JP3271836B2 - Surface treatment method for aluminum and its alloys by submerged discharge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for hardening aluminum and its alloys by submerged electric discharge in a liquid. It is possible to provide high hardness (Hv 300 to 1500) and high shape accuracy to parts requiring wear resistance such as engine parts.

[0002]

2. Description of the Related Art When imparting wear resistance to aluminum and its alloys, Al having a high hardness (Hv 200) typified by an Al-Si alloy is conventionally used.
Although alloys have been applied, 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
(2) Ion nitriding: thickness several μm / 5hr, hardness Hv2000 (3) Ion beam mixing: thickness 18 to 36 μm / h
r, hardness Hv 1000 or less (4) Thermal CVD (WC): thickness 620 μm / hr, hardness Hv2
000 (W): thickness 620 μm / hr, hardness Hv 50-60
0 However, treatment temperature Tp = 600 ° C. (5) Plating: After performing Ni-P plating, Cu plating, etc., 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 several μm
６０60 μm and hardness is Hv450-800. (6) Thermal spraying (Mo, TiN / Ti): thickness 300 μm, hardness H
v500-600

[0004] Of the above surface coatings, thermal spraying has a high deposition rate, but has poor adhesion, and requires rework in order to obtain shape accuracy. In the cases of (1) to (5), the adhesion is good, but the film formation rate is low, and a vacuum tank, an electrolytic tank and the like are required as processing equipment. Those requiring high-temperature treatment have poor shape accuracy.

[0005] Other alloying methods such as arc melting, plasma melting, electron beam alloying, and laser alloying have the advantages of good adhesion and short processing time, but have the advantage of macrosegregation. There are drawbacks such as defects in the structure, generation of pores, and the need to rework the surface. Also, these machining properties are generally poor.

The above prior arts have many drawbacks as surface hardening techniques for aluminum and its alloys. In other words, it is difficult to satisfy the following conditions and to be economically viable and to keep the working environment clean. Also, it is difficult to limit the region to be cured with high dimensional accuracy. Increase the deposition rate. Good adhesion. A thick film of several tens μm can be formed. If necessary, sufficient hardness can be controlled. Does not cause dimensional changes, etc., due to thermal effects on the base material. No cracks or the like are generated on the surface layer. Good workability (no need for vacuum chamber, no special dust-proof device, easy automation).

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

[0008]

Means for Solving the Problems The inventor of the present invention has conducted intensive experiments and researches to solve the above-mentioned problems, and as a result, has found that it is possible by applying a pulse discharge technique in a liquid.

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

According to another aspect of the present invention, the above-described electric discharge machining is used as a primary treatment, and after the primary treatment is performed, electric discharge machining (secondary treatment) is performed using an electrode made of a material having relatively low consumption. The gist of the present invention is to provide a method for surface treatment of aluminum and its alloys by in-liquid discharge, wherein the surface layer formed by the primary treatment is remelted to form a dense surface layer and the dimensional accuracy is improved.

[0011]

The present invention will be described below in more detail.

As the working electrode used in the present invention, a single powder of a metal which is easily carbonized or a powder obtained by adding a binding metal to a powder mixture of two or more kinds and compressing it into a desired shape is used. Examples of metals that are easily carbonized include Ti, Zr, V, Ta, Cr, and M.
o, W, Mn, Nb or alloys containing these elements. In particular, when an electrode containing 1 to 10 wt% of Nb is used, the toughness of the surface layer can be increased.

The binding metal may be any metal that acts as a binder when the above metal powder is formed. For example, one or more of aluminum powder, tin powder and zinc powder are added.

The other electrode is made of aluminum or various aluminum alloys to be processed. It is desirable that the material to be processed is previously formed into a desired machining shape by ordinary electric discharge machining.

A liquid which decomposes and generates carbon by electric discharge is used as the electric discharge machining liquid. For example, petroleum, kerosene, or a liquid containing a carbon compound may be used. Such a machining fluid is decomposed by electric discharge to generate carbon, and reacts with the above-mentioned easily carbonizable metal to form a carbide, thereby forming 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 electric discharge conditions (current value, pulse width, duty factor, etc.) and the discharge flow rate of the working fluid.

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

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

At the time of the electric discharge machining in the secondary treatment, an electrode made of a material with relatively low consumption, such as Cu, graphite, and tungsten, is used instead of the electrode for the primary treatment.
The shape of the electrode is desirably an electrode having a desired shape that enables correction processing to reach a target size. For that purpose, an electrode (electrode that is not easily consumed) when the shape is processed by ordinary electric discharge machining prior to the primary treatment may be used as the electrode for the secondary treatment.

In order to carry out the modification processing to reach the target dimensions, the discharge treatment is performed while the dimensions of the surface layer are modified by measuring the thickness or the shape.

Next, an embodiment of the present invention will be described.

[0021]

[Embodiment 1] This embodiment is an example in which primary processing (electric discharge machining) is performed using the apparatus shown in FIGS. In the figure, reference numeral 1 denotes a processing electrode formed of a green compact, which is bonded 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 machining power source 10 (the anode and the cathode can be inverted) and is immersed in a machining tank 3 ′ containing a machining fluid 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. Fifteen
Is a Z-axis scale, and 16 is a pointer indicating a progress position on the main shaft side.
Is input to Reference numeral 11 denotes a current transformer for detecting discharge current, and reference numeral 12 denotes a synchroscope for observing discharge current and voltage. Numeral 14 denotes a machining fluid discharge amount programming device which controls a machining fluid supply pump 8 for supplying the machining fluid 7 in the tank 7 '. An ejector 9 generates a jet of a machining liquid.

Reference numeral 18 denotes a base material (Al or an alloy thereof) to be processed, which 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 its signal is input to the program device 13 for electric discharge conditions.

First, the material to be treated is aluminum alloy A
DC12 (including Si 11.2%, Cu 2.74%) flat plate
(2.5 mm thick). For the electrode material, Ti powder, which is a metal that is easily carbonized, and Al powder as a binding metal are used for Ti:
Al = 36: 64 (wt%) mixed powder (powder particle size: 44 μm or less) was compression-molded (molding pressure Pe: 24.5 to 4.5%).
441 MPa) was used. The electric discharge machining fluid and electric discharge conditions are as follows.

<Electric discharge machining fluid> Machining fluid: kerosene, jet pressure Pi: 0 to 78 KPa <Electric discharge conditions> 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) = 0.8-68% (where τr: pause time)

Under the above conditions, electric discharge machining (primary treatment) was performed to form a surface layer on the surface of the base material. The surface layer, the X-ray diffraction pattern of FIG. 3, TiC, TiAl, Al, that is a surface layer made of TiAl ₃ were confirmed. The discharge treatment conditions when the surface layer shown in FIG. 4 was obtained were as follows: 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 = 9.8 K
Pa.

FIG. 4 shows the results of examining the relationship between the pulse width τp, the thickness h of the surface layer, and the volume fraction of 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 reaches about 50 μm in about 2 minutes, and the film formation rate is high.

FIG. 5 shows the results of examining the effects of the processing time tw and the Ti particle size on the volume fraction of carbide TiC in the surface layer. Processing time is about 150 seconds and TiC volume ratio is 50
%, There is a tendency for the volume fraction of TiC to increase as the processing time increases. In addition, as the Ti particle size is smaller, the volume ratio of TiC increases in a shorter time.

FIG. 6 shows the results of examining the relationship between the volume ratio of TiC in the surface layer and the jet pressure Pi of the machining fluid when the discharge treatment is performed continuously and intermittently. The volume ratio of TiC is larger when the process is performed continuously than when it is performed intermittently, and the volume ratio of TiC is larger 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 result of examining the effect of the jet pressure Pi of the working fluid on the surface layer thickness h. The larger the jet pressure Pi, the smaller the surface layer thickness h.

FIG. 8 shows the result of examining the element distribution in the cross section of the surface layer. The composition is graded in the surface layer, and the outermost surface of the surface layer has many Ti components and C components, and A
The components of l and Si are small. Therefore, the outermost surface indicates 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, and the base material component increases and decreases in hardness as approaching the base material surface. Even when the temperature of the object is high or low, the material acts as a buffer on the surface composition and the internal structure, so that a surface structure that prevents the occurrence of cracks and the like can be provided.

[0032]

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

In order to reduce the TiC concentration at the beginning of the electric discharge process, the pulse width τp is selected to be as small as about 20 μs, and the machining fluid flow is programmed to be strongly jetted. As the time elapses, the pulse width τp becomes τp = 100 μs, τp = 500 μ
If s is set to be large, three layers having different TiC concentrations can be formed as surface layers.

At this time, the stage at which each program is switched may be monitored using an ultrasonic thickness gauge 17 for directly measuring the thickness of the surface layer. In other cases, the progress of the main shaft side 16 with respect to the Z-axis scale 15 cannot be directly used as the processing progress because the green compact electrode is formed so as to increase the wear. The ratio (adhesion ratio ε) between the thickness H of the electrode to be treated and the consumption length L of the electrode is determined for each material of the green compact electrode, and the thickness H is used from the following equation. That is, H = L−
S (where S is the progress of the spindle), H = S / (1
/ Ε-1). If ε = about 0.1, then H−
S / 9, and the adhesion thickness H can be determined from the progress S of the main shaft.

[0035]

Embodiment 3 In this embodiment, a tough surface layer is formed. In the experiment, an electrode mixed as Ti: Al = 36: 64 (wt%) as in Example 1 was used as a green compact electrode.
Using an electrode mixed at a ratio of Ti: Al: Nb = 32: 58: 10 (wt%), Pe: 441 MPa, discharge current value
(Maximum current) Ip = 20 A, pulse width τp = 200 μ
Under the conditions of s and effective pulse Rp = 0.33%, electric discharge treatment was performed with the working fluid 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 performed, cracks were generated by bending at 90 ° in the case of the (Ti + Al) compacted electrode, but (Ti + Al + N
b) In the case of the green compact electrode, no crack was generated by bending at 90 °.

[0036]

[Embodiment 4] This embodiment is an example in which after the discharge treatment of the primary treatment is performed, the discharge machining of the secondary treatment is performed. Shown in Example 1
The surface layer obtained by the primary treatment using the (Ti + Al) green compact electrode is subjected to a discharge treatment using an electrode having a shape substantially corresponding to the shape of the workpiece to be treated and made of a material with relatively little wear. Next processing) is performed.

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

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

First, after machining the shape of the material to be processed by ordinary electric discharge machining, the machining electrode is stored in the exchange mechanism, and a tool for measurement is attached from the exchange mechanism. The depth is measured and stored in a storage device (depth D).

Next, the primary processing is performed, and when the secondary processing is switched, first, after the surface layer thickness H is determined, the surface layer thickness is subtracted from the numerical value previously stored in the storage device, and the approach depth of the main shaft is determined. M (M = D−H) is determined.

In the secondary processing (correction processing), the approach processing of only M is performed, but after the processing is completed, the measurement tool is automatically switched to perform the measurement. When the thickness falls within the allowable range, the operation is completed. FIG. 11 shows these process diagrams.

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

[0043]

As described in detail above, according to the present invention,
Surface hardening treatment with high film forming speed of several tens of μm, high adhesion, sufficient and necessary hardness, no dimensional change due to heat on the base material, and no cracks in the surface layer It can be performed. In addition, a vacuum layer and a dust proof device are not required, and the workability is originally good, and automation is easy. It is suitable as a surface hardening treatment for molds, engine parts and the like.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a surface treatment apparatus using discharge in liquid.

FIG. 2 is a view for explaining a thickness measuring means of a surface layer in the surface treatment apparatus of FIG. 1;

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

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

FIG. 5 is a diagram showing the influence of the processing time tw and the Ti particle 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 and the magnitude of the jet pressure Pi of the machining fluid when the discharge treatment is performed continuously and intermittently.

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

FIG. 8 is a diagram showing 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 view schematically showing an apparatus for secondary processing.

FIG. 11 is a process diagram of a shape machining, a primary treatment, and a secondary treatment by a common electric discharge machining.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Green compact electrode (for primary processing) 2 Surface of material to be processed 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 feed Supply pump 9 Ejector 10 Electrode for electric discharge machining 11 Current transformer for detecting discharge current 12 Synchronoscope for observing discharge current voltage 13 Electric discharge condition programming device 14 Machining fluid discharge amount programming device 15 Z-axis scale 16 Shows the progress position on the main shaft side Pointer 17 Ultrasonic thickness gauge 18 Base material 19 Electrode exchange mechanism 20 Table moving mechanism

Continuation of the front page (56) References JP-A-53-100932 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 26/00

Claims (8)

(57) [Claims] 1. A machining fluid which is formed by adding a binding metal to a simple powder or a mixed powder of two or more kinds of metals that are easily carbonized and compression-molding the powder into a desired shape as an electrode for electric discharge machining, and decomposing and generating carbon by electric discharge. Wherein, by subjecting the material to be treated, aluminum and its alloy, to electrical discharge machining as the other electrode, forming a surface layer in which the metal and its carbide are mixed on the surface of the material to be treated, A surface treatment method for alloys by submerged discharge. 2. The metal which is easily carbonized is Ti, Zr, V, T
The method of claim 1, wherein a, Cr, Mo, W, Mn, Nb. 3. An Nb content of 1 to 10 wt.
%. 4. The method according to claim 1, wherein at least one of aluminum powder, tin powder and zinc powder is added as the binding metal. 5. The method according to claim 1, wherein the processing liquid is a liquid containing petroleum or a carbon compound. 6. The electric discharge machining according to claim 1, which is a primary treatment, and after performing the primary treatment, an electric discharge machining (secondary treatment) is performed by using an electrode made of a material with relatively little consumption. A method of refining a surface layer formed by a primary treatment to form a dense surface layer and improve dimensional accuracy by discharging submerged aluminum and its alloys. 7. The method of claim 6, wherein the relatively less wearable material is Cu, graphite, tungsten. 8. The method according to claim 6, wherein the electric discharge machining (secondary treatment) is performed while modifying the dimensions of the surface layer by measuring the thickness or the shape.