Patent Publication Number: US-2023135888-A1

Title: Method for manufacturing liquid-cooling jacket and friction stir welding method

Description:
TECHNICAL FIELD 
     The present invention relates to a method for manufacturing a liquid-cooling jacket and a friction stir welding method. 
     BACKGROUND ART 
     A method for manufacturing a liquid-cooling jacket utilizing friction stir welding is performed. For example, Patent Literature 1 discloses a method for manufacturing a liquid-cooling jacket.  FIG.  12    is a cross sectional view showing a conventional method for manufacturing a liquid-cooling jacket. In the conventional method for manufacturing a liquid-cooling jacket, friction stir welding is performed to a butted portion J 10  where a side face  102   c  of a sealing body  102  made of an aluminum alloy is butted against a step side face  101   c  of a stepped portion of a jacket body  101  made of an aluminum alloy. Further, in the conventional method for manufacturing a liquid-cooling jacket, friction stir welding is performed in a state that only a stirring pin FD 2  of a rotary tool FD is inserted in the butted portion J 10 . Furthermore, in the conventional method for manufacturing a liquid-cooling jacket, the rotary tool FD is relatively moved in a state that a rotation axis XA of the rotary tool FD overlaps with the butted portion J 10 . 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2015-131321 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     In general, the jacket body  101  tends to have a complex shape, so, for example, in some cases, the jacket body  101  is made of a casting material of a 4000 series aluminum alloy, and a member having a relatively simple shape such as the sealing body  102  is made of an expansible material of a 1000 series aluminum alloy. Thus, in some cases, a liquid-cooling jacket is manufactured by joining members made of different kinds of aluminum alloys together. In such cases, in general, the jacket body  101  has a higher hardness than the sealing body  102 . Hence, in a case where friction stir welding is performed in such a manner as that shown in  FIG.  12   , the material resistance to the stirring pin FD 2  to receive from the jacket body  101  is larger than that to receive from the sealing body  102 . As the result, it is difficult to stir different kinds of materials with good balance by the stirring pin FD 2  of the rotary tool FD, so that there exists a problem that a cavity defect is caused in a plasticized region formed by joining to reduce the joint strength. 
     Further, after a liquid-cooling jacket is manufactured, in some cases, quality control of the liquid-cooling jacket is performed, for example, by ultrasonic flaw detection. In this inspection, the presence or absence of poor joining can be detected by the ultrasonic flaw detection. However, there is a problem that it is not possible to know where the rotary tool has passed. 
     From such a view point, it is an object of the present invention to provide a method for manufacturing a liquid-cooling jacket and a friction stir welding method, the methods being capable of appropriately joining different kinds of aluminum alloys and knowing where the rotary tool has passed. 
     Solution to Problem 
     In order to solve the problem, the present invention is characterized by a method for manufacturing a liquid-cooling jacket, in which a jacket body provided with a bottom portion and a peripheral wall portion rising from a peripheral edge of the bottom portion, and a sealing body to seal an opening portion of the jacket body are friction stir welded, wherein the jacket body is made of a material harder than the sealing body, wherein a rotary tool used for friction stirring is provided with a shoulder portion and a stirring pin hanging down from a center of a bottom face of the shoulder portion, and wherein an outer circumferential face of the stirring pin is inclined to have a smaller diameter with increasing distance toward a tip thereof, the method comprising: a preparation process in which a peripheral wall stepped portion having a step bottom face and a step side face is formed along an inner peripheral edge of the peripheral wall portion, the step side face rising from the step bottom face toward the opening portion; a placing process in which by placing the sealing body on the jacket body, a first butted portion is formed so that the step side face of the peripheral wall stepped portion and an outer peripheral side face of the sealing body are butted against each other, and a second butted portion is formed so that the step bottom face overlaps with a back face of the sealing body; a primary joining process in which a coarse portion having a predetermined width is formed in the vicinity of the step side face within a plasticized region while the rotary tool is being moved one round along the first butted portion to perform friction stirring in a state that the tip of the stirring pin of the rotary tool being rotated is inserted to the same depth as or slightly deeper than the step bottom face and the bottom face of the shoulder portion is in contact with the sealing body and the stirring pin is slightly in contact with at least an upper portion of the jacket body; and an inspection process in which a passed position of the stirring pin is specified by performing, after the primary joining process, a flaw detection to detect the coarse portion. 
     According to this manufacturing method, the metal of the sealing body in the first butted portion is mainly stirred to be plastically fluidized because of the frictional heat between the sealing body and the stirring pin, so that the step side face and an outer peripheral side face of the sealing body can be joined together in the first butted portion. Further, since friction stirring is performed in a state that the bottom face of the shoulder portion is in contact with the front face of the sealing body and the stirring pin is slightly in contact with at least the upper portion of the step side face of the jacket body, metal mixing into the sealing body from the jacket body can be reduced as much as possible while ensuring the joint strength. Hereby, the metal of the sealing body is mainly frictionally stirred in the first butted portion, so that lowering of the joint strength can be suppressed. 
     Further, since the stirring pin is inserted to the same depth as or slightly deeper than the step bottom face, metal mixing into the sealing body from the jacket body can be reduced as much as possible while enhancing the joint strength of the second butted portion. Furthermore, by deliberately forming the coarse portion having the predetermined width, the passed position of the stirring pin can be detected through flaw detection. Hereby, the quality control work can be more easily performed. 
     Further, the present invention is characterized by a method for manufacturing a liquid-cooling jacket, in which a jacket body provided with a bottom portion and a peripheral wall portion rising from a peripheral edge of the bottom portion, and a sealing body to seal an opening portion of the jacket body are friction stir welded, wherein the jacket body is made of a material harder than the sealing body, wherein a rotary tool used for friction stirring is provided with a shoulder portion and a stirring pin hanging down from a center of a bottom face of the shoulder portion, and wherein an outer circumferential face of the stirring pin is inclined to have a smaller diameter with increasing distance toward a tip thereof, the method comprising: a preparation process in which a peripheral wall stepped portion having a step bottom face and a step side face is formed along an inner peripheral edge of the peripheral wall portion, the step side face rising from the step bottom face toward the opening portion, and the sealing body is formed to have a thickness larger than a height dimension of the step side face of the peripheral wall stepped portion; a placing process in which by placing the sealing body on the jacket body, a first butted portion is formed so that the step side face of the peripheral wall stepped portion and an outer peripheral side face of the sealing body are butted against each other, and a second butted portion is formed so that the step bottom face overlaps with a back face of the sealing body; a primary joining process in which a coarse portion having a predetermined width is formed in the vicinity of the step side face within a plasticized region while the rotary tool is being moved one round along the first butted portion to perform friction stirring in a state that the tip of the stirring pin of the rotary tool being rotated is inserted to the same depth as or slightly deeper than the step bottom face and the bottom face of the shoulder portion is in contact with the sealing body and the stirring pin is slightly in contact with at least an upper portion of the jacket body; and an inspection process in which a passed position of the stirring pin is specified by performing, after the primary joining process, a flaw detection to detect the coarse portion. 
     According to this manufacturing method, the metal of the sealing body in the first butted portion is mainly stirred to be plastically fluidized because of the frictional heat between the sealing body and the stirring pin, so that the step side face and an outer peripheral side face of the sealing body can be joined together in the first butted portion. Further, since friction stirring is performed in a state that the bottom face of the shoulder portion is in contact with the front face of the sealing body and the stirring pin is slightly in contact with at least the upper portion of the step side face of the jacket body, metal mixing into the sealing body from the jacket body can be reduced as much as possible while ensuring the joint strength. Hereby, the metal of the sealing body is mainly frictionally stirred in the first butted portion, so that lowering of the joint strength can be suppressed. 
     Further, since the stirring pin is inserted to the same depth as or slightly deeper than the step bottom face, metal mixing into the sealing body from the jacket body can be reduced as much as possible while enhancing the joint strength of the second butted portion. Furthermore, by deliberately forming the coarse portion having the predetermined width, the passed position of the stirring pin can be detected through flaw detection. Hereby, the quality control work can be more easily performed. Metal shortage of the joined portion can be prevented by enlarging the thickness of the sealing body. 
     Furthermore, the present invention is characterized by a method for manufacturing a liquid-cooling jacket, in which a jacket body provided with a bottom portion and a peripheral wall portion rising from a peripheral edge of the bottom portion, and a sealing body to seal an opening portion of the jacket body are friction stir welded, wherein the jacket body is made of a material harder than the sealing body, wherein a rotary tool used for friction stirring is provided with a shoulder portion and a stirring pin hanging down from a center of a bottom face of the shoulder portion, and wherein an outer circumferential face of the stirring pin is inclined to have a smaller diameter with increasing distance toward a tip thereof, the method comprising: a preparation process in which a peripheral wall stepped portion having a step bottom face and a step side face is formed along an inner peripheral edge of the peripheral wall portion, the step side face obliquely rising from the step bottom face toward the opening portion to spread, and the sealing body is formed to have a thickness larger than a height dimension of the step side face of the peripheral wall stepped portion; a placing process in which by placing the sealing body on the jacket body, a first butted portion is formed to have a gap between the step side face of the peripheral wall stepped portion and an outer peripheral side face of the sealing body, and a second butted portion is formed so that the step bottom face overlaps with a back face of the sealing body; a primary joining process in which a coarse portion having a predetermined width is formed in the vicinity of the step side face within a plasticized region while the rotary tool is being moved one round along the first butted portion to perform friction stirring in a state that the tip of the stirring pin of the rotary tool being rotated is inserted to the same depth as or slightly deeper than the step bottom face and the bottom face of the shoulder portion is in contact with the sealing body and the stirring pin is slightly in contact with at least an upper portion of the jacket body; and an inspection process in which a passed position of the stirring pin is specified by performing, after the primary joining process, a flaw detection to detect the coarse portion. 
     According to this manufacturing method, the metal of the sealing body in the first butted portion is mainly stirred to be plastically fluidized because of the frictional heat between the sealing body and the stirring pin, so that the step side face and an outer peripheral side face of the sealing body can be joined together in the first butted portion. Further, since friction stirring is performed in a state that the bottom face of the shoulder portion is in contact with the front face of the sealing body and the stirring pin is slightly in contact with at least the upper portion of the step side face of the jacket body, metal mixing into the sealing body from the jacket body can be reduced as much as possible while ensuring the joint strength. Hereby, the metal of the sealing body is mainly frictionally stirred in the first butted portion, so that lowering of the joint strength can be suppressed. 
     Further, since the stirring pin is inserted to the same depth as or slightly deeper than the step bottom face, metal mixing into the sealing body from the jacket body can be reduced as much as possible while enhancing the joint strength of the second butted portion. Furthermore, by deliberately forming the coarse portion having the predetermined width, the passed position of the stirring pin can be detected through flaw detection. Hereby, the quality control work can be more easily performed. Further, by forming both of the outer circumferential face of the stirring pin and the step side face to be inclined, it can be avoided that the stirring pin and the step side face largely come into contact with each other. Furthermore, metal shortage of the joined portion can be prevented by enlarging the thickness of the sealing body. 
     It is preferable that the sealing body is made of an aluminum wrought alloy material and the jacket body is made of an aluminum alloy casting material. 
     It is preferable that the rotary tool is rotated clockwise in a case where the stirring pin of the rotary tool has a spiral groove in the outer circumferential face thereof, the spiral groove being counterclockwise with increasing distance from a base toward the tip thereof, and that the rotary tool is rotated counterclockwise in a case where the stirring pin of the rotary tool has a spiral groove in the outer circumferential face thereof, the spiral groove being clockwise with increasing distance from a base toward the tip thereof. 
     Hereby, the plastically fluidized metal is led toward the tip side of the stirring pin through the spiral groove, so that the occurrence of burrs can be reduced. 
     It is preferable that in the primary joining process, a rotational direction and an advancing direction of the rotary tool are set so that within the plasticized region to be formed at a moving trace of the rotary tool, a jacket body side is an advancing side and a sealing body side is a retreating side. 
     Hereby, the jacket body side is set to be an advancing side and the stirring action around the first butted portion by the stirring pin is enhanced, so that rising of the temperature at the first butted portion is expected, and the step side face and the outer peripheral side face of the sealing body can be more firmly joined together at the first butted portion. 
     Furthermore, the present invention is characterized by a friction stir welding method in which a first member and a second member are joined together with use of a rotary tool, wherein the first member is made of a material harder than the second member, wherein the rotary tool used for friction stirring is provided with a shoulder portion and a stirring pin hanging down from a center of a bottom face of the shoulder portion, and wherein an outer circumferential face of the stirring pin is inclined to have a smaller diameter with increasing distance toward a tip thereof, the method comprising: a preparation process in which a step portion having a step bottom face and a step side face rising from the step bottom face is formed in the first member; a placing process in which by placing the second member on the first member, a first butted portion is formed so that the step side face of the step portion and a side face of the second member are butted against each other, and a second butted portion is formed so that the step bottom face overlaps with a back face of the second member; a primary joining process in which a coarse portion having a predetermined width is formed in the vicinity of the step side face within a plasticized region while the rotary tool is being moved one round along the first butted portion to perform friction stirring in a state that the tip of the stirring pin of the rotary tool being rotated is inserted to the same depth as or slightly deeper than the step bottom face and the bottom face of the shoulder portion is in contact with a front face of the second member and the stirring pin is slightly in contact with at least an upper portion of the first member; and an inspection process in which a passed position of the stirring pin is specified by performing, after the primary joining process, a flaw detection to detect the coarse portion. 
     Advantageous Effects of Invention 
     According to the method for manufacturing a liquid-cooling jacket and the friction stir welding method according to the present invention, different kinds of metals can be appropriately joined together and it is possible to know where the rotary tool has passed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a side view showing a rotary tool according to one embodiment of the present invention. 
         FIG.  2    is a perspective view showing a preparation process of a method for manufacturing a liquid-cooling jacket according to a first embodiment of the present invention. 
         FIG.  3    is a cross sectional view showing a placing process of the method for manufacturing a liquid-cooling jacket according to the first embodiment. 
         FIG.  4    is a perspective view showing a primary joining process of the method for manufacturing a liquid-cooling jacket according to the first embodiment. 
         FIG.  5    is a cross sectional view showing the primary joining process of the method for manufacturing a liquid-cooling jacket according to the first embodiment. 
         FIG.  6    is a cross sectional view showing the liquid-cooling jacket after the primary joining process of the method for manufacturing a liquid-cooling jacket according to the first embodiment is finished. 
         FIG.  7    is a plan view showing an inspection process of the method for manufacturing a liquid-cooling jacket according to the first embodiment. 
         FIG.  8    is a view showing an example that an outer circumferential face of the stirring pin is kept away from a step side face. 
         FIG.  9    is a view showing an example that the outer circumferential face of the stirring pin is in contact with the step side face to a large extent. 
         FIG.  10    is a perspective view showing a preparation process of a method for manufacturing a liquid-cooling jacket according to a second embodiment. 
         FIG.  11    is a cross sectional view showing a primary joining process of the method for manufacturing a liquid-cooling jacket according to the second embodiment. 
         FIG.  12    is a cross sectional view showing a conventional method for manufacturing a liquid-cooling jacket. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present invention will be described with reference to the drawings where appropriate. First, a rotary tool which is used in a welding method according to the present embodiment will be described. The rotary tool is a tool to be used for friction stir welding. As shown in  FIG.  1   , a rotary tool F is made of, for example, tool steel, and is mainly formed of a shoulder portion F 1  and a stirring pin F 2 . A bottom face F 1   a  of the shoulder portion F 1  is a portion for pressing plastically fluidized metal. The shoulder portion F 1  has a cylindrical shape. 
     The stirring pin F 2  hangs down from a center of the bottom face F 1   a  of the shoulder portion F 1 , and is coaxial with the shoulder portion F 1 . The stirring pin F 2  has a tapered shape such that the diameter thereof decreases with increasing distance from the shoulder portion F 1  toward the tip. The stirring pin F 2  has a spiral groove on an outer circumferential face thereof. In this embodiment, the spiral groove is formed to be counterclockwise from the base toward the tip because the rotary tool F is rotated clockwise. 
     It should be noted that in a case where the rotary tool F is rotated counterclockwise, the spiral groove is formed to be clockwise from the base toward the tip. This makes it possible to guide plastically fluidized metal generated by friction stir welding toward the tip side of the stirring pin F 2  through the spiral groove. It is therefore possible to reduce the amount of metal to be leaked out of metal members to be joined together (jacket body  2  and sealing body  3 ). 
     In this embodiment, the rotary tool F is attached to the friction stir device capable of moving in the horizontal directions as well as in the vertical directions. It should be noted that the rotary tool F may be attached to a robot arm having a tip end equipped with a rotary drive means such as a spindle unit. 
     First Embodiment 
     A method for manufacturing a liquid-cooling jacket according to an embodiment of the present invention will be described in detail with reference to the drawings. As shown in  FIG.  2   , the method for manufacturing a liquid-cooling jacket  1  according to the embodiment of the present invention is a method where the liquid-cooling jacket  1  is manufactured by performing friction stir welding to a jacket body  2  and a sealing body  3 . The liquid-cooling jacket  1  includes the sealing body  3 , on which a heating element (not shown) is placed and inside which a fluid is allowed to flow to exchange heat with the heating element. It should be noted that, hereinafter, a “front face” means the face opposite to a “back face”. 
     The method for manufacturing a liquid-cooling jacket according to this embodiment includes a preparation process, a placing process, a primary joining process and an inspection process. The preparation process is a process to prepare the jacket body  2  and the sealing body  3 . The jacket body  2  is mainly composed of a bottom portion  10  and a peripheral wall portion  11 . The jacket body  2  is made of a material mainly containing a first aluminum alloy. The first aluminum alloy is, for example, an aluminum alloy casting material such as JISH5302 ADC12 (based on Al—Si—Cu). The jacket body  2  is made of an aluminum alloy as an example in this embodiment, but may be made of another metal capable of being frictionally stirred. 
     As shown in  FIG.  2   , the bottom portion  10  is a plate-like member having a rectangular shape in a plan view. The peripheral wall portion  11  is a wall portion rising from the peripheral edge portion of the bottom portion  10  and having a rectangular frame shape. A peripheral wall stepped portion  12  is formed at an inner peripheral edge of the peripheral wall portion  11 . The peripheral wall stepped portion  12  is composed of a step bottom face  12   a  and a step side face  12   b  rising from the step bottom face  12   a . As shown in  FIG.  3   , the step side face  12   b  inclines to spread toward the outside with increasing distance from the step bottom face  12   a  and toward an opening portion. An inclination angle β of the step side face  12   b  with respect to the vertical plane may be appropriately set, and is set to, for example, 3° to 30° with respect to the vertical plane. A recessed portion  13  is defined by the bottom portion  10  and the peripheral wall portion  11 . Here, the vertical plane is defined as a plane composed of an advancing vector of the rotary tool F and a vertical vector. 
     The sealing body  3  is a plate-like member to seal the opening portion of the jacket body  2 . The sealing body  3  has a size capable of being placed on the peripheral wall stepped portion  12 . A thickness of the sealing body  3  is larger than a height dimension of the step side face  12   b . The thickness of the sealing body  3  is appropriately set so that a joined portion does not fall in shortage of metal when the primary joining process to be described later is performed. The sealing body  3  is made of a material mainly containing a second aluminum alloy. The second aluminum alloy has a hardness lower than the first aluminum alloy. The second aluminum alloy is, for example, an aluminum wrought alloy material such as JIS A1050, A1100, A6063. The sealing body  3  is made of an aluminum alloy as an example in this embodiment, but may be made of another metal capable of being frictionally stirred. It should be noted that the hardness in this description refers to Brinell hardness, which can be measured by a method in conformity with JIS Z 2243. 
     The placing process is a process to place the sealing body  3  on the jacket body  2  as shown in  FIG.  3   . In the placing process, a back face  3   b  of the sealing body  3  is placed on the step bottom face  12   a . The step side face  12   b  and an outer peripheral side face  3   c  of the sealing body  3  are butted against each other to form a first butted portion J 1 . The first butted portion J 1  may also include a case where two members are butted against each other to have an approximately V-shaped gap in cross section like this embodiment. Furthermore, the step bottom face  12   a  overlaps with the back face  3   b  of the sealing body  3  to form a second butted portion J 2 . 
     As shown in  FIGS.  4  and  5   , the primary joining process is a process where friction stir welding is performed to the jacket body  2  and the sealing body  3  with use of the rotary tool F being rotated while moving the rotary tool F one round around the sealing body  3 . 
     As shown in  FIG.  4   , when friction stirring is performed with use of the rotary tool F, the stirring pin F 2  being rotated clockwise is inserted in the sealing body  3  and moved in a state that the bottom face F 1   a  of the shoulder portion F 1  is in contact with the front face  3   a  of the sealing body  3 . The metal frictionally stirred is hardened, so that a plasticized region W 1  is formed at a moving trace of the rotary tool F. In this embodiment, the stirring pin F 2  is inserted at a start position Sp set on the sealing body  3  and the rotary tool F is moved clockwise relative to the sealing body  3 . 
     As shown in  FIG.  5   , in the primary joining process, friction stirring is performed in a state that the rotation axis X of the rotary tool F is parallel to the vertical line (vertical plane). As shown in  FIG.  3   , the inclination angle β of the step side face  12   b  is set smaller than the inclination angle α (see  FIG.  1   ) of the outer circumferential face of the stirring pin F 2 . In the primary joining process, the setting is made so that a lower portion of the outer circumferential face of the stirring pin F 2  is not in contact with the step side face  12   b  of the peripheral wall stepped portion  12  in a state that the bottom face F 1   a  of the shoulder portion F 1  is in contact with the front face  3   a  of the sealing body  3  and an upper portion of the outer circumferential face of the stirring pin F 2  is slightly brought in contact with an upper portion of the step side face  12   b  of the peripheral wall stepped portion  12 . The flat face F 3  of the stirring pin F 2  may be inserted to the same height position as the step bottom face  12   a  of the peripheral wall stepped portion  12 , but in this embodiment, the flat face F 3  is inserted to a slightly deeper position than the step bottom face  12   a  of the peripheral wall stepped portion  12 . In the primary joining process, the rotary tool F is made to leave the jacket body  2  and the sealing body  3  after the rotary tool F is moved one round around the sealing body  3  to overlap a beginning and an end of the plasticized region W 1 . 
     As shown in  FIG.  6   , by the primary joining process, the plasticized region W 1  is formed at the moving trace of the rotary tool F and a coarse portion Z is formed at a region which is in the lower portion of the plasticized region W 1  and in the vicinity of the inside of the step side face  12   b . The coarse portion Z is a region in which the plastically fluidized material has not been sufficiently stirred and the density of the plastically fluidized material is coarser than the other region. The coarse portion Z is formed continuously or intermittently in the length direction of the plasticized region W 1 . 
     As shown in  FIG.  7   , the inspection process is a process to perform a flaw detection for a liquid-cooling jacket  1 . In the inspection process, an ultrasonic flaw detection device (for example, ultrasonic imaging device (SAT) manufactured by Hitachi High-Teck GLOBAL) is used. A hollow portion U of the liquid-cooling jacket  1  in an inspection result screen R in  FIG.  7    is shown in another color. Further, the coarse portion Z is shown around the hollow portion U in another color and in a frame shape with broken lines. That is, it can be judged that the rotary tool F has passed the entire periphery of the sealing body  3  by displaying the coarse portion Z on the inspection result screen R. The region between the hollow portion U and the coarse portion Z is an area corresponding to the plasticized region W 1 . 
     It is preferable that the width Zw of the coarse portion Z is 400 μm or less, more preferably 300 μm or less, and still more preferably 200 μm or less. In a case where the width Zw of the coarse portion Z is more than 400 μm, there is a concern of poor joint strength of the first butted portion J 1 . In other words, in the case where the width Zw of the coarse portion Z is 400 μm or less, sufficient joint strength is obtained. On the other hand, it is preferable that the width Zw of the coarse portion Z is 100 μm or more. In a case where the width Zw of the coarse portion Z is less than 100 μm, there is a concern that the coarse portion Z is not shown on the inspection result screen R by the ultrasonic flaw detection device. 
     As shown in  FIG.  5   , in the primary joining process, the ratio of a region where the outer circumferential face of the stirring pin F 2  is in contact with the step side face  12   b  and the other region where the outer circumferential face of the stirring pin F 2  is not in contact with the step side face  12   b  is about 2:8 in this embodiment. The ratio may be appropriately set in a range where the jacket body  2  and the sealing body  3  are joined together with a desired strength and the coarse portion Z having the above-described predetermined width is formed. In other words, the inclination angle α of the outer circumferential face of the stirring pin F 2 , the inclination angle β of the step side face  12   b  of the peripheral wall stepped portion  12 , and the position (position in a width direction) of the rotation axis X of the stirring pin F 2  may be appropriately set in a range where the jacket body  2  and the sealing body  3  are joined together with a desired strength and the coarse portion Z having the above-described predetermined width is formed. 
     As shown in  FIG.  8   , it is preferable that the stirring pin F 2  is brought into contact at least with the upper portion of the step side face  12   b . This is because if the outer circumferential face of the stirring pin F 2  is away from the step side face  12   b , the jacket body  2  and the sealing body  3  may not be joined together or the joint strength thereof may be reduced. Further, as shown in  FIG.  9   , in a case where the contacting margin between the stirring pin F 2  and the step side face  12   b  is larger, more metal of the jacket body  2  having a higher hardness flows toward the sealing body  3  having a lower hardness. Consequently, the stirring balance between the jacket body  2  and the sealing body  3  is poor, so that there is a concern that the joint strength decreases. Furthermore, in the vicinity of the step bottom face  12   a , in a case where the outer circumferential face of the stirring pin F 2  and the step side face  12   b  are too close and also in a case where they are too far, it is difficult to form the coarse portion Z having the above-described predetermined width. 
     According to the method for manufacturing a liquid-cooling jacket according to this embodiment described in the above, the metal of the sealing body  3  at the first butted portion J 1  is mainly frictionally stirred to be plastically fluidized because of the frictional heat between the stirring pin F 2  and the sealing body  3 , so that the step side face  12   b  and the outer peripheral side face  3   c  of the sealing body  3  can be joined together at the first butted portion J 1 . Further, since friction stirring is performed in a state that the bottom face F 1   a  of the shoulder portion F 1  is in contact with the front face  3   a  of the sealing body  3  and the stirring pin F 2  is slightly in contact with at least an upper portion of the step side face  12   b  of the jacket body  2 , it is possible to reduce metal mixing from the jacket body  2  to the sealing body  3  as much as possible while ensuring the joint strength. Accordingly, since the metal of the sealing body  3  is mainly frictionally stirred at the first butted portion J 1 , lowering of the joint strength can be suppressed. 
     Further, since the stirring pin F 2  is inserted to the same depth as the step bottom face  12   a  or slightly deeper than that, it is possible to reduce metal mixing from the jacket body  2  to the sealing body  3  as much as possible while enhancing the joint strength at the second butted portion J 2 . Further, since the bottom face F 1   a  of the shoulder portion F 1  is in contact with the front face  3   a  of the sealing body  3 , it is possible to suppress an occurrence of burrs. Furthermore, by deliberately forming the coarse portion Z having the predetermined width, the passed position of the stirring pin F 2  can be detected by flaw detection. Hereby, quality control work can be more easily performed. Furthermore, by forming the sealing body  3  to have a thickness larger than the step side face  12   b , the joined portion can be prevented from falling in metal shortage. 
     In the primary joining process, a rotational direction and an advancing direction of the rotary tool F may be appropriately set. In this embodiment, the rotational direction and the advancing direction of the rotary tool F have been set so that the jacket body  2  side is an advancing side and the sealing body  3  side is a retreating side within the plasticized region W 1  to be formed at the moving trace of the rotary tool F. This enhances the stirring action by the stirring pin F 2  around the first butted portion J 1 , so that rising of the temperature at the first butted portion J 1  is expected, and the step side face  12   b  and the outer peripheral side face  3   c  of the sealing body  3  can be more firmly joined together at the first butted portion J 1 . 
     It should be noted that, an advancing side (Shear side) is a side where the relative speed of the outer periphery of the rotary tool relative to a portion to be joined takes a value that an advancing speed is added to a tangential speed at the outer periphery of the rotary tool. On the other hand, a retreating side (Flow side) is a side where the relative speed of the rotary tool relative to a portion to be joined is lowered since the rotary tool is rotated in the direction opposite to the advancing direction of the rotary tool. 
     The first aluminum alloy of the jacket body  2  has a hardness harder than the second aluminum alloy of the sealing body  3 . This can enhance the endurance of the liquid-cooling jacket  1 . Further, it is preferable that the first aluminum alloy of the jacket body  2  is an aluminum alloy casting material and the second aluminum alloy of the sealing body  3  is an aluminum wrought alloy material. In a case where the first aluminum alloy is, for example, the aluminum alloy casting material based on Al—Si—Cu such as JISH5302 ADC12, castability, strength and machinability of the jacket body  2  can be enhanced. Furthermore, in a case where the second aluminum alloy is, for example, a material of JIS A1000 series or A6000 series, processing ability and thermal conductivity can be enhanced. 
     For example, the thickness of the sealing body  3  is set larger than the height dimension of the step side face  12   b  in this embodiment, but both may be the same with each other. Further, the step side face  12   b  may not be inclined and be formed perpendicular to the step bottom face  12   a.    
     In the above embodiment, the method for manufacturing a liquid-cooling jacket that is formed by joining the jacket body and the sealing body has been described as an example, but the present invention is not limited to this specific embodiment. Although not shown in the drawings, the present invention is applicable, without being limited to a specific shape of the liquid-cooling jacket, to friction stir welding performed when a first member having a step portion and a second member to be placed on the step portion are joined together. 
     Second Embodiment 
     Next, a method for manufacturing a liquid-cooling jacket according to a second embodiment of the present invention will be described. As shown in  FIGS.  10  and  11   , the second embodiment differs from the first embodiment in that columnar supports  15  of a jacket body  2 A and a sealing body  3 A are joined together. In this embodiment, a preparation process, a placing process, a primary joining process, and an inspection process are performed. The primary joining process includes a first primary joining process and a second primary joining process. In this embodiment, differences from the first embodiment will be mainly described. 
     In the preparation process, the jacket body  2 A and the sealing body  3 A are prepared. The jacket body  2 A is provided with a bottom portion  10 , a peripheral wall portion  11 , and a plurality of columnar supports  15  (four columnar supports in this embodiment). Each columnar support  15  rises from the bottom portion  10  and has a columnar shape. Each columnar support  15  is provided with a projection portion  16  tapered to have a smaller diameter with increasing distance toward a tip thereof at the top thereof. Since the projection portion  16  is provided, a columnar support stepped portion  17  is formed on the top side of the columnar support  15 . The columnar support stepped portion  17  is composed of a step bottom face  17   a  and a step side face  17   b  inclined toward the axis thereof from the step bottom face  17   a . The sealing body  3 A has hole portions  4  formed at positions corresponding to the columnar supports  15 . Each hole portion  4  has such a size that a corresponding projection portion  16  can be inserted therein. 
     The placing process is a process in which the sealing body  3 A is placed on the jacket body  2 A. This process forms a first butted portion J 1  like the first embodiment. Further, as shown in  FIG.  11   , the step side face  17   b  of the columnar support stepped portion  17  and a hole wall  4   a  of the hole portion  4  are butted against each other to form a third butted portion J 3 . Furthermore, the step bottom face  17   a  of the columnar support stepped portion  17  overlaps with a back face  3   b  of the sealing body  3 A to form a fourth butted portion J 4 . 
     In the primary joining process, the first primary joining process in which the first butted portion J 1  and the second butted portion J 2  are joined, and the second primary joining process in which the third butted portion J 3  and the fourth butted portion J 4  are joined are performed. Description of the first primary joining process is omitted because the first primary joining process is the same as the primary joining process in the first embodiment. 
     As shown in  FIG.  11   , in the second primary joining process, an upper portion of the outer circumferential face of the stirring pin F 2  is slightly brought in contact with an upper portion of the step side face  17   b  of the columnar support stepped portion  17  and a lower portion of the outer circumferential face of the stirring pin F 2  is not brought in contact with the step side face  17   b  of the columnar support stepped portion  17 . The bottom face F 1   a  of the shoulder portion F 1  is kept in contact with the front face  3   a  of the sealing body  3 A and the front face  16   a  of the projection portion  16 . The stirring pin F 2  is inserted so that the flat face F 3  thereof is located at a position slightly deeper than the step bottom face  17   a  of the columnar support stepped portion  17 . 
     As shown in  FIG.  11   , by performing the primary joining process, a plasticized region W 2  is formed at a moving trace of the rotary tool F, and the coarse portion Z is formed in the outside vicinity of the step side face  17   b  in a lower portion of the plasticized region W 2 . The coarse portion Z is a portion in which the plastically fluidized material is not fully frictionally stirred and thus coarser than the other portions. The coarse portion Z is continuously or intermittently formed in the plasticized region W 2 . A forming method and forming conditions for the coarse portion Z are the same as that or those in the first embodiment. 
     This embodiment can attain similar effects to the first embodiment. Further, this embodiment can enhance the joint strength since the columnar supports  15  and the sealing body  3 A are joined together. Furthermore, the moving trace of the rotary tool F around the columnar supports  15  can be confirmed in the inspection process by forming the coarse portion Z in the outside vicinity of the base side of each of the projection portions  16  within the plasticized region W 2 . 
     REFERENCE SIGNS LIST 
       1  Liquid-cooling jacket 
       2  Jacket body (First member) 
       3  Sealing body (Second member) 
     F Rotary tool 
     F 1  Shoulder portion 
     F 1   a  Bottom face 
     F 2  Stirring pin 
     F 3  Flat face 
     J 1  First butted portion 
     J 2  Second butted portion 
     W 1  Plasticized region 
     Z Coarse portion