Heat-treatment-free high-toughness die-casting aluminum alloy and preparation method thereof

Abstract

The invention belongs to the field of aluminum alloy casting, and discloses a heat-treatment-free high-toughness die-casting aluminum alloy and a preparation method thereof. According to the total weight of the aluminum alloy, the aluminum alloy comprises the following components in percentage by weight: 4.0 to 6.5 percent of Mg, 1.8 to 3.0 percent of Si, 0.5 to 1.0 percent of Mn, 0 to 0.2 percent of Zr, 0 to 0.3 percent of Cr, 0.1 to 0.3 percent of Ti, 0 to 0.3 percent of Fe, 0 to 0.5 percent of alterant, less than 0.1 percent of impurity element and the balance of Al. The magnesium-rich aluminum alloy with better plasticity is obtained by controlling the ratio of Mg to Si in the aluminum alloy, then the plasticity of the alloy is further improved by applying the alterant, aging is carried out immediately by utilizing waste heat of the casting after die casting is completed, the strength of the alloy is improved through precipitation of a dispersion strengthening phase in the aging process, and the high-strength and high-toughness aluminum alloy die casting is obtained.

Description

Technical Field

[0001] The present invention belongs to the field of aluminum alloy casting, and more specifically, relates to a heat treatment-free high-strength and toughness die-cast aluminum alloy and a preparation method thereof. Background Art

[0002] Driven by energy conservation and emission reduction, lightweighting vehicles is an inevitable trend in the development of the automotive industry, and large-scale integrated aluminum alloy materials are an important means of achieving vehicle weight reduction. Integrated die-casting technology, pioneered by a certain automaker, replaces dozens of small parts with a single, large aluminum casting, significantly reducing vehicle weight and costs, and significantly driving changes in automotive manufacturing processes. The emergence of integrated die-casting technology has placed new demands on material research and development and preparation methods. On the one hand, solid solution strengthening and other factors can cause bubbling and deformation in large integrated die-castings; on the other hand, the performance of die-cast aluminum alloys must be as close as possible to that of heat-treatable aluminum alloys. Consequently, numerous institutions at home and abroad have conducted research and development and preparation of integrated die-cast, heat-treatment-free aluminum alloys.

[0003] Currently, the types of heat-treatment-free aluminum alloys being developed primarily include Al-Si and Al-Mg-Si aluminum alloys. Al-Si aluminum alloys offer excellent casting properties, but struggle to achieve both strength and toughness. Al-Mg-Si aluminum alloys have lower castability than Al-Si alloys, but can offer both excellent strength and toughness. The aluminum-magnesium-silicon alloy disclosed in CN115852215A has a tensile strength of 315 MPa, a yield strength of 215 MPa, and an elongation of 8%. However, the strength of these alloys still lags significantly behind that of T6-treated cast aluminum alloys and wrought aluminum alloys. For example, the yield strength of ZL114A aluminum alloy after T6 heat treatment can reach 275 MPa, while the yield strength of 6016 wrought aluminum alloy sheet for automotive applications can reach 280 MPa. When these Al-Mg-Si cast aluminum alloys are joined to 6016 aluminum alloy, their performance often becomes a disadvantage. Therefore, there is a need to develop higher-performing heat-treatment-free aluminum alloys to enable their large-scale application in the automotive industry. Summary of the Invention

[0004] The present invention addresses the shortcomings of existing technologies by providing a heat-treatment-free, high-strength and toughness die-cast aluminum alloy and its preparation method. By controlling the Mg:Si ratio in the aluminum alloy, the present invention achieves a magnesium-rich aluminum alloy with improved plasticity. This alloy's plasticity is further enhanced by applying a modifier. Following die-casting, the alloy is immediately aged using the residual heat of the casting. The precipitation of a dispersion-strengthening phase during the aging process increases the alloy's strength, resulting in a high-strength and toughness aluminum alloy die-casting.

[0005] In order to achieve the above objectives, the present invention provides, on the one hand, a heat treatment-free high-strength and toughness die-cast aluminum alloy. The aluminum alloy comprises, based on the total weight of the aluminum alloy: Mg 4.0-6.5wt.%, Si 1.8-3.0wt.%, Mn 0.5-1.0wt.%, Zr 0-0.2wt.%, Cr 0-0.3wt.%, Ti 0.1-0.3wt.%, Fe 0-0.3wt.%, modifier 0-0.5wt.%, impurity elements <0.1wt.%, and the remainder is Al.

[0006] According to the present invention, preferably, based on the total weight of the aluminum alloy, the aluminum alloy includes: Mg 4.0-6.5wt.%, Si 1.8-3.0wt.%, Mn 0.5-1.0wt.%, Zr 0.1-0.2wt.%, Cr 0.01-0.3wt.%, Ti 0.1-0.3wt.%, Fe 0.05-0.3wt.%, modifier 0.05-0.5wt.%, impurity elements <0.1wt.%, and the rest is Al.

[0007] According to the present invention, preferably, the modifier is a mixture of La and Ce, and based on the total weight of the aluminum alloy, the content of La is 0-0.2 wt.%, and the content of Ce is 0-0.2 wt.%.

[0008] According to the present invention, preferably, based on the total weight of the aluminum alloy, the content of La is 0.01 to 0.2 wt.%, and the content of Ce is 0.05 to 0.2 wt.%.

[0009] According to the present invention, preferably, the modifier is Sc, and the content of Sc is 0 to 0.25 wt.% based on the total weight of the aluminum alloy.

[0010] According to the present invention, preferably, the content of Sc is 0.05 to 0.25 wt. %, based on the total weight of the aluminum alloy.

[0011] According to the present invention, preferably, the content ratio of Mg to Si in the aluminum alloy is (1.8-3.0):1, so that the aluminum alloy of the present invention has excellent plasticity.

[0012] According to the present invention, preferably, at -20 to 35° C., the aluminum alloy has a tensile strength of 315 to 375 Pa, a yield strength of 230 to 280 Pa, and an elongation of 7 to 12%.

[0013] Another aspect of the present invention provides a method for preparing the heat treatment-free high-strength and toughness die-cast aluminum alloy, the method comprising the following steps:

[0014] S1: Mixing and smelting an aluminum ingot and pure silicon to obtain a first melt; mixing and smelting an aluminum-manganese master alloy, an aluminum-chromium master alloy, an aluminum-zirconium master alloy, or an aluminum-titanium master alloy with the first melt to obtain a second melt, and stirring the mixture; mixing and stirring a magnesium ingot with the stirred second melt to obtain a third melt; mixing and smelting a raw material of a modifier with the heated third melt, and allowing the mixture to stand to obtain a smelted melt; the aluminum ingot, the aluminum-manganese master alloy, the aluminum-chromium master alloy, the aluminum-zirconium master alloy, or the aluminum-titanium master alloy contains the Fe element in the aluminum alloy (therefore, the present invention does not require additional Fe addition);

[0015] S2: Under protective gas conditions, mixing a refining agent with the smelting melt, refining, and allowing to stand to obtain a refined melt;

[0016] S3: performing high vacuum die casting on the refined melt; placing the demoulded casting in an aging furnace for heat preservation; after the heat preservation is completed, the heat treatment-free high-strength and toughness die-cast aluminum alloy is obtained.

[0017] Preferably, before the residual temperature of the casting after demolding by high vacuum die casting drops to 140-160° C., the casting after demolding by high vacuum die casting is placed in an aging furnace for insulation, so as to save energy and make full use of the residual temperature of the die casting after demolding.

[0018] In the present invention, the design steps for preparing the heat treatment-free high-strength and toughness die-cast aluminum alloy are: (1) alloy composition ratio; (2) smelting and refining; (3) high vacuum die-casting; and (4) demolding casting residual temperature control and aging.

[0019] According to the present invention, preferably, in step S1:

[0020] The temperature of the first melt is 740-760°C;

[0021] The temperature of the second melt is 720-740°C;

[0022] The temperature of the third melt after heating is 720-740°C.

[0023] In the present invention, when the modifier is a mixture of La and Ce, the raw material of the modifier is an aluminum-lanthanum (La) master alloy or an aluminum-cerium master alloy; when the modifier is Sc, the raw material of the modifier is an aluminum-scandium (Sc) master alloy; before performing step S1, the aluminum ingot, pure silicon, aluminum-manganese master alloy, aluminum-chromium master alloy, aluminum-zirconium master alloy, aluminum-titanium master alloy, magnesium ingot, aluminum-lanthanum (La) master alloy, aluminum-cerium master alloy, and aluminum-scandium (Sc) master alloy need to be cleaned and dried before being smelted.

[0024] In the present invention, as a preferred embodiment, the aluminum-manganese master alloy is an Al-10Mn master alloy; the aluminum-chromium master alloy is an Al-10Cr master alloy; the aluminum-zirconium master alloy is an Al-5Zr master alloy; the aluminum-titanium master alloy is an Al-5Ti master alloy; the aluminum-lanthanum (La) master alloy is an Al-10La master alloy; and the aluminum-cerium master alloy is an Al-10Ce master alloy.

[0025] According to the present invention, preferably, in step S2:

[0026] The melt temperature during the refining process is controlled at 710-730°C; the refining time is 20-40 minutes;

[0027] The standing time is 10 to 20 minutes.

[0028] According to the present invention, preferably, in step S3:

[0029] The high vacuum die-casting conditions include: die-casting temperature 690-720°C, mold temperature 160-200°C, first-stage injection speed 0.1-0.5 m / s, and second-stage injection speed 3-5 m / s;

[0030] The holding temperature is 160-200° C. and the holding time is 0.5-20 hours. In the present invention, for die castings that require baking varnish treatment, the holding time includes the baking time of the baking varnish.

[0031] The beneficial effects of the technical solution of the present invention are as follows:

[0032] (1) The present invention obtains a magnesium-rich aluminum alloy with better plasticity by controlling the Mg:Si ratio in the aluminum alloy, and then further improves the plasticity of the alloy by applying a modifier. After the die-casting is completed, the strength of the alloy is improved by aging the die-cast part, and finally a high-strength and tough aluminum alloy die-casting is obtained. The performance gap between the new die-cast Al-Mg-Si alloy of the present invention and the 6061 aluminum alloy plate is smaller, and both are alloys with Mg and Si as the main elements. Therefore, the performance of the two when connected by welding is more obvious than that of other casting alloys. Therefore, the present invention overcomes the performance shortcomings of the Al-Mg-Si alloy and realizes its large-scale application in the automotive industry.

[0033] (2) The die castings of the present invention are demolded at a temperature between 170°C and 210°C, and the aging strengthening (anti-baking paint hardening) temperature is similar, between 160°C and 200°C. Therefore, the present invention fully utilizes the residual heat of the castings and saves energy. The present invention improves the strength of the alloy by precipitation of the dispersion-strengthening phase during the aging process, thereby obtaining a high-strength and tough aluminum alloy die casting.

[0034] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings.

[0036] Figure 1 The standard sample of the heat treatment-free high-strength and toughness die-cast aluminum alloy prepared in Example 1 of the present invention is shown.

[0037] Figure 2 The metallographic structure diagram of the heat treatment-free high-strength and toughness die-cast aluminum alloy prepared in Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0038] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Instead, these embodiments are provided to make the present invention more thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0039] Example 1

[0040] This embodiment provides a heat treatment-free high-strength and toughness die-cast aluminum alloy. Based on the total weight of the aluminum alloy, the aluminum alloy includes: Mg 6.2wt.%, Si 2.4wt.%, Mn 0.6wt.%, Zr0.12wt.%, Cr 0.05wt.%, Ti0.2wt.%, Fe 0.15wt.%, La 0.05wt.%, Ce0.1wt.%, impurity elements <0.1wt.%, and the rest is Al.

[0041] The method for preparing the heat treatment-free high-strength and toughness die-cast aluminum alloy comprises the following steps:

[0042] S1: Clean and dry aluminum ingots (purity 99.85wt.%), pure silicon, Al-10Mn master alloy, Al-10Cr master alloy, Al-5Zr master alloy, Al-5Ti master alloy, magnesium ingots (purity 99.95wt.%), Al-10La master alloy, and Al-10Ce master alloy. Then, the aluminum ingot and pure silicon are placed in a resistance furnace for mixed smelting to obtain a first melt (temperature of 750°C); Al-10Mn master alloy, Al-10Cr master alloy, Al-5Zr master alloy, Al-5Ti master alloy and the first melt are mixed and smelted, the temperature is stabilized to 730°C to obtain a second melt, and then manually stirred for 3 to 5 minutes; the magnesium ingot is mixed with the stirred second melt and manually stirred for 3 to 5 minutes to obtain a third melt; Al-10La master alloy and Al-10Ce master alloy are mixed and smelted with the third melt heated to 720°C, and allowed to stand for 5 to 10 minutes to obtain a smelted melt; the aluminum ingot, aluminum-manganese master alloy, aluminum-chromium master alloy, aluminum-zirconium master alloy or aluminum-titanium master alloy contains the Fe element in the aluminum alloy;

[0043] S2: 4AB powdered granular refining agent produced by Pyrotech and argon gas are continuously introduced into the smelting melt of step S1 through an online refiner. The argon gas introduction time (i.e., refining time) is 30 minutes. After the refining agent reacts completely, the scum and sediment are salvaged. The melt temperature during the refining process is controlled at 720°C. After refining, the melt is allowed to stand for 10-20 minutes to obtain a refined melt.

[0044] S3: The refined melt is subjected to high vacuum die casting, with a die casting temperature of 700°C, a mold temperature of 180°C, a first-level injection speed of 0.3m / s, and a second-level injection speed of 3.5m / s; the casting after demolding by high vacuum die casting is placed in an aging furnace for insulation, and the aging process is set to a holding temperature of 180°C and a holding time of 2h, and then the heat treatment-free high-strength and toughness die-cast aluminum alloy is obtained.

[0045] The standard sample of the heat treatment-free high-strength and toughness die-cast aluminum alloy prepared by the present invention is as follows: Figure 1 The metallographic structure of the alloy is shown in Figure 2 As shown, the average grain size is about 70 μm.

[0046] In this embodiment, the tensile test was performed at room temperature at 25°C using an AG-X series electronic universal testing machine from Shimadzu Corporation of Japan, with a strain rate of 0.001s. -1 The tensile strength of the alloy in this embodiment was measured to be 375 MPa, the yield strength was 280 MPa, and the elongation was 7.5%.

[0047] Example 2

[0048] This embodiment provides a heat treatment-free high-strength and toughness die-cast aluminum alloy. Based on the total weight of the aluminum alloy, the aluminum alloy includes: Mg 5.0wt.%, Si 2.0wt.%, Mn 0.7wt.%, Zr0.12wt.%, Cr 0.05wt.%, Ti0.2wt.%, Fe 0.07wt.%, Sc 0.1wt.%, impurity elements <0.1wt.%, and the rest is Al.

[0049] The method for preparing the heat treatment-free high-strength and toughness die-cast aluminum alloy comprises the following steps:

[0050] S1: Clean and dry aluminum ingots (purity 99.85wt.%), pure silicon, Al-10Mn master alloy, Al-10Cr master alloy, Al-5Zr master alloy, Al-5Ti master alloy, magnesium ingots (purity 99.95wt.%), and Al-2Sc master alloy. Then, the aluminum ingot and pure silicon are placed in a resistance furnace for mixed smelting to obtain a first melt (temperature of 750°C); Al-10Mn master alloy, Al-10Cr master alloy, Al-5Zr master alloy, Al-5Ti master alloy and the first melt are mixed and smelted, the temperature is stabilized to 730°C to obtain a second melt, and then manually stirred for 3 to 5 minutes; the magnesium ingot is mixed with the stirred second melt and manually stirred for 3 to 5 minutes to obtain a third melt; Al-2Sc master alloy is mixed and smelted with the third melt heated to 720°C, and allowed to stand for 5 to 10 minutes to obtain a smelted melt; the aluminum ingot, aluminum-manganese master alloy, aluminum-chromium master alloy, aluminum-zirconium master alloy or aluminum-titanium master alloy contains the Fe element in the aluminum alloy;

[0051] S2: 4AB powdered granular refining agent produced by Pyrotech and argon gas are continuously introduced into the smelting melt of step S1 through an online refiner. The argon gas introduction time (i.e., refining time) is 30 minutes. After the refining agent reacts completely, the scum and sediment are salvaged. The melt temperature during the refining process is controlled at 720°C. After refining, the melt is allowed to stand for 10-20 minutes to obtain a refined melt.

[0052] S3: The refined melt is subjected to high vacuum die casting, with a die casting temperature of 700°C, a mold temperature of 180°C, a first-level injection speed of 0.3m / s, and a second-level injection speed of 3.8m / s; the casting after demolding by high vacuum die casting is placed in an aging furnace for insulation, and the aging process is set to a holding temperature of 175°C and a holding time of 2h, and then the heat treatment-free high-strength and toughness die-cast aluminum alloy is obtained.

[0053] In this embodiment, the tensile test was performed at room temperature at 25°C using an AG-X series electronic universal testing machine from Shimadzu Corporation of Japan, with a strain rate of 0.001s. -1The tensile strength of the alloy of this embodiment was measured to be 340 MPa, the yield strength was 235 MPa, and the elongation was 12%.

[0054] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A heat treatment-free high-strength and toughness die-cast aluminum alloy, characterized in that: Based on the total weight of the aluminum alloy, the aluminum alloy includes: Mg 4.0-6.5wt.%, Si 1.8-3.0wt.%, Mn 0.5-1.0wt.%, Zr 0-0.2wt.%, Cr 0-0.3wt.%, Ti 0.1-0.3wt.%, Fe 0-0.3wt.%, modifier 0-0.5wt.%, impurity elements <0.1wt.%, and the rest is Al.

2. The heat treatment-free high-strength and toughness die-cast aluminum alloy according to claim 1, wherein: Based on the total weight of the aluminum alloy, the aluminum alloy includes: Mg 4.0-6.5wt.%, Si 1.8-3.0wt.%, Mn 0.5-1.0wt.%, Zr 0.1-0.2wt.%, Cr 0.01-0.3wt.%, Ti 0.1-0.3wt.%, Fe 0.05-0.3wt.%, modifier 0.05-0.5wt.%, impurity elements <0.1wt.%, and the rest is Al.

3. The heat treatment-free high-strength and toughness die-cast aluminum alloy according to claim 1, wherein: The modifier is a mixture of La and Ce, and based on the total weight of the aluminum alloy, the content of La is 0-0.2 wt.%, and the content of Ce is 0-0.2 wt.%; Preferably, based on the total weight of the aluminum alloy, the content of La is 0.01 to 0.2 wt.%, and the content of Ce is 0.05 to 0.2 wt.%.

4. The heat treatment-free high-strength and toughness die-cast aluminum alloy according to claim 1, wherein: The modifier is Sc, and the content of Sc is 0 to 0.25 wt.% based on the total weight of the aluminum alloy; Preferably, the content of Sc is 0.05 to 0.25 wt.% based on the total weight of the aluminum alloy.

5. The heat treatment-free high-strength and toughness die-cast aluminum alloy according to claim 1, wherein: The content ratio of Mg to Si in the aluminum alloy is (1.8-3.0):

1.

6. The heat treatment-free high-strength and toughness die-cast aluminum alloy according to any one of claims 1 to 5, wherein: At -20 to 35° C., the aluminum alloy has a tensile strength of 315 to 375 Pa, a yield strength of 230 to 280 Pa, and an elongation of 7 to 12%.

7. The method for preparing the heat treatment-free high-strength and toughness die-cast aluminum alloy according to any one of claims 1 to 6, characterized in that: The preparation method comprises the following steps: S1: Mixing and smelting an aluminum ingot and pure silicon to obtain a first melt; mixing and smelting an aluminum-manganese master alloy, an aluminum-chromium master alloy, an aluminum-zirconium master alloy, or an aluminum-titanium master alloy with the first melt to obtain a second melt, and stirring the mixture; mixing and stirring a magnesium ingot with the stirred second melt to obtain a third melt; mixing and smelting a raw material of a modifier with the heated third melt, and allowing the mixture to stand to obtain a smelted melt; the aluminum ingot, the aluminum-manganese master alloy, the aluminum-chromium master alloy, the aluminum-zirconium master alloy, or the aluminum-titanium master alloy contains the Fe element in the aluminum alloy; S2: Under protective gas conditions, mixing a refining agent with the smelting melt, refining, and allowing to stand to obtain a refined melt; S3: performing high vacuum die casting on the refined melt; placing the demoulded casting in an aging furnace for heat preservation; After the heat preservation is completed, the heat treatment-free high-strength and toughness die-cast aluminum alloy is obtained; Preferably, before the residual temperature of the casting after demoulding by high vacuum die casting drops to 140-160° C., the casting after demoulding by high vacuum die casting is placed in an aging furnace for heat preservation.

8. The method for preparing the heat treatment-free high-strength and toughness die-cast aluminum alloy according to claim 7, wherein: In step S1: The temperature of the first melt is 740-760°C; The temperature of the second melt is 720-740°C; The temperature of the third melt after heating is 720-740°C.

9. The method for preparing the heat treatment-free high-strength and toughness die-cast aluminum alloy according to claim 7, wherein: In step S2: The melt temperature during the refining process is controlled at 710-730°C; the refining time is 20-40 minutes; The standing time is 10 to 20 minutes.

10. The method for preparing the heat treatment-free high-strength and toughness die-cast aluminum alloy according to claim 7, wherein: In step S3: The high vacuum die-casting conditions include: die-casting temperature 690-720°C, mold temperature 160-200°C, first-stage injection speed 0.1-0.5 m / s, and second-stage injection speed 3-5 m / s; The holding temperature is 160-200°C, and the holding time is 0.5-20h.

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