CN108300884B - A kind of hypoeutectic Al-Mg2The rotten and thinning method of Si alloy - Google Patents

Abstract

A modification and refinement method of a hypoeutectic Al-Mg ₂ Si alloy, using Bi and Zr to modify and refine a hypoeutectic Al-Mg2Si alloy with a Mg ₂ Si content of 4 to 12.5wt.%. Finally, the Bi content in the melt is 0.1-0.6%, and the Zr content is 0.05-0.2%. The eutectic Mg2Si in the alloy changed from thick Chinese characters to fine fibers after Bi modification treatment, and the primary α-Al in the alloy changed from columnar crystals to equiaxed crystals after Zr refinement treatment, and the mechanical properties were greatly improved. The tensile strength and elongation of the alloy increased by 34% and 239% respectively after refinement and modification. The microstructures of hypoeutectic Al‑Mg2Si alloys with different contents of Mg2Si are significantly refined after modification and refinement treatment. At the same time, the modification of Bi and the refinement of Zr are not affected by the cooling rate, which is suitable for both metal molds and sand molds. Moreover, the Bi modifier and the Zr refiner also have the advantages of excellent long-term effect, simple treatment process and no pollution.

Description

Modification and refinement method of a hypoeutectic Al-Mg2Si alloy

technical field

The invention belongs to the technical field of aluminum alloy casting and smelting, and in particular relates to a modification and refinement method of a hypoeutectic Al-Mg ₂ Si alloy.

Background technique

In traditional Al-Si-Mg alloys, Mg ₂ Si, as the second phase, is dispersed and precipitated through solid solution-aging heat treatment to strengthen the Al matrix. In recent years, the Al-Mg ₂ Si alloy formed by directly precipitating the Mg ₂ Si phase from the aluminum liquid, which is also called the in-situ self-generated Mg ₂ Si/Al composite material in the hypereutectic composition, has been favored by scholars at home and abroad. extensive attention. Compared with the traditional Al-Si-Mg alloy, this material has higher Mg content and Mg ₂ Si phase volume fraction, and has higher specific stiffness, specific strength and wear resistance. The new lightweight materials in the field of materials and other fields have broader application prospects. However, the precipitated Mg ₂ Si in the as-cast state is relatively coarse, and the primary Mg ₂ Si is in the form of coarse dendrites with holes, while the eutectic Mg ₂ Si is in the form of coarse Chinese characters, nets, rods and flakes. Severely split the Al matrix, resulting in stress concentration, the formation of crack sources, and deterioration of the mechanical properties of the alloy. In addition, for the Al-Mg ₂ Si alloy with hypoeutectic composition, its microstructure is composed of primary α-Al and Mg ₂ Si+α-Al eutectic phase, and the morphology of primary α-Al in the as-cast state is coarse Dendritic, columnar crystals macroscopically, leading to a decline in the mechanical properties of the alloy, feeding properties, crack resistance and other casting properties.

In recent years, various techniques such as mechanical alloying, hot extrusion, rolling, heat treatment, rapid solidification and modification have been used to control the size and morphology of Mg ₂ Si phase. Among these methods, modification treatment has the advantages of simple operation, low cost, and significant modification effect. By adding modification elements such as P, La, Nd, Y, Sr, Na, Ni, Zr, and B to the alloy melt, the increase The nucleation rate of the Mg ₂ Si phase may change the growth mode of the crystal, which can effectively refine the Mg ₂ Si phase and improve the mechanical properties of the alloy.

So far, people have done a lot of research on the modification treatment of hypereutectic Al-Mg ₂ Si alloy, that is, in situ authigenic Mg ₂ Si/Al composite material, while the research on hypoeutectic Al-Mg ₂ Si alloy is scarce. There are reports. Compared with the hypereutectic Al-Mg ₂ Si alloy, the hypoeutectic Al-Mg ₂ Si alloy has better plasticity and toughness, and has better comprehensive mechanical properties, and is expected to have wider applications. The premise is that the coarse Chinese character-like, network-like and sheet-like eutectic Mg ₂ Si phases are effectively refined. At the same time, the primary α-Al dendrites are refined, so that the mechanical properties and casting properties of the alloy are further improved.

At present, there are few reports on the study of hypoeutectic Al-Mg ₂ Si alloys. Li et al. from Tianjin University carried out a solution treatment on the hypoeutectic Al _- 10Mg ₂ Si alloy at 520°C×6h followed by an aging treatment at 200°C×6h. Transformed into short fibrous and spherical shapes, the tensile strength increased from 186 MPa to 234.6 MPa, see Journal of Alloys and Compounds, 2016, 663(5):15-19. Their research also showed that the corrosion resistance of the hypoeutectic Al-10Mg ₂ Si alloy in 3.5 wt.% NaCl solution was also improved, see MaterialsCharacterization, 2016, 122(12):142-147. Lee et al. of the Korea Institute of Materials Science performed cold rolling on the AlMg5Si2Mn die-casting alloy before the homogenization treatment, so that the interconnected coarse eutectic Mg ₂ Si phases were broken into fine fragments, so that the mechanical properties of the alloy were effectively improved. , see Materials Science and Engineering A, 2017, 685(8):244-252. Although these methods can refine the eutectic Mg ₂ Si and improve the properties of the alloy such as mechanics and corrosion resistance, they have the disadvantages of many processes, complex processes and high costs. Therefore, there is an urgent need to research and develop simple and economical modifiers, refiners and modification and refinement methods suitable for hypoeutectic Al-Mg ₂ Si alloys.

So far, there is no report on the refinement of primary α-Al dendrites in hypoeutectic Al-Mg ₂ Si alloys. For cast Al-Si alloys, primary α-Al dendrites are mainly refined by adding a refiner to the alloy melt. At present, the commonly used refiners include Al-Ti, Al-B, Al-Ti-B, Al-Ti-C, Al-Zr and other master alloys, as well as KBF ₄ , K ₂ TiF ₆ , TiC and K ₂ ZrF ₆ or compound salts. Ti-based refiners such as Al–Ti, Al–5Ti–1B, and Al–Ti–C are suitable for pure aluminum and aluminum-silicon alloys with a silicon content of less than 1.5%, and for hypoeutectic cast aluminum with a silicon content of ≥5%. The refining effect of silicon alloy is not obvious, which is because the production of (Ti _{1-x Six} )Al ₃ compound reduces the amount of Al ₃ Ti and TiB ₂ as nucleating agents. Studies have shown that Al-3B, Al-3Ti-3B and other B-type refining agents have a good refining effect on hypoeutectic cast aluminum-silicon alloys with a silicon content > 4%, but B is easy to react with the metamorphic element Sr, Generate SrB ₆ , consume Sr and B. For the Al-Mg ₂ Si alloy, due to the high content of Mg in it, the refining elements are more likely to form non-nucleating compounds with Mg and modification elements, which weakens the modification and refinement effect or causes casting defects. Fakhraei et al. from the University of Tehran in Iran found that adding too much B or Zr to the Al-20Mg alloy would produce pores, resulting in a decrease in the tensile properties of the alloy. See Materials & Design, 2014, 56 (4): 557-564.

Contents of the invention

The purpose of the present invention is to overcome the problems existing in the prior art, and to provide a hypoeutectic Al-Mg2 with metamorphism, good refining effect, good decay resistance, strong applicability, applicable to _both metal molds and sand molds, and simple production process Modification and refinement method of Si alloy.

Technical solution of the present invention is:

(1) According to the batching of hypoeutectic Al-Mg ₂ Si alloy containing 4-12.5wt.% Mg ₂ Si phase by mass percentage, the amount of Mg added is: calculated amount + 10~30% of burning loss;

(2) After cleaning and drying the pure Al and aluminum-silicon intermediate alloy prepared in step (1), put them into the graphite crucible of the resistance furnace and heat them in the resistance furnace. After they are completely melted, wrap them in aluminum foil at 720 °C Press the pure Mg block preheated at 300°C into the melt with a graphite bell jar preheated at 300°C until it melts, and let it stand for 5 minutes;

(3) Press hexachloroethane, which accounts for 0.05~0.2% of the mass of the melt, into the melt obtained in step (2) with a graphite bell jar preheated at 300°C for refining and degassing. Stir at low temperature for 1~5 min, remove the scum on the surface of the melt, and obtain the refined melt;

(4) Add Bi particles to the melt obtained in step (3) at a temperature of 670°C to 730°C, and let it stand for 1 to 3 minutes to obtain a melt with a Bi content of 0.1-0.6wt.% by mass;

(5) Add Al-10Zr master alloy or Zr-containing compound to the melt obtained in step (4) at a temperature of 720°C~800°C, let it stand for 5~15min, and stir the melt for 2~ 5 min, Zr is evenly distributed to obtain a melt with a Zr content of 0.05-0.2wt.% mass percent;

(6) Refining the melt obtained in step (5) according to step (3), pouring the melt into a mold at a temperature of 700°C to 780°C to become a casting or a slab.

The Bi described in step (4) is added in the form of pure metal.

The Zr described in step (5) is added in the form of an intermediate alloy or compound.

The casting mold described in step (6) is a sand mold or a metal mold preheated at 250°C or other casting molds.

The advantage of technical solution of the present invention is mainly reflected in:

1. Using Bi pure metal particles as a modifier can effectively modify the Mg ₂ Si phase in the hypoeutectic Al-Mg ₂ Si alloy. After adding an appropriate amount of Bi to the hypoeutectic Al-Mg ₂ Si alloy, it can significantly change The morphology and size of the eutectic Mg ₂ Si were confirmed. The Mg ₂ Si phase changed from coarse Chinese character, network and sheet to fine granular and fibrous, and the volume fraction of the primary α-Al phase increased, showing obvious Metamorphic characteristics and effects, the solubility of Bi in Al is extremely low, when the melt of hypoeutectic and eutectic components reaches the eutectic reaction point, it is very easy to adsorb and gather at the growth interface of the eutectic Mg ₂ Si phase that precipitated earlier At the frontier, the eutectic Mg ₂ Si is constantly blocked from the original twin steps of the eutectic Mg 2 Si, and a large number of new reentrant twins are continuously promoted, so that the branching of the eutectic Mg ₂ Si is much more frequent than that of the unmodified one, and, The significant increase of the twin density makes the eutectic Mg ₂ Si growth characteristics change from the original anisotropy to isotropy, so the eutectic Mg ₂ Si changes sharply from the mode of limited branching and coarse sheet development before modification to A large number of frequently branched fibrous growths lead to qualitative changes in the morphology and size of the final eutectic Mg ₂ Si; in addition, the enrichment of Bi at the front of the liquid-solid interface causes the composition to be supercooled, resulting in the liquid at the front of the interface. The equilibrium crystallization temperature is greatly reduced, thereby reducing the actual undercooling of the liquid phase and reducing the growth rate of the eutectic structure, thereby achieving the purpose of refining the eutectic Mg ₂ Si.

2. The use of Al-Zr master alloy or Zr-containing compound has a significant refining effect on the primary α-Al phase in the _{hypoeutectic Al-Mg 2 Si} alloy, and an appropriate amount of After Zr, the morphology and size of the primary α-Al phase are significantly changed, making it change from coarse columnar dendrites to fine equiaxed crystals. Zr combines with Al in the alloy melt to form ZrAl ₃ phase. The lattice constant of the ZrAl ₃ phase is close to that of the primary α-Al phase, and the mismatch between them is only 0.925%. According to the heterogeneous nucleation theory, the smaller the mismatch, the stronger the bonding force between the two atoms , the easier it is to nucleate on its substrate. Therefore, ZrAl ₃ can be used as the heterogeneous nucleation core of primary α-Al, thereby refining the primary α-Al phase.

3. It has excellent modification and refinement effects on hypoeutectic Al-Mg ₂ Si alloys with different contents of Mg ₂ Si, which expands the application range of this type of alloy.

4. Both Bi modifier and Zr refiner have long-term effects, modification and refinement effects, and are not sensitive to cooling speed. They are suitable for various casting production processes such as metal molds, sand molds, and die _- casting. The adsorption and aggregation state of the Si phase growth interface front is less affected by the cooling rate, so when Bi is added to the melt, whether it is cast in a metal mold or in a sand mold, the eutectic Mg ₂ Si can be effectively refined , that is, the modification effect of Bi on the eutectic Mg ₂ Si phase in the hypoeutectic Al-Mg ₂ Si alloy is less affected by the cooling rate; in addition, because the chemical reaction between bismuth and oxygen is not easy to occur, it is necessary to keep the melt for a long time, During the pouring process, it is not easy to burn out, and ensures the lowest Bi residual amount of the metamorphic eutectic Mg ₂ Si in the melt, so that the metamorphic effect of Bi has a long-term effect.

5. Bi modifier and Zr refiner also have the advantages of easy operation, low cost, safety and environmental protection.

Description of drawings

Figure 1 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy containing 10wt.% Mg ₂ Si phase without refinement of the metal type and modification at 100 times;

Fig. 2 is the metallographic microstructure diagram of the hypoeutectic Al-Mg ₂ Si alloy containing 10wt.% Mg ₂ Si phase without refinement of the metal type and modification at 500 times;

Figure 3 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy with 0.13% Zr refinement of the metal type and 0.41% Bi modification containing 10wt.% Mg ₂ Si phase at 100 times;

Figure 4 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy with 0.13% Zr refinement of the metal type and 0.41% Bi modification containing 10wt.% Mg ₂ Si phase at 500 times;

Fig. 5 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy containing 4wt.% Mg ₂ Si phase without refinement of the metal type and modification at 100 times;

Fig. 6 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy containing 4wt.% Mg ₂ Si phase without refinement and modification of the metal type under 500 times;

Figure 7 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy with 0.09% Zr refinement of the metal type and 0.1% Bi modification containing 4wt.% Mg ₂ Si phase at 100 times;

Figure 8 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy with 0.09% Zr refinement of the metal type and 0.1% Bi modification containing 4wt.% Mg ₂ Si phase at 500 times;

Fig. 9 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy containing 12.5wt.% Mg ₂ Si phase without refinement and modification of the metal type at 100 times;

Figure 10 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy containing 12.5wt.% Mg ₂ Si phase without refinement and modification of the metal type at 500 times;

Figure 11 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy with 0.2% Zr refinement of the metal type and 0.36% Bi modification containing 12.5wt.% Mg ₂ Si phase at 100 times;

Figure 12 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy with 0.2% Zr refinement of the metal type and 0.36% Bi modification containing 12.5wt.% Mg ₂ Si phase at 500 times;

Figure 13 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy containing 10wt.% Mg ₂ Si phase without refinement of the sand mold at 100 times;

Fig. 14 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy containing 10wt.% Mg ₂ Si phase without refinement and modification of the sand mold under 500 times;

Figure 15 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy with 0.17Zr refinement of the sand mold and 0.6% Bi modification containing 10wt.% Mg ₂ Si phase under 100 times;

Figure 16 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy with 0.17Zr refinement of the sand mold and 0.6% Bi modification containing 10wt.% Mg ₂ Si phase under 500 times;

Figure 17 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy containing 13.5wt.% Mg ₂ Si phase without modification of the metal type under 500 times;

Figure 18 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy containing 13.5wt.% Mg ₂ Si phase modified by 0.44% Bi of the metal type under 500 times;

Fig. 19 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy containing 10wt.% Mg ₂ Si phase modified by metal type 0.06% Bi at 500 times;

Figure 20 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy containing 10wt.% Mg ₂ Si phase modified by 0.87% Bi of the metal type under 500 times;

Fig. 21 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy containing 10wt.% Mg ₂ Si phase refined by metal type 0.02% Zr under 100 times;

Figure 22 is a metallographic microstructure diagram of a hypoeutectic Al-Mg ₂ Si alloy with 0.64% Zr refinement of the metal type and 0.47% Bi modification containing 10wt.% Mg ₂ Si phase at 500 times;

Figure 23 is the stress-strain curve of the alloy.

Detailed ways

The present invention is applicable to hypoeutectic Al-Mg ₂ Si alloys, including the addition of various alloying elements, external and endogenous reinforcement phases, the following embodiments of the present invention are only for detailed illustration, but the present invention does not Limited to the following embodiments, all modifications and replacements under the core technical conditions of the present invention fall within the scope of the present invention.

The hypoeutectic Al-Mg ₂ Si alloy composition, modifier, refiner and melting and casting process conditions involved in the present invention are described below:

Alloy composition: the composition of Mg ₂ Si in the Al-Mg ₂ Si alloy of the present invention is limited to 4~12.5wt.%, Al-Mg ₂ Si is a eutectic alloy with a eutectic point of 13.9%, and the eutectic Mg ₂ Si phase is a strengthening phase, and its quantity, shape, size and distribution have a great influence on its mechanical properties. When Mg ₂ Si<4wt.%, the Mg ₂ Si phase is low and the alloy strength is too low; when Mg ₂ Si= 13.9wt.% (eutectic composition) and 12.5wt.%<Mg ₂ Si<13.9wt.% (near eutectic composition), our experiments show that although Bi can eliminate a small amount of blocky primary Mg ₂ Si phase, but the modification effect on eutectic Mg ₂ Si phase is not obvious, see Figure 17 and Figure 18; Mg ₂ Si is in the range of 4~12.5wt.%, with the increase of Mg ₂ Si content, the alloy strength , hardness increases, plasticity and toughness decrease; in practical applications, the number of Mg ₂ Si phases can be reasonably selected according to the requirements of the mechanical properties of the workpiece, so as to determine the final alloy composition.

Modifier: The modification effect of Bi modifier on Mg ₂ Si phase in Al-Mg ₂ Si alloy mainly depends on the content of Bi. The best modification effect is when the Bi content in the melt is 0.1~0.6%. When the content is less than 0.1%, the Mg ₂ Si phase disappears in the form of Chinese characters and appears fibrous, but there are still many strips and flakes, showing the lack of deterioration, as shown in Figure 19; when the Bi content in the melt is greater than 0.6% , most of the Mg ₂ Si phase is still not fibrous, but some strips and flakes appear, showing a metamorphic phenomenon, as shown in Figure 20.

Refining agent: The refining effect of Zr refining agent on the primary α-Al phase in Al-Mg ₂ Si alloy mainly depends on the content of Zr, that is, the amount of ZrAl ₃ generated as the heterogeneous nucleation core of primary α-Al When the Zr content in the melt is 0.05~0.2%, it has the best refinement effect. When the Zr content in the melt is less than 0.05%, there is too little ZrAl ₃ formed in the melt, and there are few nucleation sites for the primary α-Al phase. -Al is still a dendrite, showing insufficient refinement, as shown in Figure 21; when the Zr content in the melt is >0.2%, not only will the refinement effect not be enhanced, but the excessive Zr will easily form a ZrBi binary with the modifier Bi Al-Zr-Bi compound or Al-Zr-Bi ternary compound consumes Bi atoms in the melt, resulting in insufficient modification. Although some fibrous Mg ₂ Si phases are formed, most of them are still strips and flakes, as shown in Figure 22.

Smelting process: Al-Mg ₂ Si series alloys contain relatively high Mg content. This invention is a smelting process under the atmosphere, without gas protection or smelting under vacuum, but the burning loss of Mg should be strictly controlled. The measures are: preheat Mg at 300°C and wrap it with aluminum foil, press it into the melt with a graphite bell jar preheated at 300°C until it melts, then add Bi, after a little stirring, add the Al-Zr intermediate alloy, the purpose is to avoid the magnesium block and air at high temperature Direct contact with the oxygen in the solution shortens the melting of magnesium and the holding time of the melt, so that the burning loss of magnesium is controlled at 10~30%. Because of the low melting point of pure Bi, it can be melted by adding it to molten aluminum without standing still, but The Al-10Zr master alloy has a relatively high melting point. After adding it, it needs to stand still for 5-15 minutes, and after it melts, stir the melt for 2-5 minutes to make the Zr evenly distributed.

Example 1:

1. Use Al-15Si master alloy, pure Al and pure Mg to prepare hypoeutectic Al-Mg ₂ Si alloy, in which Mg and Si are added in a proportion of 10.wt% Mg ₂ Si, and the amount of Mg added is: calculated amount + 10% of the burning loss, the balance is pure Al;

2. After cleaning and drying the pure Al and aluminum-silicon master alloy prepared in step 1, put them into the graphite crucible of the resistance furnace, heat the pure Al and Al-15Si master alloy in the resistance furnace, and heat them at 720°C after they are completely melted. ℃, press the pure Mg block wrapped in aluminum foil and preheated to 300℃ into the melt with a graphite bell jar preheated to 300℃, until it melts, and let it stand for 5min;

3. Press 0.1% of the mass of hexachloroethane into the melt obtained in step 2 with a graphite bell jar preheated at 300°C, carry out refining and degassing, stir at 740°C for 3 minutes, and remove the surface of the melt The scum of the obtained refined melt;

4. For the melt obtained in step 3, add pure metal Bi particles to the melt at a temperature of 710 ° C, and let it stand for 2 minutes to obtain a melt with a Bi content of 0.41wt.% mass percentage;

5. Add Al-10Zr master alloy to the melt obtained in step 4 at a temperature of 750°C, and let it stand for 10 minutes. After it melts, stir the melt for 3 minutes to make Zr evenly distributed, and obtain a Zr content of 0.13wt .% mass percentage of the melt;

6. Press hexachloroethane accounting for 0.05% of the mass of the melt into the melt obtained in step 5 with a graphite bell jar preheated at 300°C, carry out refining and degassing, stir at a temperature of 740°C, and refine and remove slag , poured into a metal mold preheated at 250°C at a temperature of 740°C to become a casting.

The specific modification effect is shown in Figure 1, Figure 2, Figure 3 and Figure 4. The primary α-Al phase in the alloy without Bi and Zr is a thick dendrite, as shown in Figure 1, and the Mg ₂ Si phase is thick Chinese characters and laths. shape, see Figure 2; after the addition of Bi and Zr, the primary α-Al phase in the alloy changes from coarse dendrites to fine equiaxed dendrites, see Figure 3, and the Mg ₂ Si phase changes to fibrous and very small The thin strips are shown in Figure 4; the tensile strength and elongation of the alloy were 214.37MPa and 2.01% before refinement and modification, respectively, and increased to 279.44MPa and 7.02% after refinement and modification, as shown in Figure 23.

Example 2:

1. Use Al-15Si master alloy, pure Al and pure Mg to prepare hypoeutectic Al-Mg ₂ Si alloy, in which Mg and Si are added in the proportion of 4.wt% Mg ₂ Si, and the amount of Mg added is: calculated amount + 20% of burning loss, the balance is pure Al;

2. After cleaning and drying the pure Al and aluminum-silicon master alloy prepared in step 1, put them into the graphite crucible of the resistance furnace, heat the pure Al and Al-15Si master alloy in the resistance furnace, and heat them at 720°C after they are completely melted. ℃, press the pure Mg block wrapped in aluminum foil and preheated to 300℃ into the melt with a graphite bell jar preheated to 300℃, until it melts, and let it stand for 5min;

3. Press hexachloroethane accounting for 0.05% of the mass of the melt into the melt obtained in step 2 with a graphite bell jar preheated at 300°C, carry out refining and degassing, stir at 780°C for 1 min, and remove the surface of the melt The scum of the obtained refined melt;

4. For the melt obtained in step 3, add pure metal Bi particles to the melt at a temperature of 730 ° C, and let it stand for 3 minutes to obtain a melt with a Bi content of 0.1wt.% mass percentage;

5. Add Al-10Zr master alloy to the melt obtained in step 4 at a temperature of 800°C, and let it stand for 5 minutes. After it melts, stir the melt for 2 minutes to make Zr evenly distributed, and obtain a Zr content of 0.09wt .% mass percentage of the melt;

6. Press 0.2% of the mass of hexachloroethane into the melt obtained in step 5 with a graphite bell jar preheated at 300°C, carry out refining and degassing, stir at a temperature of 780°C, and refine and remove slag , poured into a metal mold preheated at 250°C at a temperature of 780°C to become a casting.

The specific modification effect is shown in Figure 5, Figure 6, Figure 7 and Figure 8. The primary α-Al phase in the alloy without Bi and Zr is a thick dendrite, as shown in Figure 5, and the Mg ₂ Si phase is thick Chinese characters and laths. shape, as shown in Figure 6; after adding Bi and Zr, the primary α-Al phase in the alloy changes from coarse dendrites to fine equiaxed dendrites, as shown in Figure 7, and the Mg ₂ Si phase changes to fibrous and very small The thin strips are shown in Figure 8; the tensile strength and elongation of the alloy before refinement and modification were 214.37MPa and 2.01%, respectively, and increased to 255.67MPa and 9.25% after refinement and modification, as shown in Figure 23.

Example 3:

1. Use Al-15Si master alloy, pure Al and pure Mg to prepare hypoeutectic Al-Mg ₂ Si alloy, in which Mg and Si are added in a ratio of 12.5wt% Mg ₂ Si, and the amount of Mg added is: calculated amount + 30 % of burning loss, the balance is pure Al;

2. After cleaning and drying the pure Al and aluminum-silicon master alloy prepared in step 1, put them into the graphite crucible of the resistance furnace, heat the pure Al and Al-15Si master alloy in the resistance furnace, and heat them at 720°C after they are completely melted. ℃, press the pure Mg block wrapped in aluminum foil and preheated to 300℃ into the melt with a graphite bell jar preheated to 300℃, until it melts, and let it stand for 5min;

3. Press 0.2% of the mass of hexachloroethane into the melt obtained in step 2 with a graphite bell jar preheated at 300°C, carry out refining and degassing, stir at 670°C for 5 minutes, and remove the surface of the melt The scum of the obtained refined melt;

4. For the melt obtained in step 3, add pure metal Bi particles to the melt at a temperature of 730° C., and let it stand for 1 min to obtain a melt with a Bi content of 0.36wt.% mass percent;

5. Add a Zr-containing compound to the melt obtained in step 4 at a temperature of 720°C, and let it stand for 15 minutes. After it melts, stir the melt for 5 minutes to make Zr evenly distributed, and obtain a Zr content of 0.2wt.%. Melt in mass percent;

6. Press hexachloroethane accounting for 0.1% of the mass of the melt into the melt obtained in step 5 with a graphite bell jar preheated at 300°C, carry out refining and degassing, stir at a temperature of 700°C, and refine and remove slag , poured into a metal mold preheated at 250°C at a temperature of 700°C to become a casting.

The specific modification effects are shown in Figure 9, Figure 10, Figure 11 and Figure 12. The primary α-Al phase in the alloy without Bi and Zr is a thick dendrite, as shown in Figure 9, and the Mg ₂ Si phase is thick Chinese characters and laths. shape, as shown in Figure 10; after adding Bi and Zr, the primary α-Al phase in the alloy changes from coarse dendrites to fine equiaxed dendrites, as shown in Figure 11, and the Mg ₂ Si phase changes to fibrous and very small The thin strips are shown in Figure 12; the tensile strength and elongation of the alloy before refinement and modification were 221.61MPa and 1.82%, respectively, and increased to 287.76MPa and 6.81% after refinement and modification, as shown in Figure 23.

Example 4:

1. Use Al-15Si master alloy, pure Al and pure Mg to prepare hypoeutectic Al-Mg ₂ Si alloy, in which Mg and Si are added in a proportion of 10.wt% Mg ₂ Si, and the amount of Mg added is: calculated amount + 15% of burning loss, the balance is pure Al;

2. After cleaning and drying the pure Al and aluminum-silicon master alloy prepared in step 1, put them into the graphite crucible of the resistance furnace, heat the pure Al and Al-15Si master alloy in the resistance furnace, and heat them at 720°C after they are completely melted. ℃, press the pure Mg block wrapped in aluminum foil and preheated to 300℃ into the melt with a graphite bell jar preheated to 300℃, until it melts, and let it stand for 5min;

3. Press 0.2% of the mass of hexachloroethane into the melt obtained in step 2 with a graphite bell jar preheated at 300°C, carry out refining and degassing, stir at 750°C for 4 minutes, and remove the surface of the melt The scum of the obtained refined melt;

4. For the melt obtained in step 3, add pure metal Bi particles to the melt at a temperature of 710 ° C, and let it stand for 3 minutes to obtain a melt with a Bi content of 0.6wt. % mass percentage;

5. Add a Zr-containing compound to the melt obtained in step 4 at a temperature of 760°C, and let it stand for 12 minutes. After it melts, stir the melt for 4 minutes to make Zr evenly distributed, and obtain a Zr content of 0.05wt. % Melt in mass percent;

6. Press hexachloroethane accounting for 0.05% of the mass of the melt into the melt obtained in step 5 with a graphite bell jar preheated at 300°C, carry out refining and degassing, stir at a temperature of 730°C, and refine and remove slag , poured into the sand mold at a temperature of 730°C.

The specific modification effects are shown in Fig. 13, Fig. 14, Fig. 15 and Fig. 16. Compared with the metal mold, under the sand mold condition, the primary α-Al phase in the alloy without adding Bi and Zr is a dendrite, and it is thicker, as shown in Fig. 13. The Mg ₂ Si phase is thick and lath, as shown in Figure 14; after adding Bi and Zr, the primary α-Al phase in the alloy transforms into a fine equiaxed dendrite, as shown in Figure 15, and the Mg ₂ Si phase changes to Thin strips, as shown in Figure 16; the tensile strength and elongation of the alloy before refinement and modification were 175.96MPa and 1.23%, respectively, and increased to 244.69MPa and 3.83% after refinement and modification, as shown in Figure 23.

Claims (3)

1. A modification and refinement method of a hypoeutectic Al-Mg ₂ Si alloy, characterized in that it comprises the following steps: (1) According to the batching of hypoeutectic Al-Mg ₂ Si alloy containing 4-12.5wt.% Mg ₂ Si phase by mass percentage, the amount of Mg added is: calculated amount + 10~30% of burning loss; (2) After cleaning and drying the pure Al and aluminum-silicon intermediate alloy prepared in step (1), put them into the graphite crucible of the resistance furnace and heat them in the resistance furnace. After they are completely melted, wrap them in aluminum foil at 720 °C Press the pure Mg block preheated at 300°C into the melt with a graphite bell jar preheated at 300°C until it melts, and let it stand for 5 minutes; (3) Press hexachloroethane, which accounts for 0.05~0.2% of the mass of the melt, into the melt obtained in step (2) with a graphite bell jar preheated at 300°C for refining and degassing. Stir at low temperature for 1~5 min, remove the scum on the surface of the melt, and obtain the refined melt; (4) Add Bi particles to the melt obtained in step (3) at a temperature of 670°C to 730°C, and let it stand for 1 to 3 minutes to obtain a melt with a Bi content of 0.1-0.6wt. % by mass; (5) Add Al-10Zr master alloy or Zr-containing compound to the melt obtained in step (4) at a temperature of 720°C~800°C, let it stand for 5~15min, and stir the melt for 2~ 5 min, Zr is evenly distributed to obtain a melt with a Zr content of 0.05-0.2wt.% mass percent; (6) Refining the melt obtained in step (5) according to step (3), pouring the melt into a mold at a temperature of 700°C to 780°C to become a casting or a slab. 2. The modification and refinement method of the hypoeutectic Al-Mg ₂ Si alloy according to claim 1, characterized in that the Bi in step (4) is added in the form of pure metal. 3. The modification and refinement method of hypoeutectic Al-Mg ₂ Si alloy according to claim 1, characterized in that the casting mold described in step (6) is a sand mold or a metal mold preheated at 250°C or other mold.