JPH062897B2 - Method for remelting metal surface - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an automotive part and various machine parts made of various metal materials such as aluminum alloy castings, which is used for locally modifying a part of the surface layer. The present invention relates to a melt processing method.

2. Description of the Related Art Recently, remelting treatment for locally improving the characteristics of a part of the surface of a part made of a metal material such as an aluminum alloy, particularly a cast part, has been attracting attention. In this remelting treatment, the surface layer of the metal material is irradiated with high-density heating energy such as TIG arc, laser beam, electron beam, or plasma arc to remelt the surface layer, and shrinkage cavities or pins are formed by subsequent rapid solidification. It is intended to remove casting defects such as holes and blow holes and to refine the metal structure to improve the characteristics of the surface layer.

As an example in which such a remelting treatment is applied to a cylinder head of an automobile engine, which is particularly made of an aluminum alloy casting, Japanese Patent Application Laid-Open No. 61-19377 of the present applicant's application is given.
There is a method described in No. 3. With this method, casting defects such as pinholes, blowholes and shrinkage cavities are likely to occur in aluminum alloy castings, and since the cylinder head is large and requires a complicated shape, the cooling rate during casting slows down and the metal structure becomes coarse. Since it is easy to generate, on the other hand, a large thermal stress is applied to the so-called intervalve portion sandwiched between the exhaust port and the intake port in the cylinder head, so that the intervalve portion is required to have excellent mechanical characteristics. That
It was made against the background, etc., high density energy such as TIG arc is applied to the intervalve portion of the cylinder head made of aluminum alloy casting to remelt / quench and resolidify,
By eliminating casting defects in the intervalvular portion and refining the microstructure of the intervalvular portion, the mechanical characteristics of the intervalvular portion, especially the characteristics corresponding to thermal stress, are improved.

Problems to be Solved by the Invention In general, the remelting process as described above is performed in FIG.
As shown in (B), T is formed on the surface of the metal substrate 1 to be treated.
While applying high-density heating energy 3 such as TIG arc by the torch 2 for IG arc, etc., the application position is continuously moved from one end 4A to the other end 4B of the region 4 to be processed, and its movement end (processing end) ) It is usual to stop the application of the high-density heating energy 3 near 4B.
However, in this case, the treated part, i.e. remelt-
At the terminal end of the re-solidified layer (bead) 9 formed by re-solidification, a recess, that is, a so-called crater 6 is usually formed on the surface. Of course, after the remelting treatment, finishing processing by grinding is usually performed in order to smooth the surface of the treated portion. However, the cutting allowance of the finishing processing is subject to process or economic constraints, and thus the crater 6 is not processed. When the depth is deep, the crater 6 remains on the finished surface 1A after finishing as shown in FIG. 4 (C), often resulting in poor appearance. Also, with such crater 6 remaining,
Since the inside of the crater 6 is highly uneven, not only does it cause a poor appearance, but also unevenness inside the crater 6 may cause stress concentration in that portion, resulting in deterioration of characteristics such as fatigue characteristics and impact characteristics. There is also.

In addition, in the case of a welding bead using a general melting rod, a slightly larger amount of the welding rod is inserted just before the end of melting to prevent the occurrence of craters at the end of the welding bead. It was difficult to prevent the occurrence of craters. Also, in the remelting process, the crater can be made shallow to some extent by gradually decreasing the arc current just before the end of the process, but it cannot be completely eliminated, and the problem as described above had to be brought about. Is the reality.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a remelting treatment method that avoids the above-mentioned problems due to the crater at the terminal end of the remelting bead. .

MEANS FOR SOLVING THE PROBLEMS The present invention relates to a remelting treatment of a metal surface in which high density heating energy is applied to the surface of a metal base material to remelt the surface layer, and the surface layer is subsequently modified by rapid solidification. In the method, when the high-density heating energy application position is continuously moved over an area on the surface of the metal base material to process the area, the surface of the metal base material to be a processing end portion is treated,
A protrusion having a large area larger than a crater generated by applying the high-density heating energy is formed in advance, and the application position of the high-density heating energy is moved to the middle part of the protrusion to end the process. It is characterized by that.

Action Figure 1 (A) to (D) shows TI as high-density heating energy.
An example of a situation in which the remelting treatment method of the present invention is carried out using a G arc is schematically shown, and the operation of the present invention will be described with reference to these drawings.

In carrying out the method of the present invention, prior to the remelting treatment, as will be shown in FIG. 1 (A), the end portion 4B of the region 4 to be treated on the surface of the metal substrate 1 will be described later. A trapezoidal projection 7 having a top whose diameter is equal to or larger than the diameter of the crater generated by irradiating the arc 3 is formed in advance. Then, as shown in FIG. 1B, the TIG arc torch 2 is continuously moved from a position above one end (starting end) 4A of the region 4 to a position above the other end (terminating end) 4B. The position of the arc 3 generated between the torch 2 and the surface of the metal substrate 1, that is, the application position of the high-density heating energy is changed from one end 4A to the other end 4B of the region 4.
Move continuously until. During this period, the metal base material surface layer in the region 4 is rapidly melted by the arc 3, and the molten pool 8 is successively rapidly cooled by the movement of the arc 3,
It becomes the re-solidified layer 9. At this time, re-solidification is performed with directionality from the base metal side to the surface, and as a result, shrinkage cavities, pinholes, blowholes, and other casting defects that were present in the metal base material surface layer are extruded to the surface side. In this state, the resolidified layer 9 having a sound structure free of casting defects is formed, and the resolidified structure is remarkably refined by the rapid solidification. As a result, the mechanical properties of the resolidified layer 9 are the same as those before treatment. Greatly improved than the state.

And, in particular, in the method of the present invention, the application of the high-density heating energy started from one end 4A of the region 4 is applied to the other end 4 of the region 4.
The process is terminated at B, that is, the position of the intermediate portion of the protrusion 7.
At this time, as shown in FIG. 1 (C), craters 6 are generated at the processing end position, but since the projections 7 are formed in advance at that portion, the deepest portion of the crater 6 also has a metal base material 1.
Even if it is shallower than the original surface level 1B, or deeper than the metal substrate surface level 1B, the depth from the substrate surface level 1B is only slight.

At the stage where the re-solidified layer 9 is formed as described above, since the surface of the re-solidified layer 9 has unevenness, finishing processing is then performed as shown in FIG. 9
Shave off the surface, including the surrounding surfaces. On this occasion,
The protrusion 7 is also scraped off. By performing such finishing, the craters 6 existing on the protrusions 7 are easily removed, and the flat finishing surface 1A is obtained. That is, as described above, even if the deepest portion of the crater 6 is shallower than or deeper than the surface level 1B of the metal substrate 1, the depth from the substrate surface level 1B is small, so that the substrate surface level 1B. The finishing depth (cutting allowance) d from the same as that of general finishing (usually 2 m
Approximately m), the crater 6 can be sufficiently removed.

Here, the depth of the crater 6 is generally about 1.5 mm ± 0.5 mm, and therefore the height of the protrusion 7 is preferably about 2 mm. Further, the area of the portion forming the protrusion 7 is
The point is that it should be larger than the formed crater 6.

In the above description, the case where the TIG arc is used as the high-density heating energy has been described, but the same applies to the case where a laser beam, an electron beam, a plasma arc or the like is used.

Example A cylinder head rough material for diesel engine engines made of an aluminum alloy made of JIS AC2B alloy,
The remelting process was performed by the method of the present invention as follows. That is, as shown in FIG. 2 and FIG. 3, when the remelting process by the TIG arc is performed on the intervalve portion 13 between the intake port 11 and the exhaust port 12 in the rough cylinder head material, the movement of the TIG arc is performed. The locus is defined as shown by the arrow 14, and the protrusion 7 is formed in advance at the portion to be the processing end portion. The protrusion 7 has a diameter of 18 mm and a height of 2 mm, and was formed by providing a recess in the mold during casting of the cylinder head rough material. Then, the TIG arc was moved according to the above-mentioned locus 14 to perform the remelting process on the intervalve part 13, and the process was terminated at the position of the protruding part 7. Here, the conditions of the remelting treatment by TIG arc are
A 3.2 mm diameter tungsten electrode rod was used, argon gas was passed as a shield gas at 25 / min, the peak current was 210 A, the base current was 180 A, and the torch moving speed was 0.75 mm / sec.

In the re-solidified layer formed by such a re-melting process, a crater with a depth of 1.5 mm ± 0.5 mm was formed in the protrusion 7 at the end of the treatment, but a rough material cutting allowance of 2 mm (protrusion By finishing with a machining allowance of 4 mm), it is possible to obtain a finished surface without craters,
Therefore, it was possible to prevent the appearance failure and to prevent the mechanical properties of the portion from being deteriorated due to the remaining craters.

EFFECTS OF THE INVENTION According to the method of the present invention, when performing the remelting treatment using the high-density heating energy for the modification of the surface layer of the metal base material, the protrusions are formed in advance in the portion to be the treatment termination portion. By doing so, it is possible to easily and sufficiently remove the craters generated in the protrusions, which are the processing end portions, by normal finishing, and thus prevent the appearance of the product from being deteriorated due to the residual craters. It is also possible to prevent deterioration of fatigue characteristics and impact characteristics due to unevenness in the crater.

[Brief description of drawings]

1 (A) to 1 (D) are schematic cross-sectional views showing stepwise an example of the remelting treatment method of the present invention, and FIG. 2 shows a main part of a cylinder head used in an embodiment of the present invention. Bottom view,
FIG. 3 is a sectional view taken along the line III-III in FIG. 2, and FIGS. 4A to 4C are schematic sectional views showing stepwise an example of a conventional remelting treatment method. DESCRIPTION OF SYMBOLS 1 ... Metal base material, 2 ... TIG arc torch, 3 ... TIG arc as high-density heating energy, 4 ... Area to be treated, 4B ... Treatment end portion, 6 ... Crater, 7 ... Projection portion, 9 ... Resolidification layer.

Claims (1)

[Claims] 1. A method for remelting a metal surface, wherein high-density heating energy is applied to the surface of a metal substrate to remelt the surface layer, and the surface layer is subsequently modified by rapid solidification. When the application position of is continuously moved over a certain area on the surface of the metal base material to process the area, on the surface of the metal base material to be the processing end portion,
A protrusion having a large area larger than a crater generated by applying the high-density heating energy is formed in advance, and the application position of the high-density heating energy is moved to the middle part of the protrusion to end the process. A method for remelting a metal surface, which comprises: