CN118880126A - A heat-resistant cast aluminum alloy - Google Patents

Abstract

The invention relates to a heat-resistant cast aluminum alloy, wherein the components thereof are, by mass percentage, Si: 10.0-15.0%, Cu: 5.5-7.8%, Mg: 0.5-1.3%, Ti: 0.14-0.81%, Zr: 0.26-0.77%, V: 0.37-0.82%, W: 0.78-1.24%, the remainder being Al and unavoidable impurity elements, and the contents of Cu, Mg and W satisfy the following conditions: Cu:Mg:W=(5-12):1:(0.85-1.83).

Description

A heat-resistant cast aluminum alloy

Technical Field

The present invention relates to a heat-resistant cast aluminum alloy having excellent high-temperature strength performance, in particular, still having satisfactory strength characteristics above 350°C, and being suitable for high-temperature applications, such as pistons, cylinder parts, turbocharger parts, etc.

Background Art

Aluminum alloy is an ideal lightweight and high-strength material and is widely used in the automotive industry. For example, in order to achieve low fuel consumption and high lightness, the casings of some automobile engines are cast from aluminum alloy.

In fact, in addition to the engine casing, many automotive parts are made of cast aluminum alloys. In particular, pistons, cylinders, turbochargers and other parts that account for a large proportion of the weight in the engine also use cast aluminum alloys in order to reduce the weight of the engine to the greatest extent. These parts are subjected to high operating temperatures during operation, so Al-Si-Cu alloys are usually used. However, in some heavy-duty vehicle engines or high-power engines, traditional Al-Si-Cu alloys cannot be used. The reason is that the main strengthening phases of Al-Si-Cu alloys, Al ₂ Cu and Al ₂ CuMg, become unstable above 250°C, gradually become coarsened and dissolved, resulting in a sharp drop in the strength of the alloy. The operating temperature of components such as pistons, cylinders, turbochargers, etc. of heavy-duty vehicle engines or high-power engines is usually above 300°C, and can reach 400°C or higher at full throttle. Traditional Al-Si-Cu alloys cannot ensure continuous and stable mechanical properties at such temperatures, which will lead to premature failure and scrapping.

Therefore, in order to give full play to the characteristics of aluminum alloy, which is lightweight and high-strength, and to ensure that heavy-duty vehicle engines or high-power engines are lightweight and have low fuel consumption, and to enable them to work continuously and stably and output power continuously, it is very necessary to develop a heat-resistant cast aluminum alloy as the material for the corresponding high-temperature working parts of the engine.

Summary of the invention

The present invention provides a heat-resistant cast aluminum alloy, which has excellent high-temperature strength performance, especially, still has satisfactory strength characteristics above 350°C, and is suitable for high-temperature applications, such as pistons, cylinder parts, turbocharger parts, etc. The high-temperature mechanical properties of the cast aluminum alloy are as follows: the tensile strength is above 165MPa at 350°C, and the tensile strength is above 120MPa at 400°C.

The technical solution of the present invention is as follows.

The invention provides a heat-resistant cast aluminum alloy. The components of the heat-resistant cast aluminum alloy are, by mass percentage, Si: 10.0-15.0%, Cu: 5.5-7.8%, Mg: 0.5-1.3%, Ti: 0.14-0.81%, Zr: 0.26-0.77%, V: 0.37-0.82%, W: 0.78-1.24%, the remainder is Al and inevitable impurity elements, and the contents of Cu, Mg and W satisfy: Cu:Mg:W=(5-12):1:(0.85-1.83).

Next, the functions of the various components of the heat-resistant cast aluminum alloy of the present invention are described.

Si: Silicon is the basic alloying element of the cast aluminum alloy of the present invention, which can effectively improve the strength and elastic modulus of the aluminum alloy, and can ensure the fluidity of the aluminum alloy melt, ensure good castability, and silicon can also improve the surface hardness and wear resistance of the aluminum alloy. If the silicon content is too low, the strength and casting performance, hardness and wear resistance cannot be guaranteed. If the silicon content is too high, the hardness and wear resistance of the aluminum alloy will be too high, which will deteriorate the machinability on the one hand and reduce the plastic elongation on the other hand. The silicon content in the aluminum alloy of the present invention is controlled at 10.0-15.0%.

Cu: Copper is a basic element for forming the strengthening phases Al ₂ Cu and Al ₂ CuMg in aluminum alloys, giving aluminum alloys relatively excellent strength properties and playing a prominent and decisive role in high-temperature strength characteristics. However, as mentioned in the background art, the high-temperature tolerance of Al ₂ Cu and Al ₂ CuMg is below 250°C. Simply relying on Al ₂ Cu and Al ₂ CuMg cannot obtain the heat-resistant cast aluminum alloy of the present invention. If the copper content is too low, the high-temperature strength cannot be guaranteed. If the copper content is too high, the continuity of the matrix will be affected due to excessive precipitation phases, and the mechanical properties of the aluminum alloy will be deteriorated. The copper content in the cast aluminum alloy of the present invention is controlled at 5.7-7.8%.

Mg: Magnesium is a basic element for forming the strengthening phases Mg ₂ Si and Al ₂ CuMg in aluminum alloys, giving aluminum alloys relatively excellent strength properties and playing a prominent and decisive role in high-temperature strength characteristics. If the magnesium content is too low, the strengthening phase is insufficient and the excellent mechanical properties of the cast aluminum alloy cannot be guaranteed. If the magnesium content is too high, the number of strengthening phases will be too large, destroying the continuity of the matrix and deteriorating the mechanical properties of the cast aluminum alloy. The magnesium content in the cast aluminum alloy of the present invention is controlled at 0.5-1.3%.

Ti, V, Zr: Titanium, vanadium, and zirconium form a single Al ₃ Ti, Al ₃ V, and Al ₃ Zr phase with the matrix aluminum element, or form an Al ₃ X (X is two or three of Ti, V, and Zr) phase. These phases precipitate in the form of fine dispersion during the high-temperature operation of the cast aluminum alloy, and play an important role in improving the high-temperature strength of the cast aluminum alloy. In order to give full play to the above effects, the addition amount of titanium in the present invention is 0.14-0.81%, the addition amount of zirconium is 0.26-0.77%, and the addition amount of vanadium is 0.37-0.82%.

W: Tungsten is added to the cast aluminum alloy of the present invention. The inventors found that the heat resistance of the cast aluminum alloy was significantly improved after adding tungsten. It is speculated that the addition of tungsten may form a doping effect on _Al2Cu and _Al2CuMg phases, so that they can still maintain good stability at higher temperatures (above 250°C), thereby improving the heat resistance of the cast aluminum alloy. In order to achieve the above effect, the tungsten addition amount of the present invention is 0.78-1.24%. If the tungsten addition amount is too low, the improvement effect of the high temperature strength of the cast aluminum alloy is insufficient. If the tungsten addition amount is too high, the high temperature strength of the cast aluminum alloy will also deteriorate.

Without being limited to the above description, the inventors have found that simply adding tungsten in the aforementioned amounts does not always produce satisfactory effects on the high temperature strength of cast aluminum alloys. Through experimental analysis and summary, the inventors have found that when the content ratio of Cu, Mg and W is controlled within a certain range, the cast aluminum alloy can always have excellent high temperature strength characteristics. This also indirectly confirms that the improvement of the high temperature strength of cast aluminum alloys by adding tungsten should be related to the influence of tungsten on _Al2Cu and _Al2CuMg phases. After repeated experiments, the inventors determined the most suitable range of the content ratio of Cu, Mg and W, namely Cu:Mg:W=(5-12):1:(0.85-1.83).

Furthermore, the Si and Mg contents of the heat-resistant cast aluminum alloy of the present invention satisfy: Si:Mg=12-24. Mg ₂ Si is also an important strengthening phase in the heat-resistant cast aluminum alloy of the present invention. By controlling Si and Mg within a reasonable range, the aluminum alloy of the present invention can effectively ensure excellent high temperature strength characteristics.

As a non-limiting description, Fe≤0.05%, Mn≤0.05% in the heat-resistant cast aluminum alloy of the present invention, iron and manganese are impurity elements in the cast aluminum alloy of the present invention, which are inevitably brought by the raw materials, and the content of iron and manganese is as low as possible, but due to cost considerations and process level limitations, controlling the upper limit of iron and manganese to 0.05% does not affect the acquisition of excellent high temperature strength of the cast aluminum alloy of the present invention.

As a non-limiting description, the heat-resistant cast aluminum alloy of the present invention needs to be subjected to aging heat treatment after casting, so as to promote the formation of _Al2Cu and _Al2CuMg phases and improve the strength and hardness of the cast aluminum alloy as a whole. According to the composition of the present invention, the inventors have determined that the aging heat treatment temperature is preferably set at 230-280°C, and the aging time is controlled at 6-12h.

As an optional step, a solution treatment step can also be performed before the aging. Solution treatment can eliminate the supersaturated solid solution phase in the cast aluminum alloy, eliminate element segregation, promote the uniform distribution of elements, and improve the mechanical properties of the cast aluminum alloy. Since the aluminum alloy of the present invention is particularly suitable for high temperature conditions, if the working temperature of the aluminum alloy of the present invention is above 280°C, aging can be performed directly without solution treatment. When solution treatment is required, the solution treatment is maintained at 490-550°C for 1-3 hours.

As a further description, the heat-resistant cast aluminum alloy of the present invention has excellent high-temperature performance, with a tensile strength of more than 165 MPa at 350° C. and more than 120 MPa at 400° C., which can meet the requirements of continuous and stable operation under high-temperature conditions.

Based on the above disclosure, it can be known that the cast aluminum alloy of the present invention has very excellent high-temperature mechanical properties, and therefore is particularly suitable for the preparation of high-temperature working parts such as pistons, cylinder parts, and turbocharger parts.

The present invention has the following beneficial effects.

The present invention obtains a cast aluminum alloy with excellent high-temperature strength by optimizing the composition of the cast aluminum alloy. In particular, the cast aluminum alloy of the present invention adds tungsten elements, and the proportions of Cu, Mg, and W are synergistically controlled, and it is found that the heat resistance of the cast aluminum alloy can be significantly improved. It is speculated that the addition of tungsten has an effect on the _Al2Cu and _Al2CuMg phases, so that they can still maintain good stability at higher temperatures (above 250°C), thereby improving the heat resistance of the cast aluminum alloy. Finally, the cast aluminum alloy obtained by the present invention has a tensile strength of more than 165MPa at 350°C and a tensile strength of more than 120MPa at 400°C. It can meet the needs of continuous and stable operation under high-temperature conditions and is suitable for manufacturing high-temperature components of heavy-duty, high-speed, and high-power engines, such as pistons, cylinder components, turbocharger components, and the like.

DETAILED DESCRIPTION

In order to enable ordinary technicians in the field to fully understand the technical solutions and beneficial effects of the present invention, further explanation is given below in conjunction with specific test examples.

The aluminum alloy melt was smelted, and the impurities Fe and Mn were controlled at 0.03±0.005%. After smelting, sand casting was used to obtain 20cm×20cm×40cm castings, and each casting was aged at 265℃ for 8.5h. The composition of each casting is shown in Table 1.

Two specimens were cut from each casting, and their tensile strength was measured at 350℃ after being kept at 350℃ for 240h, and at 400℃ after being kept at 400℃ for 240h. The dimensions of the specimens and the high-temperature strength test were carried out in accordance with the requirements of GB/T228.2-2015 (Metallic materials - Tensile test - Part 2 - High-temperature test method), and the high-temperature strength test results are recorded in Table 2.

Table 1 Chemical composition of various aluminum alloy castings (in mass percentage, %, the remainder is Al).

Table 2 Properties of various aluminum alloy castings.

Below, we will conduct a detailed analysis based on Table 1 and Table 2.

The contents of various elements and the Cu:Mg:W ratios of the cast aluminum alloys of test numbers 1-10 in Table 1 all meet the requirements of the present invention. The experiments confirm that the cast aluminum alloys finally obtained have excellent high-temperature mechanical properties, the tensile strength at 350°C is all above 165MPa, and the tensile strength at 400°C is all above 120MPa. Test numbers 1-10 are all embodiments of the present invention; and, from the perspective of Si:Mg ratios, the cast aluminum alloys of test numbers 1, 2, 4, 5, 7, 8, and 10 with Si:Mg in the range of 12-24 exhibit more excellent high-temperature performance, the tensile strength at 350°C is all above 180MPa, and the tensile strength at 400°C is all above 135MPa, indicating that reasonable Si:Mg is conducive to obtaining cast aluminum alloys with more outstanding high-temperature strength performance.

At least one of the Cu, Mg, W, and Cu:Mg:W ratio values in the cast aluminum alloy compositions of test numbers 11-20 in Table 1 does not meet the requirements of the present invention, and the high temperature tensile strength of the final cast aluminum alloy cannot meet the requirements of the present invention. Therefore, test numbers 11-20 are all comparative examples of the present invention.

The following is a detailed analysis of each comparative example.

Comparative Examples 11, 12, 13, 15, and 17 are comparative examples of Examples 1, 2, 3, 5, and 7, respectively. Mg, Mg, Cu, W, and W are adjusted relative to Examples 1, 2, 35, and 7, respectively. Although the adjusted Mg, W, and Cu are still within the scope of the invention, Cu:Mg:W does not meet the invention requirements. From the results of the high-temperature strength test, the high-temperature tensile strength of the cast aluminum alloys of Comparative Examples 11, 12, 13, 15, and 17 cannot meet the requirements of the present invention, indicating that controlling Cu:Mg:W within a reasonable range is crucial for the cast aluminum alloy to obtain excellent high-temperature strength.

Comparative Examples 14, 16, 18, 19, and 20 are comparative examples of Examples 4, 6, 8, 9, and 10, respectively. Relative to Examples 4, 6, 8, 9, and 10, W, Cu, Mg, W, and Cu are adjusted, respectively. Although the adjusted Cu:Mg:W is still within the scope of the invention, due to the excessively high or low W, Cu, Mg, W, and Cu, insufficient or excessive formation of Al ₂ Cu and Al ₂ CuMg strengthening phases, and insufficient or excessive doping effect of W on Al ₂ Cu and Al ₂ CuMg, finally, from the high temperature strength test results, the high temperature tensile strength of the cast aluminum alloys of Comparative Examples 14, 16, 18, 19, and 20 cannot meet the requirements of the present invention, indicating that controlling the contents of Cu, W, and Mg within a reasonable range is crucial for the cast aluminum alloy to obtain excellent high temperature strength.

It is not difficult to verify by comparing the above embodiments and comparative examples that the present invention optimizes the composition of the cast aluminum alloy, especially deliberately adds W and synergistically controls Cu:Mg:W, so that the high-temperature strength characteristics of the cast aluminum alloy are significantly improved, and its tensile strength at 350°C reaches more than 165MPa, and the tensile strength at 400°C reaches more than 120MPa. On this basis, synergistic control of Si:Mg can further improve the high-temperature mechanical properties of the cast aluminum alloy. The aluminum alloy shown in the present invention has outstanding high-temperature strength performance, can meet the needs of continuous and stable operation under high-temperature conditions, and is particularly suitable for manufacturing high-temperature components of heavy-duty, high-speed, and high-power engines, such as pistons, cylinder components, turbocharger components, and the like.

The above embodiments are only used to help understand the method and core idea of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. The heat-resistant cast aluminum alloy is characterized by comprising the following components in percentage by mass: si:10.0-15.0%, cu:5.5-7.8%, mg:0.5-1.3%, ti:0.14-0.81%, zr:0.26-0.77%, V:0.37-0.82%, W:0.78-1.24%, the balance being Al and unavoidable impurity elements, the contents of Cu, mg and W being as follows: cu: mg: w= (5-12): 1: (0.85-1.83).

2. The refractory cast aluminum alloy of claim 1, wherein the refractory cast aluminum alloy has Si and Mg contents that satisfy: si: mg=12-24.

3. The refractory cast aluminum alloy according to claim 2, wherein Fe and Mn in the refractory cast aluminum alloy are 0.05% or less and 0.05% or less.

4. A heat resistant cast aluminium alloy according to any one of claims 1-3, wherein the heat resistant cast aluminium alloy is subjected to an ageing heat treatment after casting.

5. The refractory cast aluminum alloy according to claim 4, wherein the aging is maintained at 230-280 ℃ for 6-12 hours.

6. The heat resistant cast aluminum alloy as recited in claim 5, further optionally including a solution treatment step prior to said aging.

7. The heat resistant cast aluminum alloy as claimed in claim 6, wherein the solution treatment is maintained at 490-550 ℃ for 1-3 hours.

8. The heat resistant cast aluminum alloy of any of claims 1-7, wherein the heat resistant cast aluminum alloy has a tensile strength of 165MPa or greater at 350 ℃.

9. The heat resistant cast aluminum alloy according to any one of claims 1 to 8, wherein the heat resistant cast aluminum alloy has a tensile strength of 120MPa or more at 400 ℃.

10. The refractory cast aluminum alloy according to any one of claims 1-9, wherein the refractory cast aluminum alloy is used in the preparation of high temperature service components such as pistons, cylinder components, turbocharger components, and the like.