JPH06272014A - Method for remelting metal surface - Google Patents

Abstract

(57) [Summary] [Purpose] To improve the thermal fatigue strength over a wide range while maintaining the same mechanical strength as the base metal. [Composition] In a method of applying high-density heat energy 1 and 2 to a metal surface while moving it to remelt the surface layer and subsequently modifying the surface layer by rapid solidification, melting by applying high-density heat energy Site 5 that still does not coagulate
Then, the wire rod 7 of the same metal is injected in a solid state. By injecting the wire material 7 of homogeneous metal, the solidification rate in the portion 5 which is melted by the application of high-density heat energy and which is not solidified yet is increased, and the thermal fatigue strength can be improved even when the metal surface has a deep melting depth.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a remelting method for locally modifying a part of a surface layer of an aluminum alloy casting or the like.

[0002]

2. Description of the Related Art A member having a complicated shape such as a cylinder head is usually formed by casting. However, the cast product has internal defects such as porosity,
Since the structure is coarse, a product with high fatigue strength cannot be obtained as compared with a forged or pressed product. In order to improve the fatigue strength of a cast product, it is necessary to reduce internal defects and refine the crystal grains. And, in order to make the crystal grains fine, it is sufficient to increase the cooling rate during solidification, but if the cooling rate is increased, not only the moldability of the casting such as the flow of molten metal and the molten metal is hindered, but also the internal The defect may be frozen and remain inside.

In the production of an aluminum alloy cylinder head, after it is once formed by casting, the portion where fatigue strength is particularly required is irradiated with high-density heating energy such as TIG arc, laser beam, electron beam or plasma arc. A method for locally modifying the surface layer by re-melting it and then rapidly solidifying it is disclosed in JP-A-61-161.
It is proposed in Japanese Patent No. 193733. This local surface modification method is called "remelting treatment" or "remelting treatment".

However, when the remelting treatment is performed over a wide range or when the thin-walled portion is remelted, the solidification rate becomes slow because the heat capacity around the remelting portion is insufficient, and a sufficiently fine chill layer is obtained. In some cases, the thermal fatigue property cannot be improved.

As a countermeasure for the above, Japanese Patent Laid-Open No. 2-15867
The publication describes a method of improving the thermal fatigue strength by melting and supplying pure aluminum to the remelted portion by a TGI arc and diluting the silicon concentration in this portion.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The method described in Japanese Patent Publication No. 67 is effective for preventing the occurrence of black lacquer, but the concentration of additives such as silicon and magnesium decreases, so that the increase in mechanical strength due to the remelt treatment cannot be obtained. .

The present invention solves the above-mentioned problems and, while maintaining the same mechanical strength as that of the base material in the remelt processing part, re-melting the metal surface capable of improving the thermal fatigue strength of a wide range of remelt processing parts. It is intended to provide a melt processing method.

[0008]

The present invention provides a method for applying a high-density thermal energy to a metal surface while moving it to re-melt the surface layer and subsequently modifying the surface layer by rapid solidification. This is a method for remelting a metal surface, which comprises injecting a wire rod of the same metal in a solid state into a portion which is melted by the application of the density heat energy and is not solidified yet.

[0009]

[Function] By injecting a wire of the same metal, the solidification rate in a portion which is melted by the application of high-density heat energy and is not yet solidified is increased by the absorption of the heat of fusion of the injected same metal wire, and a fine chill layer is formed. Therefore, the thermal fatigue strength can be improved even if the melting depth of the metal surface is deep.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of the remelting process of the present invention, and FIG. 2 is a plan view showing a portion to be subjected to the remelting process. TIG is used as high-density heating energy. A wire feeder 6 is attached to the TIG torch 1, and an aluminum alloy wire 7 of the same quality as the work base material is variably adjusted and fed. As shown in FIG. 2, remelting is performed on the portion 3 of the aluminum alloy cylinder head W having the highest heat load, between the inlet valve seat hole VI and the exit valve seat hole VE, and between these and the plug hole P. TIG was used as a heat source for the treatment, and the TIG torch 1 was supported by a 6-axis robot to control the position and speed of the remelt treatment.

In FIG. 1, an arc 2 is applied to the surface of the work W while moving the TIG torch 1 in the direction of the arrow.
The surface layer of the work heated by the arc 2 is melted to form a molten metal pool 4 indicated by a broken line immediately below the arc 2, and the portion through which the arc 2 has passed is gradually solidified. At this time, the aluminum alloy wire 7 is supplied to the molten metal part 5 which the arc 2 has passed and has not yet solidified. The aluminum alloy wire 7 is melted by the heat of the molten metal of this part 5, but the part 5 into which this wire is injected has a high solidification rate due to the absorption of the heat of melting accompanying the melting of the wire, and rapidly solidifies and becomes fine. Since the chill layer is formed, the solidified portion 3
Have improved thermal fatigue properties.

Next, a concrete example will be described with reference to FIG. Using a cylinder head made of cast aluminum alloy for diesel engine, which is formed by low-pressure casting of JIS, AC2B aluminum alloy, as a work, between the valve seats VI and VE, which are the parts with the highest heat load, and those and plug holes. In P interval 3, the remelt treatment of the present invention was performed.

First, the work W is fixed to a jig that is grounded at room temperature, and then the TIG with the wire feeder 6 is attached.
The torch 1 is supported by a robot arm, and the remelt processing unit 3 of FIG. 2 is continuously irradiated with the arc 2 to move the TIG torch 1 in the arrow direction of the drawing. When the molten metal pool 4 is formed immediately below the arc 2, the aluminum alloy wire 7 is automatically injected into the portion 5 immediately after that. Reverse polarity DC TIG is used for the arc power source, current 430A, TIG torch moving speed 8m / min, shield gas flow 28l / m
Under the in condition, a modified layer having a width of 15 mm or more and a depth of 11 mm or more was obtained.

The modified layer obtained by the above method covers the portion of the combustion chamber of the cylinder head where thermal fatigue fracture occurs, and the internal structure and mechanical properties are shown in Table 1 below. Despite being remelted in a wider area than
Both the AS value and porosity are the same as the conventional one, and the hardness is also the same as that of the base metal part.

[0015] Note, DAS value: The distance between the secondary arms 11 of the dendrite-shaped crystal grains 10 shown in FIG. The spacing D represents the size of the crystal grain.

FIG. 3 shows the relationship between the remelting pattern and the current pattern of the TIG torch. 3A shows a cross section of the remelt processing portion, and FIG. 3B shows current (I) on the vertical axis and time (T) on the horizontal axis. Energy E generated by arc 2
Is proportional to I · V / S. However, I: current, V: voltage, and S: moving speed of the torch. If V and S are constant, the energy E is proportional to I, so the melting depth is
It can be controlled by the current I.

Next, the conventional aluminum alloy wire 7
A comparison with the case where the remelt processing is performed without is described with reference to FIG. The current of the TIG torch 1 was low in the first half T1, and increased in T2, and the melting depth d1 = 5 mm in the first half and d2 = 10 mm in the second half. In the case where the aluminum alloy wire 7 was not used, the DAS value of the treated part in the first half was 6 to 8 μm, and 10 μm in the latter half. Next, after increasing the electric current, the melting is T3-T4-T5 in the latter half.
-T6, 3.06 g / m of aluminum alloy wire 7 was added as 1.0-1.5-2.5-4.
Injection was performed at a speed of 0 m / min. As a result, the DAS value was 6 to 8 μm everywhere in the molten portion. From this comparative example, it is clear that the injection of the aluminum alloy wire increases the solidification rate and improves the thermal fatigue strength even when the melting depth is deep. It is needless to say that a laser beam, an electron beam, a plasma arc, or the like can be used as the high-density heating energy in addition to the TIG arc.

[0018]

INDUSTRIAL APPLICABILITY The present invention can improve the thermal fatigue strength of a wide range of remelt-treated parts while maintaining the same mechanical strength as the base material in the remelt-treated parts.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is a plan view of a processing target portion of the present invention.

FIG. 3 is a diagram showing a relationship between a melting pattern and a current pattern of a TIG torch.

FIG. 4 is a schematic view of dendrite-shaped crystal grains.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 TIG torch 2 Arc 3 Remelt processing layer 4 Molten metal pool 5 Wire pouring and melting part 6 Wire feeder 7 Aluminum alloy wire

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location B23K 26/00 310 B 7425-4E // F02F 1/24 B 8503-3G F 8503-3G

Claims (1)

[Claims] 1. A method of applying high-density thermal energy to a metal surface while moving the same to remelt the surface layer and subsequently modifying the surface layer by rapid solidification, wherein the high-density thermal energy is applied to melt. On the part that still does not coagulate,
A method for remelting a metal surface, which comprises injecting a wire rod of the same metal in a solid state.