WO2024021367A1 - Cast al-si alloy and preparation method thereof - Google Patents

Abstract

Provided in the present invention are a cast Al-Si alloy and a preparation method thereof. The cast Al-Si alloy comprises the following components in percentage by mass: 6.0-9.0% of Si, 0-0.6% of Mg, 0-1.0% of Cu, 0-0.8% of Zn, 0-1.0% of Mn, 0.1-0.5% of Fe, 0-0.25% of Zr, 0.05%-0.25% of Ti, 0-0.3% of Re, and 0.02-0.2% of Sr, with the balance being Al and inevitable impurities, wherein the total content of impurities in the alloy is ≤ 1.0%, and the content of a single impurity is ≤ 0.15%. In the present invention, the proportion of each alloy element enables the alloy to have high strength and high plasticity. The present invention raises the Mg content of the alloy, and meanwhile, the alloy contains a relatively high content of Cu and Zn, so as to enhance the solid solution strengthening effect of the alloy in cast states, and enhance the aging strengthening effect of the alloy in aging states, thus improving the plasticity of the alloy, and reducing the negative effect thereof on the percentage elongation of the alloy; and meanwhile, other alloy elements are introduced at the same time, further improving the solid solution strengthening effect of the alloy, and effectively improving the strength and plasticity of the alloy.

Description

Cast Al-Si alloy and preparation method thereof Technical field

The invention belongs to the field of cast aluminum alloys, and specifically relates to a cast Al-Si alloy and a preparation method thereof.

Background technique

Aluminum alloy has the characteristics of low density, high specific strength and specific stiffness, good corrosion resistance, excellent electrical and thermal conductivity, and easy recycling. It has been widely used in automobile manufacturing and plays an important role in realizing lightweight automobiles. It has obvious advantages in achieving weight reduction, improving fuel utilization, and increasing output power. Among aluminum alloys used in automobiles, cast aluminum alloys account for up to 80%. Cast aluminum alloy has good fluidity and mold-filling ability, and moderate mechanical properties. It is widely used to replace cast iron materials. More and more automotive structural parts are produced by aluminum alloy gravity casting or die-casting processes.

In Al-Si cast alloys, Si is the main element, which determines the fluidity of the alloy. For ordinary gravity casting alloys, the fluidity requirements are not high, and the Si content is relatively low, as low as 5%, and most are between 6.5-8.5%. For die-casting alloys, the fluidity requirements are high, and the Si content is relatively high, mostly between 9-11%. The alloying element Mg is added to form a solid solution in the matrix and play a solid solution strengthening role. As the Mg content increases, the eutectic phase Mg ₂ Si will appear in the alloy. The solidification process of the alloy is that the matrix phase α-Al is first precipitated, and then a eutectic reaction occurs to form an α-Al+Si eutectic structure. Finally, the ternary eutectic structure α-Al+Si+Mg ₂ Si is precipitated in the final solidification zone. , ends the solidification process. During the solid solution treatment process, the Mg ₂ Si phase melts back into the matrix to form supersaturated Mg and Si; during the aging process, Mg and Si precipitate out the strengthening phase Mg ₂ Si, which strengthens the alloy. As the Mg content further increases, the plasticity of the alloy decreases. Therefore, how to improve the strength of Al-Si cast alloys while maintaining good plasticity has always been an unsolved problem that the industry is eager to solve. Copper is also an important alloying element and has solid solution strengthening effect. Cu mainly forms the Al ₂ Cu phase, but when Cu and Mg are added at the same time, α-Al, Si, Al ₂ Cu, Mg ₂ Si and the quaternary phase Q-AlCuMgSi phase are produced. Zn element is an important element in ultra-high-strength aluminum alloys. It forms ternary or quaternary aluminum-zinc alloys with alloying elements such as Mg, Cu, and Si. Adding an appropriate amount of magnesium to form a Mg ₂ Zn strengthening phase can significantly improve the strength of aluminum alloys. Therefore, it is the main alloying element of Al-Zn-Mg, Al-Zn-Si, Al-Zn-Cu-Mg and other alloys.

Gravity casting (including low-pressure casting) and die casting are the two most commonly used processes in aluminum alloy casting. Different processes have different requirements for alloys. For die-casting processes, casting sticking is a common problem. After the casting solidifies, it adheres to the surface of the mold, making it difficult to demould and easily damaging the mold. In order to prevent mold sticking, the Fe content in the alloy is generally increased, and the Fe content is controlled above 0.6%. However, the high Fe content leads to the formation of a large number of coarse Al-Fe-Si phases, seriously damaging the mechanical properties of the alloy. In order to reduce the damage to the mechanical properties of the coarse Fe-rich intermetallic compounds, Mn was substituted for Fe, and the coarse lath-like Fe-rich intermetallic compound phase was transformed into a Hanzi-like or petal-like Mn-rich intermetallic compound phase, and the mechanical properties were obtained significantly improved. Replacing Fe with Mn not only avoids the damage to the mechanical properties of coarse needle-shaped Fe-rich materials, improves the mechanical properties, but also solves the problem of castings sticking to the mold. But the alloy cost is increased. The surface of the gravity cast mold has a thicker coating, which avoids the problem of mold sticking. Therefore, in order to prevent the damage to the relative mechanical properties of Fe-rich intermetallic compounds in gravity cast aluminum alloys, the Fe content is often limited to a very low level. For example, in ZL101A, the Fe content is limited to less than 0.1%. In actual production, the Fe content in many cast Al-Si Content is limited to less than 0.12%. On the other hand, aluminum alloy scrap often contains high Fe, making it difficult to use scrap for low-Fe, high-Mn die-cast aluminum alloys or gravity-cast aluminum alloys with lower Fe content, and must be prepared using electrolytic aluminum ingots. Further Increased alloy cost.

Contents of the invention

The object of the present invention is to provide a cast Al-Si alloy and a preparation method thereof, so that the cast Al-Si alloy has both higher strength and higher plasticity.

In order to achieve the above object, the present invention adopts the following technical solution: a cast Al-Si alloy, including components and mass percentages: Si: 6.0-9.0%, Mg: 0-0.6%, Cu: 0-1.0% , Zn: 0-0.8%, Mn: 0-1.0%, Fe 0.1-0.5%, Zr: 0-0.25%, Ti: 0.05%-0.25%, Re: 0-0.3%, Sr: 0.02-0.2%, The balance is Al and inevitable impurities. The total impurity content in the alloy is ≤1.0%, and the individual impurity content is ≤0.15%.

Furthermore, the cast Al-Si alloy, in the F state (as cast), has a room temperature tensile strength of 222-307MPa, a yield strength of 104-149MPa, and an elongation of 6.1-14.3%. The cast Al-Si alloy is a T6 state, T5 state or T4 state Al-Si alloy, wherein, when in the T6 state, the room temperature tensile strength is 261-341MPa, the yield strength is 132-171MPa, and the elongation is 4.3- 9.7%;

Further, the cast Al-Si alloy is an Al-Si die-cast aluminum alloy. The Al-Si die-cast aluminum alloy includes components and mass percentages: Si: 6.5-9.0%, Mg: 0-0.6%, Cu : 0-1.0%, Zn: 0-0.8%, Mn: 0-1.0%, Fe: 0.1-0.5%, Zr: 0-0.25%, Ti: 0.05-0.25%, Re: 0-0.3%, Sr: 0.02-0.2%, the balance is Al and unavoidable impurities, the total content of impurities in the alloy is ≤ 1.0%, and the content of individual impurities is ≤ 0.15%; when preparing T6 state Al-Si alloy, the Mg content in the alloy composition is ≥ 0.25 %.

Further, the Al-Si die-cast aluminum alloy has a room temperature tensile strength of F state of 237-307MPa, a yield strength of 109-149MPa, and an elongation of 8.7-14.3%; the tensile strength of T6 state is 293-341MPa. The yield strength is 141-171MPa and the elongation is 5.9-9.7%.

Further, the cast Al-Si alloy is Al-Si gravity casting (including low-pressure casting) aluminum alloy. The Al-Si gravity casting aluminum alloy includes components and mass percentages: Si: 6.0-8.5%, Mg :0-0.6%, Cu: 0-1.0%, Zn: 0-0.8%, Fe: 0.1-0.3%, Mn: 0-0.3%, Zr: 0-0.25%, Ti: 0.05%-0.25%, Re :0-0.3%, Sr: 0.02-0.2%, the balance is Al and inevitable impurities. The total impurity content in the alloy is ≤1.0%, and the individual impurity content is ≤0.15%; when preparing the T6 state Al-Si alloy, the Mg content in the alloy composition is ≥0.25%. .

Further, the Al-Si gravity cast aluminum alloy has an F-state tensile strength of 222-298MPa, a yield strength of 104-141MPa, an elongation of 6.1-10.9%, and a T6-state tensile strength of 261-336MPa. The yield strength is 132-168MPa, and the elongation is 4.3-8.1%.

The above-mentioned preparation method of cast Al-Si alloy includes the following steps:

Step 1: Prepare materials. Prepare raw materials for each component according to the content of each component of the alloy;

Step 2: After heating and melting the raw material Al, an aluminum melt is obtained;

Step 3: Determine the composition of the aluminum melt, calculate the amount of each component, and then add other raw materials except Mg and Sr into the aluminum melt until it melts, then add the raw material Mg, and after the Mg melts, stir evenly. Obtain alloy melt; during the entire above-mentioned smelting process, control the temperature of the alloy melt to 690-750°C;

Step 4: Add a refining agent to the alloy melt for refining, then add Sr modifier for modification, and obtain a modified alloy melt;

Step 5: Degas the modified alloy melt, then add a grain refiner, stir evenly, remove the slag, and then let it stand at 690-750°C for a certain period of time before casting. After casting, the aluminum-silicon series casting is obtained Alloy castings are cast Al-Si alloys.

Further, the preparation method also includes:

Step 6: Solid solution aging treatment

(1) When it is necessary to prepare a T6 state cast Al-Si alloy, the aluminum-silicon cast alloy casting is subjected to solution-aging treatment;

(2) When it is necessary to prepare a T4 state cast Al-Si alloy, the aluminum-silicon cast alloy casting is subjected to solution treatment and aging treatment at room temperature;

(3) When it is necessary to prepare a T5 state cast Al-Si alloy, the aluminum-silicon cast alloy casting is directly subjected to aging treatment.

Further, in step 1, the raw material Al is a pure Al ingot or a mixture of returned material or recycled scrap inside the factory and pure Al ingot; the raw material Si is metallic silicon and/or aluminum-silicon master alloy; the raw material Cu is aluminum. Copper master alloy and/or copper additives; raw material Mg is industrial pure magnesium ingot; raw material Mn is aluminum-manganese master alloy and/or manganese additives; raw material Zr is aluminum-zirconium master alloy; raw material Ti is aluminum-titanium master alloy and/or titanium additives ; The raw material Zn is industrial pure zinc ingot; Re is La or/and Ce, the raw material Re is aluminum lanthanum master alloy or aluminum cerium master alloy, or aluminum-(lanthanum cerium mixed rare earth) master alloy; the raw material Al is electrolytic aluminum ingot, heavy One or more of molten aluminum ingots or cast aluminum alloy ingots.

Further, in step 4, the refining agent is a refining agent that can have a refining effect on the alloy melt, such as RJ-1 refining agent; the added mass of the refining agent is 0.2-0.8% of the total mass of the alloy melt, and the refining agent The temperature is 700-750℃, and the refining time is 20-60 minutes.

Further, in the described step 4, the Sr modifier specifically selects Al-10Sr alloy modifier. The amount of modifier added is measured by the residual amount of Sr in the alloy melt after modification, ensuring that the mass percentage of the residual amount of Sr is 0.02%-0.2%; if the Sr modifier in step 4 is not added in step 4, you can choose to add it to the aluminum melt together with Mg in step 3, or add it to the aluminum melt together with other raw materials except Mg.

Further, in step 5, degassing is performed by using a degassing machine to introduce argon gas or nitrogen gas into the modified alloy melt. The grain refiner is commercial AlTiB or AlTiC alloy, and the addition amount is 0.05-0.25% of the total weight of the alloy melt.

Further, in step 5, the casting adopts a die-casting process, preferably high-pressure die-casting. Vacuum high-pressure die casting is used for castings that require T4 and T6 treatment.

Further, in step 5, gravity casting or low-pressure casting is used for casting, and a metal mold is used to increase the cooling rate of the metal liquid. According to the size of the casting, the metal liquid is sub-rapidly cooled, and the cooling rate is 10 ⁰ -10 ² ℃/s, causing the metal liquid to solidify in a sub-rapid cooling state.

Further, in the described step 6, the solid solution treatment process used in the treatment of T4 and T6 is: insulating at 500-550°C for 2-12 hours; the aging treatment process of T4 is to place it at room temperature for more than 7 days; the aging treatment process of T5 and T6 The aging treatment process is: insulation at 120-200℃ for 2-12h.

Compared with the existing technology, the beneficial effects of the present invention are:

(1) The alloy of the present invention can be used in the cast state or in the T4, T5 or T6 state.

(2) The proportion of each alloy element in the present invention makes the alloy have both high strength and high plasticity; the present invention increases the Mg content of the alloy, and at the same time, the alloy contains higher Cu and Zn, which enhances the solidity of the alloy in the cast state. Solution strengthening effect, in the aging state, enhances the aging strengthening effect of the alloy, improves the plasticity of the alloy, and reduces its negative impact on the alloy elongation; at the same time, other alloying elements are introduced to further increase the solid solution strengthening effect in the alloy, effectively improving the alloy strength and plasticity.

Detailed ways

In the description of the present invention, it should be noted that if the specific conditions are not indicated in the examples, the conditions should be carried out in accordance with conventional conditions or the conditions recommended by the manufacturer; if the reagents or instruments used are not indicated by the manufacturer, they can all be commercially available. Regular products obtained with purchase. In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below; the embodiments of the present invention provide an aluminum-silicon cast alloy, as detailed below: The examples describe in detail the high-strength and high-plasticity aluminum-silicon casting alloy of the present invention and its preparation method.

The aluminum ingot for remelting selected in the embodiment of the present invention is Al99.70 in the national standard GB/T 1196-2008 "Aluminum Ingot for Remelting", and its aluminum content is not less than 99.70wt%; it can also be scrap remelting Aluminum ingot; when adding Mn element, choose Al-10Mn master alloy or 75Mn agent (aluminum alloy additive with a Mn mass percentage of 75%); when adding Si element, choose Al-30Si master alloy; when adding Mg element, choose Metal magnesium; when adding Cu element, choose Al-50Cu master alloy; when adding Ti element, choose Al-10Ti master alloy or 75Ti agent (aluminum alloy additive with 75% Ti content); when adding Zr element, choose Al-10Zr Master alloy. Pre-alloyed cast aluminum alloy ingots commonly used in the foundry industry can also be used, such as the aluminum ingots in the national standard GB/T 8733-2016 "Casting Aluminum Alloy Ingots". On this basis, the alloy composition can be adjusted to achieve the composition target.

All raw materials such as Al-10Sr modifier were purchased from the market.

In the embodiment of the present invention, a degassing machine is used to pass argon gas into the aluminum water, and the flow rate of the argon gas is 0.2-0.3M ³ /h.

Example A1

A preparation method for casting Al-Si alloy, including the following steps:

Step 1: Prepare materials. Prepare raw materials for each component according to the content of each component of the alloy listed in Table 1;

Step 2: After heating and melting the raw material Al, an aluminum melt is obtained;

Step 3: Determine the composition of the aluminum melt, calculate the amount of each component, and then add other raw materials except Mg into the aluminum melt until it melts, then add the raw material Mg, and after the Mg melts, stir evenly to obtain the alloy. Melt; During the entire above-mentioned smelting process, the temperature of the alloy melt is controlled to 720°C;

Step 4: After adding a refining agent to the alloy melt for refining, the amount of the refining agent added is 0.2% of the total weight of the casting alloy melt, and then adding Sr modifier for modification to obtain a modified alloy melt;

Step 5: Degas the modified alloy melt, and then add the grain refiner AlTiB alloy. The amount of AlTiB alloy added is 0.1% of the total weight of the casting alloy melt. After stirring evenly, remove the slag, then let it stand at 720°C for a certain period of time before casting. The casting process adopts high-pressure die casting. After die casting, the aluminum-silicon series casting alloy casting is obtained, which is the cast Al-Si alloy;

Step 6: The prepared Al-Si alloy product is tested for room temperature tensile properties. The room temperature tensile properties are shown in Table 1.

Examples A2-A9 and Examples A12 and A13 are the same as Example 1, except that the alloy composition is different. The alloy composition and the room temperature tensile properties of the prepared castings are shown in Table 1.

Embodiments A10 and A11 and Embodiments A14-A19 are the same as Embodiment 1, except that the alloy composition is different, the casting process adopts vacuum high-pressure die casting, and the castings need to be subjected to solid solution aging heat treatment. The alloy composition, solution aging treatment process and room temperature tensile properties of the castings after preparation are shown in Table 2.

Embodiments B1-B19 are the same as Embodiments A1-A19, except that:

(1) In terms of alloy composition: Examples A1-A19 are die-cast alloys with high Fe and Mn contents. Embodiments B1-B19 are gravity cast or low-pressure casting alloys with no mold sticking problem, and there is no need to increase the Fe and Mn content to solve the mold sticking problem. So in these examples Fe and Mn are impurity elements, the lower the better. However, in order to maximize the use of aluminum alloy scrap with higher Fe content, the content limits of Fe and Mn were intentionally increased.

(2) Casting technology: Embodiments B1-B19 are produced by using a gravity casting machine or a low-pressure casting machine to obtain an aluminum-silicon casting alloy, in which the casting mold is a metal mold;

(3) The alloy composition, solution treatment process and room temperature tensile properties of the castings after preparation are shown in Tables 3 and 4.

In terms of chemical composition, the strengthening mechanisms of aluminum alloys mainly include solid solution strengthening and age strengthening.

Solid solution strengthening: Adding alloying elements to aluminum forms an aluminum-based solid solution, causing lattice distortion and hindering the movement of dislocations, which can play the role of solid solution strengthening and improve the strength of the alloy. Elements such as Cu, Mg, Si, and Zn have large solid solubility in aluminum and can achieve large solid solution strengthening effects. However, when the element content exceeds its solid solubility in aluminum, intermetallic compound phases will precipitate in the alloy, damaging the mechanical properties of the alloy.

Aging strengthening: Because the alloying elements have a large solid solubility in aluminum alloys, they decrease sharply as the temperature decreases. Therefore, after the aluminum alloy is heated to a certain temperature and quenched (that is, after solid solution treatment), a supersaturated aluminum-based solid solution can be obtained. After aging treatment of this supersaturated aluminum-based solid solution, certain nanoscale intermetallic compound phases will precipitate in the alloy. These precipitations have a strengthening effect on the alloy. The purpose of solution treatment is to melt back the intermetallic compound phase formed during the solidification process into the matrix, and also to melt back the precipitated phase formed during the cooling process after solidification into the matrix. If excessive alloying elements are added to aluminum and the intermetallic compound phases formed during the solidification process are too large and too coarse, the solid solution treatment cannot melt back all the intermetallic compound phases. The phase is called the residual phase. If the residual phase is too large and too coarse, it will damage the mechanical properties of the alloy and reduce both strength and plasticity.

For alloys used in the prepared state (F state), the alloy is strengthened entirely by solid solution strengthening mechanism. For alloys used in the aging state (T6 state). It mainly relies on the aging strengthening mechanism to strengthen the alloy.

Mg is the most important strengthening element in Al-Si casting alloys. It is also an important solid solution strengthening element. For example, in 5000 series aluminum alloys, also known as Al-Mg series alloys, Mg is the main solid solution strengthening element; it is also an important aging strengthening element. , for example, the 6000 series alloy, also known as Al-Mg-Si alloy, has Mg as the main aging strengthening element. However, Mg has a greater tendency to segregate in Al, which adversely affects the mechanical properties of the alloy. Although the solid solution limit of Mg in Al is as high as 17.4% and the eutectic composition of Al-Mg alloy is 34% Mg, the Mg ₂ Si eutectic phase easily appears in Al-Si-Mg alloy. On the other hand, Mg and Si have very low room temperature solid solution limits in aluminum and have a strong tendency to precipitate with aging. Therefore, even if the Mg content in Al-Si alloy is very low, it is easy to form the strengthening phase Mg ₂ Si with aging. It has been reported in the literature that even if the Mg content is as low as 0.06%, the alloy has an aging strengthening effect.

The strengthening effect of Mg on Al-Si alloy can be divided into solid solution strengthening and age strengthening. For alloys with low Mg content (<0.2%Mg), solid solution strengthening is mainly the main effect, and the aging strengthening effect is very weak. As the Mg content increases, the aging strengthening effect increases and gradually changes to mainly aging strengthening. However, for alloys without heat treatment, the solid solution strengthening effect also increases with the increase of Mg content. The solid solution strengthening effect increases, but the plasticity decreases.

According to the Al-Si-Mg alloy phase diagram, in high-Si and low-Mg alloys (such as cast Al-Si alloys), during the solidification process, the Al matrix is first precipitated, and when the liquid component at the interface front reaches the Al+Si eutectic line When, L→Al+Si eutectic reaction occurs. Then, the liquid composition at the interface front changes along the eutectic line. When the liquid component at the interface front reaches the ternary eutectic point, the L→Al+Si+Mg ₂ Si ternary eutectic reaction occurs. Therefore, due to the large segregation tendency of Mg, the Mg ₂ Si eutectic phase will appear even in alloys with low Mg content. The higher the Mg content, the more and coarser the Mg ₂ Si eutectic phase will be in the as-cast structure, and its morphology will be like a Chinese character.

The size and quantity of Mg ₂ Si phase have a very important influence on the casting of Al-Si alloy. For alloys used in the T6 state, during solid solution treatment, the Mg ₂ Si phase formed during the casting process will slowly melt back into the matrix and decompose into Mg and Si atoms, forming supersaturated Mg and Si during quenching. Solid solution, Mg ₂ Si phase precipitates during aging, strengthening the alloy. However, due to the short solid solution time, it is difficult to completely remelt the coarse Mg ₂ Si phase, and the residual Mg ₂ Si will seriously damage the mechanical properties. Therefore, the content of Mg in cast Al-Si alloys is generally controlled below 0.5% to prevent the Mg ₂ Si phase formed during casting from being too coarse. For alloys with high Mg content, such as A357 alloy, the Mg content is increased to 0.65%, which is generally suitable for thin-walled parts. Through rapid cooling, the size of the Mg ₂ Si phase is reduced, which facilitates the rapid melting back of the Mg ₂ Si phase during solution treatment. For alloys used in the as-cast state, since heat treatment is not required, the Chinese character-like Mg ₂ Si eutectic phase cannot be eliminated. Therefore, it is necessary to limit the Mg content to a very low level or even completely remove the Mg element to prevent the formation of coarse Mg ₂ Si phases during casting. At present, for alloys used in the cast state, the Mg content is generally controlled below 0.2.

Cu is another important alloying element. But it mainly plays the role of age strengthening. For example, the 2000 series alloy is an age-strengthened alloy mainly composed of Cu. There is currently no solid solution strengthening alloy mainly composed of Cu. In order to exert the aging strengthening effect of Cu, the content of Cu in the alloy is relatively high to fully form a Cu-rich strengthening phase. In cast Al-Si alloys, the Cu element content is generally above 3.5%. On the other hand, the combination of Cu and Mg can form the Al ₂ CuMg phase, and the combination of Cu and Mg and Si can form the Q-AlCuMgSi phase, which has an important impact on the mechanical properties of the alloy.

Zn is also another important alloying element. But it mainly plays the role of aging strengthening. For example, the 7000 series alloy is an age-strengthening alloy mainly composed of Zn. Currently, there is no solid solution strengthening alloy mainly composed of Zn. In order to exert the aging strengthening effect of Zn, the content of Zn in the alloy is relatively high. However, among the cast Al-Si alloys of the national standard GB/T1173-2013, only the Zn content in the ZL115 alloy is 1.2-1.8%. Zn in the remaining alloys is an impurity element and needs to be strictly controlled.

The present invention uses Si, Mg, Cu and Zn in combination and achieves unexpected results. As mentioned before, Mg element has a strong tendency to segregate, and the Mg ₂ Si eutectic phase is easily formed in the final solidification zone. For Al-Si-Mg casting alloys without solution aging, the Mg ₂ Si phase cannot be eliminated through solution treatment, seriously damaging the mechanical properties, and the solid solution strengthening effect of the Mg element cannot be fully exerted. After the present invention adds Cu and Zn at the same time, the formation of the coarse Mg2Si phase is hindered, thereby avoiding damage to the mechanical properties of the _Mg2Si relative. This can appropriately relax the restrictions on Mg content, thereby further improving the strength of the alloy. Moreover, small amounts of Cu and Zn also have solid solution strengthening effects.

For Al-Si-Mg cast alloys used in the T6 state, the Mg ₂ Si phase can be eliminated by solid solution treatment, so a higher Mg content is allowed in the alloy. However, as mentioned above, if the Mg content exceeds 0.5%, a relatively coarse residual Mg ₂ Si phase will appear in the alloy, seriously damaging the mechanical properties, and the aging strengthening effect of the Mg element cannot be fully exerted. After adding Cu at the same time in the present invention, part of the Mg ₂ Si phase can be transformed into the Q-AlCuMgSi phase. During the solution treatment process, the Mg ₂ Si phase and Q-AlCuMgSi phase formed during solidification melt back, and the strengthening phase precipitates during aging to strengthen the alloy. Therefore, after adding Cu to an alloy with a high Mg content, part of the Mg ₂ Si phase is transformed into the Q-AlCuMgSi phase, thereby eliminating the residual Mg ₂ Si phase and thus avoiding the damage to the mechanical properties of the residual Mg ₂ Si relative to the other. This can further relax the restrictions on Mg content, thereby further improving the strength of the alloy. The addition of Zn element promotes the transformation of Mg ₂ Si phase into Q-AlCuMgSi phase, and small amounts of Cu and Zn also have solid solution strengthening effect.

In summary, the components of Mg and Cu in the alloy should be determined according to the usage status of the alloy. For alloys used in the cast state (F state), it is necessary to limit the Mg ₂ Si phase formed during the solidification process. It is more appropriate to design the relationship between Cu and Mg as Cu=2Mg-0.2, allowing a deviation of 0.1 up and down. For alloys used in the T4, T5 and T6 tempers, where the Mg ₂ Si phase is required as the strengthening phase, Cu is added only in the case of high Mg content. It is more appropriate to design the relationship between Cu and Mg as Cu=2(Mg-0.2)-0.2, with an upper and lower deviation of 0.1 allowed.

The elements Fe and Mn can effectively prevent castings from sticking to the mold, which is very important for die-casting production, so Fe and Mn are essential elements for die-casting alloys. However, Fe, Mn and Si form Al ₁₅ (FeMn) ₃ Si ₂ phase, which is in the shape of thick needles, laths or Chinese characters, seriously damaging the mechanical properties of the alloy. The ratio of Fe and Mn has an important influence on the morphology of the Al ₁₅ (FeMn) ₃ Si ₂ phase. When the ratio of Fe and Mn is close, the morphology of the Al ₁₅ (FeMn) ₃ Si ₂ phase takes on a fishbone shape, which can reduce the damage to mechanical properties.

There is no mold sticking problem in ordinary casting alloys, so the Fe and Mn contents should be strictly limited in these alloys. But on the other hand, Fe and Mn are common elements in aluminum alloy scrap and have higher contents. In order to effectively utilize waste materials and reduce production costs, it is necessary to use as much waste material as possible. This requires relaxing the restrictions on Fe and Mn content, which requires a balance between mechanical properties and the use of waste materials.

Sr is a modifier for hypoeutectic Al-Si alloys, which can modify the eutectic Si phase and significantly refine the eutectic Si. The dosage of Sr is generally controlled at 0.02-0.04%. High Sr content can effectively refine the Al ₁₅ (FeMn) ₃ Si ₂ phase. Especially when the ratio of Fe and Mn is close, the morphology of the Al ₁₅ (FeMn) ₃ Si ₂ phase is like a fishbone. Under the metamorphism of Sr, the fishbone shape breaks and forms small blocks, which can further reduce the Al 15 (FeMn) 3 Si 2 phase. ₁₅ (FeMn) ₃ Si ₂ relative damage to mechanical properties.

The addition of rare earth elements in the present invention has achieved good results and improved the mechanical properties of the alloy. After a large number of comparative experiments, it was found that Ce and La and their mixed rare earths have the best effect, refining the grains and reducing gases and inclusions. Casting experiments show that adding rare earths can increase the fluidity of molten aluminum and significantly improve process performance. Moreover, rare earth elements promote aging precipitation and improve mechanical properties. Example A3 shows that the mechanical properties of the alloy are improved by adding rare earth.

Comparing Example A1 and Example A2 and Example B1 and Example B2, it can be found that adding the element Mg improves the strength of the alloy, indicating that Mg plays a role in solid solution strengthening.

Embodiments A7 and B7 have higher Mg content, and Cu and Zn are added at the same time. Embodiments A8 and B8 do not contain Cu and Zn. By comparison, it is found that Embodiments A7 and B7 have better mechanical properties. It shows that in high Mg alloys, adding Cu and Zn can improve the mechanical properties.

The chemical compositions of Example A3 and Example A4 are basically the same, except that Example A4 contains 0.1% rare earth elements. By comparison, it is found that Example A4 has better mechanical properties. Examples B3 and B4 have the same situation. It shows that rare earth elements play a role in improving mechanical properties.

The Fe content in Examples A6, A9, A12-A19 and Examples B5 and B9-B16 is very high. However, by adding higher Sr, the Fe-rich phase is modified and refined, and the alloy still maintains high strength and elongation. Rate.

Examples A12 and A13 are alloys used in the F state. The alloy compositions of the two are exactly the same except for the Cu content. The Cu content of Example A12 is determined according to the Cu content rules of the F state. The Cu content of Example A13 is determined according to T6. The Cu content in the alloy was determined by rules and was reduced by 0.38%, which resulted in the appearance of a large amount of Mg ₂ Si eutectic phase in the solidification structure of the alloy, damaging the mechanical properties. Therefore, the mechanical properties of Example A13 are lower than those of Example A12. The situation is the same for Examples B12 and B13.

Examples A16 and A17 are alloys used in the T6 state. The alloy components of the two are exactly the same except for the Cu content. The Cu content of Example A16 is determined according to the Cu content rules of the T6 state. The Cu content of Example A17 is determined according to F The Cu content of the alloy is determined by the rules and increases by 0.4%, resulting in a significant reduction in the Mg ₂ Si eutectic phase in the solidified structure of the alloy, which results in a significant reduction in the Mg ₂ Si strengthening phase precipitated in the alloy during aging treatment, making the alloy The time-sensitive strengthening effect is much weaker. Therefore, the mechanical properties of Example A17 are lower than those of Example A16. The situation is the same for Examples B16 and B17.

Table 1 Chemical composition (wt%) and properties of die-cast alloys

Table 2 Chemical composition (wt%) and properties of die-cast alloys (continued table)

Table 3 Chemical composition (wt%) and properties of gravity casting alloys

Table 4 Chemical composition (wt%) and properties of gravity casting alloys (continued table)

The above technical solutions illustrate the technical ideas of the present invention and cannot be used to limit the protection scope of the present invention. Any changes and modifications made to the above technical solutions based on the technical essence of the present invention that do not deviate from the content of the technical solutions of the present invention shall belong to protection scope of the technical solution of the present invention.

Claims (10)

1. A cast Al-Si alloy, characterized in that the components and mass percentages are: Si: 6.0-9.0%, Mg: 0-0.6%, Cu: 0-1.0%, Zn: 0-0.8%, Mn: 0-1.0%, Fe 0.1-0.5%, Zr: 0-0.25%, Ti: 0.05%-0.25%, Re: 0-0.3%, Sr: 0.02-0.2%, the balance is Al and unavoidable Impurities, the total content of impurities in the alloy is ≤1.0%, and the content of individual impurities is ≤0.15%.
2. A cast Al-Si alloy according to claim 1, characterized in that, in the F state, the room temperature tensile strength of the cast Al-Si alloy is 222-307MPa, the yield strength is 104-149MPa, and the elongation Rate 6.1-14.3%. The cast Al-Si alloy is a T6 state, T5 state or T4 state Al-Si alloy, wherein, when in the T6 state, the room temperature tensile strength is 261-341MPa, the yield strength is 132-171MPa, and the elongation is 4.3- 9.7%;
3. A cast Al-Si alloy according to claim 1, characterized in that the cast Al-Si alloy is an Al-Si die-cast aluminum alloy, and the Al-Si die-cast aluminum alloy includes components and mass percentages of : Si: 6.5-9.0%, Mg: 0-0.6%, Cu: 0-1.0%, Zn: 0-0.8%, Mn: 0-1.0%, Fe: 0.1-0.5%, Zr: 0-0.25%, Ti: 0.05-0.25%, Re: 0-0.3%, Sr: 0.02-0.2%, the balance is Al and inevitable impurities, the total impurity content in the alloy is ≤ 1.0%, and the individual impurity content is ≤ 0.15%; when When preparing T6 state Al-Si alloy, the Mg content in the alloy composition should be ≥0.25%.
4. A cast Al-Si alloy according to claim 3, characterized in that the F-state room temperature tensile strength of the Al-Si die-cast aluminum alloy is 237-307MPa, the yield strength is 109-149MPa, and the elongation The tensile strength in T6 state is 293-341MPa, the yield strength is 141-171MPa, and the elongation is 5.9-9.7%.
5. A cast Al-Si alloy according to claim 1, characterized in that the cast Al-Si alloy is an Al-Si gravity cast aluminum alloy, and the Al-Si gravity cast aluminum alloy includes components and mass percentages. The content is: Si: 6.0-8.5%, Mg: 0-0.6%, Cu: 0-1.0%, Zn: 0-0.8%, Fe: 0.1-0.3%, Mn: 0-0.3%, Zr: 0-0.25 %, Ti: 0.05%-0.25%, Re: 0-0.3%, Sr: 0.02-0.2%, the balance is Al and inevitable impurities. The total impurity content in the alloy is ≤1.0%, and the individual impurity content is ≤0.15%; when preparing the T6 state Al-Si alloy, the Mg content in the alloy composition is ≥0.25%. .
6. A cast Al-Si alloy according to claim 5, characterized in that the F-state tensile strength of the Al-Si gravity cast aluminum alloy is 222-298MPa, the yield strength is 104-141MPa, and the elongation The tensile strength in T6 state is 261-336MPa, the yield strength is 132-168MPa, and the elongation is 4.3-8.1%.
7. A method for preparing cast Al-Si alloy according to any one of claims 1 to 6, characterized in that it includes the following steps:

   Step 1: Prepare materials. Prepare raw materials for each component according to the content of each component of the alloy;

   Step 2: After heating and melting the raw material Al, an aluminum melt is obtained;

   Step 3: Determine the composition of the aluminum melt, calculate the amount of each component, and then add other raw materials except Mg and Sr into the aluminum melt until it melts, then add the raw material Mg, and after the Mg melts, stir evenly. Obtain alloy melt; during the above entire smelting process, control the temperature of the alloy melt to 690-750°C;

   Step 4: Add a refining agent to the alloy melt for refining, then add Sr modifier for modification, and obtain a modified alloy melt;

   Step 5: Degas the modified alloy melt, then add a grain refiner, stir evenly, remove the slag, and then let it stand at 690-750°C for a certain period of time before casting. After casting, the aluminum-silicon series casting is obtained Alloy castings are cast Al-Si alloys.
8. A method for preparing cast Al-Si alloy according to claim 6, characterized in that the preparation method further includes:

   Step 6: Solid solution aging treatment

   (1) When it is necessary to prepare a T6 state cast Al-Si alloy, the aluminum-silicon cast alloy casting is subjected to solution-aging treatment;

   (2) When it is necessary to prepare a T4 state cast Al-Si alloy, the aluminum-silicon cast alloy casting is subjected to solution treatment and aging treatment at room temperature;

   (3) When it is necessary to prepare a T5 state cast Al-Si alloy, the aluminum-silicon cast alloy castings are directly aged.
9. A method for preparing a cast Al-Si alloy according to claim 6, characterized in that, in the step 4, the Sr modifier specifically selects Al-10Sr alloy modifier, and the amount of modifier added is determined by the modified alloy. Measure the residual amount of Sr in the melt to ensure that the mass percentage of the residual amount of Sr is 0.02%-0.2%; if the Sr modifier in step 4 is not added in step 4, you can choose to add it together with Mg in the aluminum melt in step 3. into the aluminum melt, or added to the aluminum melt together with other raw materials other than Mg.
10. A method for preparing cast Al-Si alloy according to claim 6, characterized in that in the step 6, the solid solution treatment process used in the T4 and T6 treatments is: insulation at 500-550°C for 2-12 hours ; The aging treatment process of T4 is to leave it at room temperature for more than 7 days; the aging treatment process of T5 and T6 is: keep it at 120-200℃ for 2-12h.