Abstract:
The invention provides a friction stir welding method of forming a weld portion having an excellent fatigue property in the case of welding a weld material by using a friction stir welding method. The invention provides a friction stir welding method structured such as to insert a tool provided in such a manner that a pin-shaped probe protrudes to an end surface of a columnar member to a weld material in a state of being rotated, and move the tool in a state of being rotated, thereby welding two or more weld materials in accordance with a friction stirring, in which a cavity portion is provided in a part of a weld portion of the weld material, a member is formed in the cavity portion, and the weld material is welded by the friction stirring. In accordance with the invention, since an unwelded portion is not formed near the cavity portion, a notch effect is reduced, and it is possible to form the weld member which is excellent in the fatigue property.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a friction stir welding method and a weld structure welded by the friction stir welding method. 
   2. Description of Related Art 
   A friction stir welding method is described, for example, in patent document 1 (JP-B2-2712838 (WO93/10935)), the friction stir welding method is structured such as to insert a columnar member (hereinafter, refer to as a rotating tool) made of a substantially harder material than a weld material to a weld portion of the weld material while rotating, and move the rotating tool while rotating, thereby welding by a friction heat generated between the rotating tool and the weld material. 
   The welding method softens the weld material by the friction heat between the rotating tool and the weld material, utilizes a plastic flow phenomenon coming up with the rotation of the rotating tool, and is based on a different principle from a method of melting the weld material so as to weld, for example, an arc welding or the like. 
   There is a case that a cavity portion is provided near the weld portion at a time of manufacturing the weld structure having an excellent fatigue strength by using this welding method. An upper portion of the cavity portion is welded by inserting the rotating tool from a perpendicular direction to the weld surface while rotating at a high speed. 
   In this case, there is not used a backing metal supporting a load at a time of welding. Accordingly, in the case that the weld is executed near the cavity portion, there is a possibility that an unwelded root defect is formed in the weld portion, on the basis of a deformation of the member near the cavity portion. 
   Therefore, in the case that a stress is applied to the weld portion, an unwelded portion which tends to cause a notch effect is formed, or a stress concentration to the weld portion becomes higher, so that it is considered that fatigue properties are deteriorated. However, the formation of the unwelded portion has not been researched. 
   BRIEF SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a friction stir welding method of forming a weld portion having an excellent fatigue property in the case of welding a weld material by using a friction stir welding method, and a weld structure. 
   A friction stir welding method in accordance with the present invention is structured such as to insert a rotating tool provided in such a manner that a pin-shaped probe protrudes to an end surface of a columnar member to a weld material in a state of being rotated, and move the rotating tool in a state of being rotated, thereby welding two or more weld materials in accordance with a friction stirring. Further, a cavity portion is provided in a part of a weld portion of the weld material, a member is formed in the cavity portion, and the weld material is welded by the friction stirring. 
   Further, in accordance with the present invention, there is provided a weld structure formed in a friction stir welding method of welding two or more weld materials in accordance with a friction stirring, whereby a cavity portion is provided in a part of a weld portion of the weld material, and a member is formed in the cavity portion. 
   In the case of welding in accordance with the friction stirring, there is a case that a weld is applied to a joint portion of the weld material, or there is a case that the weld is applied from one of the weld materials. 
   In this case, the cavity portion is preferably formed in a circular shape, and may be formed in a circular arc shape having a predetermined radius of curvature with respect to a direction of a weld portion of the weld material. 
   Further, the member embedded in the cavity portion is preferably constituted by a member having an approximately equal cross sectional shape to that of the cavity portion. 
   Further, the member formed in the cavity portion is preferably made of a harder material than the weld material, and a radius of the cavity portion is preferably equal to or less than one half of a thickness of the weld material. 
   In the case that the weld material is welded by using the friction stir welding method in accordance with the present invention, it is possible to provide the friction stir welding method of forming the weld portion having an excellent fatigue property and a weld structure. 
   Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a conceptual view showing a positional relation between a weld material and an embedded member in accordance with one example of a welding method of the present invention; 
       FIG. 2  is a conceptual view showing a state before welding in accordance with one example of the welding method of the present invention; 
       FIG. 3  is a conceptual view showing a state under welding in accordance with one example of the welding method of the present invention; 
       FIG. 4  is a view showing a defect generating condition in a weld portion having a cavity portion and a positional relation between a rotating tool and a weld member; 
       FIG. 5  is a view showing a cross sectional photograph in the weld portion using the embedded member; 
       FIG. 6  is a conceptual view in the case of applying a frictional stir welding method using the embedded member to a weld structure; 
       FIG. 7  is a conceptual view showing a positional relation between a weld material and an embedded member in accordance with one example of a lap welding method of the present invention; 
       FIG. 8  is a conceptual view showing a state before welding in accordance with one example of the lap welding method of the present invention; 
       FIG. 9  is a conceptual view showing a state under welding in accordance with one example of the lap welding method of the present invention; 
       FIG. 10  is a conceptual view showing a positional relation between a weld material and an embedded member in accordance with one example of a butt welding method of the present invention; 
       FIG. 11  is a conceptual view showing a state before welding in accordance with one example of the butt welding method of the present invention; and 
       FIG. 12  is a conceptual view showing a state under welding in accordance with one example of the butt welding method of the present invention; 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A description will be given below of embodiments in accordance with the present invention with reference to the accompanying drawings. 
   Embodiment 1 
     FIGS. 1 ,  2  and  3  show one example of a welding method in accordance with the present invention, and show a case of applying a friction stir welding method to a lap joint. 
     FIG. 1  shows a material  1  and a material  2  corresponding to a weld material. A cavity portion  3  and a cavity portion  4  respectively having semicircular cross sectional shapes are formed in the material  1  and the material  2 . 
   A cavity portion having a circular cross sectional shape is formed at a time of lapping the material  1  and the material  2 , thereby forming an embedded member  5  having an approximately equal cross sectional shape to the cavity portion. The material  1  and the material  2  corresponding to two weld materials having the cavity portions of the semicircular cross sectional shape are lapped via the embedded member  5 . 
   Both of the material  1  and the material  2  are made of an aluminum alloy. An applied material is essentially constituted by a material which can be friction stir welded. For example, metals such as a magnesium alloy, a copper alloy, a steel material and the like correspond thereto. 
   Both of thicknesses of the material  1  and the material  2  are 10 mm. A thickness of the applied material is determined on the basis of an applied material, a friction stir welding apparatus and a capacity of a rotating tool, however, in the case of the aluminum alloy, it is possible to apply to the thickness between about 0.5 mm and 100 mm. 
     FIG. 2  is a conceptual view of a state in which the material  1 , the material  2  and the embedded member  5  are set in such a manner as to be welded. The cavity portion  3  and the cavity portion  4  are lapped in such a manner that end portions thereof are aligned, and a cavity portion having a circular cross sectional shape is provided. The embedded member  5  is set to the cavity portion  7 . The cross sectional shape of the embedded member  5  is approximately equal to that of the cavity portion  7 . A radius of the cavity portion  7  formed by the cavity portion  3  and the cavity portion  4  having the semicircular cross sectional shape is about one half of the thickness of the material  1 . 
   In other words, in order to form the weld portion having an excellent fatigue property, it is necessary to set a member having a larger radius of curvature than the unwelded portion formed near the weld portion. 
   Accordingly, the radius of the cavity portion  7  is larger than a gap of the lap surface formed by the material  1  and the material  2 , and is limited to one half of the thickness of the material  1 . 
   The embedded member  5  is made of a steel material, and is harder than the material  1  and the material  2 . 
   In order to form the weld portion which is excellent in the fatigue property, the cross sectional shape of the cavity portion  7  and the embedded member  5  is not limited to the circular shape, but may be changed as far as a cross sectional shape has a large radius of curvature. For example, an oval shape or the like corresponds thereto. 
   Further,  FIG. 2  shows a positional relation among the rotating tool  6 , a weld line and a weld surface. The rotating tool  6  is inserted from a direction which is in parallel to the weld surface  8  and is perpendicular to the weld surface  9 . 
   An end surface  11  close to the embedded member  5  in a probe  10  existing in an end portion of the rotating tool  6  is inserted in such a manner as to be approximately in contact with the embedded member  5 , and a distance between the end surface  11  and the embedded member  5  at a time of inserting the rotating tool  6  is set to about 0.5 mm. 
     FIG. 3  shows a conceptual view of a state in which the rotating tool  6  is inserted to the weld surface  8  and the weld surface  9 , and the material  1  and the material  2  are welded along the weld line  12 . 
   The rotating tool  6  is rotated in a clockwise direction as seen from the above of the rotating tool  6 . The weld makes progress toward a far side from a near side of the material. 
   As shown in  FIG. 3 , a stir zone  13  stirred by the rotating tool  6  is formed in the weld portion in such a manner as to be in contact with the embedded member  5 . In accordance with the structure mentioned above, the unwelded portion is not formed between the stir zone  13  and the embedded member  5 . 
     FIG. 4  shows a cross section to which the friction stir welding is applied by forming only the cavity portion without using the embedded member  5 . 
   A positional relation between a material  14  and a material  15  is shown by a dotted line  16 . A cavity portion obtained by lapping the semicircular cross sectional shape is provided on a surface in which the material  14  and the material  15  are brought into contact with each other. A shape of the cavity portion before the friction stir welding is applied thereto has a circular cross sectional shape as described by a dotted line  17 . 
   A shape of the rotating tool  18  is structured such that a diameter of a shoulder portion is 10 mm, a diameter of a probe  20  is 4 mm, and a length of the probe  20  is 10 mm. 
   A description will be given of a positional relation between the rotating tool  18  and the cavity portion  17  by using  FIG. 4 . When the rotating tool  18  is inserted to the material  14  and the material  15 , a distance between an end surface  21  of the probe  20  close to the cavity portion and the cavity portion  17  is 0.2 mm. A rotating speed of the rotating tool  18  is set to 1000 rotation/min, and a welding speed is set to 100 mm/min. 
   As is understood from  FIG. 4 , a shape of the cavity portion  17  after the friction stir welding is applied thereto is largely deformed, and loses the circular shape. This is because about some hundreds kg to about one ton load is applied to the weld portion by inserting and traveling the rotating tool  18  at a time of the friction stir welding, whereby the material exposed to the load of the material  14  and the material  15  flows into the cavity portion in case that a backing metal supporting the load does not exist. 
   As mentioned above, the shape of the cavity portion provided for improving the fatigue property of the weld portion collapses. In other words, since the surface having the large radius of curvature does not exist near the weld portion, and the unwelded portion is formed in the weld surface  23 , the stress concentration to the weld portion becomes higher and the fatigue property is deteriorated, in the case that the stress is applied in the perpendicular direction to the weld surface  23 . 
   On the contrary,  FIG. 5  shows a cross section photograph in the case that the friction stir welding is applied by using the embedded member. 
   The positional relation between the rotating tool  18  and an embedded member  24  after the end of the welding is shown in  FIG. 5 . A welding condition is approximately equal to that shown in  FIG. 4 . There can be observed that the unwelded defect does not appear between the rotating tool  18  and the embedded member  24 , and a complete weld is achieved. Even in the case that the stress is applied to the weld portion, the unwelded portion is not formed, and the surface to which the stress is applied exhibits the large curvature, so that it is possible to avoid the stress concentration. 
   As mentioned above, it is possible to improve the fatigue property of the weld portion by setting the embedded member in the cavity portion having the circular cross section so as to weld. 
     FIG. 6  shows a conceptual view of a case that the welding method is applied to the weld structure. 
   The weld structure is constituted by a pressure container, and is structured such that a material  25  corresponding to a container and a material  26  corresponding to a lid are lapped over such that end portions are aligned with each other. A circular cavity portion  28  is provided in a surface  27  in which the material  25  and the material  26  are in contact with each other. A member  29  having an approximately equal cross sectional shape is embedded in the cavity portion  28 . The material  25  and the material  26  are welded in accordance with a friction stir welding method by using a rotating tool  30 . 
   A positional relation between the rotating tool  30  and the weld surface and a positional relation between the rotating tool  30  and the embedded member  29  is the same as those of  FIGS. 1 ,  2  and  3 . 
   The unwelded portion is not formed between a stir zone  31  formed thereby and the embedded member  29  even by applying the friction stir welding, and a surface having a large curvature is obtained. A space  32  is formed in an inner side thereof by welding the material  25  and the material  26 . In the case that a repeated stress is applied to a direction perpendicular to the surface  27  by the space  32 , the unwelded portion is not formed, so that it is possible to form a weld portion which is excellent in a fatigue strength. 
   The weld mentioned above can be applied to a weld structure to which the repeated stress is applied, for example, a cooling apparatus having a water channel, a pressure container or the like. 
   Embodiment 2 
     FIGS. 7 ,  8  and  9  show a welding method in accordance with the other embodiment of the present invention. 
   The present embodiment corresponds to a case that the present invention is applied to a lap joint, however, shapes of a material  33  and a material  34  are different from the material  1  and the material  2  of the embodiment 1. 
     FIG. 7  shows a positional relation among the material  33  and the material  34 , a cavity portion  38  having a semicircular cross sectional shape and a cavity portion  39  having a semicircular cross sectional shape, and an embedded member  40  having a circular cross sectional shape. The cavity portion  38  and the cavity portion  39  are provided on a surface in which the material  33  and the material  34  are brought into contact with each other, that is, a butt weld surface  35  and a butt weld surface  36 . Both of the material  33  and the material  34  are made of an aluminum alloy. The embedded member  40  is made of a harder material than the material  33  and the material  34 , and is made of a steel material. Thicknesses of the material  33  and the material  34  are the same as those shown in the embodiment 1. 
     FIG. 8  is a conceptual view showing a state in which the material  33 , the material  34 , the cavity portion  38 , the cavity portion  39  and the embedded member  40  are set in such a manner as to be welded. 
     FIG. 8  shows a positional relation among the butt weld surface  35 , the butt weld surface  36  and a rotating tool  37 . The rotating tool  37  is inserted from a direction perpendicular to the butt weld surface  35  and the butt weld surface  36 . 
   A cavity portion  41  having a circular cross sectional shape is provided by lapping the cavity portion  38  and the cavity portion  39  in such a manner that end portions thereof are aligned with each other. The embedded member  40  is set to the cavity portion  41 . A cross sectional shape of the embedded member  40  is approximately equal to the cavity portion  41 . A radius of the cavity portion  41  formed by the cavity portion  38  having the semicircular cross sectional shape and the cavity portion  39  having the semicircular cross sectional shape is approximately one half of a thickness of the material  33 , and is set to the same as described in the embodiment 1. 
   A positional relation between an end surface  43  of the embedded member  40  side in the probe  42  at a time of inserting the rotating tool  37  and the embedded member  40  is the same as described in the embodiment 1. 
     FIG. 9  shows a conceptual view of a state in which the material  33  and the material  34  are welded by inserting the rotating tool  37  to the butt weld surface  35  and the butt weld surface  36  from a direction of the material  33  while keeping the positional relation between the end surface  43  and the embedded member  40 . 
   The rotating tool  37  is rotated in a clockwise direction as seen from the above of the rotating tool  37 . A frictional stir welding makes progress toward a far side from a near side of the drawing. 
   As shown in  FIG. 9 , a stir zone  44  stirred by the rotating tool  37  is formed in the weld portion in such a manner as to be in contact with the embedded member  40 , and an unwelded portion is not formed between the stir zone and the embedded member  40 . 
   As a result, it is possible to improve a fatigue characteristic of the weld portion. 
   Embodiment 3 
     FIGS. 10 ,  11  and  12  show the other embodiment in accordance with the present invention. The embodiment corresponds to a case that the frictional stir welding is applied to a butt joint. 
     FIG. 10  shows a positional relation among a material  45  and a material  46 , a cavity portion  47  having a semicircular cross sectional shape and a cavity portion  48  having a semicircular cross sectional shape, and an embedded member  49  having a circular cross sectional shape. 
   The cavity portion  47  and the cavity portion  48  are provided on a surface in which the material  45  and the material  46  are brought into contact with each other. Both of the material  45  and the material  46  are made of an aluminum alloy. An applied material is the same as described in the embodiment 1. Thicknesses of the material  45  and the material  46  are both set to 10 mm. 
     FIG. 11  is a conceptual view showing a state in which the material  45 , the material  46 , the cavity portion  47 , the cavity portion  48  and the embedded member  49  are set in such a manner as to be welded. 
   A cavity portion  50  having a circular cross sectional shape is provided by lapping the cavity portion  47  and the cavity portion  48  in such a manner that end portions thereof are aligned with each other. A cross sectional shape of the embedded member  49  is approximately equal to the cavity portion  50 . A radius of the cavity portion  50  formed by the cavity portion  47  and the cavity portion  48  is approximately one half of a thickness of the material  45  and the material  46 . 
     FIG. 11  shows a positional relation between a rotating tool  51  and a weld line. 
   The rotating tool  51  is inserted from a direction perpendicular to a butt weld line  53 . A lower end surface  55  in a probe  54  existing in an end portion of the rotating tool  51  is inserted to a position which is approximately in contact with the embedded member  49 , and a distance between the end surface  55  and the embedded member  49  at a time of inserting the rotating tool  51  is set to about 0.1 mm. 
     FIG. 12  shows a conceptual view of a state in which the material  45  and the material  46  are welded by inserting the rotating tool  51  along the weld line  53 . 
   The rotating tool  51  is rotated in a clockwise direction as seen from the above of the rotating tool  51 . A welding makes progress toward a far side from a near side of the drawing. 
   As shown in  FIG. 12 , a stir zone  56  stirred by the rotating tool  51  is formed in the weld portion in such a manner as to be in contact with the embedded member  49 . 
   In accordance with the structure mentioned above, an unwelded portion is not formed between the stir zone  56  and the embedded member  49 . A load from about some hundreds of kg to about one ton is applied to the weld portion by inserting and traveling the rotating tool  51  at a time of the friction stir welding, however, since the embedded member  49  supporting the load is provided, the curvature is not changed, and the unwelded portion is not formed, so that it is possible to support the load. In the case that a repeated stress is applied in a perpendicular direction to the weld surface, the unwelded portion is not formed. Accordingly, it is possible to form the weld portion which is excellent in a fatigue strength. 
   In accordance with these embodiments, since the unwelded portion is not formed near the cavity portion, the notch effect is reduced, and it is possible to form the weld member which is excellent in the fatigue property. 
   The present invention relates to the friction stir welding method of welding in a state in which the cavity portion is provided in the weld surface, and the embedded member is formed in the cavity portion, in the case of applying the friction stir welding. 
   It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.