CN1603030A - Pseudo semisolid thixotropy forming method for high-melting-point alloy - Google Patents

Abstract

A high-melting point fine powder material and another low-melting point coarse powder material are evenly mixed according to a certain volume ratio (generally 7:3, 6:4), and cold and hot compacted into a semi-solid body, and then Then heat the billet to the melting temperature higher than the low melting point material but lower than the melting temperature of the high melting point material, so that the billet is at a pseudo-semi-solid temperature, or placed in the pressure chamber of the die-casting machine to realize pseudo-semi-solid thixotropic die casting, or placed in a closed mold , to achieve pseudo-semi-solid thixotropic forging.

Description

Pseudo-semi-solid thixotropic forming method for high melting point alloys

1. The technical field to which the invention belongs:

Material Processing Engineering

2. Background technology:

There are many powder forming methods, mainly three types: one type of densification process mainly depends on sintering, including hot press sintering (hot press sintering); hot isostatic press sintering (hot isostatic press sintering); activated sintering (activated sintering); microwave sintering). The other type, densification mainly relies on extrusion plastic deformation, which is also accompanied by sintering, including hot hydrostatic extrusion and surface coasting forging. The third type mainly relies on rapid solidification and accumulation forming under the action of self-fluxing, such as powder spray forming (osprey method).

On the basis of the research on the existing methods, the applicant proposes a brand-new forming method, that is, the pseudo-semi-solid thixotropic forming method of high-melting point alloys. It has the characteristics of plastic deformation, less liquid phase junction and rapid solidification. The biggest feature of the process is that the process is simple and can directly form complex ceramics or superalloys and intermetallic compounds, especially nano-ceramics or nano-superalloys. Compound parts.

3. Contents of the invention:

i) Invention principle

The present invention is extended from the study of semi-solid forming mechanism. At the semi-solid temperature, the semi-solid slurry has a primary phase (i.e. high melting point phase - solid phase), and a low melting point phase (i.e. eutectic phase) distributed in the grain boundary. Figure 1 shows 7A04 (LC4 ) The semi-solid structure of the alloy: the primary phase is α and the eutectic phase is distributed around the α phase. Under the action of force, the eutectic phase wraps the primary phase α, flows and fills, solidifies under high pressure and deforms plastically. The present invention is based on this idea, if the high melting point phase is a kind of ceramic fine powder (such as Al ₂ O ₃ , SiC, AlN, Si ₃ N ₄ etc.), or superalloy powder (such as Fe, Ni, Cr etc.), or Intermetallic compound powder (such as TiAl, Ti ₃ Al, etc.). Low melting point is a kind of metal coarse powder (such as Sn, Zn, Al, etc.), according to a certain volume ratio (into 8:2, 7:3, 6:4), uniformly mixed together, showing low distribution of high melting point powder around When the melting point powder is heated to the melting temperature of the low melting point powder, the uniform powder will show the characteristics of a semi-solid slurry, and under pressure, it will produce thixotropic flow, high-pressure solidification and plastic deformation (as shown in Figure 2 of the accompanying drawing).

ii) Process

The technical process is represented by the block diagram in Figure 3 of the accompanying drawings.

iii) Process parameters:

①Powder mixing process parameters:

The powder mixing is carried out on a drum-type powder mixing machine, and chrome-plated steel balls are used. The process parameters are shown in the table (in SiC _p ): Material Mixing time (h) Drum speed(r/min) Steel ball to powder mass ratio 20Vol%Al/ _SiCp 30Vol%Al/ _SiCp 40Vol%Al/ _SiCp 607580 203040 1:11.25:11.5:1

②Cold pressing process parameters:

Use one-way pressure (or two-way pressure) for cold compaction, process parameters: pressure P=100MPa, holding time τ=10min.

③Vacuum degassing:

The degree of vacuum can be selected as required: 10 ^-1 ~ 10 ^-5 mmHg.

④Hot pressing process:

The hot pressing can be carried out by applying unidirectional pressure (or bidirectional pressure). The hot pressing temperature is lower than the melting temperature of the low-melting point powder; the heating adopts gas-protected resistance furnace or induction heating; the choice of lubricant depends on the material of the workpiece.

⑤Secondary remelting process:

Remelting temperature: It should be higher than the liquidus temperature of low melting point alloy powder, and the holding time can be selected according to the shortest dimension of 10sec/mm according to the size of the billet. The remelting temperature is shown in the table below: Material aluminum alloy magnesium alloy tin zinc alloy Tin antimony alloy Remelting temperature, ℃ 680～720 620～640 420～500 250～300

⑥Thixoforming

Pseudo-semi-solid die forging process parameters:

● Mold temperature: >400℃.

● Specific pressure: >100MPa.

● Holding time: >0.5～1.5sec/mm.

● Lubrication: oil colloidal graphite.

Pseudo-semi-solid die-casting process parameters:

● Mold temperature: 200～300℃.

● Specific pressure: 60~100MPa.

● Injection speed: 0.5～1.0m/sec.

● Filling speed: 25~40m/sec.

● Pressure holding time: 5~10sec.

● Lubrication: oil colloidal graphite.

⑦ Positive effects of the invention:

The positive effects of the invention are as follows: i) Compared with traditional powder forming and sintering, it can form more complex powder parts; No need for degreasing and sintering, and the process flow is short; iii) Compared with powder forging, powder pseudo-semi-solid die forging not only has a lower deformation temperature, but also lower deformation force; iv) Powder pseudo-semi-solid forming, low melting point (liquid phase) can be very good It is filled in the gap between high-melting point particles, and after plastic deformation, the two powders are tightly fused together, and its parts have higher performance than traditional powder forming, powder injection, and good quality stability; v) because the forming temperature is much lower than that of nano-powder The crystal growth temperature of the crystal opens a new way for the formation of high melting point nanomaterials.

4. The attached document states:

The main contents of the present invention will be described below in conjunction with the accompanying drawings.

Figure 1 is a microstructure diagram of 7A04 under secondary remelting (t=615°C, τ=5min).

In the drawings, 1. α(Al) phase, 2. Eutectic phase.

Fig. 2 is a microstructure diagram of high melting point powder particles and low melting point powder particles under pressure, producing thixotropic flow, high pressure solidification and plastic deformation.

In the accompanying drawings, 1. high melting point powder particles, 2. low melting point powder.

Figure 3 is a process diagram of the forming method.

Figure 4 is a structural diagram of the screw extruder.

In the attached drawings, 1. Part, 2. Mold, 3. Heater, 4. Powder, 5. Hopper, 6. Feeding port, 7. Rotary drive device, 8. High-speed die device, 9. Shear screw , 10. Spout

Figure 5 is a diagram of a semi-solid thixotropic forging die.

In the accompanying drawings, 1. bolt, 2. upper template, 3. punch backing plate, 4. punch, 5. punch plate, 6. pin shaft, 7. slide plate, 8. guide post, 9. pivot pin, 10. Hook plate, 11. Hook pin, 12. Die, 13. Guide sleeve, 14. Die plate, 15. Locating pin, 16. Lower template, 17. Liquid forging, 18. Backing plate, 19. Ejector , 20. Bolt, 21. Upper concave formwork

5. Application examples

Example 1, V ₂ O ₅ (nm)+Sn alloy (μm), after mixing according to 6:4, put into the funnel 2 in accompanying drawing 4, and send into the high-temperature screw mixer and be heated to Sn alloy fusing point, to mix The material spiral is a piston, which is injected into the die-casting mold at high speed through the nozzle. The characteristics of this example, ready-made equipment can be used, the temperature control is not strict, and the forming is easy to control.

Example 2, Al2O3 (μm) + 2Al2 aluminum powder (μm), mixed according to 6:4, formed into a billet after cold pressing, vacuum degassing, hot pressing, secondary heating and remelting, semi-solid thixotropic forging, mold The figure is shown in Figure 5 of the attached drawing.

Process parameters:

Secondary heating temperature: >700°C.

Mold preheating temperature: >400°C.

Specific pressure: >100MPa.

Holding time: select according to 1sec/mm.

Lubrication: Oil-based graphite.

The shape of the workpiece is a cup-shaped piece with a flange.

6. The purpose and task of the invention

Find a simple, low-cost, fast-forming complex ceramic parts, high-temperature alloy and intermetallic compound parts, nano-material parts, and expand their application in engineering.

Claims (5)

1. The present invention requires the legal protection scope:
2. 1, high-melting-point fine powder material and low melting point corase meal material by 8: 2,7: 3,6: 4, mix cold pressing+be hot pressed into semisolid blank at 5: 5.
3. 2, with the semisolid blank of (1) preparation, carry out the product that pseudo-semisolid die casting or pseudo-semisolid die forging are produced.
4. 3,,, 7: 3,6: 4, mix, cold pressing+hot forming nanometer semisolid blank at 5: 5 according to 8: 2 with high melting point nm dusty material and low melting point micron powder.
5. 4, with the semisolid blank of (3) preparation, carry out pseudo-semisolid die casting, or the product of pseudo-semisolid die forging production.

Images