High-strength heat-resistant heat-treatment-free Al-Si alloy and preparation method thereof

Abstract

The invention relates to a high-strength heat-resistant heat-treatment-free Al-Si alloy and a preparation method thereof, and belongs to the technical field of aluminum alloy materials. The problem that the high-temperature mechanical property of the cast heat-resistant aluminum-silicon alloy in the prior art is sharply attenuated is solved. The heat treatment-free Al-Si alloy comprises the following components in percentage by mass: 18%-21% of Si, 0.5%-2.5% of Ni, 1.2%-1.8% of Cu, 0.65%-0.85% of Mg, 0.4%-1.0% of Fe, more than 0 and less than or equal to 0.3% of Mn, less than or equal to 0.05% of P and the balance of Al and inevitable impurity elements. The heat-treatment-free Al-Si alloy has excellent room-temperature tensile property and high-temperature tensile property; after long-time thermal exposure, good room-temperature tensile property and high-temperature tensile property are still maintained; the method has important value in the industrial field, especially the automotive field.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy materials, and particularly relates to a high-strength, heat-resistant, heat-treatment-free Al-Si alloy and a preparation method thereof. Background Art

[0002] In recent years, as people's environmental awareness grows, energy conservation and emission reduction have received more and more attention in all walks of life, especially in the automotive industry, where lightweight design has become the mainstream. The sharp decline in mechanical properties of structural parts during high-temperature service has become a key shortcoming affecting service safety. This has directly led to the current industry's tendency to use heavier steel for structural parts that need to withstand service temperatures above 200°C, while being cautious about the use of lightweight aluminum alloys. Therefore, the development of lightweight, high-strength, heat-resistant alloys has become an important research direction in the field of materials.

[0003] Al-Si alloys have been widely used in aerospace, automobile, shipbuilding and other fields due to their high specific strength, excellent wear resistance and castability. With the rapid development of industrial technology, the strength and service temperature requirements of parts are constantly increasing, and existing commercial aluminum alloys are difficult to meet the growing demand. Summary of the invention

[0004] In view of this, the present invention solves the problem of rapid attenuation of high-temperature mechanical properties of cast heat-resistant aluminum-silicon alloys in the prior art, and provides a high-strength, heat-resistant, heat-treatment-free Al-Si alloy and a preparation method thereof.

[0005] The technical solutions adopted by the present invention to achieve the above-mentioned purpose are as follows.

[0006] In a first aspect, the present invention provides a high-strength, heat-resistant, heat-treatment-free Al-Si alloy, which comprises, by mass percentage, 18% to 21% Si, 0.5% to 2.5% Ni, 1.2% to 1.8% Cu, 0.65% to 0.85% Mg, 0.4% to 1.0% Fe, 0<Mn≤0.3%, P≤0.05%, and the rest being Al and unavoidable impurity elements.

[0007] Preferably, in terms of mass percentage, it includes: 20.19% to 20.26% Si, 0.66% to 2.44% Ni, 1.46% to 1.49% Cu, 0.76% to 0.81% Mg, 0.42% to 0.81% Fe, 0.19% to 0.2% Mn, 0.011% to 0.014% P, and the rest are Al and unavoidable impurity elements.

[0008] Preferably, the mass percentage of the unavoidable impurity elements is ≤0.1%.

[0009] In a second aspect, the present invention further provides a method for preparing the above-mentioned high-strength, heat-resistant, heat-treatment-free Al-Si alloy, comprising the following steps:

[0010] Step 1: weigh pure Al, pure Mg, Al-Si master alloy, Al-Cu master alloy, Al-Ni master alloy, Al-Fe master alloy, Al-Mn master alloy and Al-P master alloy according to proportion;

[0011] Step 2: Melt pure Al and Al-Si master alloy, remove surface scum, stir and mix evenly to obtain a melt;

[0012] Step 3: Add Al-Cu master alloy, Al-Ni master alloy, Al-Fe master alloy and Al-Mn master alloy to the melt in sequence, stir evenly and keep warm after they are completely melted;

[0013] Step 4: Wrap the pure Mg with aluminum foil and press it into the melt. After it is completely melted, stir it evenly and keep it warm.

[0014] Step 5: Wrap Al-P with aluminum foil and press it into the melt. After it is completely melted, stir it evenly and keep it warm.

[0015] Step 6: Add a slag remover to the melt, stir evenly, skim off impurities, pass argon gas into the melt for refining, and skim off impurities again;

[0016] Step 7: When the melt is cooled to 800±2.5°C, the melt is poured into a steel mold preheated to 200±2.5°C to obtain a casting.

[0017] Preferably, in step 1, the purity of the pure Al is ≥ 99.9%, and the purity of the pure Mg is ≥ 99.9%.

[0018] Preferably, in step 1, the Al-Si master alloy is Al-50wt%Si, the Al-Cu master alloy is Al-50wt%Cu, the Al-Ni master alloy is Al-10wt%Ni, the Al-Fe master alloy is Al-75wt%Fe, the Al-Mn master alloy is Al-10wt%Mn, and the Al-P master alloy is Al-3wt%P.

[0019] Preferably, in step 2, the melting temperature is 850±2.5° C. and the stirring time is 2 min.

[0020] Preferably, in step 3, the stirring time is 5 minutes and the insulation time is 10 minutes.

[0021] Preferably, in step 4, the stirring time is 2 minutes and the insulation time is 5 minutes.

[0022] Preferably, in step 2 and step 4, the pure Al and pure Mg are respectively freed from surface oxide films and preheated to 200°C.

[0023] Preferably, in step 5, the stirring time is 2 minutes and the insulation time is 30 minutes.

[0024] Preferably, in step 6, the stirring time is 2 min.

[0025] Preferably, in step 6, the purity of the nitrogen is 99.99%, and the ventilation time of the nitrogen is 2 minutes.

[0026] Preferably, in step 6, the amount of the slag remover is 1 wt% of the mass of the melt.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The high-strength, heat-resistant, heat-treatment-free Al-Si alloy of the present invention adds a specific mass percentage of Cu, Mg, Ni, Fe, and Mn elements to the Al-Si alloy, wherein the addition of Ni and Mn elements can inhibit the formation of needle-shaped β-Fe phases, and at the same time, the size and distribution of the T phase (Al9FeNi), δ phase (Al3CuNi), and γ phase (Al7Cu4Ni) in the alloy can be regulated to obtain a better synergistic strengthening effect. The Fe element is an inevitable impurity element when recycled aluminum is used. In the heat-resistant alloy of the present invention, a relatively high content of Fe element is added, and the iron phase is transformed into a beneficial high-temperature strengthening phase, which can promote the utilization rate of the heat-resistant alloy for recycled aluminum. At the same time, the heat-resistant aluminum alloy of the present invention can obtain good mechanical properties without heat treatment strengthening. The above advantages can greatly improve production efficiency and save production costs.

[0029] The embodiments show that the heat-treatment-free Al-Si alloy of the present invention has excellent room temperature tensile properties and high temperature tensile properties. And after long-term heat exposure, it still maintains good room temperature tensile properties and high temperature tensile properties. Its room temperature tensile strength is ≥252MPa, and its yield strength is ≥208MPa. Its tensile strength at 300°C is ≥241MPa, and its yield strength is ≥190MPa. After heat exposure, its room temperature tensile strength is ≥196MPa, and its yield strength is ≥135MPa. Its tensile strength at 300°C is ≥181MPa, and its yield strength is ≥126MPa.

[0030] The high-strength, heat-resistant, heat-treatment-free Al-Si alloy of the present invention has important value in the industrial field, especially in the automotive field. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments and comparative examples of the present invention, the drawings required for use in the embodiments and comparative examples will be briefly introduced below. Obviously, the drawings described below are only some embodiments and comparative examples of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 This is a photo of the cast structure of the aluminum alloy prepared in Example 1 of the present invention.

[0033] Figure 2 This is a photo of the cast structure of the aluminum alloy prepared in Example 2 of the present invention.

[0034] Figure 3 This is a photo of the cast structure of the aluminum alloy prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with embodiments and comparative examples.

[0036] Example 1

[0037] The high-strength, heat-resistant, heat-treatment-free Al-Si alloy comprises, by mass percentage, 20.2% Si, 0.66% Ni, 1.49% Cu, 0.76% Mg, 0.42% Fe, 0.20% Mn, 0.012% P, and the remainders are Al and unavoidable impurity elements, and the content of unavoidable impurity elements is ≤0.1%.

[0038] The preparation of the high-strength, heat-resistant, heat-treatment-free Al-Si alloy of this embodiment comprises the following steps:

[0039] Step 1: Weigh pure Al, pure Mg, Al-50wt% Si, Al-50wt% Cu, Al-10wt% Ni, Al-75wt% Fe, Al-10wt% Mn and Al-3wt% P in proportion.

[0040] Step 2: pure Al and Al-50wt% Si together with a graphite crucible are placed in a resistance furnace for melting at a melting temperature of 850° C. After complete melting, the scum on the surface of the melt is removed, and then stirred for 2 minutes to make the composition uniform.

[0041] Step 3: Add Al-50wt% Cu, Al-10wt% Ni, Al-75wt% Fe and Al-10wt% Mn to the melt in sequence, press into the melt, stir for 5 minutes after complete melting, and then keep warm for 10 minutes.

[0042] Step 4: Wrap pure Mg with aluminum foil and press it into the melt. After it is completely melted, stir for 2 minutes and then keep warm for 5 minutes.

[0043] Step 5: Wrap Al-3wt%P with aluminum foil and press it into the melt. After it is completely melted, stir it for 2 minutes and then keep it warm for 30 minutes.

[0044] Step 6: Add 1 wt% of slag remover to the melt, stir for 2 minutes, then introduce high-purity argon (99.99%) for refining, and skim off impurities on the melt surface again.

[0045] Step 7: When the melt temperature drops to 800°C, it is cast into a steel mold preheated to 200°C, and then air-cooled to room temperature to obtain an ingot.

[0046] Step 8: Perform a heat exposure test on the obtained ingot: the heat exposure test temperature is selected to be 400°C and the time is 100h.

[0047] The ingot obtained in step 7 was subjected to a tensile test, and the ingot after the heat exposure test in step 8 was quenched and subjected to a tensile test. The results are shown in Tables 1 and 2.

[0048] Example 2

[0049] The high-strength, heat-resistant, heat-treatment-free Al-Si alloy comprises, by mass percentage, 20.19% Si, 1.45% Ni, 1.49% Cu, 0.81% Mg, 0.66% Fe, 0.19% Mn, 0.011% P, and the remainders are Al and unavoidable impurity elements, wherein the content of unavoidable impurity elements is ≤0.1%.

[0050] The same melting and casting methods were carried out as in Example 1; then a heat exposure experiment and quenching were carried out, and the heat exposure temperature and time were the same as in Example 1. The room temperature and high temperature mechanical properties of the alloy were tested by a universal material testing machine. The results are shown in Tables 1 and 2.

[0051] Example 3

[0052] The high-strength, heat-resistant, heat-treatment-free Al-Si alloy comprises, by mass percentage, 20.26% Si, 2.44% Ni, 1.46% Cu, 0.78% Mg, 0.81% Fe, 0.19% Mn, 0.014% P, and the remainder Al and unavoidable impurity elements, wherein the content of unavoidable impurity elements is ≤0.1%.

[0053] The same melting and casting methods were carried out as in Example 1; then a heat exposure experiment and quenching were carried out, and the heat exposure temperature and time were the same as in Example 1. The room temperature and high temperature mechanical properties of the alloy were tested by a universal material testing machine. The results are shown in Tables 1 and 2.

[0054] Comparative Example 1

[0055] The A390 alloy in the prior art has the following components, by mass percentage: Si is 16% to 18%, Cu is 4% to 5%, Mg is 0.45% to 0.65%, Fe<0.5%, Mn<0.1%, Ti<0.2%, Zn<0.1%, and the rest are Al and avoidable impurity elements, and the content of unavoidable impurity elements is ≤0.1%.

[0056] A390 aluminum alloy is a hypereutectic aluminum-silicon alloy. Due to its good mechanical properties, wear resistance, small thermal expansion coefficient and other characteristics, it is widely used in the manufacture of engine pistons and other automotive parts with high wear resistance requirements.

[0057] The room temperature and high temperature mechanical properties of the alloy were tested by a universal material testing machine (the testing method and conditions were the same as those in Example 1). The results are shown in Table 3.

[0058] Table 1 Room temperature tensile test results of alloys of Examples 1-3

[0059]

[0060]

[0061] Table 2 High temperature tensile test results of alloys of Examples 1-3

[0062]

[0063] Table 3 Tensile properties of alloys of comparative example 1

[0064]

[0065] It can be seen from Tables 1 to 3 that the tensile strength of the alloy of the present invention at 300°C in the cast state is 241 MPa, far exceeding the 88 MPa of the T6 state A390 alloy. The alloy of the present invention solves the problem of the rapid attenuation of high temperature mechanical properties of cast heat-resistant aluminum-silicon alloys.

[0066] Obviously, the above embodiments are merely examples for clear explanation, and are not intended to limit the embodiments. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. Heat-treatment-free Al-Si alloy, characterized in that: Calculated by mass percentage, it includes: 18% to 21% Si, 0.5% to 2.5% Ni, 1.2% to 1.8% Cu, 0.65% to 0.85% Mg, 0.4% to 1.0% Fe, 0<Mn≤0.3%, P≤0.05%, and the rest are Al and unavoidable impurity elements.

2. The heat treatment-free Al-Si alloy according to claim 1, characterized in that: Calculated by mass percentage, it includes: 20.19% to 20.26% Si, 0.66% to 2.44% Ni, 1.46% to 1.49% Cu, 0.76% to 0.81% Mg, 0.42% to 0.81% Fe, 0.19% to 0.2% Mn, 0.011% to 0.014% P, and the rest are Al and unavoidable impurity elements.

3. The method for preparing the heat-treatment-free Al-Si alloy according to claim 1 or 2, characterized in that: The following steps are involved: Step 1: weigh pure Al, pure Mg, Al-Si master alloy, Al-Cu master alloy, Al-Ni master alloy, Al-Fe master alloy, Al-Mn master alloy and Al-P master alloy according to proportion; Step 2: Melt pure Al and Al-Si master alloy, remove surface scum, stir and mix evenly to obtain a melt; Step 3: Add Al-Cu master alloy, Al-Ni master alloy, Al-Fe master alloy and Al-Mn master alloy to the melt in sequence, stir evenly and keep warm after they are completely melted; Step 4: Wrap the pure Mg with aluminum foil and press it into the melt. After it is completely melted, stir it evenly and keep it warm. Step 5: Wrap Al-P with aluminum foil and press it into the melt. After it is completely melted, stir it evenly and keep it warm. Step 6: Add a slag remover to the melt, stir evenly, skim off impurities, pass argon gas into the melt for refining, and skim off impurities again; Step 7: When the melt is cooled to 800±2.5°C, the melt is poured into a steel mold preheated to 200±2.5°C to obtain a casting.

4. The method for preparing the heat-treatment-free Al-Si alloy according to claim 3, characterized in that: In step 1, the purity of the pure Al is ≥99.9%, and the purity of the pure Mg is ≥99.9%; The Al-Si master alloy is Al-50wt%Si, the Al-Cu master alloy is Al-50wt%Cu, the Al-Ni master alloy is Al-10wt%Ni, the Al-Fe master alloy is Al-75wt%Fe, the Al-Mn master alloy is Al-10wt%Mn, and the Al-P master alloy is Al-3wt%P.

5. The method for preparing the heat-treatment-free Al-Si alloy according to claim 3, characterized in that: In step 2, the melting temperature is 850±2.5° C., and the stirring time is 2 min.

6. The method for preparing the heat-treatment-free Al-Si alloy according to claim 3, characterized in that: In step 3, the stirring time is 5 minutes and the insulation time is 10 minutes.

7. The method for preparing the heat-treatment-free Al-Si alloy according to claim 3, characterized in that: In step 4, the stirring time is 2 minutes and the insulation time is 5 minutes.

8. The method for preparing the heat-treatment-free Al-Si alloy according to claim 3, characterized in that: In step 2 and step 4, the pure Al and pure Mg are respectively freed from surface oxide films and preheated to 200°C.

9. The method for preparing the heat-treatment-free Al-Si alloy according to claim 3, characterized in that: In step 5, the stirring time is 2 minutes and the insulation time is 30 minutes.

10. The method for preparing the heat-treatment-free Al-Si alloy according to claim 3, characterized in that: In step 6, the purity of the nitrogen is 99.99%, the ventilation time of the nitrogen is 2 minutes, the stirring time is 2 minutes, and the amount of the slag remover is 1wt% of the mass of the melt.

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