A lightweight, low-cost cast aluminum-lithium alloy with excellent casting performance and a preparation method thereof

Abstract

The present invention provides a casting aluminum-lithium alloy, which comprises, by weight percentage, 2.5-3.5% Li, 3.5-5.0% Mg, 1.0-2.5% Si, 0.1-0.2% Zr, the total content of impurity elements is less than 0.25%, and the balance is Al. The present invention also provides a method for preparing the casting aluminum-lithium alloy. The casting aluminum-lithium alloy provided by the present invention has superior casting performance, low density, excellent mechanical properties and low cost, and the casting aluminum-lithium alloy prepared by the preparation method has high purity.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials and metallurgy thereof, and in particular to an aluminum-lithium alloy and a preparation method thereof. Background Art

[0002] Due to the demand for energy conservation and ecological protection, the research and development of lightweight structural materials is becoming increasingly important. Among them, aluminum-lithium alloys have the advantages of low density, high strength, and high elastic modulus, and are now widely used in the aerospace field. At present, the research and application of deformed aluminum-lithium alloys are relatively mature, but there are fewer studies on cast aluminum-lithium alloys, which are still in the initial stage. There are a large number of structural parts with small structures, complex shapes, and fine cavities in various aircraft that need to be cast. Therefore, the research and development of cast aluminum-lithium alloys is of great significance to promoting the lightweighting of aerospace structural parts.

[0003] Superior casting performance is the basis for the actual production and application of cast aluminum-lithium alloy. At present, the composition of cast aluminum-lithium alloy mainly refers to deformed aluminum-lithium alloy, using Al-Cu-Li system.

[0004] Patent CN 104451272 B discloses a lightweight, high-strength cast aluminum-lithium alloy and its preparation method, wherein the elements are 1.5% to 2.5% Cu, 2% to 3% Li, 0.4-1.2% Mg, 0.2% to 0.8% Zn, 0.3% to 0.8% Ag, 0.1% to 0.8% Mn, and 0.08% to 0.25% Zr. The addition of Cu will widen the solid-liquid phase interval of the cast aluminum-lithium alloy (when the Cu content is 1.5% to 4.5%, the solid-liquid phase interval is approximately 95 to 107°C), reduce the casting performance of the alloy, increase the alloy's hot cracking and shrinkage tendency, seriously affect the overall mechanical properties of the component, and reduce the product yield. In addition, the density of Cu is 8.96g / cm 3 The addition of Cu will increase the density of the aluminum-lithium alloy and cannot give full play to the advantage of the low density of the aluminum-lithium alloy.

[0005] Patent CN 109797322B discloses a lightweight cast aluminum-lithium alloy and its preparation method, with the mass fraction of each element being: 2.5-3.5% Li, 5.2-9.2% Mg, 0.08-0.20% Zr, 0.08-0.30% Sc. Although the patent avoids the addition of Cu, its high Mg content will result in a large solid-liquid phase interval (when the Mg content is 5.2%-9.2%, the solid-liquid phase interval is about 102-115°C), resulting in poor alloy casting performance. Moreover, the addition of Sc element will significantly increase the alloy cost.

[0006] It can be seen that the currently developed casting aluminum-lithium alloy systems lack superior casting properties, which limits the actual production and application of casting aluminum-lithium alloys and is also the key reason for the current lack of research on casting aluminum-lithium alloys.

[0007] Therefore, in order to further promote the application of cast aluminum-lithium alloys in the aerospace field, the current key is to develop cast aluminum-lithium alloys with superior casting performance, low density, excellent mechanical properties and low cost. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a casting aluminum-lithium alloy with superior casting performance, low density, excellent mechanical properties and low cost and a preparation method thereof.

[0009] To solve the above technical problems, the present invention provides a casting aluminum-lithium alloy, which includes, by weight percentage, 2.5-3.5% Li, 3.5-5.0% Mg, 1.0-2.5% Si, 0.1-0.2% Zr, the total content of impurity elements is less than 0.25%, and the balance is Al.

[0010] The present invention also provides a method for preparing a cast aluminum-lithium alloy, comprising the following steps:

[0011] The raw materials are prepared according to the alloy components in the weight percentage, including pure Al, pure Li, Al-Si master alloy, Al-Mg master alloy and Al-Zr master alloy;

[0012] Preheat the raw materials except pure Li at 200-220°C for 2-4 hours;

[0013] Melting pure Al, and adding Al-Si master alloy and Al-Zr master alloy when the pure Al melt is heated to 770-790° C. to obtain a first alloy melt;

[0014] After the temperature of the first alloy melt rises back to 770-790° C., the first alloy melt is cooled to 730-740° C. and an Al-Mg master alloy is added to obtain a second alloy melt;

[0015] When the temperature of the second alloy melt rises back to 730-740° C., a covering agent is sprinkled on the surface of the second alloy melt and pure Li is pressed into the second alloy melt using a graphite bell jar under argon protection to obtain a third alloy melt;

[0016] When the temperature of the third alloy melt rises to 750-760° C., stirring the third alloy melt;

[0017] The third alloy melt is cooled to 730-740°C for refining;

[0018] After refining, the third alloy melt is cooled to 710-720°C, allowed to stand, slag removed, and cast to obtain an aluminum-lithium alloy;

[0019] The aluminum-lithium alloy is subjected to solution treatment and aging treatment.

[0020] Furthermore, the covering agent is a mixed solvent of LiCl and LiF, and the weight ratio of LiCl to LiF is 3:1.

[0021] Furthermore, the refining is performed by refining the third alloy melt using hexachloroethane under argon protection.

[0022] Furthermore, the standing time is 15-20 minutes, and the steel mold for casting is preheated to 200-220°C in advance.

[0023] Furthermore, the solution treatment adopts a two-stage solution treatment: the aluminum-lithium alloy is first treated at 380-420°C for 6-10 hours, and then treated at 480-530°C for 10-15 hours.

[0024] Furthermore, the aging treatment is to treat the aluminum-lithium alloy at 150-200° C. for 20-30 hours.

[0025] The present invention provides a cast aluminum-lithium alloy that does not contain metal elements such as Cu and Ag, has a narrow solid-liquid phase interval, reduces shrinkage and thermal cracking tendencies, and enables the alloy to have good casting properties. In addition, the present invention does not add heavy metal elements such as Cu, Ag, Zn and Mn, so that the alloy has a lower density, achieves lightweight alloys, and gives full play to the low-density advantage of aluminum-lithium alloys. In addition, the present invention provides a cast aluminum-lithium alloy that does not contain precious metal elements such as Sc, has low cost, has high economic value, and is conducive to the actual production and application of cast aluminum-lithium alloys.

[0026] In addition, the present invention provides a cast aluminum-lithium alloy, which optimizes the addition content of Mg element. Mg plays a solid solution strengthening effect on one hand, and reduces the solubility of Li in Al on the other hand, promotes the aging precipitation of Al3Li phase, and improves the strength of the alloy. However, if the Mg content exceeds 5.0%, the solid-liquid phase interval is large, the casting performance of the alloy is reduced, and the smelting process is dangerous, the loss increases, and when vacuum smelting is adopted, the equipment cost will be increased. However, if the Mg element content is too low, the strengthening effect is insufficient, so the present invention controls the Mg content to 3.5-5.0%.

[0027] The present invention provides a casting aluminum-lithium alloy, which optimizes the addition content of Si element. Adding Si can reduce the solid-liquid phase interval, increase the melting latent heat, improve the melt fluidity, and improve the filling capacity of the melt. On the other hand, it can reduce the linear expansion coefficient, reduce the thermal cracking tendency, and comprehensively improve the casting performance of the alloy. When the Si addition amount is about 2.0%, the solid-liquid phase interval can be reduced to about 54°C, but too high Si content will lead to an increase in the proportion of eutectic structure, affecting the strength and plasticity of the alloy, so the present invention controls the Si content to 1.0-2.5%.

[0028] The invention provides a cast aluminum-lithium alloy, in which the Li content is controlled within the range of 2.5% to 3.5%, thereby reducing the segregation tendency of Li, lowering the density of the alloy, and improving its strength and rigidity.

[0029] At the same time, the present invention provides a method for preparing a cast aluminum-lithium alloy, which adds the Li element by pressing pure Li into a graphite bell jar under the dual protection of a covering agent and argon gas, thereby reducing inclusions introduced by adding the Li element in the form of an Al-Li intermediate alloy, improving the purity of the melt, and improving the quality of the alloy ingot. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A flow chart of a method for preparing a cast aluminum-lithium alloy provided in an embodiment of the present invention;

[0031] Figure 2 A metallographic photograph of the cast structure of the cast aluminum-lithium alloy prepared by the method for preparing the cast aluminum-lithium alloy provided in Example 1 of the present invention;

[0032] Figure 3 A metallographic photograph of the as-cast structure of a cast aluminum-lithium alloy prepared by the method for preparing a cast aluminum-lithium alloy provided in Example 2 of the present invention;

[0033] Figure 4 A metallographic photograph of the as-cast structure of a cast aluminum-lithium alloy prepared by the method for preparing a cast aluminum-lithium alloy provided in Example 3 of the present invention;

[0034] Figure 5 This is a metallographic photograph of the cast structure of the cast aluminum-lithium alloy prepared by the cast aluminum-lithium alloy preparation method provided in Example 4 of the present invention. DETAILED DESCRIPTION

[0035] A cast aluminum-lithium alloy provided in an embodiment of the present invention comprises, by weight percentage:

[0036] 2.5-3.5% Li, 3.5-5.0% Mg, 1.0-2.5% Si, 0.1-0.2% Zr, the total content of impurity elements is less than 0.25%, and the balance is Al. The cast aluminum-lithium alloy provided by the present invention does not contain precious metal elements such as Cu, Ag, Zn, Sc, etc., has a narrow solid-liquid phase interval, excellent casting performance, low density, low cost, and excellent mechanical properties.

[0037] See also Figure 1 The present invention provides a method for preparing a cast aluminum-lithium alloy, comprising the following steps:

[0038] 1) In terms of weight percentage, the raw materials are prepared with an alloy composition of 2.5-3.5% Li, 3.5-5.0% Mg, 1.0-2.5% Si, 0.1-0.2% Zr, the total content of impurity elements is less than 0.25%, and the balance is Al, including pure Al, pure Li, Al-Si master alloy, Al-Mg master alloy and Al-Zr master alloy.

[0039] 2) Preheat the other raw materials except pure Li at 200-220°C for 2-4 hours.

[0040] 3) Continue to heat pure Al to melt it, and when the temperature of the pure Al melt rises to 770-790°C, add Al-Si master alloy and Al-Zr master alloy to obtain the first alloy melt, and raise its temperature back to 770-790°C.

[0041] 4) Cooling the first alloy melt to 730-740° C. and adding Al-Mg master alloy to obtain a second alloy melt.

[0042] 5) When the temperature of the second alloy melt rises back to 730-740° C., a covering agent is sprinkled on the surface of the second alloy melt and pure Li is pressed into the third alloy melt using a graphite bell under argon protection. The covering agent is a mixed solvent of LiCl and LiF, and the weight ratio of LiCl to LiF is controlled to be 3:1.

[0043] 6) When the temperature of the third alloy melt rises to 750-760° C., the third alloy melt is stirred.

[0044] 7) Cooling the third alloy melt to 730-740° C. for refining. The refining is performed by using hexachloroethane to refine the third alloy melt under argon protection.

[0045] 8) After refining, the third alloy melt is cooled to 710-720°C, allowed to stand, slag removed, and cast to obtain an aluminum-lithium alloy, wherein the standing time is 15-20 minutes, and the steel mold used for casting is preheated to 200-220°C in advance.

[0046] 9) The aluminum-lithium alloy is subjected to a solution treatment and an aging treatment. The solution treatment adopts a two-stage solution treatment: the aluminum-lithium alloy is first treated at 380-420°C for 6-10 hours, and then treated at 480-530°C for 10-15 hours. The aging treatment is to treat the aluminum-lithium alloy at 150-200°C for 20-30 hours.

[0047] The preparation method of the cast aluminum-lithium alloy provided by the present invention adopts the method of adding the Li element by pressing pure Li into a graphite bell jar under the dual protection of a covering agent and argon gas, which can reduce the inclusions brought in by adding the Li element in the form of an Al-Li master alloy, can improve the purity of the melt, and improve the quality of the alloy ingot.

[0048] The following is a detailed description of the method for preparing a cast aluminum-lithium alloy provided by the present invention through examples and comparative examples.

[0049] Example 1

[0050] A low-cost aluminum-lithium alloy with light weight, high strength and excellent casting performance comprises the following components in percentage by weight: 2.82% Li, 3.72% Mg, 1.23% Si, 0.15% Zr, and the balance is Al.

[0051] Pure aluminum is melted, and Al-Si master alloy and Al-Zr master alloy are added when the melt temperature rises to 770°C. After the melt temperature returns to 770°C, the melt is cooled to 740°C and Al-Mg master alloy is added. When the temperature returns to 740°C, a covering agent (LiF:LiCl=1:3) is sprinkled on the surface of the melt, and pure Li is pressed into a graphite bell under argon protection. When the temperature rises to 750°C, the melt is stirred, and the melt temperature is reduced to 740°C. Hexachloroethane is used for refining under argon protection. After refining, the melt is cooled to 720°C and allowed to stand for 15 minutes. After standing, the slag is removed and the melt is cast into a steel mold preheated to 200°C.

[0052] The castings are subjected to solution treatment and aging treatment. The solution treatment system is 400℃ / 8h+515℃ / 12h, and the aging treatment system is 175℃ / 25h.

[0053] The metallographic photograph of the cast aluminum-lithium alloy prepared by the method for preparing the cast aluminum-lithium alloy provided in the embodiment of the present invention is as follows: Figure 2 The mechanical properties, density and solid-liquid phase range of the cast aluminum-lithium alloy T6 prepared in this embodiment are shown in Table 1.

[0054] Example 2

[0055] A low-cost aluminum-lithium alloy with light weight, high strength and excellent casting performance comprises the following components in percentage by weight: 2.75% Li, 4.97% Mg, 1.64% Si, 0.14% Zr, and the balance is Al.

[0056] Pure aluminum is melted, and Al-Si master alloy and Al-Zr master alloy are added when the melt temperature rises to 780°C. After the melt temperature rises back to 780°C, the melt is cooled to 730°C and Al-Mg master alloy is added. When the temperature rises back to 730°C, a covering agent (LiF:LiCl=1:3) is sprinkled on the surface of the melt, and pure Li is pressed into a graphite bell under argon protection. When the temperature rises to 750°C, the melt is stirred, and the melt temperature is reduced to 730°C. Hexachloroethane is used for refining under argon protection. After refining, the melt is cooled to 720°C and allowed to stand for 20 minutes. After standing, the slag is removed and the melt is cast into a steel mold preheated to 200°C.

[0057] The castings are subjected to solution treatment and aging treatment. The solution treatment system is 390℃ / 10h+500℃ / 12h, and the aging treatment system is 165℃ / 30h.

[0058] The metallographic photograph of the cast aluminum-lithium alloy prepared by the method for preparing the cast aluminum-lithium alloy provided in the embodiment of the present invention is as follows: Figure 3 The mechanical properties, density and solid-liquid phase range of the cast aluminum-lithium alloy T6 prepared in this embodiment are shown in Table 1.

[0059] Example 3

[0060] A low-cost aluminum-lithium alloy with light weight, high strength and excellent casting performance comprises the following components in percentage by weight: 2.97% Li, 4.76% Mg, 2.02% Si, 0.14% Zr, and the balance is Al.

[0061] Pure aluminum is melted, and Al-Si master alloy and Al-Zr master alloy are added when the melt temperature rises to 790°C. After the melt temperature rises back to 790°C, the melt is cooled to 740°C and Al-Mg master alloy is added. When the temperature rises back to 740°C, a covering agent (LiF:LiCl=1:3) is sprinkled on the surface of the melt, and pure Li is pressed into a graphite bell under argon protection. When the temperature rises to 760°C, the melt is stirred, and the melt temperature is reduced to 740°C. Hexachloroethane is used for refining under argon protection. After refining, the melt is cooled to 710°C and allowed to stand for 20 minutes. After standing, the slag is removed and the melt is cast into a steel mold preheated to 200°C.

[0062] The castings are subjected to solution treatment and aging treatment. The solution treatment system is 380℃ / 8h+510℃ / 15h, and the aging treatment system is 170℃ / 20h.

[0063] The metallographic photograph of the cast aluminum-lithium alloy prepared by the method for preparing the cast aluminum-lithium alloy provided in the embodiment of the present invention is as follows: Figure 4 The mechanical properties, density and solid-liquid phase range of the cast aluminum-lithium alloy T6 prepared in this embodiment are shown in Table 1.

[0064] Example 4

[0065] A low-cost aluminum-lithium alloy with light weight, high strength and excellent casting performance comprises the following components in percentage by weight: 3.06% Li, 3.59% Mg, 2.44% Si, 0.14% Zr, and the balance is Al.

[0066] Pure aluminum is melted, and Al-Si master alloy and Al-Zr master alloy are added when the melt temperature rises to 790°C. After the melt temperature rises back to 790°C, the melt is cooled to 750°C and Al-Mg master alloy is added. When the temperature rises back to 750°C, a covering agent (LiF:LiCl=1:3) is sprinkled on the surface of the melt, and pure Li is pressed into a graphite bell under argon protection. When the temperature rises to 740°C, the melt is stirred, and the melt temperature is reduced to 730°C. Hexachloroethane is used for refining under argon protection. After refining, the melt is cooled to 720°C and allowed to stand for 25 minutes. After standing, the slag is removed and the melt is cast into a steel mold preheated to 200°C.

[0067] The castings are subjected to solution treatment and aging treatment. The solution treatment system is 420℃ / 8h+490℃ / 15h, and the aging treatment system is 190℃ / 20h.

[0068] The metallographic photograph of the cast aluminum-lithium alloy prepared by the method for preparing the cast aluminum-lithium alloy provided in the embodiment of the present invention is as follows: Figure 5 The mechanical properties, density and solid-liquid phase range of the cast aluminum-lithium alloy T6 prepared in this embodiment are shown in Table 1.

[0069] Comparative Example 1

[0070] The cast aluminum-lithium alloy of this comparative example comprises the following components in percentage by weight: 2.1% Cu, 2.7% Li, 0.6% Mg, 0.32% Zn, 0.34% Ce, 0.21% Mn, and the balance is Al. The preparation method comprises the following steps:

[0071] (1) preparing an Al-Li master alloy containing 9.8-11 wt% Li, an Al-Cu master alloy containing 49-50 wt% Cu, an Al-Zr master alloy containing 4-5 wt% Zr, an Al-Ti-B master alloy containing 4.8-5.2 wt% Ti, an Al-Mn master alloy containing 8.9-10.6 wt% Mn, an Al-Ce master alloy containing 28-30 wt% Ce, pure zinc with an impurity content of ≤0.4 wt%, and the remainder being pure magnesium and pure aluminum;

[0072] (2) Preheating pure aluminum, pure magnesium, pure zinc, master alloys Al-Cu, Al-Zr, Al-Ti, Al-Mn, and Al-Ce to 200° C. Preheating the master alloy Al-Li for 30 minutes before adding the aluminum melt, and then melting the pure aluminum in a graphite crucible;

[0073] (3) After the aluminum ingot is melted, Al-Cu master alloy is added at 760°C. After the aluminum liquid temperature rises to 760°C, Al-Mn master alloy is directly added to the aluminum liquid. When the aluminum liquid temperature reaches 750°C, pure Zn is added. When the temperature rises to 770°C, flux (LiF: LiCl = 1: 3) is sprinkled on the surface of the aluminum liquid and Al-Li master alloy is directly added under argon protection. After the aluminum liquid temperature rises to 760°C, master alloys Al-Ce, Al-Ti-B and pure Mg are added. Finally, when the temperature reaches 770°C, Al-Zr master alloy is added. After the Al-Zr master alloy is melted, the surface scum is removed and flux is sprinkled, and the mixture is stirred for 3 minutes.

[0074] (4) After stirring, the temperature of the aluminum liquid is lowered to 740°C, and then the aluminum liquid is refined with C2Cl6 for 5 minutes without power off. After refining, the temperature is lowered to 710°C and allowed to stand for 3 minutes;

[0075] (5) After standing, the slag and flux on the surface of the aluminum liquid are skimmed off and casting is performed to obtain a cast aluminum-lithium alloy, and the steel mold for casting is preheated to 200° C.;

[0076] (6) subjecting the obtained alloy to a double-stage solution treatment at 450°C / 9h+515°C / 26h and warm water quenching;

[0077] (7) The alloy after solution treatment is subjected to a single-stage aging treatment at 175°C for 18 hours to obtain a cast aluminum-lithium alloy.

[0078] The mechanical properties, density and solid-liquid phase range of the T6 state of the cast aluminum-lithium alloy prepared in this comparative example are shown in Table 1.

[0079] Comparative Example 2

[0080] The cast aluminum-lithium alloy of this comparative example comprises the following components in weight percentage: 1.9% Cu, 3.6% Li, 0.55% Mg, 0.67% Ag, 0.34% Mn, 0.16% Zr, and the balance is Al. The preparation method thereof comprises the following steps:

[0081] (1) preparing an Al-Li master alloy containing 9.8-11 wt% Li, an Al-Cu master alloy containing 49-50 wt% Cu, an Al-Zr master alloy containing 4-5 wt% Zr, an Al-Ti-B master alloy containing 4.8-5.2 wt% Ti, an Al-Mn master alloy containing 8.9-10.6 wt% Mn, an Al-Ce master alloy containing 28-30 wt% Ce, pure zinc with an impurity content of ≤0.4 wt%, and the remainder being pure magnesium and pure aluminum;

[0082] (2) Preheating pure aluminum, pure magnesium, pure zinc, master alloys Al-Cu, Al-Zr, Al-Ti, Al-Mn, and Al-Ce to 200° C. Preheating the master alloy Al-Li for 30 minutes before adding the aluminum melt, and then melting the pure aluminum in a graphite crucible;

[0083] (3) After the aluminum ingot is melted, Al-Cu master alloy is added at 760°C. After the aluminum liquid temperature rises to 760°C, Al-Mn master alloy is directly added to the aluminum liquid. When the aluminum liquid temperature reaches 750°C, pure Zn is added. When the temperature rises to 770°C, flux (LiF: LiCl = 1: 3) is sprinkled on the surface of the aluminum liquid and Al-Li master alloy is directly added under argon protection. After the aluminum liquid temperature rises to 760°C, master alloys Al-Ce, Al-Ti-B and pure Mg are added. Finally, when the temperature reaches 770°C, Al-Zr master alloy is added. After the Al-Zr master alloy is melted, the surface scum is removed and flux is sprinkled, and the mixture is stirred for 3 minutes.

[0084] (4) After stirring, the temperature of the aluminum liquid is lowered to 740°C, and then the aluminum liquid is refined with C2Cl6 for 5 minutes without power off. After refining, the temperature is lowered to 710°C and allowed to stand for 3 minutes;

[0085] (5) After standing, the slag and flux on the surface of the aluminum liquid are skimmed off and casting is performed to obtain a cast aluminum-lithium alloy, and the steel mold for casting is preheated to 200° C.;

[0086] (6) subjecting the obtained alloy to a double-stage solution treatment at 450°C / 9h+515°C / 26h and warm water quenching;

[0087] (7) The alloy after the solution treatment is subjected to a single-stage aging treatment at 150°C for 45 hours to obtain a cast aluminum-lithium alloy.

[0088] The mechanical properties, density and solid-liquid phase range of the T6 state of the cast aluminum-lithium alloy prepared in this comparative example are shown in Table 1.

[0089] Comparative Example 3

[0090] The cast aluminum-lithium alloy of this comparative example includes the following components in weight percentage: 3.22% Li, 9.12% Mg, 0.22% Sc, 0.16% Zr, and the balance is Al. The preparation method thereof includes the following steps:

[0091] (1) preparing an Al-Li master alloy containing 9.8-11 wt% Li, an Al-Cu master alloy containing 49-50 wt% Cu, an Al-Zr master alloy containing 4-5 wt% Zr, an Al-Ti-B master alloy containing 4.8-5.2 wt% Ti, an Al-Mn master alloy containing 8.9-10.6 wt% Mn, an Al-Ce master alloy containing 28-30 wt% Ce, pure zinc with an impurity content of ≤0.4 wt%, and the remainder being pure magnesium and pure aluminum;

[0092] (2) Preheat pure aluminum, pure magnesium, pure zinc, master alloys Al-Cu, Al-Zr, Al-Ti, Al-Mn, and Al-Ce to 180° C. Preheat the master alloy Al-Li 30 minutes before adding the aluminum melt, and then melt the pure aluminum in a graphite crucible;

[0093] (3) After the aluminum ingot is melted, Al-Cu master alloy is added at 750°C. After the aluminum liquid temperature rises to 750°C, Al-Mn master alloy is directly added to the aluminum liquid. When the aluminum liquid temperature reaches 740°C, pure Zn is added. When the temperature rises to 760°C, flux (LiF: LiCl = 1: 3) is sprinkled on the surface of the aluminum liquid and Al-Li master alloy is directly added under argon protection. After the aluminum liquid temperature rises to 750°C, master alloys Al-Ce, Al-Ti-B and pure Mg are added. Finally, when the temperature reaches 760°C, Al-Zr master alloy is added. After the Al-Zr master alloy is melted, the surface scum is removed and flux is sprinkled, and the mixture is stirred for 5 minutes.

[0094] (4) After stirring, the temperature of the aluminum liquid is lowered to 730°C, and then the aluminum liquid is refined with C2Cl6 for 8 minutes without power off. After refining, the temperature is lowered to 710°C and allowed to stand for 5 minutes;

[0095] (5) After standing, skimming off the scum and flux on the surface of the aluminum liquid and casting to obtain a cast aluminum-lithium alloy, and preheating the steel mold for casting to 180° C.;

[0096] (6) subjecting the obtained alloy to a double-stage solution treatment at 430°C / 9h+525°C / 28h, and cold water quenching;

[0097] (7) The alloy after the solution treatment is subjected to a single-stage aging treatment at 160°C for 36 hours to obtain a cast aluminum-lithium alloy.

[0098] The mechanical properties, density and solid-liquid phase range of the T6 state of the cast aluminum-lithium alloy prepared in this comparative example are shown in Table 1.

[0099] Comparative Example 4

[0100] The preparation method of this comparative example is the same as that of Example 1 of the present invention, except that: this comparative example includes the following parts in percentage by weight: 2.82% Li, 4.32% Mg, 3.35% Si, 0.17% Zr, and the balance is Al.

[0101] The mechanical properties, density and solid-liquid phase range of the T6 state of the cast aluminum-lithium alloy prepared in this comparative example are shown in Table 1.

[0102] Table 1

[0103]

[0104] It can be seen from Figures 2-5 that the cast aluminum-lithium alloy prepared by the cast aluminum-lithium alloy preparation method provided by the present invention has a spherical cast grain morphology with a size between 20 and 50 μm. Compared with the coarse dendrite morphology of the Al-Cu-Li system, the regular and smaller grain morphology is conducive to the flow and shrinkage compensation of the liquid metal, so that the alloy has good casting properties.

[0105] Comparing Examples 1-4 with Comparative Example 1-2, it can be seen that compared with the Al-Cu-Li system, the solid-liquid phase interval of the present invention is greatly reduced, the casting performance is significantly improved, and the density is reduced by about 7%. Comparing Examples 1-4 with Comparative Example 3, it can be seen that the present invention can significantly reduce the solid-liquid phase interval and improve the casting performance while maintaining low density by reducing the Mg content and regulating the Si content. Comparing Examples 1-4 with Comparative Example 4, it can be seen that although the solid-liquid phase solidification interval decreases when the Si content increases, when the Si content is too high, the alloy will undergo brittle fracture, and the alloy strength and elongation will significantly decrease, which cannot meet the performance requirements of structural parts.

[0106] In summary, the present invention, by regulating the content of Mg and Si elements without adding precious metal elements such as Cu, Ag, Zn, Sc, etc., obtains a cast aluminum-lithium alloy with a narrow solid-liquid phase interval, excellent casting performance, low density, low cost, and excellent mechanical properties, which is helpful to promote the actual production and application of cast aluminum-lithium alloys.

[0107] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A cast aluminum-lithium alloy, characterized in that: In terms of weight percentage, the alloy comprises: 2.5-3.5% Li, 3.5-5.0% Mg, 1.0-2.5% Si, 0.1-0.2% Zr, the total content of impurity elements is less than 0.25%, and the balance is Al; the preparation method of the cast aluminum-lithium alloy comprises the following steps: The raw materials are prepared according to the alloy components in the weight percentage, including pure Al, pure Li, Al-Si master alloy, Al-Mg master alloy and Al-Zr master alloy; Preheat the raw materials except pure Li at 200-220°C for 2-4 hours; Melting pure Al, and adding Al-Si master alloy and Al-Zr master alloy when the pure Al melt is heated to 770-790° C. to obtain a first alloy melt; After the temperature of the first alloy melt rises back to 770-790° C., the first alloy melt is cooled to 730-740° C. and an Al-Mg master alloy is added to obtain a second alloy melt; When the temperature of the second alloy melt rises back to 730-740° C., a covering agent is sprinkled on the surface of the second alloy melt and pure Li is pressed into the second alloy melt using a graphite bell jar under argon protection to obtain a third alloy melt; When the temperature of the third alloy melt rises to 750-760° C., stirring the third alloy melt; The third alloy melt is cooled to 730-740°C for refining; After refining, the third alloy melt is cooled to 710-720°C, allowed to stand, slag removed, and cast to obtain an aluminum-lithium alloy; The aluminum-lithium alloy is subjected to solution treatment and aging treatment.

2. The cast aluminum-lithium alloy according to claim 1, characterized in that: The covering agent is a mixed solvent of LiCl and LiF, and the weight ratio of LiCl to LiF is 3:

1.

3. The cast aluminum-lithium alloy according to claim 1, characterized in that: The refining is to refine the third alloy melt by using hexachloroethane under the protection of argon gas.

4. The cast aluminum-lithium alloy according to claim 1, characterized in that: The standing time is 15-20 minutes, and the steel mold used for casting is preheated to 200-220°C in advance.

5. The cast aluminum-lithium alloy according to claim 1, characterized in that: The solution treatment adopts a two-stage solution treatment: the aluminum-lithium alloy is first treated at 380-420° C. for 6-10 hours, and then treated at 480-530° C. for 10-15 hours.

6. The cast aluminum-lithium alloy according to claim 1, characterized in that: The aging treatment is to treat the aluminum-lithium alloy at 150-200° C. for 20-30 hours.

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