CN114262810B - Preparation method of hypoeutectic die-casting aluminum-silicon alloy material - Google Patents
Preparation method of hypoeutectic die-casting aluminum-silicon alloy material Download PDFInfo
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Abstract
The invention provides a preparation method of a hypoeutectic die-casting aluminum-silicon alloy material, which comprises the following steps: melting aluminum ingot, silicon and iron additive in a smelting furnace, stirring and melting; adding a preheated boronizing agent for boronizing, refining by adopting a sodium-free refining agent, then adding preset magnesium, degassing by adopting inert gas for 20-30 minutes when the temperature of molten aluminum is 750-770 ℃, and adding a preheated aluminum-strontium intermediate alloy for modification when the temperature of the molten aluminum is 740-760 ℃; continuing to degas by using inert gas for 20-30 minutes, and adding the preheated seed crystal alloy; and solidifying and cooling after casting. The hypoeutectic die-casting aluminum-silicon alloy material prepared by the preparation method of the hypoeutectic die-casting aluminum-silicon alloy material has the advantages of higher elongation, higher toughness and higher heat conductivity coefficient.
Description
Technical Field
The invention belongs to the technical field of die-casting aluminum alloy, and particularly relates to a preparation method of a hypoeutectic die-casting aluminum-silicon alloy material.
Background
It is known to the person skilled in the art that in aluminium-silicon alloys it is difficult to combine an increase in both high strength and high thermal conductivity. Generally, an increase in the reinforcing elements silicon, copper, magnesium, etc. results in a decrease in the heat conductive property and toughness. The publication No. CN110983119B discloses a high-strength high-heat-conductivity die-casting aluminum alloy material and a preparation method thereof, and the disclosed high-strength high-heat-conductivity die-casting aluminum alloy material comprises the following components in percentage by weight except aluminum: 9-13% of silicon; iron, the content is 0.4-0.9%; copper, the content is 0.1-0.8%; magnesium, the content is 0.1-0.5%; 0.01-0.05% of modified material, 0.1-3% of nano material, wherein the nano material is an aluminum boron carbon nano material, the heat conductivity coefficient of the high-strength high-heat-conductivity die-casting aluminum alloy material is 170W/(m.K), and the tensile strength reaches 335 MPa. However, the scheme aims at the improvement of eutectic aluminum-silicon alloy, and the improvement of hypoeutectic aluminum-silicon alloy is not researched.
For the field of aluminum-silicon alloy, eutectic aluminum-silicon alloy has been studied to have high strength and high thermal conductivity, but the eutectic aluminum-silicon alloy has poor toughness and low elongation. For practical production, because the alloy material is a base material, the specific preparation requirements at the rear end are various, and the various market demands cannot be met only by eutectic aluminum-silicon alloy, people still expect a certain breakthrough in the performance of the hypoeutectic aluminum-silicon alloy. For example, also in die casting, eutectic aluminum-silicon alloys are easily die cast, while the die cast formability of hypoeutectic aluminum-silicon alloys depends on the specific dimensional conditions of the workpiece. However, hypoeutectic aluminum-silicon alloy is not sensitive to gas like eutectic aluminum-silicon alloy when being die-cast, and is particularly suitable for semi-solid forming because of larger liquid-solid phase temperature difference of hypoeutectic aluminum-silicon alloy, and a semi-solid casting formed by semi-solid casting can eliminate gas and impurities and has less generated air holes. Meanwhile, the hypoeutectic aluminum-silicon alloy has higher elongation and higher toughness than the eutectic aluminum-silicon alloy, and the hypoeutectic aluminum-silicon alloy is preferably selected for some heat dissipation devices and devices with high strength and toughness. Therefore, the research on the performance of the eutectic aluminum-silicon alloy or the hypoeutectic aluminum-silicon alloy is necessary, and once a mark with better performance is generated, the method has great significance for social production.
Along with the development of industries such as domestic communication, electronic equipment, high-strength and high-toughness structural parts for transportation and the like, particularly the erection of a 5G high-speed network platform, the hypoeutectic aluminum-silicon alloy also meets the requirement of higher performance. According to the data of the national standards of GB/T15115 die casting aluminum alloy and GB/T15114 aluminum alloy die casting, the mechanical property of the typical hypoeutectic die casting aluminum-silicon alloy YL104 meets the following indexes: tensile strength of 220MPa, elongation of 2 percent and hardness of 70 HBW. According to the data of Japanese industrial standard of JISH5302-2006 aluminum alloy die casting, the average value of the main mechanical properties of the hypoeutectic die-casting aluminum-silicon alloy ADC10 meets the following indexes: tensile strength 241MPa, elongation 1.5%, hardness 73.6 HBW. For the two standards, no requirement is provided for the heat-conducting performance index of the hypoeutectic die-casting aluminum-silicon alloy, and only the requirement is provided for the mechanical performance, so that the requirement of a high heat-conducting application scene cannot be met, and the application of the hypoeutectic die-casting aluminum-silicon alloy to the communication industry cannot be well realized.
In conclusion, the heat conductivity coefficient and the toughness of the existing aluminum-silicon alloy can be ensured to be higher, and the eutectic aluminum-silicon alloy cannot be relied on only, so that the performance improvement development of the hypoeutectic aluminum-silicon alloy is emphasized from the characteristics of the material type. However, because the eutectic aluminum-silicon alloy and the hypoeutectic aluminum-silicon alloy have different metallographic structure structures, the hypoeutectic aluminum-silicon alloy with corresponding performance cannot be obtained by adjusting the silicon content of the high-strength high-heat-conductivity eutectic aluminum-silicon alloy with better performance, and the hypoeutectic aluminum-silicon alloy with high strength and high heat conductivity cannot be obtained.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a preparation method of a hypoeutectic die-casting aluminum-silicon alloy material with higher elongation, higher toughness and higher heat conductivity coefficient.
The invention provides a preparation method of a hypoeutectic die-casting aluminum-silicon alloy material, which comprises the following steps:
s1, melting the aluminum ingot, the silicon and the iron additive in a melting furnace, stirring and melting;
s2, adding a preheated boronizing agent into molten aluminum at the temperature of 760-780 ℃ for boronization, stirring and melting, and then standing for 30-50 minutes;
s3, refining by adopting a sodium-free refining agent, then adding preset magnesium, and stirring and melting;
s4, degassing for 20-30 minutes by using inert gas when the temperature of the aluminum liquid is 750-770 ℃, removing slag after degassing when the boiling height of the alloy liquid is less than 15cm and the air pressure is 0.15-0.25 MPa;
s5, adding preheated aluminum-strontium intermediate alloy for modification treatment when the temperature of aluminum liquid is 740-760 ℃;
s6, continuing to adopt inert gas to degas for 20-30 minutes, wherein the boiling height of the alloy liquid is less than 15cm and the air pressure is 0.15-0.25 MPa during degassing;
s7, adding preheated seed crystal alloy when the temperature of the aluminum liquid is 700-750 ℃;
and S8, solidifying and cooling after casting, wherein the solidification and cooling process adopts the combination of water-cooling mold bottom and ingot surface spraying.
Preferably, the formula of the aluminum-silicon alloy material comprises the following components in percentage by weight: si: 6.5 to 8.9 percent; fe: 0.5-1.2; cu: less than or equal to 0.3 percent; mn: less than or equal to 0.3 percent; mg: 0.1 to 0.6 percent; zn: less than or equal to 0.3 percent; sr: less than or equal to 0.1; ti: less than or equal to 0.1 percent; b: less than or equal to 0.1 percent; seed crystal alloy addition: 0.1 to 1 percent; the adding amount of the boronizing agent B is 0.01 to 0.1 percent; pb: less than or equal to 0.1 percent; sn: less than or equal to 0.01 percent; cd: less than or equal to 0.01 percent; sum of other unavoidable, commonly occurring impurity elements: less than or equal to 0.2 percent; the balance being Al.
Preferably, the ratio of Cu: less than 0.1%,.
Preferably, the main components and the process conditions of the aluminum alloy material satisfy the following functional relationship:
yk＝102.818+42.732Si-267.313Fe+108.264Mg+258.088Sr+33.495JZ-362.443PHJ；
yq＝204.039-9.995Si-28.572Fe+59.408Mg-35.355Sr+18.512JZ-34.449PHJ；
ys＝-74.153+18.028Si-70.493Fe+5.219Mg+93.572Sr-8.901JZ-154.212PHJ；
yy＝159.076-17.544Si+68.21Fe+26.241Mg+3.047Sr-5.866JZ+66.031PHJ；
yd＝7.468+2.547Si-11.609Fe-4.919Mg+16.091Sr+0.373JZ+8.142PHJ；
yr＝90.506+10.554Si-26.331Fe-53.261Mg+148.618Sr-5.644JZ+95.185PHJ
wherein: JZ represents the addition of the seed alloy; PHJ represents the addition amount of the boronating agent B, tensile strength is represented by yk, yield strength is represented by yq, elongation is represented by ys, hardness is represented by yy, electrical conductivity is represented by yd, and thermal conductivity is represented by yr.
Preferably, the thermal conductivity coefficient of the hypoeutectic die-casting aluminum-silicon alloy material is represented by y, and the electrical conductivity is represented by x, so that the electrical conductivity and the thermal conductivity of the hypoeutectic die-casting aluminum-silicon alloy material satisfy the following functional relationship:
y＝6.5743x+25.097。
preferably, the seed crystal material is a submicron aluminum-titanium-carbon-boron seed crystal alloy, and the submicron aluminum-titanium-carbon-boron seed crystal alloy comprises the following components in percentage by weight: ti: 1.8-2.2%, C: 0.28-0.35%, B: 0.28-0.35% and the balance of Al.
Preferably, in the step S3, the specific steps of refining with a sodium-free refining agent are: when the temperature of the aluminum liquid is 760 ℃ to 780 ℃, inert gases such as nitrogen or argon are taken as carrier gases and 0.2 to 0.5 percent of granular sodium-free refining agent is added for refining, and the speed of loading the refining agent during refining is 0.5 to 1 kg/min.
Preferably, in step S8, the casting specifically includes: when the temperature of the aluminum liquid is 680-750 ℃, continuous or semi-continuous casting of aluminum ingots is adopted, and nitrogen or argon is adopted in the casting process to carry out online degassing through 1 or a plurality of preheated gas permeable bricks which are arranged in a special degassing device or are arranged at the bottom of a launder and are densely distributed with 15-25 mu m micropores.
Preferably, in the steps S1-S8, the stirring and melting tool is a graphite tool, and the stirring speed is 200-.
Preferably, the boronizing agent is an aluminum boron master alloy or a boron-containing flux.
Preferably, the step S1 is specifically: adding 85-90% of aluminum ingot and all silicon, melting, heating to 830-860 ℃, adding iron additive when the temperature is 830-860 ℃ and the silicon is melted uniformly, stirring to melt, standing for 20-30 minutes, adding the rest 10-15% of aluminum ingot, and melting.
The hypoeutectic die-casting aluminum-silicon alloy material prepared by the preparation method of the hypoeutectic die-casting aluminum-silicon alloy material has the advantages of higher elongation, higher toughness and higher heat conductivity coefficient.
Detailed Description
The technical solutions of the present invention are further described in detail with reference to specific examples so that those skilled in the art can better understand the present invention and can implement the present invention, but the examples are not intended to limit the present invention.
The embodiment of the invention provides a preparation method of a hypoeutectic die-casting aluminum-silicon alloy material, which comprises the following steps:
s1, melting aluminum ingots, silicon and iron additives in a melting furnace, and stirring and melting;
s2, adding a preheated boronizing agent to carry out boronizing treatment when the temperature of the molten aluminum is 760-780 ℃, stirring and melting, and then, standing for 30-50 minutes. By adding the boronizing agent, the dissolved B reacts with trace transition metal elements such as Ti, V, Zr, Cr and the like dissolved in the aluminum melt to form transition metal borides, and the transition metal borides are precipitated to the bottom of the furnace, so that the content of the elements in the aluminum alloy is reduced, and the improvement of the conductivity is facilitated, however, some negative effects can be brought by adding the boronizing agent. Firstly, more villiaumite inclusions are difficult to remove, and secondly, the coarse AlB is introduced after the impurities are added2Or AlB12The particles, three, are susceptible to "poisoning" reactions with Sr in the aluminum melt that counteract the beneficial effects. Therefore, the smelting preparation process is different from the boronizing treatment process in the smelting of the conventional conductive aluminum alloy. The preparation process of the invention strictly limits the processing time, the processing temperature and the matching of the process steps of the boronization treatment, the amount can not be increased, the operation sequence can not be inverted, and the net standing time is enough, so that the benefits and the hazards can be approached.
S3, refining the molten aluminum at 760-780 ℃ by adopting a sodium-free refining agent, then adding preset magnesium, and stirring and melting;
s4, degassing for 20-30 minutes by using inert gas when the temperature of the aluminum liquid is 750-770 ℃, removing slag after degassing when the boiling height of the alloy liquid is less than 15cm and the air pressure is 0.15-0.25 MPa;
s5, adding preheated aluminum-strontium intermediate alloy for modification treatment when the temperature of aluminum liquid is 740-760 ℃;
s6, continuing to degas for 20-30 minutes by using inert gas, wherein the boiling height of the alloy liquid is less than 15cm and the gas pressure is 0.15-0.25 MPa during degassing;
s7, adding preheated seed crystal alloy when the temperature of the aluminum liquid is 700-750 ℃;
and S8, solidifying and cooling after casting, wherein the solidification and cooling process adopts the combination of water-cooling mold bottom and ingot surface spraying.
The preparation method of the hypoeutectic die-casting aluminum-silicon alloy material provided by the embodiment breaks through the standard grade performance of the hypoeutectic die-casting aluminum-silicon alloy material at home and abroad. According to the data of the national standards of GB/T15115 die casting aluminum alloy and GB/T15114 aluminum alloy die casting, the mechanical property of the typical hypoeutectic die casting aluminum-silicon alloy YL104 meets the following indexes: tensile strength of 220MPa, elongation of 2 percent and hardness of 70 HBW. According to the data of Japanese industrial standard of JISH5302-2006 aluminum alloy die casting, the average value of the main mechanical properties of the hypoeutectic die-casting aluminum-silicon alloy ADC10 meets the following indexes: tensile strength 241MPa, elongation 1.5%, hardness 73.6 HBW. For the two standards, no requirement is provided for the heat-conducting performance index of the hypoeutectic die-casting aluminum-silicon alloy, the aluminum alloy belongs to the high-performance hypoeutectic die-casting aluminum-silicon alloy, and compared with the traditional hypoeutectic die-casting aluminum-silicon alloy, the aluminum alloy has the biggest characteristics and advantages of better mechanical property and excellent heat-conducting performance. The material can meet the requirements of 5G high-speed network equipment on high-strength high-heat-conductivity aluminum alloy at present.
According to the preparation method of the hypoeutectic die-casting aluminum-silicon alloy material, the heat conductivity coefficient in a die-casting state is more than or equal to 160w/m.k, the die-casting tensile strength is more than or equal to 280MPa, the die-casting elongation is more than or equal to 10%, and the die-casting hardness is more than or equal to 80 HBW. The performance of the aluminum-silicon alloy material is obviously better than that of the typical hypoeutectic die-casting aluminum-silicon alloy material in the standard.
If corresponding heat treatment is carried out on the die casting, high-strength high-heat-conductivity performance or high-toughness performance of various different combinations can be realized. For example, with a heat treatment of T5, it is possible to achieve: the tensile strength is more than or equal to 230MPa, the yield strength is more than or equal to 130MPa, the elongation is more than or equal to 10 percent, the hardness is more than or equal to 65HBW, the electric conductivity is more than or equal to 24.5MS/m, the heat conductivity coefficient is more than or equal to 185W/m.k, and the like, and the high-strength high-heat-conductivity high-speed composite material is suitable for high-strength high-heat-conductivity high-speed network communication equipment facilities or structural members of high-toughness automobile transportation equipment.
The preparation method of the hypoeutectic die-casting aluminum-silicon alloy material strictly limits and controls the procedures of various production process links of adding various materials including the adding sequence of trace metal elements, the temperatures (including smelting temperature, refining temperature, degassing temperature and casting temperature) of different stages, the refining mode, the degassing method, the deslagging requirement, the stirring operation, the component adjustment, the casting cooling and the like. Particularly aiming at the condition that oxide inclusions and pinholes in the aluminum alloy directly influence various performances of the casting, the purification and the exhaust are taken as the key points of purification. By reasonably selecting and distributing the types and the proportions of the refining agents, the effects of the refining agents on impurity removal and exhaust are researched, the optimal combination of the addition amount of the refining agents and the time for adopting carrier gas nitrogen or argon is finally determined, the possibility of product quality reduction caused by oxidation and pinholes is reduced, and the quality of aluminum alloy melts and cast ingots is ensured and improved. By optimizing the components of the product and the processes of all the working procedures in the preparation process, good metal inheritance of the quality of the hypoeutectic die-casting aluminum-silicon alloy material is reserved for the subsequent die-casting products.
In a preferred embodiment, the formulation of the aluminum-silicon alloy material is as follows by weight percent: si: 6.5 to 8.9 percent; fe: 0.5-1.2; cu: less than or equal to 0.3 percent; mn: less than or equal to 0.3 percent; mg: 0.1 to 0.6 percent; zn: less than or equal to 0.3 percent; sr: less than or equal to 0.1; ti: less than or equal to 0.1 percent; b: less than or equal to 0.1 percent; seed crystal alloy addition: 0.1 to 1 percent; the adding amount of the boronizing agent B is 0.01 to 0.1 percent; pb: less than or equal to 0.1 percent; sn: less than or equal to 0.01 percent; cd: less than or equal to 0.01 percent; sum of other unavoidable, commonly occurring impurity elements: less than or equal to 0.2 percent; the balance being Al. The invention optimizes the proportion of each component of the aluminum alloy aiming at the property and the characteristic of the hypoeutectic die-casting aluminum-silicon alloy, improves the heat-conducting property, the corrosion resistance and the toughness of the aluminum alloy material by reasonably reducing the content of elements such as copper, manganese, zinc and the like, and improves the mechanical property of the hypoeutectic die-casting aluminum-silicon alloy on the basis of ensuring the heat-conducting property and the casting property by regulating and controlling magnesium and trace elements such as titanium, boron, strontium and the like and a modification treatment mode. In the process of optimizing alloy components, complex interaction among a plurality of elements is fully researched and exerted, domestic and foreign standards related to comparison are realized, high strength, high heat conduction and good toughness are improved at the same time, and the contradiction that the high strength, the high heat conduction and the high toughness cannot be well considered at the same time is solved.
In the preparation method of the hypoeutectic die-casting aluminum-silicon alloy material, the aluminum alloy material comprises metal elements such as silicon, iron, copper, manganese, magnesium, zinc and the like, and modification and refinement materials such as strontium, titanium, boron, carbon and the like besides matrix aluminum. A small amount of submicron aluminum titanium carbon boron seed crystal alloy material is added after refining purification, deslagging and degassing. Meanwhile, the content of copper and zinc elements in the aluminum alloy material is reduced, and the corrosion resistance of the aluminum alloy material is greatly improved. The submicron grade metamorphic material is mainly used for refining an alpha-Al phase, solves the problems of uneven grain refining distribution and stress concentration, reduces shrinkage porosity, improves compactness, improves mechanical properties such as strength and the like, reduces crack tendency, has long-lasting grain refining and improves the quality of products.
Through studies on this unique aluminum alloy, it was found that the influence of each individual element or modified material on the properties within the content (or addition amount) range is not all linear or monotonously increasing (or decreasing) within the normal distribution range of μ ± 2 σ, and there are also influences of quadratic forms (having extreme values), and even influences of curves of multiple peak (valley) values of quartic forms. And when the single elements and metamorphic materials are subjected to complex interaction together, the influence on the performance forms a new transformed functional relationship. The elemental constituents and the added amounts of the metamorphic materials which make up the alloy need not only be within the control limits, but the effects on performance after their interaction need to be simultaneously satisfied in accordance with these characteristic functional relationships after transformation within a deviation of + -2 sigma.
In the preparation method of the hypoeutectic die-casting aluminum-silicon alloy material, the Si content is represented by x, and the tensile strength is represented by ykThat is, the yield strength is represented by yqThe elongation is represented by ysExpressed as hardness yyExpressed as conductivity, using ydExpressed as the thermal conductivity coefficient, yrAnd (4) showing. In hypoeutectic die cast aluminum silicon alloys, Si is usually one of the strengthening elements. However, aiming at the hypoeutectic die-casting aluminum-silicon alloy material, through research, the single Si content and the performance satisfy the following functional relationship:
yk＝54.488x2-834.208x + 3460.62. That is, its influence on tensile strength is not monotonously increasing or decreasing, and its influence is a parabola whose opening is upward, and a minimum value exists at a Si content of about 7.65%.
yq＝-32.217x2+473.164 x-1606.22; that is, it does not have a monotonic increase or decrease in yield strength, which is a downward opening parabola that has a maximum at about 7.34% Si.
ys＝34.933x2-526.056x + 1988.442; that is, its effect on elongation is not a monotonic increase or decrease, and its effect is a parabola with an upward opening, with a minimum at a Si content of about 7.53%.
yy＝-46.641x2+706.236 x-2589.288; that is, its influence on hardness is not monotonously increasing or decreasing, and its influence is a parabola open downward, and a maximum value exists at a Si content of about 7.57%.
yd＝10.162x2-153.395x + 595.694; that is, its effect on the conductivity is not a monotonic increase or decrease, its effect is a parabola open upward, with a minimum at a Si content of about 7.55%.
yr＝64.255x2-965.2x + 3758.8; that is, its effect on the thermal conductivity rate is not monotonically increasing or decreasing, and its effect is a parabolic curve with an upward opening, with a minimum at a Si content of about 7.51%.
In hypoeutectic die cast aluminum silicon alloys, the influence of the Fe element is generally twofold. On one hand, the die casting agent is beneficial to providing good die casting performance, increases the fluidity and is not easy to stick to a die; on the other hand, the needle-shaped beta-AlFeSi phase formed by the method generally reduces the mechanical property and the heat conducting property. The Fe content is represented by x, and the tensile strength is represented by ykThat is, the yield strength is represented by yqThe elongation is represented by ysExpressed by the hardness yyExpressed in terms of conductivity using ydExpressed as the thermal conductivity coefficient, yrShow, forAccording to the hypoeutectic die-casting aluminum-silicon alloy material, through research, the single Fe content and the performance meet the following functional relationship:
yk＝-292.565x2+304.063x + 209.493; that is, its effect on tensile strength is not a monotonic increase or decrease, and its effect is a downward opening parabola that has a maximum at an Fe content of about 0.52%.
yq＝1606.667x2-2084.063x + 779.941; that is, its effect on yield strength is not monotonically increasing or decreasing, and its effect is a parabola opening upward, with a minimum at an Fe content of about 0.65%.
ys＝-715.309x2+904.01 x-261.631; that is, its effect on elongation is not a monotonic increase or decrease, and its effect is a downward opening parabola that has a maximum at an Fe content of about 0.63%.
yy＝887.21x2-1104.034x + 406.595; that is, its influence on hardness is not monotonously increasing or decreasing, and its influence is a parabola whose opening is upward, and there is a minimum value at an Fe content of about 0.62%.
yd＝-250.162x2+314.465 x-76.819; that is, its effect on the conductivity is not a monotonic increase or decrease, its effect is a downward opening parabola, which has a maximum at a Fe content of about 0.63%.
yr＝-1728.4x2+2193.6 x-527.416; that is, its effect on the thermal conductivity rate is not monotonically increasing or decreasing, and its effect is a downward opening parabola that has a maximum at an Fe content of about 0.63%.
In hypoeutectic die-cast aluminum-silicon alloys, the Mg element generally has a strengthening effect, but may also have negative effects on the electrical conductivity and the thermal conductivity. The Mg content is represented by x, and the tensile strength is represented by ykExpressed that the yield strength is taken as yqThe elongation is represented by ysExpressed as hardness yyExpressed as conductivity, using ydExpressed as the thermal conductivity coefficient, yrShows that through research, the single Mg content and the performance satisfy the following functional relationship:
yk＝122137.75x4-95382x3+24111.5x2-2055.55x + 300.37; that is, it has a quartic function relationship with respect to the influence of tensile strength, and its curve has peak-to-valley alternation within a set content range, and tensile strength is increased faster as Mg tends to the upper limit.
yq＝82583.25x4-55514.42x3+12225.003x2-918.645x + 126.994; that is, its effect on yield strength also has a quartic function relationship, with the curve having alternating peaks and valleys within the set range of contents, and a faster increase in yield strength as Mg approaches the upper limit.
ys＝21524.412x4-18584.46x3+4980.696x2-442.566x + 22.451; that is, its effect on elongation is also a quadratically shaped function, with the curve alternating between peaks and troughs in the set range of contents, and with the trend toward the upper limit of Mg, the elongation first goes into the trough and then increases rapidly.
yy＝-1202.912x4+1689.255x3-395.063x2+47.576x + 67.955; that is, its influence on hardness also has a quartic-type functional relationship, but the curve increases in hardness substantially with increasing Mg within the set content range.
yd＝-6685.848x4+3816.072x3-682.336x2+36.541x + 19.443; that is, its effect on the conductivity also has a quartic function relationship, but the conductivity decreases faster with increasing Mg in the set content range when Mg is at the upper limit.
yr＝-62802.4x4+36806.4x3-6679.68x2+359.912x + 151.584; that is, its influence on the thermal conductivity also has a quartic function relationship, but the thermal conductivity decreases faster as Mg increases in the set content range when Mg is at the upper limit.
In the inventionIn the eutectic die-casting aluminum-silicon alloy, except that the appearance of the eutectic silicon needs to be changed and the grain structure needs to be refined, a submicron-order aluminum-titanium-carbon-boron seed crystal alloy is adopted for refining the matrix of the alpha-Al phase aluminum alloy, so that the problems of uneven grain distribution and stress concentration are solved, shrinkage porosity is reduced, compactness is improved, the crack tendency is reduced, and the improvement of the properties such as material strength is facilitated. Moreover, the grain refining effect of the crystal alloy has long-term stability, is not easy to decline, and provides good-performance metal inheritance for later aluminum ingot remelting and die casting. The content of the seed crystal alloy is represented by x, and the tensile strength is represented by ykThat is, the yield strength is represented by yqThe elongation is represented by ysExpressed as hardness yyExpressed as conductivity, using ydExpressed as the thermal conductivity coefficient, yrIt is shown that,
through research, the content and the performance of the single seed crystal alloy meet the following functional relationship:
yk21.691x + 270.638; clearly, this is a linear relationship, indicating a gradual increase in tensile strength as it is added.
yq23.938x + 114.831; obviously, this is also a linear relationship, indicating that the yield strength increases gradually as its addition increases.
ys-12.241x + 17.945; this is also a linear relationship, but it reflects a gradual decrease in elongation as its addition increases.
yy-1.895x + 76.254; although this is also a linear relationship, the slope is small, reflecting that the hardness does not vary much within the set addition range.
yd-1.133x + 18.985; although this is also a linear relationship, the slope is also small, reflecting that the conductivity does not change much over the set range of addition.
yr-14.317x + 150.936. This is a linear relationship which reflects a gradual decrease in thermal conductivity as its addition increases.
By adding the boronizing agent, the dissolved B reacts with trace transition metal elements such as Ti, V, Zr, Cr and the like dissolved in the aluminum melt to form transition metal borides, and the transition metal borides are precipitated to the bottom of the furnace, so that the content of the elements in the aluminum alloy is reduced, and the conductivity is improved. However, the addition of the borating agent also has some negative effects. Firstly, more villiaumite inclusions are difficult to clean, secondly, the coarse AlB2 or AlB12 particles are introduced after the fluoride inclusions are added, and thirdly, the fluoride inclusions and Sr easily generate a poisoning reaction which counteracts beneficial effects in an aluminum melt. Therefore, the smelting preparation process is different from the boronizing treatment process in the smelting of the conventional conductive aluminum alloy. The preparation process of the invention strictly limits the processing time, the processing temperature and the matching of the process steps of the boronization treatment, the amount can not be increased, the operation sequence can not be inverted, and the net standing time is enough, so that the benefits and the hazards can be approached.
The content of the borating agent is represented by x, and the tensile strength is represented by ykThat is, the yield strength is represented by yqThe elongation is represented by ysExpressed by the hardness yyExpressed as conductivity, using ydExpressed as the thermal conductivity coefficient, yrIt is shown that,
through research, the content and the performance of a single boronizing agent meet the following functional relationship:
yk-13.88x + 276.203; this is a linear relationship, but the slope is small, reflecting that the tensile strength does not vary much over the set range of addition.
yq-231.367x + 124.282; it is also clear that this is a linear relationship, indicating that the yield strength decreases gradually as its addition increases.
ys73.314x + 13.804; this is also a linear relationship, which reflects an increase in elongation as its addition increases.
yy-62.468x + 76.749; this is a linear relationship, reflecting a decrease in hardness with increasing amounts of its addition.
yd36.177x + 18.15; this is also a linear relationship, reflecting the increase in conductivity with increasing amounts of its addition.
yr290.272x + 142.944. This is also a linear relationship which reflects a significant increase in thermal conductivity as its addition is increased.
In the hypoeutectic die-casting aluminum-silicon alloy, the Sr element is added to play the roles of modifying eutectic silicon and refining the grain structure, and the Sr can change the growth mechanism of the eutectic silicon, so that the crystal morphology is improved, and the crystal morphology is changed from a thick plate shape to a coral shape; meanwhile, the addition of Sr is also beneficial to promoting the phase transformation of the needle-shaped beta-AlFeSi into the Chinese character-shaped alpha-AlFeSi. The mechanical property, the electric conduction property and the heat conduction property are all beneficially influenced by different degrees and rules. However, the addition of Sr also increases the air suction degree of the aluminum liquid, increases the difficulty of degassing, and also has negative effects of different degrees and different rules on different mechanical properties and electric and heat conductivity properties. In addition, due to the fact that a boronizing agent needs to be added in the design of the alloy, Sr and B easily react with each other in an aluminum melt, beneficial effects of the Sr and the B are mutually counteracted, and therefore a toxic reaction is generated.
The strontium content in the aluminum-strontium intermediate alloy is represented by x, and the tensile strength is represented by ykThat is, the yield strength is represented by yqShowing that the elongation is ysExpressed as hardness yyExpressed as conductivity, using ydExpressed as the thermal conductivity coefficient, yrIt is shown that,
through research, the single strontium content and the performance satisfy the following functional relationship:
yk＝-3.5E+07x4+3.5E+06x3-114294.25x2+1567.65x + 266.595; that is, it has a quartic function relationship with respect to the influence of tensile strength, and its curve has peak-to-valley alternation within a set content range, and the tensile strength first goes into the peak and then rapidly decreases as Sr tends to the upper limit.
yq＝-1.49E+07x4+2.98E+06x3-87774.41x2+291.116x + 131.12; that is, its effect on yield strength also has a relationship of a quartic function, the curve of which has peak-to-valley alternation in a set content range and enters into the upper limit when Sr tends to be upperThe peak then decreases rapidly.
ys＝2319675.12x4-447.639x3+20127.576x2+82.248x + 7.881; that is, the influence of the strontium-doped eutectic silicon on the elongation rate is also in a relationship of a quartic function, the curve of the tetragonal type eutectic silicon elongation rate has peak-to-valley alternation in a set content range, and the tetragonal type eutectic silicon elongation rate is in a better state of improving the appearance of eutectic silicon when Sr tends to the middle limit, so that the elongation rate enters a peak value and then is reduced.
yy＝1.29E+07x4-2.58E+06x3+116097.42x2-2212.221x + 85.493; that is, its influence on hardness has a quartic function relationship, the curve of which has alternating peaks and valleys in a set content range, but Sr rapidly increases in hardness as Sr increases beyond the middle limit.
yd＝-620336.34x4+150934.68x3-12005.76x2+354.588x + 16.232; that is, its effect on conductivity also has a quadratic function relationship with a curve having alternating peaks and valleys in a set content range, the curve having a higher conductivity in the set content range when Sr is in two sub-ranges of the lower and upper middle limits and a relatively lower conductivity when Sr is in the lower and middle limits.
yr＝1.6E+07x4-1.6E+06x3+18581.6x2+1104.08x + 130.6. That is, the influence of the heat conductivity is also in a quartic function relationship, and the curve has alternating peaks and valleys in the set content range, the heat conductivity of the curve is higher when Sr is in two subdivided ranges of the middle lower limit and the middle upper limit in the set content range, and the heat conductivity of the curve is relatively lower when Sr is in the middle lower limit and the middle upper limit.
The above conditions are that several main alloy elements and metamorphic material additives when singly added affect the performance of the hypoeutectic die-casting aluminum-silicon alloy material of the invention. However, when several kinds exist simultaneously, the complex interaction relationship exists among the several kinds of materials, and the influence on the performance of the aluminum alloy material can generate new post-interaction change. Through research, the influence of their complex interaction on several main performances is in accordance with the following functional relationship within ± 2 σ deviation after transformation:
yk＝102.818+42.732Si-267.313Fe+108.264Mg+258.088Sr+33.495JZ-362.443PHJ；
yq＝204.039-9.995Si-28.572Fe+59.408Mg-35.355Sr+18.512JZ-34.449PHJ；
ys＝-74.153+18.028Si-70.493Fe+5.219Mg+93.572Sr-8.901JZ-154.212PHJ；
yy＝159.076-17.544Si+68.21Fe+26.241Mg+3.047Sr-5.866JZ+66.031PHJ；
yd＝7.468+2.547Si-11.609Fe-4.919Mg+16.091Sr+0.373JZ+8.142PHJ；
yr＝90.506+10.554Si-26.331Fe-53.261Mg+148.618Sr-5.644JZ+95.185PHJ
wherein: JZ represents the addition of the seed alloy; PHJ represents the addition of the boronizing agent B, and the tensile strength is ykThat is, the yield strength is represented by yqThe elongation is represented by ysExpressed as hardness yyExpressed as conductivity, using ydExpressed as the thermal conductivity coefficient, yrAnd (4) showing.
The linear function relations of the hypoeutectic die-casting aluminum-silicon alloy material comprehensively reflect the trend and the quantitative degree of the influence of the hypoeutectic die-casting aluminum-silicon alloy material on six main properties within the range of the set content or the addition amount in the interaction of a plurality of main elements and metamorphic materials.
(1) Mg, Sr, Si and submicron-grade aluminum-titanium-carbon-boron seed crystal alloy have a great improvement effect on tensile strength, and Fe and a boronizing agent reduce the tensile strength.
(2) The Mg and submicron aluminum titanium carbon boron seed crystal alloy has obvious effect of improving the yield strength, and the Sr, the boration agent, the Fe and the Si have the effect of reducing the yield strength.
(3) Sr, Si, Mg can improve the elongation, while boration agent, Fe and submicron aluminum titanium carbon boron seed crystal alloy can reduce the elongation.
(4) The boration agent, Mg, Fe and Sr are beneficial to improving the hardness, and Si and submicron-grade aluminum-titanium-carbon-boron seed alloy have slight influence on the hardness.
(5) Sr and the boronizing agent have the effect of improving the conductivity, Si and the submicron-scale aluminum-titanium-carbon-boron seed crystal alloy have a slight positive correlation with the conductivity, and Fe and Mg have the effect of reducing the conductivity.
(6) Sr and the boronizing agent have a great promotion effect on the heat conductivity coefficient, Si also has a positive correlation effect on the heat conductivity coefficient, Mg and Fe have obvious reduction influence on the heat conductivity coefficient, and the submicron-grade aluminum-titanium-carbon-boron seed crystal alloy has a slightly negative correlation effect on the heat conductivity coefficient.
In a preferred embodiment, Cu: < 0.1%, Si: 7-8%, and the boronizing agent is an aluminum-boron intermediate alloy or a boron-containing flux.
In a preferred embodiment, the thermal conductivity of the hypoeutectic die-cast aluminum-silicon alloy material is represented by y, and the electrical conductivity is represented by x, then the electrical conductivity and the thermal conductivity of the hypoeutectic die-cast aluminum-silicon alloy material satisfy the following functional relationship: y 6.5743x + 25.097. In the hypoeutectic die-casting aluminum-silicon alloy, in order to obtain high strength, high electric conductivity, high heat conductivity and high toughness, the hypoeutectic die-casting aluminum-silicon alloy is ensured by adopting the combination of various composite measures and a smelting process. The boronizing agent is adopted for boronizing treatment, so that the electrical conductivity of the hypoeutectic die-casting aluminum-silicon alloy material is further improved, and the heat conductivity coefficient positively correlated with the hypoeutectic die-casting aluminum-silicon alloy material is also improved.
In addition to the composition of the components and the functional relationship according to the above interaction, the hypoeutectic die-cast aluminum-silicon alloy of the invention also has a unique and rigorous material process preparation method matched with the hypoeutectic die-cast aluminum-silicon alloy. If the preparation method is violated, the negative effects such as poor high-strength high-heat-conductivity properties, poor high-toughness properties, deterioration failure quality reduction, increased alloy loss, increased manufacturing cost, etc. are caused.
According to the functional relation after the interaction, the hypoeutectic die-casting aluminum-silicon alloy material prepared by setting the specific element composition and the addition amount of the modified material within the control range of the alloy and strictly performing process control according to the preparation method can achieve the high performance index.
In a preferred embodiment, the seed crystal material is a submicron aluminum titanium carbon boron seed crystal alloy, and the composition of the submicron aluminum titanium carbon boron seed crystal alloy comprises the following components in percentage by weight: ti: 1.8-2.2%, C: 0.28-0.35%, B: 0.28-0.35% and the balance of Al.
In a preferred embodiment, in step S3, the refining with the sodium-free refining agent includes the following specific steps: when the temperature of the aluminum liquid is 760 ℃ to 780 ℃, inert gases such as nitrogen or argon are taken as carrier gases and added into 0.2 to 0.5 percent of granular sodium-free refining agent for refining, and the speed of loading the refining agent during refining is 0.5 to 1 kg/min;
in a preferred embodiment, in the step S8, the casting specifically includes: when the temperature of the aluminum liquid is 680-750 ℃, continuous or semi-continuous casting of aluminum ingots is adopted, and nitrogen or argon is adopted in the casting process to carry out online degassing through 1 or a plurality of preheated gas permeable bricks which are arranged in a special degassing device or are arranged at the bottom of a launder and are densely distributed with 15-25 mu m micropores.
In the preferred embodiment, in the steps S1-S8, the stirring and melting tool is made of graphite, and the stirring speed is 200-.
In order that the technical solutions of the present invention may be further understood and appreciated, several preferred embodiments are now described in detail.
Preparation method 1
The method comprises the following steps:
(1) adding 85-90% of aluminum ingot and all silicon, melting and heating to 830-860 ℃.
(2) The iron additive is added after the temperature is 830-860 ℃ and the silicon is melted uniformly.
(3) Stirring to melt, and standing for 20-30 min.
(4) Adding the rest 10-15% of aluminum ingot to melt.
(5) Adding a preheated boronizing agent for boronizing when the temperature of the aluminum liquid is 760 and 780 ℃. Stirring and melting, and standing for 30-50 minutes.
(6) When the temperature of the aluminum liquid is 760 and 780 ℃, inert gases such as nitrogen or argon are taken as carrier gases and 0.2 to 0.5 percent of granular smokeless, tasteless and environment-friendly sodium-free refining agent without harmful components is added for refining. The refining agent is loaded at a rate of 0.5 to 1 kg/min during refining.
(7) Adding preheated magnesium at 750-770 ℃, and uniformly stirring and melting.
(8) And sampling and inspecting components after the magnesium is melted uniformly.
(9) And degassing for 20-30 minutes by using inert gases such as nitrogen or argon and the like when the temperature of the aluminum liquid is 750 and 770 ℃. During degassing, the boiling height of the alloy liquid is less than 15cm, and the air pressure is between 0.15 and 0.25 MPa.
(10) And (6) removing slag.
(11) Adding preheated Al-Sr intermediate alloy for modification treatment when the temperature of molten aluminum is 740-760 ℃.
(12) And continuing to use inert gas such as nitrogen or argon to degas for 20-30 minutes. During degassing, the boiling height of the alloy liquid is less than 15cm, and the air pressure is between 0.15 and 0.25 MPa.
(13) The sample was tested for conductivity (this step can be ignored without conductivity requirement).
(14) The chemical components are qualified, the conductivity of the sample meets the control requirement, and when the temperature of the aluminum liquid is 700-750 ℃, the preheated seed crystal alloy is added, and the mixture is melted and stirred uniformly and then is placed for 5-15 minutes. The seed crystal alloy can also be uniformly added into an aluminum liquid launder in a continuous mode during casting. If the components in the step are not qualified, the components are required to be adjusted to be qualified, and if the conductivity is not qualified, the operations in the step (11) and the subsequent steps are repeated.
(15) And the aluminum liquid is continuously or semi-continuously cast into aluminum ingots at the temperature of 680-750 ℃.
(16) The casting process adopts nitrogen or argon to carry out online degassing through 1 or a plurality of preheated gas permeable bricks which are arranged in a special degassing device or are arranged at the bottom of the launder and are densely distributed with 15-25 mu m micropores. To ensure that the density equivalent is less than or equal to 1 percent.
(17) The solidification and cooling process combines the water-cooling mold bottom and the ingot surface spraying, so as to be beneficial to refining crystal grains.
The stirring is carried out in the center of the aluminum liquid in a rotating mode that the tool made of graphite material which does not react with the aluminum liquid is in the rotating speed range of 200 plus 500 rpm. The rotating speed is set to drive the molten aluminum to rotate and flow, so that the melts can be fully contacted with each other in the vertical direction and the horizontal direction to achieve homogenization, and meanwhile, the downward air suction of a vortex generated by a rotating center is avoided.
Comparative method 1
Compared with the preparation method 1, in the comparison method 1, the aluminum-strontium intermediate alloy is firstly adopted to carry out modification treatment in the step (11), and then the preheated boronizing agent is added to carry out boronizing treatment, namely compared with the preparation method 1, the boronizing treatment in the comparison method 1 is carried out after modification. The remaining steps are the same as in preparation method 1.
Comparative method 2
In comparison with production method 1, the seed alloy was added between step (6) in comparative method 2, that is, in comparison with production method 1, the seed alloy was added before refining in comparative method 2, and the rest of the steps were the same as in production method 1.
Comparative method 3
Compared with the preparation method 1, the degassing steps of the step (9) and the step (12) are eliminated, and the rest steps are the same as the preparation method 1.
The formulations and preparation methods of examples 1 to 4 and comparative examples 1 to 4 are shown in Table 1.
TABLE 1
The alloy ingots prepared in examples 1 to 4 and comparative examples 1 to 4 were subjected to die-casting, and then tested for tensile strength (MPa), yield strength (MPa), elongation (%), Hardness (HBW), electrical conductivity (MS/m), and thermal conductivity (W/m.k), as shown in table 2.
TABLE 2
In summary, it can be seen that the hypoeutectic die-cast aluminum-silicon alloy materials prepared in the embodiments 1 to 4 of the present invention still have high tensile strength, high yield strength, long elongation, high electrical conductivity and high thermal conductivity after being die-cast and formed. After the heat treatment in the embodiment 4, the electric conductivity of the die-casting mold can be further improved to 24.61MS/m and the heat conductivity coefficient can be further improved to 186.27W/m.k.
In comparative example 1, the boronizing treatment is carried out after the modified eutectic silicon, the process sequence of the boronizing treatment is changed, and the electric conduction performance and the heat conduction performance are obviously reduced. The modification of Sr and the modification of B are changed in sequence, so that Sr and B are easy to react with each other in the aluminum melt, the beneficial effects of the Sr and B are mutually counteracted, and then the toxic reaction is generated, so that the modification is ineffective. If the metamorphic material needs to be added again for metamorphic treatment, the cost of the metamorphic material is increased.
In comparative example 2, the addition of the seed alloy before refining changed the order of addition of the seed alloy, the strength properties of the alloy decreased, and the elongation was less than 10%.
In comparative example 3, the Mg content is higher than the control range, and the electric and thermal conductivity is lowered.
In the comparative example 4, the degassing process of several links is cancelled, the degassing link is cancelled, the pinholes are serious, and a plurality of performances are seriously deviated from the interaction function relationship. The electrical conductivity, thermal conductivity, and strength and elongation all drop sharply.
COMPARATIVE EXAMPLE 5 (eutectic aluminum-silicon alloy)
The raw materials are proportioned according to the weight percentage: silicon, content 12.0%; iron, content 0.554%; copper, content 0.230%; magnesium, content 0.301%; 0.0302% of strontium; tin, content 0.00018%; lead, content 0.0003%; cadmium, content 0.0013%.
The alloy is prepared according to the mixture ratio, and the steps are as follows:
an aluminum ingot and silicon are put into a furnace and heated to melt them into a metal solution. The temperature of the metal solution reaches 835 ℃, after the silicon is completely melted, stirring for 8 minutes, removing scum, dispersing and adding an iron element additive into the metal solution, stirring for more than 5 minutes after the metal solution is completely melted, and adding a copper element additive for alloying after the scum is removed.
After the metal solution is completely melted, the temperature of the metal solution is reduced to 760 ℃, then a refining agent is mixed with nitrogen, and the mixture is blown into the metal solution to refine and purify the melt and remove slag. And (4) after the blowing of the refining agent is finished, removing the scum. The nitrogen degassing was then continued for 20 minutes.
Magnesium was added and melted, left to stand for 5 minutes and the metal solution was degassed with nitrogen. The metal solution was then sampled to check the composition, ensuring that the composition was within the following ranges: 9-13% of silicon; iron, the content is 0.4-0.9%; copper, the content is 0.1-0.5%; magnesium, the content is 0.1-0.5%; tin, the content is less than or equal to 0.01 percent; lead, the content is less than or equal to 0.1 percent; cadmium, the content is less than or equal to 0.01 percent; the total amount of impurities is not more than 0.2%; the balance being aluminum.
After the components are qualified, controlling the temperature at 740-750 ℃, adding 1% of aluminum boron carbon nano material, and standing for 10 minutes after the aluminum boron carbon nano material is completely and uniformly melted;
controlling the temperature at 730 ℃ and 750 ℃, adding 0.04 percent of strontium for modification treatment, and degassing the metal solution in the furnace by adopting nitrogen for 5-10 minutes after the mixture is purified and placed for a period of time.
Sampling again and checking to ensure that the components meet the following conditions: 9-13% of silicon; iron, the content is 0.4-0.9%; copper, the content is 0.1-0.5%; magnesium, the content is 0.1-0.5%; 0.01 to 0.05 percent of strontium; tin, the content is less than or equal to 0.01 percent; lead, the content is less than or equal to 0.1 percent; cadmium, the content is less than or equal to 0.01 percent; the sum of the total impurities is not more than 0.2%; the balance being aluminum and a small amount of nanomaterial.
And after the components are qualified, controlling the temperature of the aluminum liquid within the range of 730-750 ℃ to cast aluminum alloy ingots. During the process of casting the aluminum ingot, the bottom air brick is arranged on the filter box for on-line degassing, and the aluminum liquid is further purified, so that the density equivalent of the aluminum liquid is less than 1 percent, and the diameter of the micro-hole of the air brick is 15-25 mu m. And obtaining the aluminum alloy ingot material after casting.
Comparative example 6
Compared with example 1, the content of silicon in comparative example 6 is 12.0%, and the formula and preparation method are the same as those of example 1. The die casting mechanical properties, the material thermal conductivity and the die casting thermal conductivity were compared for inventive example 1 with comparative examples 5 and 6. The material thermal conductivity coefficient refers to the thermal conductivity coefficient of the prepared material, and the die-casting thermal conductivity coefficient refers to the thermal conductivity coefficient of the material after die-casting molding. Specific data are shown in table 3.
TABLE 3
In summary, it can be seen that the preparation method of the hypoeutectic die-casting aluminum-silicon alloy material provided in embodiment 1 of the present invention is developed for the hypoeutectic die-casting aluminum-silicon alloy material, and when the silicon content is higher in comparative example 6 and the material is a eutectic aluminum-silicon alloy, the specific preparation method of the alloy ratio of the preparation method is not suitable for the eutectic aluminum-silicon alloy.
It can be seen from the data of comparative example 5 that, compared with the existing eutectic aluminum-silicon alloy with excellent performance, high strength and high thermal conductivity, the thermal conductivity of the hypoeutectic die-cast aluminum-silicon alloy material prepared in example 1 is further improved, and the elongation and the electrical conductivity are both obviously improved. The application field of the hypoeutectic die-casting aluminum-silicon alloy material is widened, and the method has a very prominent technical effect.
The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by the present specification, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (7)
1. The preparation method of the hypoeutectic die-casting aluminum-silicon alloy material is characterized by comprising the following steps of:
s1, melting aluminum ingots, silicon and iron additives in a melting furnace, and stirring and melting;
s2, adding a preheated boronizing agent into molten aluminum at the temperature of 760-780 ℃ for boronization, stirring and melting, and then standing for 30-50 minutes;
s3, refining by adopting a sodium-free refining agent, then adding preset magnesium, and stirring and melting;
s4, degassing for 20-30 minutes by using inert gas when the temperature of the aluminum liquid is 750-770 ℃, removing slag after degassing when the boiling height of the alloy liquid is less than 15cm and the air pressure is 0.15-0.25 MPa;
s5, adding preheated aluminum-strontium intermediate alloy for modification treatment when the temperature of aluminum liquid is 740-760 ℃;
s6, continuing to degas for 20-30 minutes by using inert gas, wherein the boiling height of the alloy liquid is less than 15cm and the gas pressure is 0.15-0.25 MPa during degassing;
s7, adding preheated seed crystal alloy when the temperature of the aluminum liquid is 700-750 ℃;
and S8, solidifying and cooling after casting, wherein the solidification and cooling process adopts the combination of water-cooling mold bottom and ingot surface spraying.
The formula of the aluminum-silicon alloy material is as follows: si: 6.5 to 8.9 percent; fe: 0.5-1.2; cu: less than or equal to 0.3 percent; mn: less than or equal to 0.3 percent; mg: 0.1 to 0.6 percent; zn: less than or equal to 0.3 percent; sr: less than or equal to 0.1; ti: less than or equal to 0.1 percent; b: less than or equal to 0.1 percent; seed crystal alloy addition: 0.1 to 1 percent; the adding amount of the boronizing agent B is 0.01 to 0.1 percent; pb: less than or equal to 0.1 percent; sn: less than or equal to 0.01 percent; cd: less than or equal to 0.01 percent; sum of other unavoidable, commonly occurring impurity elements: less than or equal to 0.2 percent; the balance of Al;
the seed crystal material is a submicron aluminum-titanium-carbon-boron seed crystal alloy, and the submicron aluminum-titanium-carbon-boron seed crystal alloy comprises the following components in percentage by weight: ti: 1.8-2.2%, C: 0.28-0.35%, B: 0.28-0.35% and the balance of Al;
the main components and the process conditions of the aluminum alloy material meet the following functional relationship:
yk＝102.818+42.732Si-267.313Fe+108.264Mg+258.088Sr+33.495JZ-362.443PHJ；
yq＝204.039-9.995Si-28.572Fe+59.408Mg-35.355Sr+18.512JZ-34.449PHJ；
ys＝-74.153+18.028Si-70.493Fe+5.219Mg+93.572Sr-8.901JZ-154.212PHJ；
yy＝159.076-17.544Si+68.21Fe+26.241Mg+3.047Sr-5.866JZ+66.031PHJ；
yd＝7.468+2.547Si-11.609Fe-4.919Mg+16.091Sr+0.373JZ+8.142PHJ；
yr＝90.506+10.554Si-26.331Fe-53.261Mg+148.618Sr-5.644JZ+95.185PHJ
wherein: JZ represents the addition of the seed alloy; PHJ represents the addition of the boronizing agent B, and the tensile strength is ykThat is, the yield strength is represented by yqShowing that the elongation is ysExpressed as hardness yyExpressed as conductivity, using ydExpressed as the thermal conductivity coefficient, yrAnd (4) showing.
2. The method for producing a hypoeutectic die-cast aluminum-silicon alloy material according to claim 1, wherein the ratio of Cu: is less than 0.1 percent.
3. The method for preparing a hypoeutectic die-cast aluminum-silicon alloy material according to claim 1, wherein the thermal conductivity of the hypoeutectic die-cast aluminum-silicon alloy material is represented by y, and the electrical conductivity is represented by x, so that the electrical conductivity and the thermal conductivity of the hypoeutectic die-cast aluminum-silicon alloy material satisfy the following functional relationship:
y＝6.5743x+25.097。
4. the method for preparing the hypoeutectic die-cast aluminum-silicon alloy material according to claim 1, wherein in the step S3, the refining with the sodium-free refining agent comprises the following specific steps: when the temperature of the aluminum liquid is 760 ℃ to 780 ℃, inert gases such as nitrogen or argon are taken as carrier gases and 0.2 to 0.5 percent of granular sodium-free refining agent is added for refining, and the speed of loading the refining agent during refining is 0.5 to 1 kg/min.
5. The method for preparing the hypoeutectic die-casting aluminum-silicon alloy material according to claim 1, wherein in the step S8, the casting comprises the following specific steps: when the temperature of the aluminum liquid is 680-750 ℃, continuous or semi-continuous casting of aluminum ingots is adopted, and nitrogen or argon is adopted in the casting process to carry out online degassing through 1 or a plurality of preheated gas permeable bricks which are arranged in a special degassing device or are arranged at the bottom of a launder and are densely distributed with 15-25 mu m micropores.
6. The method for preparing a hypoeutectic die-cast Al-Si alloy material according to claim 1, wherein in the steps S1-S8, the stirring and melting tool is a graphite tool, and the stirring speed is 200-500 rpm.
7. The method of preparing a hypoeutectic die cast aluminium silicon alloy material according to claim 1, wherein the boronating agent is an aluminium boron intermediate alloy or a boron containing flux;
the step S1 specifically includes: adding 85-90% of aluminum ingot and all silicon, melting, heating to 830-860 ℃, adding iron additive when the temperature is 830-860 ℃ and the silicon is melted uniformly, stirring to melt, standing for 20-30 minutes, adding the rest 10-15% of aluminum ingot, and melting.
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