Al-Si alloy with Al (Fe, Mn, V) Si phase and preparation method thereof

Abstract

The invention discloses an Al-Si alloy with an Al (Fe, Mn, V) Si phase, which comprises the following components in percentage by weight: 6.5 to 7.5 percent of Si, 0.3 to 0.45 percent of Mg, 0.15 to 0.3 percent of Fe, 0 to 0.025 percent of Sr, the mass ratio of Mn element to V element to Fe element is 2: 1: 3, namely the mass ratio of Mn element to V element must be 2: 1, and the balance of Al. The phase structure comprises an alpha-Al phase, a eutectic Si phase, a Fe-rich phase Al (Fe, Mn, V) Si phase and a Mg2Si phase; the Al (Fe, Mn, V) Si phase is granular and is uniformly distributed in eutectic Si, and the size of the Al (Fe, Mn, V) Si phase is 1-10 [mu] m; the grain size of alpha-Al is 541.4 + / -70.8 [mu] m, the secondary dendritic crystal arm spacing is 26.4 + / -3.9 [mu] m, and the length of an Al (Fe, Mn, V) Si phase is 39.0 + / -8.3 [mu] m. Under the condition that the cooling rate is 0.4 DEG C / s, the hardness of the Al-Si alloy is 87.4 + / -4.5 HV and the yield strength of the Al-Si alloy is 156.9 + / -7.9 MPa after 150 min aging at the temperature of 150 DEG C. The preparation method comprises the following steps: 1, preparing an A356-Fe-Mn-V melt; (2) preparation of an as-cast state A356-Fe-Mn-V-Sr alloy is carried out; and 3, preparation of A356-Fe-Mn-V-Sr in a heat treatment state is carried out.

Description

Technical Field

[0001] The present invention relates to the field of aluminum alloy materials and their preparation, and particularly relates to an Al-Si alloy with Al(Fe,Mn,V)Si phase and a preparation method thereof. Background Art

[0002] The A356 alloy has a problem that a high Fe content leads to the formation of brittle Fe-rich phases, which seriously reduces the mechanical properties of the alloy. Therefore, the most direct solution is to strictly control the Fe content within 0.15 wt.%. However, when preparing recycled A356 alloy, due to the purity of the recycled materials, it is impossible to keep the Fe content below 0.15 wt.% in actual production. The current solution in the industry is to control the Fe content between 0.15 wt.% and 0.3 wt.%. However, within the above Fe content range, the Fe-rich phase exists as needle-like β-Al5FeSi, resulting in a problem of reduced mechanical properties of the alloy. Therefore, it is necessary to adjust the morphology of the Fe-rich phase to eliminate the stress concentration caused by its needle-like structure, thereby improving the mechanical properties of the alloy.

[0003] In order to improve the morphology of the Fe-rich phase, currently, the method of increasing the cooling rate is usually adopted to transform the needle-like β-Fe phase into a skeletal α-Fe or δ-Fe phase to improve the mechanical properties of the alloy. For example, in the existing literature 1 (Effect of CoolingRate on the Microstructure Evolution and Mechanical Properties of Iron-RichAl-Si Alloy[J].Materials,2022,15), by performing secondary melting in a high-frequency induction melting furnace and blowing on a copper roller with a rotation speed of 2000 revolutions / min, the cooling rate of the alloy is increased from 10 ℃ / s to 670℃ / s, so that the Fe-rich phase in the alloy is transformed from an 80-μm needle-like β-Al5FeSi phase into a 10-μm skeletal δ-Al3FeSi2 phase, and the elongation of the alloy is increased from 0.9% to 4.9%. In addition to the problem that this technical solution requires the use of complex blowing technology, resulting in high production costs, there is also a problem that when applied to large structural castings represented by wheel hubs, the cooling rate of the central part cannot meet the requirements of this technical solution, that is, this technical solution cannot be applied to large structural castings.

[0004] For large structural castings, the coarsening of the Fe-rich phase can be inhibited by adding refinement and modification elements, especially through the refinement treatment of the Fe-rich phase, and by adjusting the microstructure of the alloy, ultimately improving the mechanical properties of the alloy. For example, in the existing literature 2 (Enhancing the Strength and Toughness of A356.2-0.15Fe Aluminum Alloy by Trace Mn and Mg Co-Addition[J].Metals,2023,13.), by adding 0.075 wt.% Mn to the A356-0.15Fe alloy and controlling Mn / Fe at 0.5, the needle-like β-AlSiFe phase is transformed into the skeletal α-Al(Fe,Mn)Si phase. Under the T6 heat treatment condition, the elongation of the alloy is increased by 70.7%. Although this technical solution can effectively improve the elongation of the alloy, the improvement effect on the yield strength is negligible, resulting in the inability to meet the mechanical property requirements of the application scenario of large structural castings represented by wheel hubs.

[0005] To improve the yield strength of the alloy, the current conventional solution is to add elements with solid solution strengthening effect to improve the mechanical properties of the alloy. For example, in the existing literature 3 (The effect of Ni and V trace elements on the mechanical properties of A356 aluminium foundry alloy in as-cast and T6 heat treated conditions[J].Materials Science and Engineering:A,610:414-26.), by adding V element to the A356 alloy, under the T6 heat treatment condition, through the solid solution strengthening effect of the V element, the yield strength of the alloy is effectively improved, and the improvement amplitude reaches 18.4%. However, the elongation of the alloy obtained by this technical solution is only 1%, which can be ignored. The reason is that in this technical solution, the Fe-rich phase in the alloy still maintains the needle-like β-AlSiFe phase structure, which will directly lead to a decrease in the elongation of the alloy.

[0006] In order to simultaneously improve the strength and elongation of the alloy to meet the mechanical property requirements of the hub structural parts in applications, various elements that have modification and refinement effects and solid solution effects on the Fe-rich phase can be added to the alloy. For example, the existing literature 4 (Yang Yong, CN110804698A, a processing technology for high-performance recycled aluminum based on changing the morphology of the Fe-rich phase, 2019-10-24) uses the simultaneous addition of Mn element and V element to effectively improve the morphology of the Fe-rich phase in the Al-Si alloy, and at the same time, the strength and elongation of the alloy are increased by 32% and 106% respectively. However, in order to achieve the technical effects of this technical solution, a large amount of additional auxiliary modifiers must be added, for example, TeO2 and YF3, that is, essential technical features. Its function is to inhibit the nucleation of the Fe-rich phase in the alloy, thereby reducing the size of the Fe-rich phase, and then significantly improving the alloy properties. The direct consequence of the above addition of a large amount of auxiliary modifiers is to significantly increase the cost of alloy preparation, increase the complexity of the production process, and reduce the production consistency. At the same time, this technical solution also has an essential technical feature, which separately defines the proportional relationship between the Mn element and the Fe element, and separately defines the proportional relationship between the V element and the Fe element. Among them, the mass ratio of the Mn element to the Fe element is 0.246, and the mass ratio of the V element to the Fe element is 0.027, that is, the proportional relationship between the Mn element and the V element is not defined. In this technical solution, although the Mn element and the V element are added, their addition amounts are relatively small, and the needle-like and flaky β-AlFeSi phase cannot be fully refined, resulting in incomplete modification and refinement of this phase. In addition, due to the too fast cooling rate during the melting process, the supercooling degree of the Fe-rich phase is too high, so that all the small amounts of V element are dissolved into the Al matrix and cannot act together with the Mn element to synergistically refine the Fe-rich phase. The reason for restricting this essential technical feature and the corresponding technical effects of this technical solution is that since the invention purpose of this technical solution is to achieve the refinement effect of the Fe-rich phase by adding the Mn element, and adding the V element to dissolve into the Al matrix, there is no synergistic effect between the two technical effects obtained by the essential technical features of adding the Mn element and the V element. Therefore, based on the above principle, under the condition that the fast cooling rate is >10 °C / s, this technical solution only obtains the refinement effect of the Mn element on the Fe-rich phase and the effect of the V element simply dissolving into the Al matrix separately, and does not obtain the technical effect of forming a new Fe-rich phase, so that the technical effect of adjusting the organizational structure cannot be achieved, and finally the performance of the alloy obtained by this technical solution still cannot meet the application requirements.

[0007] From the prior art, it can be known that the existing technical difficulty is that it is impossible to inhibit the growth of the Fe-rich phase in the alloy and meet the requirements of the mechanical properties of recycled A356 for large structural castings represented by hubs without adding a large amount of modifiers and at a normal cooling rate of 0.4-1 °C / s. Summary of the Invention

[0008] The object of the present invention is to provide an Al-Si alloy with an Al(Fe,Mn,V)Si phase and a preparation method thereof. Aiming at the existing technical problems, the basic principle involved in the present invention is as follows: by using the combined addition of Mn element and V element, and utilizing the enrichment effect of Mn and V in the Fe-rich phase, the morphology of the Fe-rich phase is refined synergistically. The coarsening of the Fe-rich phase is inhibited and the distribution of the Fe-rich phase is adjusted, thereby significantly improving the yield strength of the alloy.

[0009] The specifically designed technical features include:

[0010] 1. According to the performance requirement of improving the yield strength of the alloy, control the mass ratio of the total content of the added Mn element and V element to the Fe content to be 1:1. On this basis, adjust the mass ratio of the Mn element and V element, and simultaneously achieve the effects of inhibiting the diffusion and growth of the Fe element in the Fe-rich phase, and avoiding the coarsening of the Fe-rich phase or the formation of brittle phases due to the content of the added elements;

[0011] 2. Based on the defined casting conditions, that is, under the condition of a slow cooling rate of 0.4 - 1 °C / s, reduce the supercooling degree of the Fe-rich phase, promote the uniform progress of the phase transformation, and achieve the balanced distribution of the Mn element and V element in the Fe-rich phase, thereby enhancing the refinement effect on the Fe-rich phase, so as to avoid the increase in the supercooling degree of the Fe-rich phase caused by too high a cooling rate, so that the V element cannot play a synergistic refinement role on the Fe-rich phase and only plays a solid solution strengthening role on the matrix. At the same time, form the Al(Fe,Mn,V)Si phase, and finally achieve the improvement of the yield strength of the alloy.

[0012] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0013] An Al-Si alloy with an Al(Fe,Mn,V)Si phase, the composition of the Al-Si alloy in addition to containing Al element, Si element, Mg element, Fe element and Sr element, also contains Mn element and V element,

[0014] And, the range of the composition of the alloy is: Si: 6.5 - 7.5 wt.%, Mg: 0.3 - 0.45 wt.%, Fe: 0.15 - 0.3 wt.%, Sr: 0 - 0.025 wt.%. In addition, the mass ratio of the Mn element, V element and Fe element is 2:1:3, that is, the mass ratio of the Mn element and V element must be 2:1, and Al is the balance;

[0015] The phase structure of the alloy includes α-Al phase, eutectic Si phase, Al(Fe,Mn,V)Si phase and Mg2Si phase;

[0016] The Al(Fe,Mn,V)Si phase is an Fe-rich phase, which is formed by the diffusion of Mn and V elements into the β-AlFeSi phase.

[0017] The Al(Fe,Mn,V)Si phase is granular and uniformly distributed in the eutectic Si, with a size of 1-10 μm;

[0018] The grain size of the α-Al is 541.4±70.8 μm, the secondary dendrite arm spacing is 26.4±3.9 μm, and the length of the Al(Fe,Mn,V)Si phase is 39.0±8.3 μm;

[0019] The hardness of the Al-Si alloy is 87.4±4.5 HV, and the yield strength is 156.9±7.9 MPa.

[0020] A preparation method of an Al-Si alloy with an Al(Fe,Mn,V)Si phase includes the following steps:

[0021] Step 1, preparation of the A356-Fe-Mn-V melt. The Al-7Si-0.3Mg alloy and the Al-20Fe, Al-20Mn, and Al-10V alloys meet a certain mass ratio. First, under a certain heating temperature condition, the Al-7Si-0.3Mg alloy is melted to obtain the Al-7Si-0.3Mg alloy melt, simply referred to as the A alloy melt. Then, the Al-20Fe, Al-20Mn, and Al-10V are added to the A melt and completely melted to obtain the A356-0.3Fe-0.2Mn-0.1V alloy melt, simply referred to as the AF-MV-2 / 1 alloy melt;

[0022] In the said Step 1, the mass ratio of the Al-7Si-0.3Mg alloy to the Al-20Fe, Al-20Mn, and Al-10V alloys is 1:0.015:0.01:0.01, and the heating temperature for obtaining the Al-7Si-0.3Mg alloy melt is 780-820 °C;

[0023] Step 2: Preparation of as-cast A356-Fe-Mn-V-Sr alloy. First, cool the AF-MV-2 / 1 alloy melt obtained in Step 1 to a certain temperature condition with the furnace. Then, add Al-10Sr with a certain addition amount to the AF-MV-2 / 1 alloy melt to obtain an A356-0.3Fe-0.2Mn-0.1V-0.025Sr alloy melt, simply referred to as the AFS-MV-2 / 1 alloy melt. After that, under certain conditions, keep the AFS-MV-2 / 1 alloy melt warm. Subsequently, under certain conditions, introduce high-purity argon gas into the AFS-MV-2 / 1 alloy melt. At the same time, preheat the mold. Finally, pour the AFS-MV-2 / 1 alloy melt into the mold and cool the AFS-MV-2 / 1 alloy melt at a certain cooling rate to obtain the as-cast A356-0.3Fe-0.2Mn-0.1V-0.025Sr alloy, simply referred to as AFS-MV-2 / 1-ca;

[0024] In the said Step 2, the temperature for obtaining the AFS-MV-2 / 1 alloy melt is 720 - 780 °C, the addition amount of Al-10Sr is 0.25 wt.%, the holding temperature is 720 - 750 °C, and the holding time is 30 - 60 min;

[0025] The conditions for introducing the high-purity argon gas are that the gas flow rate is 0.25 L / min and the gas introduction time is 3 min;

[0026] The cooling rate is 0.4 °C / s;

[0027] The method for achieving a cooling rate of 0.4 °C / s is that the preheating temperature of the mold is 500 °C;

[0028] Step 3: Preparation of heat-treated A356-Fe-Mn-V-Sr. First, solutionize the AFS-MV-2 / 1-ca obtained in Step 2 under certain conditions, and perform water cooling after solutionizing. Then, age under certain conditions to obtain the heat-treated A356-0.3Fe-0.2Mn-0.1V-0.025Sr alloy, that is, an Al-Si alloy with Al(Fe,Mn,V)Si phase, simply referred to as AFS-MV-2 / 1-ht;

[0029] In the said Step 3, the conditions for solutionizing are that the solutionizing temperature is 520 - 560 °C and the solutionizing time is 260 - 300 min;

[0030] In the said Step 3, the conditions for aging are that the aging temperature is 130 - 170 °C and the aging time is 130 - 170 min.

[0031] The technical effects of the present invention are known through detection:

[0032] It can be known from polarized light detection that when Mn element and V element are added to as-cast Al-Si alloy, the grain size and secondary dendrite arm spacing of the alloy are uniform, that is, there is no phenomenon of uneven grains. Further, the α-Al grain size and secondary dendrite arm spacing are statistically analyzed by the line intercept method, and the values are 541.4±70.8μm and 26.4±3.9μm respectively, showing no substantial difference from the grain size and secondary dendrite arm spacing of recycled A356 alloy. The statistical results of polarized light indicate that the addition of Mn element and V element has no substantial effect on the grain size and secondary dendrite arm spacing of the alloy, which are both controlled by the casting conditions, i.e., the cooling rate.

[0033] It can be known from SEM test and EDS detection that when Mn element and V element are added to as-cast Al-Si alloy, the Fe-rich phase is distributed in eutectic Si in a granular form. Among them, Fe element, Mn element, and V element are uniformly distributed in the granular Fe-rich phase. Further, after statistical analysis by Image Pro plus, the average size of the granular Fe-rich phase is 1-10μm, and the average size of the ten longest Fe-rich phases is 39.0±8.3μm. The test results show that by adding Mn element and V element, the synergistic refinement effect on the Fe-rich phase can be achieved, forming a new microstructure with Al(Fe,Mn,V)Si phase.

[0034] It can be known from hardness test and tensile property test that when Mn element and V element are added to as-cast Al-Si alloy, the hardness value reaches 87.4±4.5HV, and the yield strength reaches 156.9±7.9MPa. The test results show that the direct technical effect of forming the new Al(Fe,Mn,V)Si phase in the alloy is to improve the hardness and yield strength of the alloy.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] 1. By limiting the mass ratio of the total amount of Mn element and V element to Fe element to 1 and the mass ratio between Mn and V elements to 2, the Fe-rich phase can be fully modified and refined, enabling the undercooling degree of the Fe-rich phase to be reduced under the condition of a slow cooling rate of 0.4-1°C / s, allowing the V element to uniformly diffuse and distribute in the Fe-rich phase, and generating a new granular Al(Fe,Mn,V)Si phase.

[0037] It should be noted that the Al(Fe,Mn,V)Si phase has not been recorded in the existing literature.

[0038] 2. Without adding any auxiliary modifiers, the present invention successfully forms a new granular Al(Fe,Mn,V)Si phase by precisely controlling the refinement of the Fe-rich phase, enabling the hardness of the alloy in the heat-treated state to reach 87.4±4.5HV and the yield strength to reach 156.9±7.9MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is the SEM microstructure diagram of the alloy in Example 1 in the as-cast state;

[0040] Figure 2 It is the yield strength change curve of the alloys in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 in the heat-treated state;

[0041] Figure 3 It is the SEM microstructure diagram of the alloy in Comparative Example 1 in the as-cast state;

[0042] Figure 4 It is the SEM microstructure diagram of the alloy in Comparative Example 2 in the as-cast state;

[0043] Figure 5 It is the SEM microstructure diagram of the alloy in Comparative Example 2 in the as-cast state. DETAILED DESCRIPTION OF THE INVENTION

[0044] In order to facilitate the distinction of various alloys and their basic information involved in each example and comparative example, Table 1 is provided.

[0045] Table 1 Summary Table of Alloy Compositions of Examples and Comparative Examples

[0046]

[0047]

[0048] Example 1

[0049] A preparation method of an Al-Si alloy with an Al(Fe,Mn,V)Si phase, comprising the following steps:

[0050] Step 1, Preparation of A356-Fe-Mn-V Melt. First, prepare raw materials under the condition that the mass ratio meets the chemical formula A356-0.3Fe-0.2Mn-0.1V. Specifically, 4432 g of Al-7Si-0.3Mg alloy, 48.3 g of Al-20Fe master alloy, 45.5 g of Al-20Mn master alloy, and 45.5 g of Al-10V master alloy. Then, preheat the crucible and master alloys at a preheating temperature of 400 °C. After that, melt the Al-7Si-0.3Mg alloy at a melting temperature of 800 °C for a melting time of 2 h. Then, keep the melt temperature at 800 °C, add the Al-20Fe master alloy, Al-20Mn master alloy, and Al-10V master alloy, and completely immerse them in the melt. After complete melting, the A356-0.3Fe-0.2Mn-0.1V alloy melt, simply referred to as AF-MV-2 / 1, can be obtained.

[0051] Step 2, Preparation of As-cast A356-Fe-Mn-V-Sr Alloy. First, cool the AF-MV-2 / 1 obtained in Step 1 in the furnace to 740 °C. Then, with the addition amount of Al-10Sr being 0.25 wt.%, that is, 11.3 g of Al-10Sr master alloy, add Al-10Sr to AF-MV-2 / 1 to obtain the A356-0.3Fe-0.2Mn-0.1V-0.025Sr alloy melt, simply referred to as AFS-MV-2 / 1. After that, keep AFS-MV-2 / 1 at an insulation temperature of 740 °C for an insulation time of 40 min. Subsequently, introduce high-purity argon into AFS-MV-2 / 1 at a ventilation rate of 0.25 L / min for a ventilation time of 3 min. At the same time, in order to achieve a cooling rate of 0.4 °C / s, preheat the mold at a preheating temperature of 500 °C. Finally, pour AFS-MV-2 / 1 into the mold and cool AFS-MV-2 / 1 at a cooling rate of 0.4 °C / s to obtain the as-cast A356-0.3Fe-0.2Mn-0.1V-0.025Sr alloy, simply referred to as AFS-MV-2 / 1-ca.

[0052] Step 3, Preparation of Heat-treated A356-Fe-Mn-V-Sr. First, solutionize the AFS-MV-2 / 1-ca obtained in Step 2 at a solutionizing temperature of 540 °C for a solutionizing time of 280 min. After solutionizing, perform water cooling. Then, age at an aging temperature of 150 °C for an aging time of 150 min to obtain the heat-treated A356-0.3Fe-0.2Mn-0.1V-0.025Sr alloy, that is, an Al-Si alloy with Al(Fe,Mn,V)Si phase, simply referred to as AFS-MV-2 / 1-ht.

[0053] To prove and quantify the grain size and secondary dendrite arm spacing of α-Al in AFS-MV-2 / 1-ca, PLM tests were carried out, and the grain size and secondary dendrite arm spacing were quantitatively counted. The specific method for PLM quantitative statistics is that the magnification of the polarized light pictures is 50 times, the number of polarized light pictures is 10, and the intercept method is used to count the grain size and secondary dendrite arm spacing of α-Al, and the average value is calculated as the grain size and secondary dendrite arm spacing of α-Al. The test results show that in AFS-MV-2 / 1-ca, the grain size of α-Al is 541.4 ± 70.8 μm, and the secondary dendrite arm spacing is 26.4 ± 3.9 μm.

[0054] To prove and quantify the size of the Fe-rich phase in AFS-MV-2 / 1-ca, SEM tests were carried out, and the size of the Fe-rich phase was quantitatively counted. The specific method for SEM quantitative statistics is that the magnification of the scanning pictures is 200 times, the number of scanning pictures is 5, the lengths of the largest 10 Fe-rich phases are counted, and the average value is calculated as the length of the Fe-rich phase. The test results are as Figure 1 shown in Table 2. In AFS-MV-2 / 1-ca, the Fe-rich phase is distributed in a granular form, and the length is 39.0 ± 8.3 μm.

[0055] To prove the phase composition of the Fe-rich phase in AFS-MV-2 / 1-ca, EDS tests were carried out. The test results are as Figure 1 shown. In AFS-MV-2 / 1-ca, in the granular Fe-rich phase, in addition to Al, Si, Fe, and Mn elements, V element is also evenly distributed in the Fe-rich phase, forming a new granular Al(Fe,Mn,V)Si phase; further, according to the EDS test results, it can be known that the Fe-rich phase is Al(Fe,Mn,V)Si phase, and the phase composition of the Al(Fe,Mn,V)Si phase is: Al: 75.51 ± 0.45 at.%, Si: 10.04 ± 0.31 at.%, Fe: 7.94 ± 0.15 at.%, Mn: 5.65 ± 0.12 at.%, V: 0.86 ± 0.04 at.%.

[0056] Table 2 The as-cast microstructure characteristics and T6-state mechanical properties of the alloys in the comparative examples and examples

[0057]

[0058] To prove the hardness of AFS-MV-2 / 1-ht, hardness tests were carried out. The test results are shown in Table 2. The hardness of AFS-MV-2 / 1-ht is 87.4 ± 4.5 HV;

[0059] To prove the yield strength of AFS-MV-2 / 1-ht, tensile tests were carried out. The test results are asFigure 2 As shown in Table 2, the yield strength of AFS-MV-2 / 1-ht is 156.9 ± 7.9 MPa.

[0060] To prove the roles of Mn and V elements in the technical solution, Comparative Example 1, Comparative Example 2, and Comparative Example 3 are provided.

[0061] Among them,

[0062] Comparative Example 1 is an alloy without adding Mn and V elements, and the specific alloy composition is A356 - 0.3Fe - 0.025Sr;

[0063] Comparative Example 2 is an alloy with only V element added, and the specific alloy composition is A356 - 0.3Fe - 0.3V - 0.025Sr;

[0064] Comparative Example 3 is an alloy with only Mn element added, and the specific alloy composition is A356 - 0.3Fe - 0.3Mn - 0.025Sr.

[0065] Comparative Example 1

[0066] A preparation method of an alloy without adding Mn and V elements. The steps not specifically described are the same as those in Example 1, except that: in Step 1, the Al-20Mn and Al-10V master alloys are not added.

[0067] In Step 1, an A356 - 0.3Fe melt can be obtained, simply referred to as AF;

[0068] In Step 2, an as-cast alloy of A356 - 0.3Fe - 0.025Sr can be obtained, simply referred to as AFS-ca alloy;

[0069] In Step 3, a heat-treated alloy of A356 - 0.3Fe - 0.025Sr can be obtained, simply referred to as AFS-ht alloy.

[0070] To prove and quantify the grain size and secondary dendrite arm spacing of α-Al in AFS-ca, a PLM test was conducted. The test results are shown in Table 2. In AFS-ca, the grain size of α-Al is 579.2 ± 104.7 μm, and the secondary dendrite arm spacing is 27.7 ± 3.4 μm. Comparing with Example 1, it can be seen that adding Mn and V elements has no substantial effect on the grain size and secondary dendrite arm spacing of the alloy.

[0071] To prove and quantify the size of the Fe-rich phase in AFS-ca, an SEM test was conducted. The test results are as Figure 3As shown in Table 2, in the AFS-ca alloy, the Fe-rich phase in the alloy is distributed in the form of needle-like flakes with a length of 118.5 ± 39.8 μm. Comparing with Example 1, it can be seen that adding Mn element and V element can significantly reduce the length of the Fe-rich phase, and the reduction amplitude reaches 66.9%.

[0072] To prove the phase composition of the Fe-rich phase in AFS-ca, EDS test was carried out. The test results are as Figure 3 shown. In AFS-ca, only the uniform distribution of Al element, Si element and Fe element exists in the needle-like Fe-rich phase, which is the β-AlFeSi phase. Comparing with Example 1, it can be seen that after adding Mn element and V element, Mn element and V element can be uniformly distributed in the Fe-rich phase to form a new granular Al(Fe,Mn,V)Si phase.

[0073] To prove the hardness of AFS-ht, hardness test was carried out. The test results are shown in Table 2. The hardness of the AFS-ht alloy is 80.1 ± 5.3 HV. Comparing with Example 1, it can be seen that adding Mn element and V element can significantly improve the hardness of the alloy, and the improvement amplitude reaches 17.3%.

[0074] To prove the yield strength of AFS-ht, tensile test was carried out. The test results are as Figure 2 shown in Table 2. The yield strength of the AFS-ht alloy is 136.2 ± 6.8 MPa. Comparing with Example 1, it can be seen that adding Mn element and V element can significantly improve the yield strength of the alloy, and the improvement amplitude reaches 14.7%.

[0075] The comparative analysis between Comparative Example 1 and Example 1 shows that adding Mn element and V element can regulate the microstructure. Specifically, the needle-like β-AlSiFe phase is transformed into the granular α-Al(Fe,Mn,V)Si phase, thereby refining the size of the Fe-rich phase, and further improving the hardness and yield strength of the alloy.

[0076] Comparative Example 2

[0077] A preparation method of an alloy only adding V element. The steps not specially described are the same as those in Example 1, and the differences are as follows: in Step 1, instead of adding Al-Mn master alloy, only Al-V master alloy is added.

[0078] In Step 1, the A356-0.3Fe-0.3V melt can be obtained, which is simply called AF-V-3.

[0079] In Step 2, the as-cast alloy of A356-0.3Fe-0.3V-0.025Sr can be obtained, which is simply called AFS-V-3-ca.

[0080] Alloy A356-0.3Fe-0.3V-0.025Sr in the heat-treated state can be obtained in Step 3, which is abbreviated as AFS-V-3-ht.

[0081] To prove and quantify the grain size and secondary dendrite arm spacing of α-Al in AFS-V-3-ca, PLM tests were carried out. The test results are shown in Table 2. In AFS-V-3-ca, the grain size of α-Al is 487.3±176.0 μm, and the secondary dendrite arm spacing is 27.7±3.6 μm.

[0082] By comparing Comparative Example 2 with Comparative Example 1, the influence of adding V element alone on the technical effect can be confirmed; at the same time, by comparing Comparative Example 2 with Example 1, the influence of further adding Mn element on the technical effect can be confirmed. The conclusion after comparison is that adding V element and further adding Mn element have no substantial influence on the grain size and secondary dendrite arm spacing of the alloy.

[0083] To prove and quantify the size of the Fe-rich phase in AFS-V-3-ca, SEM tests were carried out. The test results are as Figure 4 shown in Table 2. In AFS-V-3-ca, the Fe-rich phase in the alloy is distributed in the form of needles and flakes, with a length of 85.7±17.7 μm.

[0084] It can be seen from comparing Comparative Example 2 with Comparative Example 1 that adding V element alone can reduce the length of the Fe-rich phase, and the reduction amplitude is only 27.9%;

[0085] It can be seen from comparing Comparative Example 2 with Example 1 that further adding Mn element can further significantly reduce the length of the Fe-rich phase, and the reduction amplitude reaches 54.5%.

[0086] To prove the phase composition of the Fe-rich phase in AFS-V-3-ca, EDS tests were carried out. The test results are as Figure 4 shown. In AFS-V-3-ca, only the uniform distribution of Al element, Si element and Fe element exists in the needle-like and flaky Fe-rich phase, which is the β-AlFeSi phase.

[0087] It can be seen from comparing Comparative Example 2 with Comparative Example 1 that adding V element alone has no modification effect on the Fe-rich phase, and it is still the needle-like and flaky β-AlFeSi phase, that is, new granular Al(Fe,Mn,V)Si phase cannot be formed.

[0088] It can be seen from comparing Comparative Example 2 with Example 1 that further adding Mn element can play a role in refining and modifying the Fe-rich phase and form a new Al(Fe,Mn,V)Si phase.

[0089] To prove the hardness of AFS-V-3-ht, a hardness test was conducted. The test results are shown in Table 2, and the hardness of AFS-V-3-ht is 78.8 ± 6.9 HV.

[0090] By comparing Comparative Example 2 with Comparative Example 1, it can be seen that the influence of adding only V element on the hardness of the alloy is negligible;

[0091] By comparing Comparative Example 2 with Example 1, it can be seen that further adding Mn can increase the hardness of the alloy, and the increase amplitude reaches 10.9%.

[0092] To prove the yield strength of AFS-V-3-ht, a tensile test was conducted. The test results are as Figure 2 shown in Table 2, and the yield strength of AFS-V-3-ht is 136.7 ± 0.5 MPa.

[0093] By comparing Comparative Example 2 with Comparative Example 1, it can be seen that the influence of adding only V element on the yield strength of the alloy is negligible;

[0094] By comparing Comparative Example 2 with Example 1, it can be seen that further adding Mn element can increase the yield strength of the alloy, and the increase amplitude reaches 14.8%.

[0095] The comparative analysis of Comparative Example 2 with Comparative Example 1 and Example 1 shows that adding only V element cannot increase the hardness and yield strength of the alloy; moreover, only by adding Mn element and V element simultaneously can the needle-like and flaky β-AlSiFe phase be transformed into the granular α-Al(Fe,Mn,V)Si phase, thereby realizing the technical effect of refining the size of the Fe-rich phase and improving the hardness and yield strength of the alloy.

[0096] Comparative Example 3

[0097] A preparation method of an alloy adding only Mn element. The steps not specifically described are the same as those in Example 1, except that: in Step 1, no Al-V master alloy is added, and only Al-Mn master alloy is added.

[0098] In Step 1, an A356-0.3Fe-0.3Mn melt can be obtained, simply referred to as AF-M-3;

[0099] In Step 2, an as-cast alloy of A356-0.3Fe-0.3Mn-0.025Sr can be obtained, simply referred to as AFS-M-3-ca;

[0100] In Step 3, a heat-treated alloy of A356-0.3Fe-0.3Mn-0.025Sr can be obtained, simply referred to as AFS-M-3-ht.

[0101] To prove and quantify the grain size and secondary dendrite arm spacing of α-Al in AFS-M-3-ca, PLM tests were conducted. The test results are shown in Table 2. In AFS-M-3-ca, the grain size of α-Al is 599.5 ± 101.2 μm, and the secondary dendrite arm spacing is 27.8 ± 3.6 μm.

[0102] By comparing Comparative Example 3 and Comparative Example 1, the influence of adding only Mn element on the technical effect can be confirmed. At the same time, by comparing Comparative Example 3 and Example 1, the influence of further adding V element on the technical effect can be confirmed. The conclusion after comparison is that adding Mn element and further adding V element have no substantial influence on the grain size and secondary dendrite arm spacing of the alloy.

[0103] To prove and quantify the size of the Fe-rich phase in AFS-M-3-ca, SEM tests were conducted. The test results are as Figure 5 shown in Table 2. In AFS-M-3-ca, the Fe-rich phase is distributed in particles, and the length is 52.6 ± 16.0 μm.

[0104] By comparing Comparative Example 3 and Comparative Example 1, it can be seen that adding only Mn element can reduce the length of the Fe-rich phase, and the reduction amplitude is 55.1%;

[0105] By comparing Comparative Example 3 and Example 1, it can be seen that further adding V element can further effectively reduce the length of the Fe-rich phase, and the reduction amplitude reaches 25.9%.

[0106] Further analyzing the conclusions of Comparative Example 2 and Comparative Example 3 regarding the size of the Fe-rich phase, it can be seen that the influence of adding Mn element and adding V element on the size of the Fe-rich phase is independent of each other.

[0107] Through the analysis of the grain size, secondary dendrite arm spacing, and the size of the Fe-rich phase, it is impossible to draw the conclusion that adding Mn element and V element simultaneously can obtain a synergistic effect.

[0108] To prove the phase composition of the Fe-rich phase in AFS-M-3-ca, EDS tests were conducted. The test results are as Figure 5 shown. In AFS-M-3-ca, only the uniform distribution of Al element, Si element, Fe element, and Mn element exists in the granular Fe-rich phase, which is α-Al(Fe,Mn)Si phase.

[0109] By comparing Comparative Example 3 and Comparative Example 1, it can be seen that adding only Mn element has a refinement and modification effect on the Fe-rich phase, forming a granular α-Al(Fe,Mn)Si phase, that is, it is also impossible to form a new granular Al(Fe,Mn,V)Si phase.

[0110] By comparing Comparative Example 3 and Example 1, it can be seen that further adding V element can further refine and modify the Fe-rich phase, forming a new Al(Fe,Mn,V)Si phase.

[0111] To prove the hardness of AFS-M-3-ht, a hardness test was carried out. The test results are shown in Table 2, and the hardness of AFS-M-3-ht is 76.3±4.4HV.

[0112] By comparing Comparative Example 3 and Comparative Example 1, it can be seen that the influence of adding Mn element alone on the hardness of the alloy is negligible;

[0113] By comparing Comparative Example 3 and Example 1, it can be seen that further adding V element can significantly increase the hardness of the alloy, and the increase amplitude reaches 14.5%;

[0114] To prove the yield strength of AFS-M-3-ht, a tensile test was carried out. The test results are as Figure 2 shown in Table 2, and the yield strength of AFS-M-3-ht is 130.7±2.7MPa.

[0115] By comparing Comparative Example 3 and Comparative Example 1, it can be seen that the reduction amplitude of adding Mn element alone to the hardness of the alloy is 4.4%, which also belongs to the negligible situation;

[0116] By comparing Comparative Example 3 and Example 1, it can be seen that further adding V element can significantly improve the yield strength of the alloy, and the increase amplitude reaches 20.0%.

[0117] Through the comparative analysis of Comparative Example 2 with Comparative Example 1 and Example 1, it is shown that when the slow cooling rate is 0.4-1°C / s, adding Mn element alone cannot improve the hardness and yield strength of the alloy; and only when adding Mn element and V element simultaneously, and ensuring that the mass ratio of the total added content of Mn element and V element to the Fe content is kept at 1:1, on this basis, adjusting the mass ratio of Mn element and V element to 2:1, transforming the needle-like and flaky β-AlSiFe phase into a new granular α-Al(Fe,Mn,V)Si phase, so as to achieve the technical effect of refining the size of the Fe-rich phase and improving the hardness and yield strength of the alloy.

[0118] Based on the conclusions of Comparative Example 2 and Comparative Example 3 regarding the hardness and yield strength of the alloy, it can be determined that when the slow cooling rate is 0.4-1°C / s, only when adding Mn element and V element simultaneously, and ensuring that the mass ratio of the total added content of Mn element and V element to the Fe content is kept at 1:1, on this basis, adjusting the mass ratio of Mn element and V element to 2:1, after the appearance of the new granular α-Al(Fe,Mn,V)Si phase, can the hardness and yield strength be significantly improved, that is, there is a synergistic effect.

Claims

1. An Al-Si alloy with an Al(Fe,Mn,V)Si phase, characterized in that: The composition of the Al-Si alloy contains, in addition to Al element, Si element, Mg element, Fe element and Sr element, also Mn element and V element. Moreover, the composition range of the alloy is as follows: Si: 6.5 - 7.5 wt.%, Mg: 0.3 - 0.45 wt.%, Fe: 0.15 - 0.3 wt.%, Sr: 0 - 0.025 wt.%. In addition, the mass ratio of Mn element, V element and Fe element is 2:1:3, that is, the mass ratio of Mn element and V element must be 2:1, and Al is the balance. The phase structure of the alloy includes α-Al phase, eutectic Si phase, Al(Fe,Mn,V)Si phase and Mg2Si phase. The Al(Fe,Mn,V)Si phase is a Fe-rich phase, which is formed by the diffusion of Mn element and V element into the β-AlFeSi phase.

2. The Al-Si alloy having an Al(Fe,Mn,V)Si phase according to claim 1, characterized in that: The Al(Fe,Mn,V)Si phase is granular and evenly distributed in the eutectic Si, with a size of 1 - 10 μm.

3. The Al-Si alloy having an Al(Fe,Mn,V)Si phase according to claim 1, characterized in that: The grain size of the α-Al is 541.4 ± 70.8 μm, the secondary dendrite arm spacing is 26.4 ± 3.9 μm, and the length of the Al(Fe,Mn,V)Si phase is 39.0 ± 8.3 μm.

4. The Al-Si alloy with an Al(Fe,Mn,V)Si phase according to claim 1, characterized in that: The hardness of the Al-Si alloy is 87.4 ± 4.5 HV, and the yield strength is 156.9 ± 7.9 MPa.

5. A method for preparing an Al-Si alloy with an Al(Fe,Mn,V)Si phase, characterized in that It includes the following steps: Step 1, Preparation of A356-Fe-Mn-V melt. The Al-7Si-0.3Mg alloy and Al-20Fe, Al-20Mn and Al-10V alloys meet a certain mass ratio. First, under a certain heating temperature condition, the Al-7Si-0.3Mg alloy is melted to obtain the Al-7Si-0.3Mg alloy melt, simply referred to as A alloy melt. Then, Al-20Fe, Al-20Mn and Al-10V are added to the A melt and completely melted to obtain the A356-0.3Fe-0.2Mn-0.1V alloy melt, simply referred to as AF-MV-2 / 1 alloy melt. Step 2, Preparation of as-cast A356-Fe-Mn-V-Sr alloy. First, the AF-MV-2 / 1 alloy melt obtained in Step 1 is cooled in the furnace to a certain temperature condition. Then, with a certain addition amount of Al-10Sr, Al-10Sr is added to the AF-MV-2 / 1 alloy melt to obtain the A356-0.3Fe-0.2Mn-0.1V-0.025Sr alloy melt, simply referred to as AFS-MV-2 / 1 alloy melt. After that, under certain conditions, the AFS-MV-2 / 1 alloy melt is kept warm. Subsequently, under certain conditions, high-purity argon gas is introduced into the AFS-MV-2 / 1 alloy melt. At the same time, the mold is preheated. Finally, the AFS-MV-2 / 1 alloy melt is cast into the mold and cooled at a certain cooling rate to obtain the as-cast A356-0.3Fe-0.2Mn-0.1V-0.025Sr alloy, simply referred to as AFS-MV-2 / 1-ca. Step 3: Preparation of heat-treated A356-Fe-Mn-V-Sr. First, solutionize the AFS-MV-2 / 1-ca obtained in Step 2 under certain conditions, followed by water cooling after solutionizing. Then, perform aging under certain conditions to obtain the heat-treated A356-0.3Fe-0.2Mn-0.1V-0.025Sr alloy, i.e., an Al-Si alloy with Al(Fe,Mn,V)Si phase, abbreviated as AFS-MV-2 / 1-ht.

6. The method according to claim 5, wherein: In Step 1, the mass ratio of the Al-7Si-0.3Mg alloy to the Al-20Fe, Al-20Mn, and Al-10V alloys is 1:0.015:0.01:0.01, and the heating temperature for obtaining the Al-7Si-0.3Mg alloy melt is 780 - 820 °C.

7. The method according to claim 5, wherein: In Step 2, the temperature for obtaining the AFS-MV-2 / 1 alloy melt is 720 - 780 °C, the addition amount of Al-10Sr is 0.25 wt.%, the holding temperature is 720 - 750 °C, and the holding time is 30 - 60 min. The conditions for introducing high-purity argon are that the gas flow rate is 0.25 L / min and the gas introduction time is 3 min. The cooling rate is 0.4 °C / s.

8. The method according to claim 5, characterized in that: The method for achieving a cooling rate of 0.4 °C / s is that the preheating temperature of the mold is 500 °C.

9. The method according to claim 5, characterized in that: In Step 3, the solutionizing conditions are that the solutionizing temperature is 520 - 560 °C and the solutionizing time is 260 - 300 min. In Step 3, the aging conditions are that the aging temperature is 130 - 170 °C and the aging time is 130 - 170 min.

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