-toughness die-casting magnesium alloy is characterized by comprising the following elements in percentage by mass: 9.5 to 10.4 percent of Al, 1.0 to 3.0 percent of Ca, 0.1 to 0.6 percent of Mn, 0.01 to 0.3 percent of Sr, and the balance of Mg and impurity elements.
2. The high strength die-cast magnesium alloy according to claim 1, wherein the mass percentage of the inevitable impurity elements is 0% to 0.15%.
3. The high strength and toughness die-cast magnesium alloy as claimed in claim 1, wherein the contents of each element in percentage are as follows: 10% of Al, 3% of Ca, 0.3% of Mn, 0.1% of Sr and the balance of Mg and impurity elements.
4. The high strength and toughness die-cast magnesium alloy as claimed in claim 1, which is prepared by the following method steps:
s1, preparing raw materials according to the mass proportion of each element of the magnesium alloy;
s2, mixing the raw materials in the step S1, and then smelting to obtain a melt;
s3, carrying out vacuum die-casting by using the melt in the step S2 to obtain a die-casting piece;
and S4, carrying out isothermal heat treatment on the die casting in the step S3 to obtain the high-strength and high-toughness die-casting magnesium alloy.
5. The high-toughness die-cast magnesium alloy according to claim 4, wherein the step S1 is specifically as follows: taking pure Mg, pure Al, mg-Ca intermediate alloy, mg-Mn intermediate alloy and Mg-Sr intermediate alloy according to the selected mass percentage to prepare raw materials;
preheating the raw materials configured in the step S1 before the step S2, specifically: preheating the pure Mg, the pure Al, the Mg-Ca intermediate alloy, the Mg-Mn intermediate alloy and the Mg-Sr intermediate alloy in the step S1 at 100-200 ℃ for 5-12h.
6. The high strength and toughness die-cast magnesium alloy according to claim 4, wherein the step S2 specifically comprises:
(1) Heating the pure magnesium melt to 650-780 ℃ by adopting a solvent-free refining method, and sequentially adding the weighed rest raw materials in the step S1 into the middle upper part of the magnesium melt by using a feeding tool;
(2) Stirring for 5-30 min to make the raw material flow fully in the magnesium melt and react;
(3) Keeping the temperature and standing for 30-120 minutes to enable the raw materials to react in the magnesium melt, thereby achieving the purpose of standing and refining.
7. The high strength die cast magnesium alloy as claimed in claim 6, wherein the refining is carried out under a protective gas, and the protective gas is SF 6 And CO 2 Mixed gas of (1), shielding gas flow rate SF 6 ：0.01-1.0L/min；CO 2 ：0.1-30L/min。
8. The high strength and toughness die-cast magnesium alloy according to claim 4, wherein the process parameters when the melt is used for vacuum die-casting in the step S3 are as follows: degree of vacuum 50 kPa, casting temperature: 685 ℃, mold temperature: and (3) performing high-injection speed at 200 ℃:6.0 m/s, slow pressing speed: 0.2 m/s and injection time: 4s, cooling time: and 5s.
9. The high-strength high-toughness die-casting magnesium alloy according to claim 4, wherein the medium-temperature heat treatment in the step S4 is specifically as follows: preserving the temperature of the die casting at 380-480 ℃ for 12-36h; the pressure of the protective gas applied in the process is 180-220 MPa.
10. The high strength and toughness die-cast magnesium alloy according to claim 9, wherein the die-cast article is heat-insulated at 430 ℃ for 24 hours; the treatment is carried out under protective gas pressure of 200 MPa.
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