JP2020001086A - Surface modification method for light metal casting - Google Patents

Abstract

To provide a surface modification method for a light metal casting, which enables a surface to be further refined in a location, particularly requiring strength, of a surface of the light metal casting by a friction stirring process.SOLUTION: A surface modification method for a light metal casting includes a friction stirring process in which the casting is surface-modified by rotating and feed-moving a rotating shaft and a rotor in the state of pressing the rotating shaft and the rotor against a casting surface. The side, on which the rotative direction and feed direction of the rotating shaft and the rotor correspond to each other, is positioned in a part where strength is desired to be increased by modification of the light metal casting. Thus, the rotating shaft and the rotor is feed-moved while being rotated.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a method for modifying a surface of a light metal casting.

  2. Description of the Related Art A surface modification technique using a friction stir process (FSP: Friction Stir Processing) is known to improve the variation in material properties and the deterioration in quality due to coarsening of a solidified structure in a light metal casting such as an aluminum alloy. Patent Literature 1 discloses an additive for modifying a metal structure when a surface of a light metal casting is refined to a metal structure by a friction stir process in a surface modification technique of a light metal casting by a friction stirring process. Is disclosed.

JP-A-2004-255440

  By the way, in a member that may receive a large impact, it is desirable that the member be destroyed when the impact is received, as intended in the design. For example, it is preferable that each member used in the vehicle is designed so that when the vehicle receives an impact such as a collision, the members are broken so that the impact received by the occupant is as small as possible.

  In a vehicle, a member having a complicated shape is often formed of a light metal casting. For example, members such as a suspension tower, a rear side member, and a cylinder block of an engine in a vehicle are formed of a light metal casting. It is desirable that a member made of such a light metal casting be destroyed when subjected to an impact as intended by the design.

  When a member formed of a light metal casting has a portion where stress tends to concentrate, there is a possibility that the portion contains an internal defect, and in that case, the strength is most likely to be the weakest. For example, when a member formed of a light metal casting has a welded portion where stress is likely to be concentrated, there is a high possibility that breakage will occur in a region near the welded location when subjected to an impact. However, it is difficult to control the way in which destruction occurs in a region near the welding point in terms of design. Therefore, when a member formed of a light metal casting has a welded portion, when an impact is applied, the destruction occurs not in a region near the welded portion, but in a portion where the manner of occurrence of the destruction is easily designed and controlled. Need to be In other words, it is necessary to increase the strength in the region near the welded portion than the strength of a portion where the manner in which fracture occurs can be easily controlled in design. For these reasons, in the surface modification of the light metal casting, it is desired that the metal structure be refined in places where strength is particularly required, than in places where strength is not required.

  In view of the above background, an object of the present invention is to provide a light metal casting which can be made to have a finer metallographic structure at locations where strength is particularly required on the surface of the light metal casting by a friction stir process. It is to provide a surface modification method.

  The present invention relates to a method for modifying a surface of a light metal casting by a friction stir process of rotating and rotating the rotating shaft and the rotor while pressing the rotating shaft and the rotor against the surface of the casting to modify the surface of the casting. And rotating the rotating shaft and the rotor so that the side where the rotating direction and the feeding direction of the rotating shaft and the rotor are coincident comes to a portion where the strength of the light metal casting is desired to be improved by reforming. It is to be fed and moved.

  The present inventor has proposed that the rotational direction of the rotating shaft and the rotor and the feeding direction are closer to each other than near the side (RS) where the rotating direction and the feeding direction of the rotating shaft and the rotor are opposite to each other on the surface subjected to friction stirring. It was found that the metal structure on the surface was further refined in the vicinity of the side where AS coincided with (AS). By making the portion where the strength is to be increased more by the modification in the light metal casting come to the AS, after performing the surface modification, in the portion where the strength is to be further increased, the metal structure of the surface is further refined, The strength can be made higher.

  Further, the feed movement is performed a plurality of times in the same feed direction, and in each feed movement, the path of the next feed movement is parallel to the path of the previous feed movement by a predetermined width equal to or less than the diameter of the rotor. It may be carried out by shifting to. In this way, a part that has not been AS on the previous feed movement path becomes AS on the next feed movement path or subsequent feed movement paths. Thereby, the surface of the member formed of the light metal casting can be uniformly refined.

  Further, the side where the rotation direction and the feed direction of the rotating shaft and the rotor coincide with the feed direction is located on the edge side of the light metal casting, and the feeding movement is performed according to a path orbiting the rotating shaft and the rotor along the edge of the light metal casting. You may make it do. By setting the AS on the edge side and the RS on the inner side in the member formed of the light metal casting, the metal structure on the surface is refined at a location near the edge. Thereby, the strength of the outer periphery of the member formed of the light metal casting can be further increased.

  According to the present invention, the surface of the light metal casting can be made finer at places where strength is particularly required by the friction stir process.

It is a figure showing the schematic structure of the friction stirrer used for the surface modification method of the light metal casting concerning this embodiment. It is a microscope picture of the metal structure in the surface of the member formed with the aluminum alloy casting before modification. It is a schematic diagram explaining the outline of the friction stirring process by a friction stirring device. It is a schematic diagram explaining the difference of the modification effect by friction stirring. It is a schematic diagram explaining the characteristic point of the surface modification method of the light metal casting concerning this Embodiment. It is a schematic diagram explaining the characteristic point of the surface modification method of the light metal casting concerning this Embodiment. It is a schematic diagram explaining the characteristic point of the surface modification method of the light metal casting concerning this Embodiment. It is a flowchart shown about the flow of the surface modification method of the light metal casting concerning this Embodiment. It is a schematic diagram explaining another example of how to make a rotary tool and a probe move. It is a mimetic diagram explaining still another example of how to carry out rotation movement of a rotating tool and a probe.

  Hereinafter, the present invention will be described through embodiments of the invention, but the invention according to the claims is not limited to the following embodiments. Also, not all of the configurations described in the embodiments are necessarily indispensable as means for solving the problem. The following description and drawings are appropriately omitted and simplified for clarity of explanation. In the drawings, the same elements are denoted by the same reference numerals, and a repeated description is omitted as necessary.

  The method for modifying the surface of a light metal casting according to the present embodiment includes a method of rotating and rotating the rotating shaft and the rotor while pressing the rotating shaft and the rotor against the surface of the casting to perform frictional modification on the surface of the casting. This is a method of modifying the surface of a light metal casting by a stirring process. The light metal casting is a casting formed of a light metal such as an aluminum alloy or a magnesium alloy. The surface modification of the light metal casting mainly means to make the metal structure finer on the surface of the light metal casting and to remove internal defects such as cavities. First, the friction stirrer used in the method for modifying the surface of a light metal casting according to the present embodiment will be described.

  FIG. 1 is a diagram showing a schematic configuration of a friction stirrer 1 used in a method for modifying a surface of a light metal casting according to the present embodiment. As shown in FIG. 1, the friction stirrer 1 includes a main shaft driving unit 2, a moving mechanism 3, a rotating tool 4 as a rotating shaft, and a probe 5 as a rotator.

  The spindle drive unit 2 has a rotary drive shaft (not shown) rotated by an electric motor (not shown). The spindle drive unit 2 is supported via a moving mechanism 3 on a column 7 fixed vertically to the pedestal unit 6. A work table 8 is provided on the base 6. A work W, which is a member formed of a light metal casting, is placed on the work table 8.

  The moving mechanism 3 has a lifting / lowering mechanism (not shown) and a feed moving mechanism (not shown). The lifting and lowering mechanism moves the spindle drive unit 2 in a direction perpendicular to the workpiece W (that is, in the direction of the rotary drive shaft of the spindle). The feed moving mechanism moves the spindle drive unit 2 in a feed direction that is horizontal with respect to the workpiece W.

  The rotary tool 4 is a cylindrical member that is rotated by the spindle drive unit 2, and the center axis of the cylinder coincides with the axis of the rotation drive shaft of the spindle drive unit 2. At the lower end of the rotary tool 4, a pressing surface that is a horizontal surface capable of pressing the upper surface of the work W is formed. The rotating tool 4 is formed of a metal material such as stainless steel, which has a higher hardness and a higher melting point than the base material of the work W.

  The probe 5 is a cylindrical member having a smaller diameter than the rotary tool 4, and is fixedly installed on the pressing surface of the rotary tool 4 so as to protrude downward from the center of the pressing surface. The center axis of the cylinder of the probe 5 is coaxial with the center axis of the cylinder of the rotary tool 4. The probe 5 is formed of a metal material having a higher hardness and a higher melting point than the base material of the workpiece W, similarly to the rotary tool 4. The cylindrical side surface of the probe 5 may be threaded in a direction opposite to the direction in which the probe 5 is rotated. In this case, for example, if the direction in which the probe 5 is rotated is clockwise, the cylindrical side surface of the probe 5 is threaded counterclockwise. Thereby, the agitation of the portion of the work W softened by the frictional heat can be further promoted.

  Next, a method for modifying the surface of a light metal casting according to the present embodiment will be described. In the following description, the configuration of the friction stirrer 1 will be appropriately referred to FIG.

  FIG. 2 is a micrograph of a metal structure on a surface of a member formed of an aluminum alloy casting before modification (ADT10-F). In FIG. 2, the portion that looks black is eutectic silicon. As shown in FIG. 2, in a member formed of an aluminum alloy casting, many portions where eutectic silicon exists as coarse precipitate particles R <b> 1 without being refined in the metal structure.

  FIG. 3 is a schematic diagram illustrating an outline of a friction stir process performed by the friction stir device 1. As shown in FIG. 3, the rotary tool 4 and the probe 5 are lowered in the direction of the arrow A which is the rotation axis direction of the main shaft by the lifting / lowering pressing mechanism of the moving mechanism 3 (see FIG. 1). The rotary tool 4 and the probe 5 are rotated at a high speed in the direction of the arrow C (clockwise) while the upper surface of the workpiece W is pressed. That is, the rotating tool 4 and the probe 5 are brought into frictional contact with the base material of the work W. The frictional heat generated at this time maintains the temperature range in which the light metal material, which is the base material of the work W, does not melt and plastically deforms, so that the base material of the work W is softened and stirred. Thereby, coarse precipitate particles of the metal structure (see FIG. 2) on the surface of the workpiece W are pulverized to make the metal structure finer, and also to remove internal defects such as cavities.

  As described above, the rotary tool 4 and the probe 5 are pressed against the workpiece W to rotate at high speed, and the rotary tool 4 is moved by the feed moving mechanism of the moving mechanism 3 in the direction of arrow B which is the feed direction. As a result, the surface layer of the work W is reformed along the movement path L of the rotary tool 4 by friction stirring. That is, the surface layer Wa of the work W subjected to the friction stir processing is surface-modified.

  FIG. 4 is a schematic diagram for explaining a difference in a reforming effect by friction stirring. Here, FIG. 4 is a diagram viewed from the arrow A in FIG. In FIG. 4, the side where the rotation direction C (C1) of the rotary tool 4 and the probe 5 coincides with the feed direction B is AS (Advanced Side), and the rotation direction C (C2) of the rotary tool 4 and the probe 5 and the feed direction B. The side opposite to the above is referred to as RS (Recreating Side). The present inventor has found that in the surface Wa subjected to friction stirring, the vicinity of the AS is more refined in the vicinity of the AS than in the vicinity of the RS, and the effect of improving the strength and ductility is greater. .

  FIG. 5 to FIG. 7 are schematic diagrams illustrating the features of the method for modifying the surface of a light metal casting according to the present embodiment. Here, FIG. 5 is a view of a workpiece W1 which is a member formed of a light metal casting as viewed from a feed direction of the rotary tool 4 and the probe 5. The upper part of FIG. 6 is a view of the work W1 viewed from the feed direction of the rotary tool 4 and the probe 5, and the lower part of FIG. 6 is a view of the work W1 viewed from the axial direction of the rotary tool 4 and the probe 5. FIG. 7 is a view of the work W1 as viewed from the feed direction of the rotary tool 4 and the probe 5.

  As shown in FIG. 5, it is assumed that a workpiece W1, which is a member formed of a light metal casting, has a welding portion S1 at which stress is easily concentrated. The region S2 near the welding location S1 is likely to contain internal defects, and is likely to be the weakest in terms of strength. For this reason, when the work W1 receives an impact, there is a high possibility that destruction will occur in the region S2 near the welding location S1. However, in the region S2 near the welding point S1, it is difficult to control how the fracture occurs in terms of design, and therefore, when the work W1 receives an impact, the fracture occurs at least in the region S2 near the welding point S1. I don't want it. For this reason, it is necessary to increase the strength of the region S2 near the welding point S1 than the strength of the region other than the region S2 such as the region S3 and the region S4.

  Therefore, in the method for modifying the surface of a light metal casting according to the present embodiment, as shown in FIG. 6, a side where the rotation direction and the feed direction of the rotary tool 4 and the probe 5 coincide with the area S2 near the welding point S1. To be the AS. That is, the AS on the side where the rotation direction of the rotary tool 4 and the probe 5 coincides with the feed direction comes to a portion where the strength of the work W1 is to be increased by the reforming. At this time, the RS on the side where the rotation direction and the feed direction of the rotating tool 4 and the probe 5 are opposite to each other comes to the region S3. Thus, the rotary tool 4 and the probe 5 are set, and the rotary tool 4 and the probe 5 are sent while being rotated.

  FIG. 7 is a photomicrograph of the metal structure on the surface of the workpiece W1 after the method for modifying the surface of a light metal casting described with reference to FIGS. 5 and 6 is performed. Here, the work W1 is an aluminum alloy casting (ADT10-F). In FIG. 7, P1 shows a micrograph of a metal structure in a region S2 near the welding point S1 in the surface layer Wa of the work W1 on which the friction stir processing has been performed. Further, a micrograph of the metal structure of the region S3 in the surface layer Wa of the work W1 subjected to the frictional stirring is shown in P2, and a micrograph of the metal structure in the region S4 is shown in P3. In P1, P2, and P3 in FIG. 7, the portions that appear black are eutectic silicon.

  As shown in FIG. 7, P1 which is a micrograph of the metal structure in the region S2 is eutectic silicon compared to P2 which is a micrograph of the metal structure in the region S3 and P3 which is a micrograph of the metal structure in the region S4. Can be confirmed to be more finely distributed. The region S3 is a region which was located in the direction of the RS when the friction stir processing was performed. However, although the metal structure is refined as compared with the base material of the work W1 shown in FIG. 2, the refinement is sufficiently performed. There are many places that do not exist. The metal structure of the region S4 between the region S2 and the region S3 is finer than that of the region S3, but the metal structure is not finer than that of the region S2.

  As described above, in the region S2 where the strength is particularly required on the surface of the work W1 after the surface modification method of the light metal casting according to the present embodiment, the region other than the region S2 The surface can be made finer and the strength can be further increased as compared with S3 and the region S4.

  FIG. 8 is a flowchart showing the flow of the method for modifying the surface of a light metal casting according to the present embodiment. As shown in FIG. 8, first, the AS, which is the side where the rotation direction of the rotary tool 4 and the probe 5 coincides with the feed direction, comes to a part where the strength is to be further increased by the reforming of the light metal casting. On the other hand, the rotation tool 4 and the probe 5 are positioned (Step S1). Subsequently, the rotating tool 4 and the probe 5 are pressed against the surface of the light metal casting while rotating (Step S2). Subsequently, the rotary tool 4 and the probe 5 are fed and moved along a predetermined path (step S3).

  FIG. 9 is a schematic diagram illustrating another example (an example different from FIG. 6) of a method of moving the rotary tool 4 and the probe 5 in a feed movement. Here, the upper part of FIG. 9 is a view as seen from the feed direction of the rotary tool 4 and the probe 5, and the lower part of FIG. 9 is a view as seen from the axial direction of the rotary tool 4 and the probe 5. As shown in FIG. 9, the feed movement of the rotary tool 4 and the probe 5 is performed a plurality of times in the same feed direction B, and each feed movement is performed by changing the path L2 of the next feed movement to the path L1 of the previous feed movement. Alternatively, the probe 5 may be shifted in parallel by a predetermined width J equal to or less than the diameter D of the probe 5. In this way, the portion that was not AS in the previous feeding movement path L1 becomes AS in the next feeding movement path L2 or the subsequent feeding movement path, so that the surface of the workpiece W is evenly distributed. It can be miniaturized.

  FIG. 10 is a schematic diagram illustrating still another example (an example different from FIGS. 6 and 9) of a method of moving the rotary tool 4 and the probe 5 in a feed movement. Here, FIG. 10 is a diagram viewed from the axial direction of the rotating tool 4 and the probe 5. As shown in FIG. 10, the rotating tool 4 and the probe 5 are arranged such that the AS where the rotation direction and the feed direction coincide with each other comes to the edge M side of the workpiece W2 which is a member formed of light metal casting. The probe 4 and the probe 5 may be fed and moved according to a path L3 circling along the edge M. In this way, by setting the AS to the edge M and the RS to the inside of the work W2, the metal structure on the surface is refined at a position near the edge M. Thereby, the strength of the outer periphery of the work W2 can be further increased.

  As described above, the present invention has been described with reference to the above embodiments. However, the present invention is not limited only to the configuration of the above embodiments, and those skilled in the art will be within the scope of the claims of the present application. Of course, it includes various variations, modifications, and combinations that can be made.

DESCRIPTION OF SYMBOLS 1 Friction stirrer 2 Spindle drive part 3 Moving mechanism 4 Rotary tool 5 Probe 6 Pedestal part 7 Post 8 Work table W, W1, W2 Work

Claims (3)

A method for modifying the surface of a light metal casting by a friction stir process of rotating and rotating the rotating shaft and the rotor while pressing the rotating shaft and the rotor on the surface of the casting to modify the surface of the casting.
To the portion of the light metal casting that is desired to increase the strength by reforming, the feed is performed while rotating the rotary shaft and the rotor so that the side where the rotation direction and the feed direction of the rotary shaft and the rotor coincide with each other comes. Surface modification method for light metal castings. The feed movement is performed a plurality of times in the same feed direction,
2. The surface of the light metal casting according to claim 1, wherein each feed movement is performed by shifting a path of a next feed movement in parallel with a path of a previous feed movement by a predetermined width equal to or less than a diameter of the rotor. Reforming method.   The side where the rotation direction and the feeding direction of the rotating shaft and the rotor coincide with each other comes to the edge side of the light metal casting, and the rotating shaft and the rotor are fed and moved according to a path orbiting along the edge of the light metal casting. The method for modifying a surface of a light metal casting according to claim 1.