A method for improving the hot cracking resistance of a non-heat-treated aluminum alloy and a high hot cracking resistance non-heat-treated aluminum alloy

Abstract

The application belongs to the field of metal material casting, and discloses a method for improving the hot crack resistance of heat treatment-free aluminum alloy and high hot crack resistance heat treatment-free aluminum alloy. The method comprises the following steps: melting heat treatment-free aluminum alloy to obtain a melt; adding Zr, and optionally Sc and / or Er, to the melt, stirring, degassing, cooling and standing to obtain an alloy melt; carrying out high-temperature melt ultrasonic treatment on the alloy melt to obtain a high-temperature melt, pouring into a mold and carrying out casting to obtain high hot crack resistance heat treatment-free aluminum alloy. The application can effectively control the microstructure and hot crack resistance of the aluminum alloy, and obtain high-quality heat treatment-free aluminum alloy castings with refined solidification structure and eliminated casting hot cracks.

Description

Technical Field

[0001] This invention belongs to the field of metal material casting, and more specifically, relates to a method for improving the hot crack resistance of heat-free aluminum alloys and a heat-free aluminum alloy with high hot crack resistance. Background Technology

[0002] Heat-free aluminum alloy castings have wide applications in modern automobile manufacturing. With the rapid development of integrated die-casting technology for aluminum alloys, several challenges arise. Firstly, to improve the mechanical properties of heat-free aluminum alloys, elements such as Cu and Zn are added. While this improves mechanical properties, it reduces their resistance to hot cracking. Secondly, die-cast parts are becoming increasingly larger and more complex, inevitably generating significant stress during solidification. Therefore, the thermal crack resistance of heat-free aluminum alloy materials faces a significant challenge.

[0003] In previous studies, various methods have been developed to improve the hot cracking properties of aluminum alloys. For example, applying a magnetic field during the aluminum alloy casting process can refine the solidification structure, thereby improving hot cracking in the casting. However, since heat-free aluminum alloys are mostly used in die casting, the castings are large and thin with a fast solidification rate, making it difficult to apply a magnetic field during solidification. Ultrasonic treatment to refine the solidification structure of aluminum alloys has become a mature process. Previous studies on ultrasonic melt treatment can be broadly divided into two categories: one is high-temperature melt ultrasonic treatment, which can achieve degassing; the other is to achieve ultrasonic refinement, which usually requires treatment at lower melt temperatures (close to the liquidus temperature or even within the solid-liquid two-phase temperature range). These temperature conditions are clearly unsuitable for the die casting process of heat-free aluminum alloys.

[0004] Because previous studies on aluminum alloy microalloying have mostly focused on exploring the relationship between composition, microstructure, and mechanical properties, there are few reports on the impact on casting performance. Therefore, there is currently no appropriate method to improve the hot cracking problem of heat-free aluminum alloys. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of hot cracking during the integrated die casting process of large-size aluminum alloy castings. It proposes a method to improve the hot cracking resistance of heat-treated aluminum alloys and a high-resistance heat-treated aluminum alloy. This invention enables effective control of the microstructure and hot cracking resistance of aluminum alloys, resulting in high-quality heat-treated aluminum alloy castings with refined solidification structure and elimination of casting hot cracks.

[0006] To achieve the above objectives, the present invention provides a method for improving the hot crack resistance of heat-treated aluminum alloys, the method comprising the following steps:

[0007] S1: Melt the heat-free aluminum alloy to obtain a melt; add Zr, and optionally Sc and / or Er to the melt, stir, degas, cool and let stand to obtain an alloy melt;

[0008] S2: The alloy melt is subjected to high-temperature melt ultrasonic treatment to obtain a high-temperature melt, which is then poured into a mold for casting to obtain a high-temperature crack-resistant aluminum alloy that does not require heat treatment.

[0009] According to the present invention, preferably, the chemical composition of the heat-free aluminum alloy includes Mg, Si, Mn, Fe, Cu and Al; preferably, based on the total weight of the heat-free aluminum alloy, the heat-free aluminum alloy includes 4.0-7.0% Mg, 1-3% Si, 0.4-0.8% Mn, 0.1-0.2% Fe, 1.5-3.0% Cu, and the remainder being Al.

[0010] According to the present invention, preferably, when Zr, and optionally Sc and / or Er, are added to the melt, the temperature of the melt is 730-780°C.

[0011] According to the present invention, preferably, the amount of Zr added is less than 0.25%, the amount of Sc added is less than 0.25%, and the amount of Er added is less than 0.25% based on the total weight of the alloy melt. Preferably, based on the total weight of the alloy melt, the alloy melt comprises 4.0-7.0% Mg, 1-3% Si, 0.4-0.8% Mn, 0.1-0.2% Fe, 1.5-3.0% Cu, 0.15-0.2% Sc, 0.15-0.2% Zr, and the remainder is Al.

[0012] According to the present invention, preferably, the temperature of the alloy melt is 670-710°C.

[0013] According to the present invention, preferably, the high-temperature melt ultrasonic treatment is carried out in a holding furnace, and the temperature of the alloy melt is 670-710°C during the high-temperature melt ultrasonic treatment.

[0014] According to the present invention, preferably, the ultrasonic frequency of the high-temperature melt ultrasonic treatment is 19-21 kHz, the ultrasonic power is 1.0-3.0 kW, and the treatment time is 30-300 s.

[0015] According to the present invention, preferably, the high-temperature melt ultrasonic treatment includes inserting an ultrasonic tool head preheated to 670-710°C into the alloy melt for ultrasonic treatment.

[0016] According to the present invention, preferably, the insertion depth is 15-30 mm.

[0017] According to the present invention, preferably, the casting is at least one of die casting, squeeze casting and gravity casting.

[0018] In another aspect, the present invention provides a high-heat-crack-resistant aluminum alloy prepared by the method described above for improving the heat-crack resistance of heat-free aluminum alloys.

[0019] In this invention, the thermal crack resistance of heat-free aluminum alloys is improved by adjusting the chemical composition of the aluminum alloy and employing high-temperature melt ultrasonic treatment. First, the composition of the heat-free aluminum alloy is adjusted to induce the precipitation of second-phase particles at high temperatures. These particles have lattice parameters similar to those of the aluminum alloy, enabling heterogeneous nucleation through coherent relationships. Second, high-temperature melt ultrasonic treatment further improves the surface wettability of the particles through ultrasonic cavitation, thereby enhancing their heterogeneous nucleation ability. The ultrasonic flow effect further promotes the uniform distribution of the second-phase particles in the melt. The aluminum alloy melt containing a large number of uniformly distributed heterogeneous nucleation particles exhibits a significantly refined solidification structure during casting, thus significantly improving the thermal crack resistance of the aluminum alloy. Specifically, firstly, Zr, along with optional Sc and / or Er, is added during the smelting of heat-free aluminum alloys. Through stirring, degassing, and cooling, an aluminum alloy melt is obtained, allowing second-phase particles (such as Al3Zr, Al3(ScZr)) to precipitate at high temperatures, providing conditions for heterogeneous nucleation. Secondly, ultrasonic treatment is performed under high-temperature melt conditions to improve the nucleation ability of the particles and promote their uniform distribution within the melt. When the aluminum alloy melt containing a large number of uniformly distributed heterogeneous nucleation particles is poured into a mold and solidifies, significant refinement of the solidification structure is achieved, thereby significantly improving the aluminum alloy's resistance to hot cracking.

[0020] The beneficial effects of the technical solution of the present invention are as follows:

[0021] This invention, by adjusting parameters such as the amount of trace elements added, melt treatment temperature, and ultrasonic power, can effectively control the microstructure and hot crack resistance of aluminum alloys, resulting in high-quality, heat-free aluminum alloy castings with refined solidification structure and eliminated casting hot cracks. This method can also be used in the melt treatment process before extrusion casting or gravity casting, and is suitable for widespread application in the field of cast aluminum alloys.

[0022] The method of this invention has the advantages of simple process, flexible operation, significant effect, and wide applicability:

[0023] (1) Simple process: Aluminum alloy micro-alloying and ultrasonic melt treatment are both mature processes that are easy to implement and do not require special training of operators or setting up of operation positions.

[0024] (2) Flexible operation: The temperature of the aluminum alloy melt can be controlled by a temperature controller, and the ultrasonic melt process parameters (frequency, power, processing time) can be adjusted at any time as needed;

[0025] (3) Significant effect: The combined application of microalloying and ultrasonic treatment can significantly refine the solidification structure and improve the resistance to hot cracking; at the same time, it reduces the hot cracking problem of die castings and is also conducive to improving the yield of aluminum alloy die castings and reducing manufacturing costs.

[0026] (4) Wide applicability: This invention is carried out in a high-temperature molten state, so it is not only applicable to the pretreatment of the die casting process, but can also be extended to the casting process of other aluminum alloys.

[0027] (5) The method of the present invention does not require modification of equipment such as die casting machine, and the cost is low. Furthermore, the content of trace elements and ultrasonic treatment parameters can be adjusted according to the characteristics of heat-free aluminum alloy and its die casting process. The process window can be adjusted within a large range as needed, and finally heat-free aluminum alloy with excellent mechanical and casting properties can be obtained.

[0028] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0029] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0030] Figure 1(a) shows the solidification process time-stress-temperature curve of the aluminum alloy obtained by the method for improving the hot crack resistance of heat-free aluminum alloy according to Embodiment 1 of the present invention.

[0031] Figure 1(b) shows the solidification process time-stress-temperature curve of a heat-free aluminum alloy provided in Comparative Example 1 of the present invention for hot crack resistance testing.

[0032] Figure 2(a) shows an aluminum alloy sample obtained by a method for improving the hot crack resistance of heat-free aluminum alloys according to Embodiment 1 of the present invention.

[0033] Figure 2(b) shows a heat-free aluminum alloy sample provided by Comparative Example 1 of the present invention. Detailed Implementation

[0034] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0035] Example 1

[0036] This embodiment provides a method for improving the hot crack resistance of heat-free aluminum alloys, the method comprising the following steps:

[0037] S1: Melting was carried out in a resistance furnace using a graphite clay crucible. First, industrial pure aluminum was melted at 750℃. Then, Si blocks, Fe powder, Cu granules, Al-Mn master alloy, Al-Sc master alloy, and Al-Zr master alloy were added to the aluminum melt in sequence, and finally, industrial pure magnesium was added. After all the alloying elements melted, the mixture was mechanically stirred for 10 minutes, then cooled to 720℃ and C2Cl6 was added for degassing. Subsequently, the temperature was further lowered to 700℃ and allowed to stand for 10 minutes to obtain the alloy melt.

[0038] The alloy melt comprises, by total weight, 6.0% Mg, 2.5% Si, 0.6% Mn, 0.15% Fe, 2.3% Cu, 0.18% Sc, 0.15% Zr, with the remainder being Al.

[0039] S2: Turn on the power of the ultrasonic processing equipment (ultrasonic metal melt processing equipment (model TJS-3000) manufactured by Hangzhou Chenggong Ultrasonic Co., Ltd.), set the ultrasonic frequency to 20kHz and the power to 1200W, and insert the ultrasonic tool head, preheated to 700℃, into the alloy melt (insertion depth 28mm) for ultrasonic melt processing. The ultrasonic processing time is 60s. The ultrasonic processing is carried out in a holding furnace to ensure that the temperature of the alloy melt is maintained at 700±3℃, so as to obtain a high-temperature melt.

[0040] The thermal crack resistance test mold is preheated at 250℃. The high-temperature melt is poured into the thermal crack resistance test mold to carry out the thermal crack resistance test. The time-stress-temperature curve of the aluminum alloy solidification process is recorded, and the macroscopic crack condition is observed.

[0041] Comparative Example 1

[0042] This comparative example uses a heat-free aluminum alloy for hot crack resistance testing. Based on the total weight of the heat-free aluminum alloy, it comprises 6.0% Mg, 2.5% Si, 0.6% Mn, 0.15% Fe, 2.3% Cu, with the remainder being Al. This heat-free aluminum alloy was not subjected to ultrasonic treatment by the high-temperature melt.

[0043] The results of the hot crack resistance test of Example 1 and Comparative Example 1 are shown in Figures 1 and 2. It can be seen that the sample of Example 1, which added trace amounts of Zr and Sc and underwent high-temperature melt ultrasonic treatment, did not show macroscopic cracks after the hot crack resistance test. However, the sample of Comparative Example 1, which did not add Zr and Sc and did not undergo high-temperature melt ultrasonic treatment, cracked after the hot crack resistance test. The solidification process time-stress-temperature curves of Example 1 and Comparative Example 1 showed the same results. Therefore, it can be seen that the method of the present invention can significantly improve the hot crack resistance of aluminum alloys.

[0044] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they 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 method of improving the hot tear resistance of a non-heat-treatable aluminum alloy, characterized in that, The method includes the following steps: S1: Melt the heat-free aluminum alloy to obtain a melt; add Zr and Sc to the melt, and then stir, degas, cool and let stand to obtain an alloy melt; Based on the total weight of the alloy melt, the alloy melt comprises 4.0-7.0% Mg, 1-3% Si, 0.4-0.8% Mn, 0.1-0.2% Fe, 1.5-3.0% Cu, 0.15-0.2% Sc, 0.15-0.2% Zr, with the remainder being Al; S2: The alloy melt is subjected to high-temperature melt ultrasonic treatment to obtain a high-temperature melt, which is then poured into a mold for casting to obtain a high-temperature crack-resistant aluminum alloy that does not require heat treatment. The high-temperature melt ultrasonic treatment is carried out in a holding furnace, and the temperature of the alloy melt during the high-temperature melt ultrasonic treatment is 670-710℃. The high-temperature melt ultrasonic treatment involves inserting an ultrasonic tool head, preheated to 670-710°C, into the alloy melt for ultrasonic treatment.

2. The method of improving hot tear resistance of a non-heat-treatable aluminum alloy of claim 1, wherein, When Zr and Sc are added to the melt, the temperature of the melt is 730-780°C.

3. The method for improving the hot crack resistance of heat-treated aluminum alloys according to claim 1, wherein, The ultrasonic frequency for the high-temperature melt ultrasonic treatment is 19-21kHz, the ultrasonic power is 1.0-3.0kW, and the treatment time is 30-300s.

4. The method for improving the hot crack resistance of heat-free aluminum alloys according to claim 1, wherein, The insertion depth is 15-30mm.

5. The method for improving the hot crack resistance of heat-treated aluminum alloys according to claim 1, wherein, The casting is at least one of die casting, squeeze casting, and gravity casting.

6. The high-heat-crack-resistant heat-treated aluminum alloy prepared by the method for improving the heat-crack resistance of heat-treated aluminum alloys according to any one of claims 1-5.

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