JPH0770761A - Surface treating method of aluminum and alloy thereof by discharge in liquid - Google Patents

Abstract

PURPOSE:To efficiently form the surface cured layer high in hardness especially, excellent in wear resistance and favorable in adhesion and dimensional precision on the surface of Al and its alloy. CONSTITUTION:The molding body obtained by adding the binding metal of Al powder, Sn powder or Zn powder to the element powder or the powdery mixture of more than two kinds of the metal easy to be carbonized such as Ti, Zr, V, Ta, Cr, Mo, W, Mn, or Nb and by being subjected to a compression molding in a desired shape is used as the electrode for an electric discharge machining. The surface layer mixing above metal and its carbide is formed on the surface of the material to be treated by subjecting Al and its alloy being the material to be treated to the electric discharge machining using as the other electrode in the working liq. in which carbon is formed by decomposition by discharge.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for surface hardening aluminum and its alloys by submerged discharge, and particularly to a die for reducing weight by making aluminum for improving fuel cost in aircrafts, automobiles, etc. It is possible to provide a sufficient hardness (Hv 300 to 1500) and a high shape accuracy to a portion of an engine part or the like that requires wear resistance.

[0002]

2. Description of the Related Art When imparting wear resistance to aluminum and its alloys, Al having a high hardness (Hv200) represented by Al-Si alloys has hitherto been used.
Alloys have been applied, but they have poor machinability and insufficient hardness.

Further, the following curing treatments are also performed, but each has its advantages and disadvantages. (1) Hard alumite: Thickness 1 μm or less, hardness Hv450
Below (2) Ion nitriding: thickness of several μm / 5 hr, hardness Hv2000 (3) Ion beam mixing: thickness of 18 to 36 μm / h
r, hardness Hv 1000 or less (4) Thermal CVD (WC): thickness 620 μm / hr, hardness Hv 2
000〃 (W): Thickness 620 μm / hr, hardness Hv50-60
0 However, processing temperature Tp = 600 ° C. (5) Plating: Ni-P plating, Cu plating, etc. are performed, and then diffusion is performed by heating. In many cases, the plating time is several hours and the heating temperature is 400 to 600 ° C. Thickness is a few μm
.About.60 .mu.m and hardness is Hv450-800. (6) Thermal spraying (Mo, TiN / Ti): thickness 300 μm, hardness H
v500-600

Of the above-mentioned surface coatings, thermal spraying has a high film-forming rate, but the adhesion is poor, and reprocessing is required to obtain shape accuracy. In the cases of (1) to (5), the adhesion is good, but the film formation rate is slow, and a vacuum tank, an electrolytic tank, etc. are required as processing equipment. In addition, those requiring high temperature treatment have poor shape accuracy.

In addition, there are alloying methods such as arc melting, plasma melting, electron beam alloying and laser alloying, which have the advantages of good adhesion and short treatment time, but due to macroscopic segregation. There are drawbacks such as tissue defects, generation of pores, and the need to rework the surface. Also, their machining characteristics are generally poor.

The above-mentioned conventional techniques have many drawbacks as surface hardening techniques for aluminum and its alloys. That is, it is difficult to satisfy the following plural conditions, to be economically viable, and to keep the working environment clean. Further, it is difficult to limit the area that is cured with high dimensional accuracy. Increase the film formation rate. Good adhesion. A thick film of several tens of μm can be formed. If necessary, sufficient hardness can be controlled. Does not give dimensional changes to the base material due to heat. No cracks or the like occur on the surface layer. Good workability (no vacuum tank required, no special dustproof device, easy automation).

The present invention solves the above-mentioned drawbacks of the prior art and efficiently forms a surface-hardened layer on the surface of aluminum and its alloys, which has particularly high hardness and excellent wear resistance, and also has good adhesion and dimensional accuracy. An object is to provide a surface treatment method that can be formed.

[0008]

The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, have found that it is possible to apply the pulse discharge technique in liquid.

That is, according to the present invention, an electrode for electric discharge machining is formed by adding a binding metal to a powder of a metal which is easily carbonized or a mixed powder of two or more kinds, and compression-molding the powder into a desired shape.
In the working fluid that decomposes and produces carbon by electric discharge, aluminum and its alloy, which is the material to be treated, are subjected to electrical discharge machining as the other electrode to form a surface layer on the surface of the material to be treated in which the above metal and its carbide are mixed. The gist is a surface treatment method of aluminum and its alloys by in-liquid discharge.

According to another aspect of the present invention, the electric discharge machining described above is used as a primary treatment, and after the primary treatment is performed, an electric discharge machining (secondary treatment) is performed by using an electrode made of a material with relatively little wear. Thus, the gist is a surface treatment method by in-liquid discharge of aluminum and its alloy, which is characterized by remelting the surface layer formed by the primary treatment to form a dense surface layer and improving dimensional accuracy.

[0011]

The present invention will be described in more detail below.

For the working electrode used in the present invention, a single powder of a metal that is easily carbonized or a mixed powder of two or more kinds of powders, to which a binding metal is added and compression-molded into a desired shape, is used. Metals that are easily carbonized include Ti, Zr, V, Ta, Cr, and M.
Examples include o, W, Mn, Nb or alloys containing these elements. Especially when an electrode containing 1 to 10 wt% of Nb is used, the toughness of the surface layer can be enhanced.

As the binding metal, any metal may be used as long as it has a function of a binder when the powder of the above metal is molded, and for example, one or more kinds of aluminum powder, tin powder and zinc powder are added.

For the other electrode, aluminum or various aluminum alloys which are the materials to be treated are used. It is desirable that the material to be processed has a desired processed shape in advance by ordinary electric discharge machining.

A liquid which decomposes and produces carbon by electric discharge is used as the electric discharge machining liquid. Examples thereof include petroleum, kerosene, and liquids containing carbon compounds. Such a working liquid is decomposed by electric discharge to generate carbon, and reacts with the above-mentioned metal that is easily carbonized to form a carbide, whereby a surface layer in which the carbide and the metal are mixed on the surface of the material to be treated. To form. The mixing ratio of the carbide in the surface layer can be controlled by changing the electrical discharge conditions (current value, pulse width, duty factor, etc.) and the discharge flow rate of the working liquid.

The electric discharge machining conditions may be appropriately determined in consideration of the mixing ratio of carbides in the surface layer, the film forming thickness and the like.

Further, in the present invention, the above-mentioned electric discharge machining is used as a primary treatment, and the surface layer obtained by performing this primary treatment is subjected to an electric discharge machining using an electrode made of a material with relatively little wear as a secondary treatment. By performing the above, the surface layer formed by the primary treatment can be remelted to form a dense surface layer, and the dimensional accuracy can be improved.

In the electric discharge machining of the secondary treatment, instead of the electrode for the primary treatment, an electrode made of a material with relatively low wear such as Cu, graphite and tungsten is used.
The shape of this electrode is preferably an electrode having a desired shape that enables correction processing to reach a target dimension. For that purpose, the electrode (the electrode which is less likely to be worn) when the shape is processed by the usual electric discharge machining prior to the primary processing may be used as the secondary processing electrode.

In order to perform the correction processing to reach the target dimension, the discharge treatment is performed while the dimension of the surface layer is corrected by measuring the thickness or the shape.

Next, examples of the present invention will be described.

[0021]

Example 1 This example is an example in which primary treatment (electric discharge machining) was performed using the apparatus shown in FIGS. 1 and 2. In the figure, reference numeral 1 denotes a processing electrode made of a green compact, which is adhered to the tip of a metal rod 5 made of copper or the like using a conductive adhesive 4. The electrode 1 is connected to an electric discharge power source 10 (anode and cathode can be reversed), and is immersed in a machining tank 3 ′ containing a machining liquid 3.

The machining electrode 1 can be moved up and down by the servo device 6, and the distance between the discharge electrodes can be adjusted. 15
Is a Z-axis scale, 16 is a pointer indicating the progress position on the spindle side, and this signal is a program device 13 for discharge electrical conditions.
Entered in. Reference numeral 11 is a current transformer for detecting the discharge current, and 12 is a synchroscope for observing the discharge current voltage. Reference numeral 14 denotes a machining fluid discharge amount programming device, which controls a machining fluid feed pump 8 for feeding the machining fluid 7 in the tank 7 '. Reference numeral 9 is an ejector for generating a jet of the working fluid.

Reference numeral 18 denotes a material to be processed which is a base material (Al or its alloy) and is connected to the electric discharge machining power source 10. 2 is the surface of the material to be treated. An ultrasonic thickness gauge 17 for directly measuring the thickness of the surface layer is provided on the back surface of the base material 18, and the signal thereof is input to the program device 13 for electrical discharge conditions.

First, aluminum alloy A is used as the material to be treated.
Flat plate of DC12 (including 11.2% Si and 2.74% Cu)
(Thickness of 2.5 mm) was used. For the electrode material, Ti powder, which is a metal that is easily carbonized, and Al powder as a binding metal, were used as Ti:
A mixture powder (powder particle size 44 μm or less) mixed at a ratio of Al = 36: 64 (wt%) is compression molded (molding pressure Pe: 24.5 to
A powder electrode of 441 MPa) was used. The electric discharge machining liquid and electric discharge conditions are as follows.

<Electric Discharge Machining Fluid> Machining fluid: kerosene, jet pressure Pi: 0 to 78 KPa <Discharge electrical condition> Pulse width (time during which one discharge current flows) τp: 32
Discharge current value (maximum current value) Ip: 5 to 24 A Effective pulse Rp (Duty factor D) = τp / (τp + τ)
r) = 0.8 to 68% (where τr: rest time)

Electrical discharge machining (primary treatment) was performed under the above conditions to form a surface layer on the surface of the base material. From the X-ray diffraction pattern of FIG. 3, it was confirmed that this surface layer was a surface layer composed of TiC, TiAl, Al and TiAl ₃ . The discharge treatment conditions when the surface layer in the figure is obtained are: pulse width τp = 512 μs, discharge current value Ip = 20 A, Rp = D = 33% (τr: 1040
μs), Pe: 441 MPa, working fluid jet pressure Pi = 9.8K
It is Pa.

FIG. 4 shows the results of examining the relationship between the pulse width τp, the surface layer thickness h, and the volume ratio of the carbide TiC in the surface layer. Although the processing time is constant at 3 minutes, it can be seen that the thickness h of the surface layer and the volume fraction of the carbide TiC in the surface layer increase as the pulse width τp increases. The processing time is about 2 minutes and the thickness reaches about 50 μm, which is a high film forming rate.

FIG. 5 shows the results of examining the effects of the processing time tw and the Ti grain size on the volume fraction of the carbide TiC in the surface layer. The processing time is about 150 seconds and the volume ratio of TiC is 50.
%, There is a tendency that the volume ratio of TiC increases as the processing time increases. Further, the smaller the Ti grain size, the more quickly the TiC volume ratio increases.

FIG. 6 shows the results of examining the relationship between the volume ratio of TiC in the surface layer when the discharge treatment is continuously performed and when the discharge treatment is intermittently performed, depending on the magnitude of the jet pressure Pi of the working fluid. The volume ratio of TiC is higher when it is continuously performed than when it is intermittent, and the volume ratio of TiC is higher when the jet pressure Pi of the working fluid is smaller. This indicates that removing the carbon generated by the discharge reduces the volume ratio.

FIG. 7 shows the results of examining the influence of the jet pressure Pi of the working liquid on the surface layer thickness h. The larger the jet pressure Pi, the smaller the surface layer thickness h.

FIG. 8 shows the results of examining the element distribution in the surface layer cross section. The composition is graded in the surface layer, and the outermost surface of the surface layer contains a large amount of Ti and C components, and A constituting the base material
There are few components of l and Si. Therefore, the outermost surface shows that the volume ratio of TiC is high. This means that, as shown in the hardness distribution of the surface layer in FIG. 9, the hardness of the outermost surface is high, the base material component increases as it approaches the surface of the base material, and the hardness decreases. The object acts as a buffer against the surface composition and the internal structure even when the operating temperature is high or low, so that a surface structure that prevents the occurrence of cracks can be provided.

[0032]

Example 2 In this example, based on various experiments of Example 1, the hardness of the outermost surface as the surface layer is high (the concentration of TiC is high), and the concentration of TiC is low on the innermost surface in contact with the base material. This is an example of forming a surface layer having such a distribution.

Since it is desired to reduce the TiC concentration in the initial stage of the electric discharge process, the pulse width τp is selected to be as narrow as about 20 μs, and the machining liquid flow is programmed to be strongly jetted. With the passage of time, the pulse width τp is τp = 100μs, τp = 500μ
If s is set to be large, three layers having different TiC concentrations can be formed as the surface layers.

At this time, at which stage each program is switched may be monitored using an ultrasonic thickness gauge 17 which directly measures the thickness of the surface layer. In other cases, since the powder compact electrode is made to consume much, the progress 16 on the spindle side with respect to the Z-axis scale 15 cannot be directly used as the machining progress. The ratio (adhesion rate ε) of the adhesion thickness H to the processing material and the electrode wear length L is investigated for each material of the powder compact electrode, and the adhesion thickness H is used from the following equation. That is, H = L-
Since S (where S is the degree of progress of the main axis), H = S / (1
/ Ε-1). If ε = 0.1, then H−
It becomes S / 9, and the adhesion thickness H can be known from the progress S of the spindle.

[0035]

Example 3 This example is an example of forming a surface layer having toughness. In the experiment, as the green compact electrode, an electrode mixed with Ti: Al = 36: 64 (wt%) as in Example 1,
An electrode mixed with Ti: Al: Nb = 32: 58: 10 (wt%) was used, and Pe: 441 MPa, discharge current value.
(Maximum value of current) Ip = 20A, pulse width τp = 200μ
Under the conditions of s, effective pulse Rp = 0.33%, the discharge treatment was performed with the working liquid jet pressure Pi = 9.8 KPa. As a result, a surface layer having a thickness of about 100 μm was obtained. When a bending test was conducted, cracks occurred at 90 ° bending in the case of (Ti + Al) green compact electrode, but (Ti + Al + N
b) In the case of the powder compact electrode, no crack was generated at 90 ° bending.

[0036]

[Embodiment 4] This example is an example in which the electrical discharge machining of the secondary treatment is performed after the electrical discharge treatment of the primary treatment is performed. As shown in Example 1
For the surface layer obtained by the primary treatment with the (Ti + Al) green compact electrode, an electric discharge treatment is performed using an electrode made of a material that has a shape that substantially corresponds to the shape of the workpiece to be processed and that consumes relatively little. Next process) is performed.

FIG. 10 shows an apparatus for secondary processing. In addition to the apparatus for primary treatment shown in FIG.
A base material moving mechanism 20 is provided. The electrode used when the shape is processed by the usual electric discharge machining is replaced with the electrode for primary treatment after the primary treatment and used as the electrode for secondary treatment. If the electrode low consumption electrical condition is used as the processing condition, the progress of the processing machine spindle (servo mechanism 6) may be used as the processing progress.

In order to accurately measure the thickness of the coating layer and correct it by the secondary treatment, the following steps are performed.

First, after the shape of the material to be processed is processed by ordinary electric discharge machining, the machining electrode is housed in the exchange mechanism and a measuring tool is attached from the exchange mechanism, and the upper surface of the material to be processed is used as a reference. The depth is measured and stored in a storage device (depth D).

Next, when the primary processing is performed and the secondary processing is switched, first, if the surface layer thickness H is determined, the surface layer thickness is subtracted from the value previously stored in the storage device to determine the penetration depth of the spindle. Define M (M = D-H).

In the secondary processing (correction processing), only M ingress processing is performed, but after the processing is completed, the measurement tool is automatically switched to perform measurement. When the thickness is within the allowable range, the work is completed. These process drawings are shown in FIG.

FIG. 12 shows an example in which a secondary treatment (correction processing) is performed on the die surface treatment. The mold has a shape accuracy of ± 0.01
It is often necessary to keep it around mm. As can be seen from FIG. 4, the thickness of the surface layer obtained by the primary treatment using the powder compact electrode reaches several tens of μm by electric discharge machining within a few minutes. Therefore, in order to maintain the shape accuracy within ± 0.01 mm (± 10 μm), secondary processing may be required. In FIG.
(1) shows a state in which a die shape is machined by electric discharge machining using a normal electric discharge machining electrode (Cu), and (2) shows a green compact electrode for primary treatment (Ti: Fe = 50: 50 (wt%))
Shows the state in which the surface layer was formed by the electric discharge treatment of the primary treatment, and (3) shows that the electrode is again replaced with a normal electric discharge machining electrode and the secondary treatment (correction machining) is performed with a machining accuracy of ± 0.01 mm. It shows the finished state.

[0043]

As described in detail above, according to the present invention,
Surface hardening treatment with fast film deposition rate of several tens of μm, high adhesion, sufficient hardness as necessary, no dimensional change due to heat effect on the base material, and no cracks in the surface layer It can be performed. In addition, it does not require a vacuum layer or a dustproof device, and is originally good in workability and easy to automate. It is suitable for surface hardening of molds, engine parts, etc.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of a surface treatment apparatus using in-liquid discharge.

FIG. 2 is a diagram for explaining a surface layer thickness measuring means in the surface treatment apparatus of FIG.

FIG. 3 is an X-ray diffraction pattern of the surface layer obtained in the example.

FIG. 4 is a diagram showing a relationship between a pulse width τp, a surface layer thickness h, and a volume ratio of a carbide TiC in the surface layer.

FIG. 5 is a diagram showing the influence of processing time tw and Ti grain size on the volume fraction of carbide TiC in the surface layer.

FIG. 6 is a diagram showing the relationship between the volume ratio of TiC in the surface layer when the discharge treatment is continuously performed and when the discharge treatment is intermittently performed, depending on the magnitude of the jet pressure Pi of the working fluid.

FIG. 7 is a diagram showing the influence of the jet pressure Pi of the working liquid on the surface layer thickness h.

FIG. 8 is a diagram showing an element distribution in a cross section of a surface layer.

FIG. 9 is a diagram showing a hardness distribution of a surface layer.

FIG. 10 is an explanatory diagram showing an outline of an apparatus for secondary processing.

FIG. 11 is a process drawing of shape processing, primary processing, and secondary processing by electric discharge machining that is common to all.

12 (a) to 12 (c) are explanatory views of each step when a secondary treatment is applied to the mold surface treatment.

[Explanation of symbols]

 1 Powder compact electrode (for primary treatment) 2 Surface of material to be treated 3 Processing liquid 3'Processing tank 4 Conductive adhesive 5 Metal rod 6 Servo mechanism between discharge electrodes 7 Processing liquid 7'Processing liquid circulation tank 8 Processing liquid feeding Feed pump 9 Ejector 10 Electrode for electric discharge machining 11 Current transformer for detecting discharge current 12 Synchroscope for observing discharge current and voltage 13 Discharge electrical condition programming device 14 Machining fluid discharge amount programming device 15 Z-axis scale 16 Indicates the progress position on the spindle side Pointer 17 Ultrasonic thickness gauge 18 Base material 19 Electrode replacement mechanism 20 Table movement mechanism

Claims (8)

[Claims] 1. A machining fluid that decomposes and produces carbon by electric discharge by using an electrode for electric discharge machining, which is obtained by adding a binding metal to a powder of a metal that easily carbonizes or a mixed powder of two or more kinds, and compression-molding it into a desired shape. In, aluminum and its alloy, which is a material to be treated, is formed on the surface of the material to be treated by electric discharge machining of the other electrode to form a surface layer in which the metal and its carbide are mixed. Surface treatment method of liquid alloy by electric discharge. 2. A metal which is easily carbonized is Ti, Zr, V or T.
The method according to claim 1, wherein a, Cr, Mo, W, Mn, Nb. 3. The amount of Nb in the electric discharge machining electrode is 1 to 10 wt.
The method according to claim 2, wherein the content is%. 4. The method according to claim 1, wherein at least one of aluminum powder, tin powder and zinc powder is added as a binding metal. 5. The method according to claim 1, wherein the working liquid is a liquid containing petroleum or a carbon compound. 6. The electric discharge machining according to claim 1 is used as a primary treatment, and after the primary treatment is performed, an electric discharge machining (secondary treatment) is performed by using an electrode made of a material with relatively little wear. A method for surface treatment of aluminum and its alloys by submerged discharge, which comprises remelting the surface layer formed by the primary treatment to form a dense surface layer and improving dimensional accuracy. 7. The method according to claim 6, wherein the relatively low wear material is Cu, graphite, or tungsten. 8. The method according to claim 6, wherein the electrical discharge machining (secondary treatment) is performed while the dimension of the surface layer is corrected by measuring the thickness or shape.