CN103160717B - A kind of rotten hypereutectic Al-Si alloy extrusion casting forming method of processing - Google Patents

Abstract

A metamorphic processing hypereutectic Al-Si alloy extrusion casting molding method, the molten metal is modified before being poured, and then injected into the mold, and the extrusion head of the extruder is quickly lowered to start pressurizing the molten metal to make the metal The billet is forcibly fed and solidified, and the billet is taken out after pressure maintaining. Through the implementation of the technical solution of the invention, the product quality and various performance indexes produced by the prior art are correspondingly improved, and the casting has high strength and high toughness.

Description

A kind of metamorphic treatment hypereutectic Al-Si alloy extrusion casting molding method

technical field

The invention relates to a extrusion casting forming method, in particular to a method for modifying a hypereutectic Al-Si alloy by extrusion casting.

Background technique

Hypereutectic high-silicon aluminum alloy has good wear resistance, good corrosion resistance, small thermal cracking tendency, high volume stability and low thermal expansion coefficient. It is an ideal alloy for new pistons such as automobiles and motorcycles. . In this material, with the increase of the silicon content, a large amount of primary silicon appears in the structure, especially the primary silicon in the form of thick needles, which severely splits the alloy matrix, and the silicon phase tip and corners will cause stress concentration, which is obvious. Reduce the mechanical properties of the alloy, especially affect its plasticity. At present, there are many methods for refining silicon phase, such as suspension casting method, spray deposition method, ultrasonic vibration method, rapid solidification method, etc. Although these methods have achieved certain effects, due to the limitation of production scale and the excessive requirements Harsh, and thus have been subject to certain restrictions in production. The mechanical properties of hypereutectic high-silicon aluminum alloy castings depend to a large extent on the morphology and distribution of Si phase in the matrix. Therefore, improving the morphology and distribution of eutectic Si phase and primary Si phase can not only improve the alloy Mechanical properties, but also can further improve the wear resistance of the alloy. The modification of the hypereutectic Al-Si alloy is mainly to refine the crystal grains of the primary Si phase, and change the grains of the original massive primary Si phase and the coarse acicular eutectic Si phase into fine grains, so as to improve its comprehensive performance. The modification of the primary Si phase of the hypereutectic Al-Si alloy is mainly by providing foreign crystal cores to the alloy liquid to make it the crystal core of the primary Si phase, thereby increasing the number of crystal cores to inhibit their growth and achieve The purpose of uniform crystal structure refinement. Squeeze casting process is characterized by high material utilization rate, significantly reduced defects such as pores and shrinkage cavities inside castings, refined grains and dense structures, etc., and solidification under pressure can not only refine the alloy structure, but also make A1- The eutectic point of Si alloy shifts to the right, reducing the amount of coarse primary Si phase. Therefore, the method of extrusion casting can also refine the silicon phase in the hypereutectic Al-Si alloy, and the mechanical properties of the alloy can be greatly improved. The above two processes are combined to ensure the refinement of the silicon phase and improve the mechanical properties of the alloy, while the production process is simple and easy to operate.

Contents of the invention

The invention provides a method for preparing a high-strength and tough hypereutectic Al-Si alloy casting, and aims to improve the density, mechanical properties and productivity of the hypereutectic Al-Si alloy casting.

To achieve the above object, the present invention adopts the following technical solutions:

A metamorphic treatment hypereutectic Al-Si alloy squeeze casting molding method, characterized in that: the method is carried out according to the following steps:

The top of the mold is provided with a diversion groove connected to the crucible, and the pouring device is used to inject the molten metal into the mold through the diversion groove. The composition of the molten metal is: silicon 17.0-19.0%, copper 1.0-2.0%, magnesium 0.3-0.7% %, nickel 0.5-1.0%, iron 0.5-1.0%, manganese 0.3-0.7%, chromium 0.5-1.0%, molybdenum 0.3-0.7%, phosphorus 0.07-0.15%, the sum of impurities ≤ 0.5%, the balance is aluminum, and The extrusion head of the extruder is lowered rapidly, and the molten metal is started to be pressurized, so that the metal billet is forcibly fed and solidified, and the billet is taken out after the pressure is maintained.

Before the molten metal is poured into the mould, a modificator is added for metamorphic treatment, kept warm for 5-15 minutes, and then poured.

The modificator is strontium, which is added in an amount of 0.02-0.06% of the total mass of the molten metal. It can be added in the form of a master alloy, or it can be pressed into the molten metal as a powder and stirred, or it can be added together with a refining agent.

The modificator is phosphorus, which is added in an amount of 0.5-1.5% of the total mass of the molten metal. It can be added in the form of an intermediate alloy, or it can be pressed into the molten metal as a powder and stirred, or it can be added together with a refining agent.

Before the molten metal is injected into the mould, the mold needs to be heated to 200-300° C., and the mold should be coated with paint.

When the molten metal is poured into the mould, the pouring temperature of the molten metal is 690-780°C.

The descending speed of the extrusion head is 0.1mm/s-12mm/s, and the specific pressure is 70MPa-1500Mpa.

The pressure holding time is 10s-60s.

Through the implementation of the technical scheme of the invention, the method is simple to operate, easy to control, high in product quality, and can improve the qualification rate and production efficiency of high-silicon hypereutectic Al-Si alloy products.

Description of drawings:

Fig. 1 is the structural representation of extrusion casting metal ingot mold;

Fig. 2 is the unmodified hypereutectic Al-17.5Si alloy phase structure of metal mold gravity casting;

Fig. 3 is the metamorphic hypereutectic Al-17.5Si alloy phase structure of metal mold gravity casting;

Fig. 4 is the unmodified hypereutectic Al-17.5Si alloy phase structure of metal mold squeeze casting;

Fig. 5 is the metamorphic hypereutectic Al-17.5Si alloy phase structure of metal mold squeeze casting;

Fig. 6 is a schematic diagram of the forming process of the present invention.

Explanation of reference signs:

1. Extrusion head, 2. Diversion groove, 3. Cover plate, 4. Metal billet cavity, 5. Heating box, 6. Choke block, 7. Bolt rod, 8. Ejector rod.

detailed description:

The present invention adopts metal molds and squeeze casting methods to improve the molding technology, wherein the equipment for preparing hypereutectic Al-Si alloy products includes extruders, metal billet molds and heat treatment furnaces, wherein the extrusion metal billet mold periphery It is a resistance wire, which uses resistance wire to heat the mold and is equipped with a thermocouple to control the temperature of the mold. Above the mold is the extrusion head that can quickly descend to the position that needs to be extruded. ejection mechanism. The requirement for the extrusion machine is that the extrusion force can be accurately controlled and the extrusion speed can be guaranteed. When heating in the heat treatment furnace, the temperature must be uniform and the temperature control must be accurate, otherwise the related performance may decrease due to the uneven structure of the billet, which cannot meet the requirements.

The present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, the top of the mold is provided with a diversion groove 2 connected to the crucible, and the molten metal is injected into the metal billet cavity 4 of the mold through the diversion groove 2 through the pouring device, and the bottom of the metal billet cavity 4 is set There is choke block 6. The mold needs to be heated and coated with a heating box 5 before injection. The composition of molten metal by weight percentage is: silicon 17.0-19.0%, copper 1.0-2.0%, magnesium 0.3-0.7%, nickel 0.5-1.0%, iron 0.5-1.0%, manganese 0.3-0.7%, zirconium 0-0.4%, Cerium 0-0.28%, Lanthanum 0-0.12%, Praseodymium 0-0.02%, Niobium 0-0.08%, Chromium 0.5-1.0%, Molybdenum 0.3-0.7%, Phosphorus 0.07-0.15%, the sum of impurities ≤ 0.5%, the balance for aluminum. Firstly, the molten metal is subjected to a metamorphic treatment, and then kept warm for 5-15 minutes. Afterwards, the molten metal is poured, and the extrusion head 1 is quickly pressed down to reach the cover plate 3, so as to ensure that the molten metal is subjected to the device at one time in a liquid state. set pressure. During this process, the metal ingot can be forcibly fed and solidified by means of the extrusion force, kept under pressure for a period of time, the extrusion head 1 is raised, and the ingot is slowly pushed out by the ejector pin 8 . Relevant process parameters: the pouring temperature of liquid metal is 780°C, the mold temperature is 300°C, the extrusion speed is 8mm/s, the specific pressure is 1000MPa, the holding time is 40s, the billet diameter is Φ70mm, and the height is 100mm.

Take off the formed metal billet, remove the burrs, peripheral oxide scales and impurities, the overall process flow of the present invention is shown in Figure 6. In this process, due to the effect of pressure, the solidification equilibrium state is destroyed, and the solid solubility of the alloy solidified under pressure is expanded. solidification. On the one hand, the solidification temperature of the molten metal rises under pressure. As a result, the matrix has already begun to nucleate and grow before the alloy elements have time to nucleate and grow, so that the alloy elements are forced to split in the matrix dendrites. In the gap between, a eutectic structure is formed. On the other hand, there are also many alloying elements dissolved in the matrix, which increases the solid solubility, which can be explained by the relationship between the diffusion coefficient and the melt viscosity, so that the extruded billet has good plasticity.

In addition, the modification process is also the key of the present invention. The addition of the modification agent can form metal oxide or intermetallic compound particles as crystal nuclei with a certain component or impurity in the alloy liquid, and reduce the nucleation work and increase the nucleation rate. The specific composition of the modifier can vary according to the alloy liquid, but there is a unified principle:

It cannot react with the metal elements in the alloy liquid, causing the elements to cancel each other out and weaken the metamorphic effect;

To ensure that its metamorphic effect has a certain long-term effect, and there is no incubation period;

Ensure that its cost is low and will not have a great impact on the cost of the entire product;

The modification agent must be added to improve the structure and morphology of the alloy, and improve the mechanical properties of the alloy. It has no adverse side effects on the original alloy and is not harmful to the human body;

The density is similar to the alloy liquid, the melting point is between the modification temperature of the alloy liquid and the pouring temperature, and it is easy to float and slag after modification;

According to the specific alloy liquid, consider its addition amount and addition method.

For example, the strontium modifier acts on the eutectic Si phase to change its needle-like shape, and the added content is 0.02-0.06% of the total mass; the phosphorus modifier acts on the primary Si phase to change its angular block shape, and the added content is 0.5-1.5% of the total mass.

Adding method: It can be added in the form of master alloy, or it can be pressed into alloy liquid as powder and stirred, and it can also be added together with refining agent.

In the following, only the extrusion casting molding process of Al-17.5Si binary alloy will be used to illustrate the problem.

Figures 2 and 3 are the comparisons of the gravity casting structures. It can be clearly seen that the gravity casting alloy structure is mainly composed of primary Si phase, eutectic Si phase structure and Al matrix. Without modification treatment, it can be seen from Figure 2 that the primary Si phase is thick and massive, with irregular shapes and sharp edges and corners, which severely splits the Al matrix and seriously reduces the mechanical properties of the alloy, especially the plasticity. The eutectic Si phase is in the shape of needles or slabs, and is distributed in the Al matrix in a disorderly manner. It is easy to generate stress concentration under stress, resulting in the generation of crack sources and reducing the performance of the alloy. After adding strontium modification treatment, it can be seen from Figure 3 that the primary Si phase is still coarse and massive, which is basically the same as that of the unmodified one, but the eutectic Si phase has undergone significant changes, that is, the morphology of the eutectic Si phase has begun to change. The transformation from sheet to branch, that is, the transformation to metamorphic structure, thus reduces the stress concentration and the performance of the alloy is also significantly improved.

Figures 4 and 5 are comparisons of squeeze casting structures. The alloys with the same composition, the structure solidified under pressure is composed of primary α-Al dendrite structure and eutectic Si phase, and the primary Si phase can hardly be found. Without modification treatment, it can be seen from Figure 4 that the primary α-Al dendrite structure is very developed and dense, which is conducive to the improvement of alloy performance. The eutectic Si phase changes from the original needle sheet or lath to very fine layer sheet, Thereby reducing the splitting effect on the matrix and reducing the possible stress concentration in the matrix, thus improving the mechanical properties of the alloy to a large extent, especially the plasticity is greatly improved. After adding strontium modification treatment, it can be seen from Figure 5 that the primary α-Al dendrite structure is still very developed and dense, which is also conducive to the improvement of alloy properties, and the eutectic Si phase changes from the original very fine layer sheet to dense The fine coral-like tissue is distributed among the dendrites. Because of this, the mechanical properties of the alloy have been further improved, as shown in Table 1:

Table 1.

Below is the specific embodiment of the present invention:

Example 1:

Step 1. Metal liquid modification treatment, adding 0.02% of strontium in the form of master alloy to the total mass of the metal liquid, and then keeping it warm for 5 minutes;

Step 2. Utilize the pouring device to inject the molten metal after the metamorphic treatment into the mold through the diversion groove. The components of the molten metal are by weight percentage: 17.0% silicon, 1.0% copper, 0.3% magnesium, 0.5% nickel, 0.5% iron, manganese 0.3%, chromium 0.5%, molybdenum 0.3%, phosphorus 0.07%, the sum of impurities ≤ 0.5%, the balance is aluminum, before the molten metal is injected into the mold, the mold needs to be heated to 200°C, and the mold should be coated with paint; the molten metal injection In the mold, the pouring temperature of the molten metal is 690°C;

Step 3. Rapidly lower the extrusion head of the extrusion machine, and start to pressurize the molten metal, so that the metal ingot is forcibly fed and solidified. The extrusion head descends at a speed of 0.1mm/s, and the specific pressure is 70Mpa;

Step 4. After the metal ingot is kept under pressure, the ingot is taken out, and the time for keeping the pressure is 10s.

Example 2:

Step 1. Metal liquid modification treatment, press strontium powder accounting for 0.06% of the total mass of the metal liquid into the metal liquid and stir, and then keep warm for 15 minutes;

Step 2. Utilize the dumping device to inject the metal liquid after the metamorphic treatment into the mold through the diversion groove. The components of the metal liquid are by weight percentage: 19.0% silicon, 2.0% copper, 0.7% magnesium, 1.0% nickel, 1.0% iron, manganese 0.7%, chromium 1.0%, molybdenum 0.7%, phosphorus 0.15%, the sum of impurities ≤ 0.5%, the balance is aluminum, before the molten metal is injected into the mold, the mold needs to be heated to 300°C and coated with paint on the mold; molten metal injection In the mold, the pouring temperature of the molten metal is 780°C;

Step 3. Rapidly lower the extrusion head of the extrusion machine, and start to pressurize the molten metal, so that the metal ingot is forcibly fed and solidified. The extrusion head descends at a speed of 12mm/s, and the specific pressure is 1500Mpa;

Step 4. After the metal ingot is kept under pressure, the ingot is taken out, and the time for keeping the pressure is 60s.

Example 3:

Step 1. Metal liquid modification treatment, adding strontium accounting for 0.04% of the total mass of the metal liquid together with the refining agent into the metal liquid, and then keeping it warm for 10 minutes;

Step 2. Utilize the pouring device to inject the molten metal after the deterioration treatment into the mold through the diversion groove. The components of the molten metal are by weight percentage: 18.0% silicon, 1.5% copper, 0.5% magnesium, 0.8% nickel, 0.7% iron, manganese 0.6%, 0.8% chromium, 0.5% molybdenum, 0.1% phosphorus, the sum of impurities ≤ 0.5%, the balance is aluminum, before the molten metal is injected into the mold, the mold needs to be heated to 250 ° C and coated with paint on the mold; molten metal injection In the mold, the pouring temperature of the molten metal is 750°C;

Step 3. Rapidly lower the extrusion head of the extrusion machine, and start to pressurize the molten metal, so that the metal billet is forcibly fed and solidified. The extrusion head descends at a speed of 8mm/s, and the specific pressure is 500Mpa;

Step 4. After the metal ingot is kept under pressure, the ingot is taken out, and the time for keeping the pressure is 30s.

Example 4:

Step 1. Metal liquid modification treatment, adding phosphorus accounting for 1% of the total mass of the metal liquid in the form of an intermediate alloy, and then keeping it warm for 8 minutes;

Step 2. Utilize the pouring device to inject the metal liquid after the metamorphic treatment into the mold through the diversion groove. The components of the metal liquid are by weight percentage: 17.5% silicon, 1.3% copper, 0.4% magnesium, 0.6% nickel, 0.9% iron, manganese 0.5%, 0.6% chromium, 0.4% molybdenum, 0.09% phosphorus, the sum of impurities ≤ 0.5%, the balance is aluminum, before the molten metal is injected into the mold, the mold needs to be heated to 230 ° C and coated with paint on the mold; molten metal injection In the mold, the pouring temperature of the molten metal is 700°C;

Step 3. Rapidly lower the extrusion head of the extrusion machine, and start to pressurize the molten metal, so that the metal billet is forcibly fed and solidified. The extrusion head descends at a speed of 10mm/s, and the specific pressure is 100Mpa;

Step 4. After the metal ingot is kept under pressure, the ingot is taken out, and the time for keeping the pressure is 40s.

Example 5:

Step 1. Metal liquid modification treatment, the phosphorus powder accounting for 0.5% of the total mass of the metal liquid is pressed into the metal liquid and stirred, and then kept for 12 minutes;

Step 2. Utilize the pouring device to inject the metal liquid after the metamorphic treatment into the mold through the diversion groove. The components of the metal liquid are by weight percentage: 18.5% silicon, 1.8% copper, 0.6% magnesium, 0.7% nickel, 0.8% iron, manganese 0.4%, 0.9% chromium, 0.6% molybdenum, 0.12% phosphorus, the sum of impurities ≤ 0.5%, the balance is aluminum, before the molten metal is injected into the mold, the mold needs to be heated to 280 ° C and coated with paint on the mold; molten metal injection In the mold, the pouring temperature of the molten metal is 770°C;

Step 3. Rapidly lower the extrusion head of the extrusion machine, and start to pressurize the molten metal, so that the metal billet is forcibly fed and solidified. The extrusion head descends at a speed of 1.0mm/s, and the specific pressure is 1000Mpa;

Step 4. After the metal ingot is kept under pressure, the ingot is taken out, and the time for keeping the pressure is 20s.

Embodiment 6:

Step 1. Metal liquid metamorphism treatment, adding phosphorus accounting for 1.5% of the total mass of the metal liquid together with the refining agent into the metal liquid, and then keeping it warm for 6 minutes;

Step 2. Utilize the pouring device to inject the metal liquid after the metamorphic treatment into the mold through the diversion groove. The components of the metal liquid are by weight percentage: 19% silicon, 1.1% copper, 0.45% magnesium, 0.9% nickel, 0.6% iron, manganese 0.55%, 0.7% chromium, 0.45% molybdenum, 0.14% phosphorus, the sum of impurities ≤ 0.5%, the balance is aluminum, before the molten metal is injected into the mold, the mold needs to be heated to 210°C and coated with paint on the mold; molten metal injection In the mold, the pouring temperature of the molten metal is 730°C;

Step 3. Rapidly lower the extrusion head of the extrusion machine, and start to pressurize the molten metal, so that the metal billet is forcibly fed and solidified. The extrusion head descends at a speed of 0.3mm/s, and the specific pressure is 800Mpa;

Step 4. After the metal ingot is kept under pressure, the ingot is taken out, and the time for keeping the pressure is 50s.

Claims (1)

1. the rotten hypereutectic Al-Si alloy extrusion casting forming method of processing, is characterized in that: described method is carried out according to following steps:

Die tip is provided with the guiding gutter being connected with crucible, utilize tilting device that molten metal is injected to mould by guiding gutter, molten metal composition is by weight percentage: silicon 17.0～19.0%, copper 1.0～2.0%, magnesium 0.3～0.7%, nickel 0.5～1.0%, iron 0.5～1.0%, manganese 0.3～0.7%, chromium 0.5～1.0%, molybdenum 0.3～0.7%, phosphorus 0.07～0.15%, impurity summation≤0.5%, surplus is aluminium, and the extrusion head of extruder is declined rapidly, start molten metal to pressurize, make the feeding solidifying by force of metal billet, after pressurize, billet is taken out,

The decrease speed of extrusion head is 0.1mm/s～12mm/s, and specific pressure is 70MPa～1500Mpa;

Molten metal injects before mould, adds alterant processings of go bad, is incubated 5-15min, and then pours into a mould;

When alterant is strontium, addition is the 0.02-0.06% of molten metal gross mass, adds, or is pressed into molten metal and stirs as powder, or add together with refining agent with intermediate alloy form;

Or when alterant be phosphorus, addition is the 0.5-1.5% of molten metal gross mass, adds, or be pressed into molten metal and stir as powder with intermediate alloy form, or adds together with refining agent;

Before molten metal injects mould, mould need to be heated to 200～300 DEG C, and on mould, scribbles coating;

When molten metal injects mould, the pouring temperature of molten metal is 690～780 DEG C; Dwell time is 10s～60s.