CN115652159A - High-strength and high-toughness die-casting magnesium alloy and preparation method thereof - Google Patents
High-strength and high-toughness die-casting magnesium alloy and preparation method thereof Download PDFInfo
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- 229910052749 magnesium Inorganic materials 0.000 claims abstract description 69
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- 238000010438 heat treatment Methods 0.000 claims abstract description 29
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- 239000012535 impurity Substances 0.000 claims abstract description 25
- 229910052746 lanthanum Inorganic materials 0.000 claims abstract description 25
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Abstract
The invention discloses a high-strength and high-toughness die-casting magnesium alloy and a preparation method thereof, wherein the magnesium alloy comprises the following components in percentage by mass: 2.7-3.4% Al, 3.8-4.8% La, 3.5-4.5% zn, 0.2-0.5% mn, wherein Al/La = 68-72%, the balance being magnesium and unavoidable impurities, the sum of the percentages by weight of the impurities not exceeding 0.2%; the preparation method comprises the working procedures of material preparation, smelting, melt transfer, die-casting forming, heat treatment and the like. Compared with the existing Mg-Al-RE alloy, the Mg-Al-La-Zn-Mn alloy has higher strength and better plasticity, and is a high-strength and high-toughness die-casting magnesium alloy with both strong plasticity and plasticity.
Description
Technical Field
The invention belongs to the technical field of metal structural materials, and relates to a high-strength and high-toughness die-casting magnesium alloy and a preparation method thereof.
Background
The light weight of the automobile is one of the most effective measures for reducing energy consumption and pollutant emission. In recent years, with the continuous increase of automobile output and holding capacity, the problems of energy consumption, safety, environmental protection and the like in China are increasingly prominent, and the automobile lightweight technology becomes an important means for promoting the sustainable development of the automobile industry, improving the fuel economy of automobiles and reducing the emission of automobile exhaust. The magnesium alloy is used as a metal structure material with the lowest density, has the characteristics of high specific strength and specific rigidity, good vibration damping performance, excellent electromagnetic shielding performance, excellent heat conducting performance and the like, and has become an important development direction of an automobile lightweight technology. The research of Changan automobiles shows that magnesium alloy is adopted to replace aluminum alloy to prepare parts such as automobile seat basins, engine oil bottom cases, engine valve chamber covers, transmission left case end covers, transmission left cases, transmission right cases and the like, so that weight reduction of 31.8, 33.3, 37.4, 37.1, 37.0 and 36.8% can be realized respectively, and the weight reduction effect is obvious.
The die-casting molding has the characteristics of high production efficiency, high dimensional precision, fine and fine casting microstructure, better mechanical property, capability of producing castings with thin walls and complex shapes and the like, and is the casting process with the widest application range of the magnesium alloy at present. With the development and popularization of vacuum die casting technology, the problem of internal air holes which seriously limit the quality of die castings is improved to a great extent. In the vacuum die casting process, gas in a die cavity of the die casting die is pumped out, so that air holes in a die casting piece are obviously reduced, the mechanical property and the surface quality of the die casting piece are obviously improved, and the application range of the magnesium alloy die casting piece is expanded.
At present, the die-casting magnesium alloy in commercial application is mainly Mg-Al series alloy, such as AZ91D of Mg-Al-Zn series, AM50 and AM60 of Mg-Al-Mn series, and AE42 and AE44 magnesium alloy of Mg-Al-RE series. Among the most widely used commercial magnesium alloys are AZ91D and AM60, both of which possess excellent castability. Among the above alloys, AE44 (Mg-4 Al-4RE, RE is La/Ce mischmetal) is a die-cast magnesium alloy with higher strength, higher plasticity and good casting performance, and the typical mechanical properties of the alloy in the die-cast state are as follows: the yield strength is 130-150 MPa, the tensile strength is 230-250 MPa, the elongation is 8-14%, the mechanical property of the alloy is further improved to the following level after the die casting and artificial aging treatment (T5): the yield strength is 140-160 MPa, the tensile strength is 245-265 MPa, and the elongation is 8-14%. In order to promote the application of magnesium alloy, the development of die-casting magnesium alloy materials with better strong plasticity becomes one of the main development directions in the field of magnesium alloy die-casting at present. Therefore, chinese patent CN201810812693.2 discloses a technical scheme for improving the strong plasticity of the alloy by adding 0.01-3.0 wt% of one or more elements of Gd, Y, sm, nd, er, eu, ho, tm, lu, dy and Yb on the basis of AE44 alloy, and the strong plasticity of the alloy is obviously improved. The die casting practice shows that elements such as Gd, Y, sm, nd, er, eu, ho, tm, lu, dy, yb and the like have high surface activity and are easy to oxidize in the die casting production process, obvious oxide skin can be generated, the oxide skin is rolled into a casting, the strength and plasticity of the alloy are obviously reduced, and the part containing the oxide skin on the casting and the part without the oxide skin have huge difference in mechanical properties. Therefore, the ideal die-casting magnesium alloy has high obdurability and good casting performance, namely, low oxidation tendency, low hot cracking tendency and good fluidity. The development of high-strength and high-toughness die-casting magnesium alloy with good casting performance is one of the industrial problems which are urgently needed to be solved in the field of magnesium alloy die-casting at present.
The existing die-casting magnesium alloy is not subjected to heat treatment or only subjected to low-temperature artificial aging treatment (T5), but cannot be subjected to high-temperature solid solution and low-temperature aging treatment (T6) which can obviously improve the mechanical property of the alloy, and the main reason is that a die-casting piece mostly has a complex special-shaped structure, and the size of the casting piece can be obviously changed during high-temperature solid solution treatment, so that the casting piece after heat treatment cannot meet the size requirement easily, and a large amount of casting pieces are scrapped. The die-casting magnesium alloy can not carry out T6 heat treatment, and the improvement of the mechanical property of the casting is limited.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a high-strength and high-toughness die-casting alloy and a preparation method thereof; according to the invention, through the proportion adjustment of Al/RE elements and the alloying of Zn elements, on the basis of AE44 magnesium alloy, solid-solution Zn elements and a small amount of Mg-Zn precipitation phases are introduced, so that the yield strength and tensile strength of the alloy are obviously improved while the plasticity and casting performance of the alloy are not reduced, and the application of the die-casting magnesium alloy on main bearing members in the field of rail transit such as automobiles is facilitated.
The purpose of the invention is realized by the following technical scheme:
in a first aspect, the invention provides a high-strength and high-toughness die-casting magnesium alloy, which comprises the following components in percentage by weight:
Al：2.7～3.4％，
La：3.8～4.8％，
Zn：3.5～4.5％，
Mn：0.2～0.5％，
wherein Al/La = 68-72%, the balance being magnesium and unavoidable impurities, the sum of the percentages by weight of said impurities not exceeding 0.2%.
The invention adopts Al and La as main alloy elements: the existing research shows that Al element in AE44 magnesium alloy reacts with rare earth La and Ce element to generate Al 11 RE 3 Phase, suppressing Mg of poor thermal stability 17 Al 12 The formation of the phase improves the room temperature and high temperature strength of the alloy; rather than a discontinuous precipitated phase Mg 17 Al 12 The elimination of the phase improves the alloy strength and the alloy plasticity; high content of Al 11 RE 3 The phase also ensures that the AE44 magnesium alloy has good flowing property and thermal cracking resistance, compared with Gd, Y, sm, nd, er, eu, ho, tm, lu, dy, yb and the like, the La and Ce elements have lower oxidation tendency, and obvious oxide skin can not be generated, so that the strength and the plasticity of the alloy can not be obviously reduced; these factors result in good casting process performance of AE44 magnesium alloys. AE44 magnesium alloy is made of Al 11 RE 3 The phase and an alpha-Mg matrix phase, wherein a small amount of Al and Ce elements are dissolved in the alpha-Mg matrix. Al (aluminum) 11 RE 3 The phase and small amount of Al and Ce solid solution elements contribute to the strength of the alloy, butThe contribution effect is weak, which is also the main reason why the yield strength is not significantly improved in the AE44 alloy, although room temperature plasticity is significantly improved, compared to the AZ91D magnesium alloy.
The invention adopts Zn as a secondary main alloy element: from the foregoing analysis, it is known that in order to further improve the strength of the AE44 magnesium alloy, a new strengthening method must be introduced. The prior research shows that the alloy is compatible with dispersion strengthening (Al) 11 RE 3 Phase) is a more effective strengthening method for magnesium alloys than solid solution strengthening (Al, ce elements), and in general, precipitation strengthening is a strengthening method that is both advantageous and disadvantageous for high strength and toughness alloys because it improves the strength of magnesium alloys and reduces the plasticity of the alloys. The study shows that the La/Ce mixed rare earth is adjusted to be La element, and the relative content of the La element and Al element is adjusted to be La/Al<Adjusting the atomic ratio of La/Al =3/11 can significantly reduce the contents of Al and La elements in the α -Mg matrix, and provide conditions for introducing other solid solution elements. On the basis, the solid solution strengthening of Zn element and the precipitation strengthening of Mg-Zn phase are introduced by adding Zn element, so that the overall strengthening effect of the alloy can be obviously improved.
The invention adopts Mn as a secondary alloy element: the existing research shows that the Mn element can improve the corrosion resistance of the alloy, remove the Fe element in the melt, form an Al-Mn precipitated phase during the subsequent aging treatment of die casting, and improve the strength of the alloy. The research shows that when La/Al =3/11, the addition of Mn element mainly plays a role in improving the corrosion resistance of the alloy; the content of the produced Zn-Mn precipitated phase is lower, and the strengthening effect of the Zn-Mn precipitated phase is weaker than that of the Mg-Zn precipitated phase.
Preferably, the impurity element includes at least one of silicon, iron, copper, and nickel, and the content of silicon is not more than 0.01%, the content of iron is not more than 0.01%, the content of copper is not more than 0.03%, and the content of nickel is not more than 0.005%.
In a second aspect, the invention also provides a preparation method of the high-strength high-toughness die-casting magnesium alloy, which comprises the following steps:
s1, preparing materials: preparing pure Mg, pure Al, pure Zn, mg-La intermediate alloy and Al-Mn intermediate alloy raw materials according to the proportion;
s2, smelting: melting pure magnesium under a protection condition; after melting, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, heating the melt and adding Al-Mn intermediate alloy; and after the Al-Mn intermediate alloy is melted, adjusting the temperature of the melt, and refining to obtain the melt for later use.
S3, die-casting forming: die-casting the melt to obtain a casting;
s4, heat treatment: and (3) carrying out ultralow-temperature solution treatment and artificial aging treatment on the casting to obtain the high-strength and high-toughness die-casting magnesium alloy.
Preferably, in step S1, the raw materials are prepared and then subjected to preheating treatment, wherein the preheating temperature is 200-250 ℃ and the preheating time is 3-8 hours.
Preferably, in step S2, the protection condition is that the magnesium alloy melt is in SF 6 And CO 2 Or smelting the magnesium alloy melt under the protection of a covering agent.
Preferably, in the step S2, the melting temperature of the magnesium liquid is 700-720 ℃; the temperature of the melt is 740 to 760 ℃; adjusting the temperature of the melt to 750-760 ℃; refining is uninterrupted refining, and standing for 15-25 min for later use after refining.
Preferably, in step S3, the melt is transferred before die casting: and (3) transferring the alloy melt in the step (S2) into a magnesium alloy quantitative pouring furnace beside a die casting machine through a liquid conveying pipe, or pouring the alloy melt in the step (S2) into an ingot and then remelting the ingot in the magnesium alloy quantitative furnace beside the die casting machine to obtain the magnesium alloy melt for die casting.
Preferably, in step S3, the melt die casting is a molding technique using high vacuum die casting. The high vacuum die-casting molding technology is a vacuum die-casting molding technology which adopts the process sequence of die assembly, vacuumizing, quantitative pouring, die-casting molding and die opening and workpiece taking, and the vacuum degree in a die cavity before the quantitative pouring of the magnesium alloy melt is less than or equal to 50mbar.
As a further preferable scheme, in step S3, in the vacuum die-casting forming technology, the punch performs injection molding at a relatively high speed after the melt is poured.
As a further preferable mode, in step S3, the higher rate means that the injection rate of the punch is 3m/S or more.
Preferably, in step S4, the ultralow temperature solution treatment is solution treatment at 290 to 310 ℃ for 4 to 8 hours, and the artificial aging treatment is aging treatment at 160 to 180 ℃ for 8 to 32 hours. The ultralow temperature solution treatment and the artificial aging treatment can improve the strength and plasticity of the vacuum die-casting magnesium alloy, the size deformation of the casting in the process of solution treatment is obviously reduced, and the high-strength and high-toughness die-casting magnesium alloy is obtained.
More preferably, in step S4, the alloy after the ultra-low temperature solution treatment is cooled in the air and then subjected to artificial aging treatment.
Compared with the prior art, the invention has the main technical characteristics as follows:
(1) Compared with the conventional AE44 magnesium alloy, the alloy has obvious difference in chemical composition. The difference is mainly reflected in three aspects: (1) the variety of rare earth elements in the alloy is changed, the AE44 alloy is La/Ce mixed rare earth, and only the rare earth element La is adopted in the invention; (2) the Al/RE is obviously reduced, in the AE44 alloy, the Al/RE is 100 percent, in the invention, the Al/RE is only 68-72%; (3) the Zn content is obviously increased, the AE44 alloy does not contain or only contains trace Zn element, the Zn content in the invention is as high as 3.5-4.5%.
(2) The conventional AE44 magnesium alloy is generally subjected to low-temperature artificial aging treatment, T5 treatment for short. The invention provides an ultralow temperature solution treatment method for the first time, namely the ultralow temperature of 290-310 ℃ is adopted for solution treatment, on one hand, partial Zn element can be ensured to be dissolved in a magnesium matrix in a solid way, the foundation is provided for the subsequent artificial aging, the solid solution strengthening effect of the Zn element and the precipitation strengthening effect of an Mg-Zn phase are introduced, and the mechanical property of the alloy is obviously improved; on the other hand, in the case of a liquid, the extremely low solution temperature significantly reduces deformation during the solution treatment of the casting, namely, the ultralow temperature solution treatment method can meet the requirements of reducing the size deformation of the casting and improving the performance of the casting at the same time.
(3) Die casting with conventional AE44 compared with the magnesium alloy, the magnesium alloy has the advantages that, the alloy of the invention has higher yield strength, tensile strength and room temperature plasticity. As shown in fig. 1, room temperature tensile properties of the conventional vacuum die cast AE44 magnesium alloy (comparative example 1) are: the yield strength is 144 +/-7 MPa 256 +/-8 MPa of tensile strength elongation of 11.8 +/-1.2%; the room-temperature tensile property of the alloy after conventional vacuum die casting is that the yield strength is 195 +/-4 MPa, the tensile strength is 302 +/-8 MPa, and the elongation is 12.8 +/-1.6%. The yield strength, the tensile strength and the elongation are respectively improved: 41MPa, 46MPa, 1.0%, relative amplification of 28.5%, 18.0% and 8.5%.
(4) Compared with CN201810812693.2 patent alloy, the oxidation resistance of elements in the alloy is better, not easy to generate oxide skin defect, and has excellent casting performance, the magnesium alloy die casting with stable structure and performance can be obtained, and the application of the alloy on the main bearing parts of rail transit such as automobiles and the like can be realized.
Drawings
Non-limiting by reading with reference to the following figures the detailed description of the illustrative embodiments is provided, other features, objects and advantages of the invention will become more apparent:
FIG. 1 is a typical room temperature tensile curve for an alloy: curve 1 is a typical room temperature tensile curve for the Mg-3.1Al-4.5La-4.0Zn-0.3Mn die-cast magnesium alloy of example 1, and curve 2 is a typical room temperature tensile curve for the AE44 die-cast magnesium alloy of comparative example 1. Compared with AE44 alloy, the alloy of the invention has obviously improved strength and plasticity.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will aid those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any manner. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the concept of the invention. All falling within the scope of the invention.
Example 1
The embodiment relates to a high-strength and high-toughness die-casting magnesium alloy which comprises the following components in percentage by mass: 3.1% Al, 4.5% La, 4.0% Zn, 0.3% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
This example relates to a method for preparing high strength magnesium die-cast alloy as described above, wherein the melting step is performed in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Zn, mg-90La intermediate alloy and Al-20Mn intermediate alloy are prepared in proportion and preheated at 225 ℃ for 4 hours.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the melt temperature to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and casting the alloy melt into an ingot under the gas protection condition, and remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein the specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the die cavity, the die cavity of the die starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumizing is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar during the die-casting process.
(5) And (3) heat treatment: after die casting, the tensile test bar is subjected to solution treatment for 4 hours at 300 ℃, then air cooling is carried out after the solution treatment, and then the solution treatment is carried out for 16 hours at 160 ℃ to obtain the high-strength high-toughness die-casting magnesium alloy.
The room temperature mechanical properties of the die-cast magnesium alloy T6 prepared in the embodiment of Mg-3.1Al-4.5La-4.0Zn-0.3Mn are as follows: the yield strength is 195 +/-4 MPa, the tensile strength is 302 +/-8 MPa, and the elongation is 12.8 +/-1.6%. Typical room temperature tensile curves for the alloys are shown in FIG. 1.
Example 2
The embodiment relates to a high-strength and high-toughness die-casting magnesium alloy which comprises the following components in percentage by mass: 3.1% Al, 4.5% La, 3.5% Zn, 0.3% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
This example relates to a method for preparing high strength magnesium die-cast alloy as described above, wherein the melting step is performed in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Zn, mg-90La intermediate alloy and Al-20Mn intermediate alloy are prepared in proportion and preheated at 225 ℃ for 4 hours.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the melt temperature to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and pouring the alloy melt into an ingot under the gas protection condition, and then remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the die cavity, the die cavity of the die starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumizing is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar during the die-casting process.
(5) And (3) heat treatment: after die casting, the tensile test bar is subjected to solution treatment for 4 hours at 300 ℃, then air cooling is carried out after the solution treatment, and then the solution treatment is carried out for 16 hours at 160 ℃ to obtain the high-strength high-toughness die-casting magnesium alloy.
The room temperature mechanical properties of the die-cast magnesium alloy T6 prepared in the embodiment of Mg-3.1Al-4.5La-3.5Zn-0.3Mn are as follows: the yield strength is 172 +/-4 MPa, the tensile strength is 286 +/-6 MPa, and the elongation is 14.8 +/-1.4%.
Example 3
The embodiment relates to a high-strength and high-toughness die-casting magnesium alloy which comprises the following components in percentage by mass: 3.1% Al, 4.5% La, 4.5% Zn, 0.3% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
This example relates to a method for preparing a high strength and toughness die-cast magnesium alloy as described above, wherein the smelting process is carried out in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Zn, mg-90La intermediate alloy and Al-20Mn intermediate alloy are prepared in proportion and preheated at 225 ℃ for 4 hours.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the temperature of the melt to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and casting the alloy melt into an ingot under the gas protection condition, and remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the die cavity, the die cavity of the die starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumizing is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar during the die-casting process.
(5) And (3) heat treatment: after die casting, the tensile test bar is firstly subjected to solution treatment for 6 hours at 300 ℃, then is subjected to air cooling after the solution treatment, and then is subjected to solution treatment for 16 hours at 160 ℃ to obtain the high-strength high-toughness die casting magnesium alloy.
The die-casting magnesium alloy prepared by the embodiment with Mg-3.1Al-4.5La-4.5Zn-0.3Mn has the mechanical properties at room temperature in the T6 state as follows: the yield strength is 204 +/-5 MPa, the tensile strength is 312 +/-9 MPa, and the elongation is 9.6 +/-1.0%.
Example 4
The embodiment relates to a high-strength and high-toughness die-casting magnesium alloy which comprises the following components in percentage by mass: 2.7% Al, 3.8% La, 4.0% Zn, 0.3% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
This example relates to a method for preparing a high strength and toughness die-cast magnesium alloy as described above, wherein the smelting process is carried out in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Zn, mg-90La intermediate alloy and Al-20Mn intermediate alloy are prepared in proportion and preheated for 4 hours at 225 ℃.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the temperature of the melt to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and casting the alloy melt into an ingot under the gas protection condition, and remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the cavity, the mold cavity starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumization is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar in the die-casting process.
(5) And (3) heat treatment: after die casting, the tensile test bar is subjected to solution treatment for 4 hours at 300 ℃, then air cooling is carried out after the solution treatment, and then the solution treatment is carried out for 16 hours at 160 ℃ to obtain the high-strength high-toughness die-casting magnesium alloy.
The die-casting magnesium alloy prepared by the embodiment with Mg-2.7Al-3.8La-4.0Zn-0.3Mn has the room temperature mechanical properties of T6 state as follows: the yield strength is 192 +/-4 MPa, the tensile strength is 296 +/-7 MPa, and the elongation is 13.2 +/-1.2%.
Example 5
The embodiment relates to a high-strength and high-toughness die-casting magnesium alloy which comprises the following components in percentage by mass: 3.4% Al, 4.8% La, 4.0% Zn, 0.3% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
This example relates to a method for preparing a high strength and toughness die-cast magnesium alloy as described above, wherein the smelting process is carried out in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Zn, mg-90La intermediate alloy and Al-20Mn intermediate alloy are prepared in proportion and preheated for 4 hours at 225 ℃.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the melt temperature to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and pouring the alloy melt into an ingot under the gas protection condition, and then remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the cavity, the mold cavity starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumization is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar in the die-casting process.
(5) And (3) heat treatment: after die casting, the tensile test bar is subjected to solution treatment for 4 hours at 300 ℃, then air cooling is carried out after the solution treatment, and then the solution treatment is carried out for 16 hours at 160 ℃ to obtain the high-strength high-toughness die-casting magnesium alloy.
The die-casting magnesium alloy prepared by the embodiment with Mg-3.4Al-4.8La-4.0Zn-0.3Mn has the room temperature mechanical properties of T6 state as follows: yield strength 198 +/-4 MPa, tensile strength 305 +/-8 MPa and elongation rate 11.4 +/-1.0 percent.
Example 6
The embodiment relates to a high-strength and high-toughness die-casting magnesium alloy which comprises the following components in percentage by mass: 3.1% Al, 4.5% La, 4.0% Zn, 0.2% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
This example relates to a method for preparing high strength magnesium die-cast alloy as described above, wherein the melting step is performed in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Zn, mg-90La intermediate alloy and Al-20Mn intermediate alloy are prepared in proportion and preheated for 4 hours at 225 ℃.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the temperature of the melt to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and casting the alloy melt into an ingot under the gas protection condition, and remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein the specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the die cavity, the die cavity of the die starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumizing is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar during the die-casting process.
(5) And (3) heat treatment: after die casting, the tensile test bar is subjected to solution treatment for 4 hours at 300 ℃, then air cooling is carried out after the solution treatment, and then the solution treatment is carried out for 16 hours at 160 ℃ to obtain the high-strength high-toughness die-casting magnesium alloy.
The die-casting magnesium alloy prepared by the embodiment with Mg-3.1Al-4.5La-4.0Zn-0.2Mn has the room temperature mechanical properties of T6 state as follows: the yield strength is 192 +/-5 MPa, the tensile strength is 296 +/-7 MPa, and the elongation is 12.4 +/-1.1%.
Example 7
The embodiment relates to a high-strength and high-toughness die-casting magnesium alloy which comprises the following components in percentage by mass: 3.1% Al, 4.5% La, 4.0% Zn, 0.5% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
This example relates to a method for preparing high strength magnesium die-cast alloy as described above, wherein the melting step is performed in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Zn, mg-90La intermediate alloy and Al-20Mn intermediate alloy are prepared in proportion and preheated at 225 ℃ for 4 hours.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the temperature of the melt to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and casting the alloy melt into an ingot under the gas protection condition, and remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein the specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the die cavity, the die cavity of the die starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumizing is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar during the die-casting process.
(5) And (3) heat treatment: after die casting, the tensile test bar is firstly subjected to solution treatment for 4 hours at 300 ℃, then is subjected to air cooling after the solution treatment, and then is subjected to solution treatment for 16 hours at 160 ℃, so that the high-strength and high-toughness die-casting magnesium alloy is obtained.
The die-casting magnesium alloy prepared by the embodiment with Mg-3.1Al-4.5La-4.0Zn-0.5Mn has the room temperature mechanical properties of T6 state as follows: the yield strength is 201 +/-3 MPa, the tensile strength is 309 +/-9 MPa, and the elongation is 9.4 +/-0.8%.
Example 8
The embodiment relates to a high-strength and high-toughness die-casting magnesium alloy which comprises the following components in percentage by mass: 3.1% Al, 4.5% La, 4.0% Zn, 0.3% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
This example relates to a method for preparing high strength magnesium die-cast alloy as described above, wherein the melting step is performed in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Zn, mg-90La intermediate alloy and Al-20Mn intermediate alloy are prepared in proportion and preheated at 225 ℃ for 4 hours.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the melt temperature to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and casting the alloy melt into an ingot under the gas protection condition, and remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the magnesium alloy tensile test bar die-casting molding is completed on a 400-ton horizontal die-casting machine by adopting a specific vacuum die-casting molding technology which adopts the process sequence of die assembly, vacuum pumping, quantitative pouring, die-casting molding and die-opening workpiece taking. The specific details of the vacuum die-casting forming technology are referred to in chinese patent application CN202110806610.0 "a method and apparatus for vacuum die-casting forming of aluminum/magnesium alloy", and compared with conventional vacuum die-casting, the specific vacuum die-casting forming technology has two characteristics: on one hand, the equipment is improved, a quantitative pouring system controlled by a hydraulic piston is added, a pouring gate is sealed, and the sealing of a plunger chip piston ring is added; on the other hand, the vacuumizing process is different, in the specific vacuum die-casting forming technology, vacuumizing is started after a mold is closed and before melt is poured, the vacuumizing opening sequence is earlier, and the total vacuumizing time can be adjusted within a large range as required, such as 1-30 seconds. The specific vacuum die-casting forming technology can obviously reduce the content of air holes in the die-casting piece, obviously reduce the oxidation of the aluminum/magnesium alloy melt in the pouring and mold filling processes, and obviously reduce the casting defects of pre-crystallization and cold shut in the die-casting piece. In this embodiment, the implementation process of the specific vacuum die-casting molding technology is briefly described as follows: after the die is closed, opening a vacuum valve to vacuumize the die cavity and the pressure chamber; opening a quantitative pouring system to pour the magnesium alloy melt after the vacuum degree of the die cavity reaches 50 mbar; and closing the quantitative pouring system after pouring is finished, and then directly performing high-speed injection by using a punch to finish the die-casting molding of the magnesium alloy melt. The specific die-casting technological parameters are as follows: the mold temperature was 250 ℃, the pouring temperature was 700 ℃ and the injection rate was 3.5m/s.
(5) And (3) heat treatment: after die casting, the tensile test bar is subjected to solution treatment for 4 hours at 300 ℃, then air cooling is carried out after the solution treatment, and then the solution treatment is carried out for 16 hours at 160 ℃ to obtain the high-strength high-toughness die-casting magnesium alloy.
The room temperature mechanical properties of the die-cast magnesium alloy T6 prepared in the embodiment of Mg-3.1Al-4.5La-4.0Zn-0.3Mn are as follows: the yield strength is 193 +/-5 MPa, the tensile strength is 305 +/-7 MPa, and the elongation is 15.6 +/-1.2%.
Comparative example 1
The comparative example relates to an AE44 high-strength and high-toughness die-casting magnesium alloy, which comprises the following components in percentage by mass: 4.0% Al, 4.0% RE, 0.3% Mn, wherein RE is cerium-rich misch metal (2.54% Ce,1.46% La), the total content of impurity elements Si, fe, cu and Ni is less than 0.2 percent, and the balance is Mg.
The comparative example relates to a preparation method of the high-strength high-toughness die-casting magnesium alloy, wherein the smelting process is carried out in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, cerium-rich mischmetal and Al-20Mn intermediate alloy are prepared in proportion and preheated for 4 hours at 225 ℃.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al and cerium-rich mischmetal into the magnesium liquid; to be alloyed with after the molten materials are completely melted, the molten materials are mixed, when the temperature of the melt is raised to 750 ℃, adding Al-Mn intermediate alloy; after the Al-Mn intermediate alloy is melted, adjusting the temperature of the melt to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and pouring the alloy melt into an ingot under the gas protection condition, and then remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting the conventional high-vacuum die-casting technology, the specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the cavity, after the punch head moves beyond the gate, the die cavity starts to be vacuumized, after high-speed injection starts, the vacuumization stops, the lowest vacuum degree of the vacuum valve is less than 100mbar in the die casting process.
(5) And (3) heat treatment: after die casting, the tensile test bar is subjected to aging treatment for 4 hours at 225 ℃ (T5 treatment) to obtain the high-strength high-toughness die-casting magnesium alloy AE44.
The room temperature mechanical properties of the die-casting magnesium alloy T5 prepared by the comparative example in the state of Mg-4.0Al-4.0RE-0.3Mn are as follows: the yield strength is 144 +/-7 MPa, the tensile strength is 256 +/-8 MPa, and the elongation is 11.8 +/-1.2%. The room temperature strength of the alloy is significantly reduced compared to example 1.
Comparative example 2
The comparative example relates to a high-strength and high-toughness die-casting magnesium alloy, which comprises the following components in percentage by mass: 4.0% Al, 4.0% RE, 4.0% Zn, 0.3% Mn, wherein RE is cerium-rich misch metal (2.54% Ce,1.46% La), the total content of the impurity elements Si, fe, cu and Ni is less than 0.2%, the balance being Mg.
This comparative example relates to a method for producing a high strength die-cast magnesium alloy as described above, wherein the melting step is carried out in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Zn, cerium-rich mischmetal and Al-20Mn master alloy are prepared in proportion and preheated for 4 hours at 225 ℃.
(2) Smelting: after preheating of pure magnesium in melting under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and cerium-rich mischmetal into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the temperature of the melt to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: casting the alloy melt into an ingot under the gas protection condition, remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine, obtaining the magnesium alloy melt for die-casting molding.
(4) Die-casting and forming: adopts the conventional high vacuum die casting technology to be horizontal at 400 tons the die casting machine completes the die casting of the magnesium alloy tensile test bar, the specific die-casting process parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the cavity, the mold cavity starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumization is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar in the die-casting process.
(5) And (3) heat treatment: after die-casting forming, the tensile test bar is subjected to aging treatment for 4 hours at 225 ℃ (T5 treatment) to obtain the high-strength high-toughness die-casting magnesium alloy.
Mg-4.0Al-4.0RE-4.0Zn-0.3 prepared by the comparative example the room temperature mechanical properties of the Mn die-casting magnesium alloy in the T5 state are as follows: the yield strength is 155 plus or minus 9MPa, the tensile strength is 244 plus or minus 6MPa, and the elongation is 7.8 plus or minus 0.9 percent. The room temperature strength and plasticity of the alloy are significantly reduced compared to example 1.
Comparative example 3
The comparative example relates to a high-strength and high-toughness die-casting magnesium alloy, which comprises the following components in percentage by mass: 3.1% Al, 4.5% La, 3.0% Zn, 0.3% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
The comparative example relates to a preparation method of the high-strength high-toughness die-casting magnesium alloy, wherein the smelting process is carried out in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: preparing pure Mg, pure Al, pure Zn, mg-90La intermediate alloy and Al-20Mn intermediate alloy according to a certain proportion, and preheated at 225 ℃ for 4 hours.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the melt temperature to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and pouring the alloy melt into an ingot under the gas protection condition, and then remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the die cavity, the die cavity of the die starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumizing is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar during the die-casting process.
(5) And (3) heat treatment: after die casting, the tensile test bar is subjected to solution treatment for 4 hours at 300 ℃, then air cooling is carried out after the solution treatment, and then the solution treatment is carried out for 16 hours at 160 ℃ to obtain the high-strength high-toughness die-casting magnesium alloy.
The room temperature mechanical properties of the die-casting magnesium alloy T6 state prepared by the comparative example and having Mg-3.1Al-4.5La-3.0Zn-0.3Mn are as follows: yield strength of 155 +/-6 MPa, tensile strength of 274 +/-8 MPa and elongation of 15.8 +/-1.3 percent. The room temperature strength of the alloy is significantly reduced compared to example 1.
Comparative example 4
The comparative example relates to a high-strength and high-toughness die-casting magnesium alloy, which comprises the following components in percentage by mass: 3.1% Al, 4.5% La, 5.0% Zn, 0.3% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
This comparative example relates to a method for producing a high strength die-cast magnesium alloy as described above, wherein the melting step is carried out in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Zn, mg-90La intermediate alloy and Al-20Mn intermediate alloy are prepared in proportion and preheated at 225 ℃ for 4 hours.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the temperature of the melt to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and casting the alloy melt into an ingot under the gas protection condition, and remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the die cavity, the die cavity of the die starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumizing is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar during the die-casting process.
(5) And (3) heat treatment: after die casting, the tensile test bar is firstly subjected to solution treatment for 4 hours at 300 ℃, then is subjected to air cooling after the solution treatment, and then is subjected to solution treatment for 16 hours at 160 ℃, so that the high-strength and high-toughness die-casting magnesium alloy is obtained.
The room temperature mechanical properties of the die-casting magnesium alloy T6 prepared by the comparative example are as follows: the yield strength is 209 +/-7 MPa, the tensile strength is 314 +/-6 MPa, and the elongation is 6.4 +/-0.7%. The plasticity of the alloy is significantly reduced compared to example 1.
Comparative example 5
The comparative example relates to a high-strength and high-toughness die-casting magnesium alloy, which comprises the following components in percentage by mass: 3.9% Al, 5.6% La, 4.0% Zn, 0.3% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
This comparative example relates to a method for producing a high strength die-cast magnesium alloy as described above, wherein the melting step is carried out in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Zn, mg-90La intermediate alloy and Al-20Mn intermediate alloy are prepared in proportion and preheated for 4 hours at 225 ℃.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the temperature of the melt to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and casting the alloy melt into an ingot under the gas protection condition, and remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein the specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the cavity, the mold cavity starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumization is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar in the die-casting process.
(5) And (3) heat treatment: after die casting, the tensile test bar is subjected to solution treatment for 4 hours at 300 ℃, then air cooling is carried out after the solution treatment, and then the solution treatment is carried out for 16 hours at 160 ℃ to obtain the high-strength high-toughness die-casting magnesium alloy.
The room temperature mechanical properties of the die-casting magnesium alloy T6 prepared by the comparative example in the state of Mg-3.9Al-5.6La-4.0Zn-0.3Mn are as follows: the yield strength is 192 +/-6 MPa, the tensile strength is 288 +/-7 MPa, and the elongation is 5.7 +/-0.6%. The plasticity of the alloy is significantly reduced compared to example 1. Significant reduction of alloy plasticity and Al 11 La 3 High content and large size.
Comparative example 6
The comparative example relates to a high-strength and high-toughness die-casting magnesium alloy, which comprises the following components in percentage by mass: 2.2% Al, 3.1% La, 4.0% Zn, 0.3% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
The comparative example relates to a preparation method of the high-strength high-toughness die-casting magnesium alloy, wherein the smelting process is carried out in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Zn, mg-90La intermediate alloy and Al-20Mn intermediate alloy are prepared in proportion and preheated at 225 ℃ for 4 hours.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the temperature of the melt to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and pouring the alloy melt into an ingot under the gas protection condition, and then remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein the specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the die cavity, the die cavity of the die starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumizing is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar during the die-casting process. When the die is opened to take out the part after die-casting, hot cracks appear at the clamping end of part of the tensile test bar and the transition arc of the gauge length section, and the casting performance of the alloy is obviously reduced compared with that of AE44 magnesium alloy.
(5) And (3) heat treatment: after die casting, the tensile test bar is subjected to solution treatment for 4 hours at 300 ℃, then air cooling is carried out after the solution treatment, and then the solution treatment is carried out for 16 hours at 160 ℃ to obtain the high-strength high-toughness die-casting magnesium alloy.
The room temperature mechanical properties of the Mg-2.2Al-3.1La-4.0Zn-0.3Mn die casting magnesium alloy (when no crack exists) prepared by the comparative example in the T6 state are as follows: the yield strength is 182 +/-5 MPa, the tensile strength is 283 +/-8 MPa, and the elongation is 12.6 +/-0.9%. The alloy was remarkably reduced in hot cracking resistance as compared with example 1, and thus it was not suitable for use as a die casting material.
Comparative example 7
The comparative example relates to a high-strength and high-toughness die-casting magnesium alloy, which comprises the following components in percentage by mass: 3.1% Al, 4.5% La, 4.0% Cu, 0.3% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
The comparative example relates to a preparation method of the high-strength high-toughness die-casting magnesium alloy, wherein the smelting process is carried out in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Cu, mg-90La intermediate alloy and Al-20Mn intermediate alloy are prepared in proportion and preheated at 225 ℃ for 4 hours.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Cu and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the melt temperature to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and pouring the alloy melt into an ingot under the gas protection condition, and then remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the cavity, the mold cavity starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumization is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar in the die-casting process.
(5) And (3) heat treatment: after die casting, the tensile bar is firstly subjected to solution treatment for 4 hours at 300 ℃, then is subjected to air cooling after the solution treatment, and then is subjected to solution treatment for 16 hours at 160 ℃ to obtain the die casting magnesium alloy.
The room temperature mechanical properties of the die-casting magnesium alloy T6 prepared by the comparative example are as follows: yield strength of 155 +/-5 MPa, tensile strength of 264 +/-6 MPa and elongation of 5.8 +/-0.7 percent. Compared with example 1, the alloy has obviously reduced room temperature strength and plasticity.
Comparative example 8
The comparative example relates to a high-strength and high-toughness die-casting magnesium alloy, which comprises the following components in percentage by mass: 3.1% Al, 4.5% La, 1.5% Gd, 0.3% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
This comparative example relates to a method for producing a high strength die-cast magnesium alloy as described above, wherein the melting step is carried out in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: preparing pure Mg, pure Al, cerium-rich mischmetal, mg-90Gd and Al-20Mn intermediate alloy according to the proportion, and preheating for 4 hours at 225 ℃.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, cerium-rich mischmetal and Mg-Gd intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the melt temperature to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and casting the alloy melt into an ingot under the gas protection condition, and remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein the specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the die cavity, the die cavity of the die starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumizing is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar during the die-casting process.
(5) And (3) heat treatment: after die casting, the tensile test bar is subjected to solution treatment for 4 hours at 300 ℃, then air cooling is carried out after the solution treatment, and then the solution treatment is carried out for 16 hours at 160 ℃ to obtain the high-strength high-toughness die-casting magnesium alloy.
The room temperature mechanical properties of the die-casting magnesium alloy T5 prepared by the comparative example are as follows: the yield strength is 154 plus or minus 8MPa, the tensile strength is 244 plus or minus 12MPa, and the elongation is 7.2 plus or minus 2.4 percent. Compared with example 1, the alloy has obviously reduced room temperature strength and plasticity. The lower elongation and larger fluctuation of the alloy are related to the occasional discovery of oxide scale at the fracture surface.
Comparative example 9
The comparative example relates to a high-strength and high-toughness die-casting magnesium alloy, which comprises the following components in percentage by mass: 3.1% Al, 4.8% La, 4.0% zn, 0.3% mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the balance Mg, wherein Al/La =0.65.
This comparative example relates to a method for producing a high strength die-cast magnesium alloy as described above, wherein the melting step is carried out in SF 6 And CO 2 Gas mixtureUnder the protection condition, the method comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Zn, mg-90La intermediate alloy and Al-20Mn intermediate alloy are prepared in proportion and preheated at 225 ℃ for 4 hours.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the melt temperature to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and pouring the alloy melt into an ingot under the gas protection condition, and then remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein the specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the cavity, the mold cavity starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumization is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar in the die-casting process.
(5) And (3) heat treatment: after die casting, the tensile test bar is subjected to solution treatment for 4 hours at 300 ℃, then air cooling is carried out after the solution treatment, and then the solution treatment is carried out for 16 hours at 160 ℃ to obtain the high-strength high-toughness die-casting magnesium alloy.
The room temperature mechanical properties of the die-casting magnesium alloy T6 state prepared by the comparative example and having Mg-3.1Al-4.8La-4.0Zn-0.3Mn are as follows: the yield strength is 158 +/-6 MPa, the tensile strength is 252 +/-78 MPa, and the elongation is 12.4 +/-0.8%. The room temperature strength of the alloy is significantly reduced compared to example 1. When the relative content of the aluminum element in the alloy is lower than 0.68-0.72, the excessive La element reduces the solid solution amount of the Zn element during the ultralow temperature solid solution treatment, thereby reducing the solid solution strengthening and precipitation strengthening effects of the Zn element.
Comparative example 10
The comparative example relates to a high-strength and high-toughness die-casting magnesium alloy, which comprises the following components in percentage by mass: 3.4% Al, 4.5% La, 4.0% zn, 0.3% mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the balance Mg, wherein Al/La =0.76.
The comparative example relates to a preparation method of the high-strength high-toughness die-casting magnesium alloy, wherein the smelting process is carried out in SF 6 And CO 2 The method is carried out under the protection of mixed gas and comprises the following steps:
(1) Preparing materials: pure Mg, pure Al, pure Zn, mg-90La intermediate alloy and Al-20Mn intermediate alloy are prepared in proportion and preheated at 225 ℃ for 4 hours.
(2) Smelting: melting the preheated pure magnesium under the condition of gas protection; when the temperature of the magnesium liquid reaches 710 ℃, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, adding Al-Mn intermediate alloy when the temperature of the melt is raised to 750 ℃; after the Al-Mn intermediate alloy is melted, adjusting the melt temperature to 755 ℃, refining without power off, and standing for 15 minutes for later use after refining.
(3) Melt transfer: and pouring the alloy melt into an ingot under the gas protection condition, and then remelting the ingot in a magnesium alloy quantitative furnace beside a die casting machine to obtain the magnesium alloy melt for die casting.
(4) Die-casting and forming: the die-casting forming of the magnesium alloy tensile test bar is completed on a 400-ton horizontal die-casting machine by adopting a conventional high-vacuum die-casting technology, wherein specific die-casting technological parameters are as follows: the mold temperature is 250 ℃, the pouring temperature is 700 ℃, the low-speed section injection rate is 0.2m/s, and the high-speed section injection rate is 3.5m/s; the vacuum valve is positioned at the tail end of the cavity, the mold cavity starts to be vacuumized after the punch moves beyond the pouring gate, the vacuumization is stopped after the high-speed injection starts, and the lowest vacuum degree of the vacuum valve is less than 100mbar in the die-casting process.
(5) And (3) heat treatment: after die casting, the tensile test bar is subjected to solution treatment for 4 hours at 300 ℃, then air cooling is carried out after the solution treatment, and then the solution treatment is carried out for 16 hours at 160 ℃ to obtain the high-strength high-toughness die-casting magnesium alloy.
The room temperature mechanical properties of the die-casting magnesium alloy T6 prepared by the comparative example in the state of Mg-3.4Al-4.5La-4.0Zn-0.3Mn are as follows: the yield strength is 162 +/-7 MPa, the tensile strength is 256 +/-9 MPa, and the elongation is 11.4 +/-0.9%. The room temperature strength of the alloy is significantly reduced compared to example 1. When the relative content of the aluminum element in the alloy is higher than 0.68-0.72, the excessive Al element reduces the solid solution amount of the Zn element during the ultralow temperature solid solution treatment, thereby reducing the solid solution strengthening and precipitation strengthening effects of the Zn element.
Comparative example 11
The comparative example relates to a high-strength and high-toughness die-casting magnesium alloy, the chemical components of the alloy are the same as those in example 1, and the magnesium alloy comprises the following components in percentage by mass: 3.1% Al, 4.5% La, 4.0% Zn, 0.3% Mn, the total content of the impurity elements Si, fe, cu and Ni being less than 0.2%, the remainder being Mg.
The preparation method of the high-strength high-toughness die-casting magnesium alloy in the comparative example is basically the same as that of the example 1, and the difference is that: (5) heat treatment: after die casting forming, a tensile test bar is subjected to solution treatment for 4 hours at 350 ℃, air cooling is carried out after the solution treatment, and then the solution treatment is carried out for 16 hours at 160 ℃, so that the high-strength high-toughness die-casting magnesium alloy is obtained.
The room temperature mechanical properties of the die-casting magnesium alloy T6 state prepared by the comparative example and having Mg-3.1Al-4.5La-4.0Zn-0.3Mn are as follows: the yield strength is 204 +/-6 MPa, the tensile strength is 308 +/-12 MPa, and the elongation is 11.3 +/-1.4%. After heat treatment, the tensile test bar is obviously warped, the bending deformation of the gauge length section of the test bar is obvious, and the room-temperature mechanical test result is inaccurate due to size deformation. The tensile bars are comparable in strength and plasticity at room temperature but significant in dimensional deformation compared to example 1. The actual die casting mostly has a complex special-shaped structure, and the size deformation of the casting is more obvious by adopting a solution treatment process with higher temperature of 350 ℃, so that the casting after heat treatment is difficult to meet the size requirement, and the casting is scrapped in large quantity, therefore, the high-toughness die-casting magnesium alloy casting such as Mg-3.1Al-4.5La-4.0Zn-0.3Mn cannot be prepared by adopting a conventional high-temperature solution treatment process.
In conclusion, the examples and the comparative examples show that the die-casting magnesium alloy with high strength and high toughness is designed and developed by substituting La/Ce mischmetal with La/Ce, adjusting the Al/RE ratio and introducing Zn solid solution elements and Mg-Zn precipitated phases. Compared with the existing Mg-Al-RE alloy, the Mg-Al-La-Zn-Mn alloy has higher strength and better plasticity, and is a high-strength and high-toughness die-casting magnesium alloy with both strong plasticity and plasticity.
The foregoing description has described specific embodiments of the present invention. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.
Claims (10)
1. The high-strength and high-toughness die-casting magnesium alloy is characterized by comprising the following components in percentage by weight: 2.7 to 3.4 percent of Al,3.8 to 4.8 percent of La,3.5 to 4.5 percent of Zn and 0.2 to 0.5 percent of Mn; the balance being magnesium and unavoidable impurities.
2. The high strength die-cast magnesium alloy according to claim 1, wherein the mass ratio of Al to La in the alloy is 68-72%.
3. The preparation method of the high-strength high-toughness die-casting magnesium alloy according to claim 1, characterized by comprising the following steps:
s1, preparing materials: preparing pure Mg, pure Al, pure Zn, mg-La intermediate alloy and Al-Mn intermediate alloy raw materials according to the proportion;
s2, smelting: melting pure magnesium under protection conditions; after melting, adding pure Al, pure Zn and Mg-La intermediate alloy into the magnesium liquid; after the alloy is completely melted, heating the melt and adding Al-Mn intermediate alloy; after the Al-Mn intermediate alloy is melted, adjusting the temperature of the melt for refining to obtain the melt for later use.
S3, die-casting forming: die-casting the melt to obtain a casting;
s4, heat treatment: and carrying out ultralow-temperature solution treatment and artificial aging treatment on the casting to obtain the high-strength and high-toughness die-casting magnesium alloy.
4. The method for preparing the high-strength high-toughness die-cast magnesium alloy according to claim 3, wherein in the step S1, the raw materials are prepared and then subjected to preheating treatment, wherein the preheating temperature is 200-250 ℃, and the preheating time is 3-8 hours.
5. The method for preparing the high-strength high-toughness die-cast magnesium alloy according to claim 3, wherein in the step S2, the protection condition refers to that the magnesium alloy melt is in SF 6 And CO 2 Or smelting the magnesium alloy melt under the protection of a covering agent.
6. The method for preparing the high strength and toughness die-cast magnesium alloy according to claim 3, wherein in the step S2, the melting temperature of the pure magnesium is 700-720 ℃.
7. The method for preparing the high strength and toughness die-cast magnesium alloy according to claim 3, wherein in the step S2, the temperature of the melt is increased to 740 to 760 ℃.
8. The method for preparing the high-toughness die-cast magnesium alloy according to claim 3, wherein in the step S2, the temperature of the melt is adjusted to 750 to 760 ℃.
9. The method for producing a high strength/toughness die-cast magnesium alloy according to claim 3, wherein the ultra-low temperature solution treatment in step S4 is solution treatment at 290 to 310 ℃ for 4 to 8 hours.
10. The method for preparing the high-strength high-toughness die-cast magnesium alloy according to claim 3, wherein in the step S4, the artificial aging treatment is aging treatment at 160-180 ℃ for 8-32 hours.
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