Patent Publication Number: US-2012027506-A1

Title: Weld joint of aluminum alloy member

Description:
TECHNICAL FIELD 
     The present invention relates to a weld joint obtained by joining one end of a wrought material formed of one of aluminum and an aluminum alloy to an end part of an aluminum alloy cast member. 
     BACKGROUND ART 
     Weld structures formed by joining an aluminum alloy wrought material to an aluminum alloy cast member have been used in actual practice. The technique disclosed in Patent Literature 1 is a conventional technique relating to such a weld structure. 
     The weld structure described in Patent Literature 1 is a subframe. The subframe is manufactured by welding a lid body to a frame body. The frame body is an aluminum alloy cast member, and the lid body is an aluminum alloy wrought material. 
     The lid body is welded to the frame body along the entire circumference. Because so-called full circumference welding is performed, the welding length is considerably increased and the welding cost is raised. In addition, the welding strain is increased, and the correction cost for correcting the strain is also increased. Manufacturing expenses for the weld structure described in Patent Literature 1 are therefore increased. 
     A conventional structure whose manufacturing expenses can be made lower than those in Patent Literature 1 is described based on  FIGS. 9 and 10  hereof. 
       FIG. 9  is a view showing an example of a conventional weld structure, wherein a subframe  100 , which is the weld structure, is a square frame obtained by connecting a right-side cast member  101 , a left-side cast member  102 , and angular tube-shaped wrought materials  103 ,  104  using four weld parts  105 . 
     As one way to reduce the weight of a vehicle, the cast members  101 ,  102  are made to be aluminum alloy cast members, and aluminum or aluminum alloy wrought materials are used for the wrought materials  103 ,  104 . 
       FIG. 10  is a cross-sectional view of a conventional weld part, wherein the wrought material  103  is inserted in the cast member  101 , and both members are joined by lap-fillet MIG welding. 
     Gaps  106 ,  106  must be provided to an inserting portion in order to smoothly insert the wrought material  103  in the cast member  101 . 
     The cast member  101  is a casting, and therefore inevitably contains gas. In addition, the melting point of the aluminum alloy casting is lower than the melting point of the aluminum alloy wrought material. 
     When lap-fillet MIG welding is performed under such conditions, the molten metal runs (leaks) from the gaps  106 ,  106 . In addition, the wrought material  103  is more difficult to melt than the cast member  101 . 
     Ensuring a throat  108  in a bead  107  becomes difficult when these main factors overlap. Defects such as insufficient strength and degraded quality of the weld part  105  occur when the throat  108  is insufficient. 
     Prior Art Literature 
     Patent Literature 
     Patent Literature 1: JP-A 2004-210013 
     SUMMARY OF INVENTION 
     Technical Problem 
     An object of the present invention is to provide a technique capable of preventing insufficient strength and degraded quality of a weld joint obtained by joining one end of an aluminum or aluminum alloy wrought material to an end part of an aluminum alloy cast member. 
     Solution to Problem 
     According to the present invention, there is provided a weld joint of an aluminum alloy member obtained by joining an end part of a wrought material formed of one of aluminum or an aluminum alloy to one end of a cast member formed of an aluminum alloy, wherein the cast member has a chamfer extending from an upper surface of the cast member toward a lower surface until a midway of a thickness of the cast member, and an inserting portion extending along a lower surface of the wrought material from a lower end of the chamfer toward a distal end of the cast member, a distance from the lower end of the chamfer to an end face at one end part of the wrought material is set at 1.0 to 1.7 times a thickness of the wrought material, the chamfer is inclined so that a groove angle with the end face at one end of the wrought material is 15 to 45°, and the groove is welded to cause the inserting portion to act as a backing metal. 
     Advantageous Effects of Invention 
     In the present invention, there is no concern that molten metal will leak out because an inserting portion assumes the role of a backing metal. The high-melting wrought material can be fully melted because molten metal accumulates in the groove. As a result, strength can be increased and a high-quality weld joint can be obtained. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view showing a wrought material set in a cast member; 
         FIG. 2  is an enlarged view of section  2  of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view showing a weld part of a weld joint according to the present invention; 
         FIG. 4  is a graph showing a correlation between a groove angle and joint efficiency; 
         FIG. 5  is a graph showing a correlation between an outer-face difference and tensile strength; 
         FIG. 6  is a graph showing a correlation between a groove space and the joint efficiency; 
         FIG. 7  is a top plan view of a weld structure; 
         FIG. 8  is a cross-sectional view taken along line  8 - 8  of  FIG. 7 ; 
         FIG. 9  is a perspective view showing a conventional weld structure; and 
         FIG. 10  is a cross-sectional view of a weld part of the conventional structure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be described below with reference to the attached drawings. 
     An embodiment of the present invention will be described with reference to the drawings. 
     A pre-weld structure  10  is formed of an aluminum alloy cast member  11  and an aluminum or aluminum alloy wrought material  12 , as shown in  FIG. 1 . These materials  11 ,  12  are integrated with each other by MIG welding at a later time. 
     A pre-weld groove shape is described in  FIG. 2 . 
     An end part of the cast member  11  is cut on an incline in the thickness direction to a height H from an upper surface  11   a  toward a lower surface  11   b,  as shown in  FIG. 2 . A section from the lower end to the end face of a chamfer  14  is cut out parallel to the lower surface  11   b.  As a result, an inserting portion  13  extending along the lower surface of the wrought material  12  is formed on the end part of the cast member  11 . 
     The slope  14  is inclined so that a groove angle θ is 15 to 45° in relation to an end face  12   a  of the wrought material  12 . 
     The wrought material  12  is separated from the slope  14  so that a root space L is obtained in which the bottom of the groove is 1.0 to 1.7 times the thickness T of the wrought material  12 . 
     The height H of the slope  14  is somewhat greater than the thickness T of the wrought material  12 , as shown in  FIG. 2 . 
     When MIG welding is performed on the groove in this form, there is no concern that molten metal will leak out because the inserting portion  13  assumes the role of a backing metal. The high-melting wrought material can be fully melted because molten metal accumulates in the groove. As a result, a bead  15  such as the one shown in  FIG. 3  can be obtained. 
     The evaluation of the bead  15  was confirmed by an experiment. 
     EXPERIMENTAL EXAMPLE 
     An experimental example according to the present invention will be described below. The present invention is not limited to the experimental example. 
     Sample material:
         Aluminum alloy cast member: AC4CH-T5 (ISO Al—Si 7 Mg), thickness: 8 mm   Aluminum alloy wrought material: 6N01-T5, thickness: 3.5 mm       

     Groove form:  FIG. 2 . However, the groove angle θ, the slope height H, and the root space L were variable. 
     Welding conditions:
         Type: MIG welding   Filler rod: A5356WY equivalent   Electric current: 230 A   Angle of rotation: 75°   Angle of advance: 15°   Welding speed: 70 cm/min       

     Verification of groove angle:
         Slope height H: 4.5 mm   Root space L: 5 mm   Groove angle θ: 10°, 15°, 30°, 45°, 50°       

     Welding was performed under the above conditions, and the joint efficiency of the resulting joint was calculated. The results are shown in  FIG. 4 . 
     The best results were produced at θ=30°, as shown in  FIG. 4 . The generally required joint efficiency is considered to be 70%, but when the efficiency was 80%, which allows for a 10% margin, the groove angle θ was in the range of 15 to 45°. 
     Verification of the outer-face difference (H−T): 
     The relationship between the thickness T of the wrought material  12  shown in  FIG. 2  and the height H of the slope  14  was investigated. The results are shown in  FIG. 5 . 
     The horizontal axis in  FIG. 5  is the outer-face difference (H−T), and T is 3.5 mm (constant). Therefore, the outer-face difference was 0 when H was 3.5 mm; 1 mm when H was 4.5 mm; and 2 mm when H was 5.5 mm. A test piece was cut out from the resulting joint and a tensile test was performed. The tensile strength was 1.13 at an outer-face difference of 1 mm, and 1.03 at an outer-face difference of 2 mm. where the tensile strength was set to 1.0 at an outer-face difference (H−T) of 0. 
     Verification of the root space L:
         Gap G: The opening (gap) between the upper surface of the inserting portion  13  and the lower surface of the wrought material  12  was set to 0, but the experiment was performed on two types of openings, one at 0 mm and the other at 1 mm.   Slope height H: 4.5 mm   Wrought material thickness T: 3.5 mm   Root space L: 4 mm (L/T=1.14), 5 mm (L/T=1.42), 6 mm (L/T=1.71)   Groove angle θ: 30°       

     Welding was performed under the above conditions, and the joint efficiency of the resulting joint was calculated. The results are shown in  FIG. 6 . 
     The solid line in  FIG. 6  shows a case in which the gap is 0, and the dashed line shows a case in which the gap is 1 mm. 
     Assuming that the required joint efficiency is 70%, the joint efficiency in the case of the solid line will exceed 70% if the root space is 1.0 (the wrought material thickness was set to 1.0) or greater. 
     An opening of 0.5 to 1.0 mm is preferred to facilitate insertion of the cast member  11  in the wrought material  12  in  FIG. 1 . 
     When the opening is 1.0 mm, the joint efficiency declines and falls below 70% at the horizontal axis point of 1.7, as shown by the dashed line. 
     A root space having points “a” to “b” shown in  FIG. 6 , in other words, having a wrought material thickness of 1.0 to 1.7, is recommended based on the aforementioned data. 
     An example in which the weld joint of the present invention is used in the subframe of a vehicle is described in  FIGS. 7 and 8 . 
     The subframe  20  as a structure is formed of a front cross part  21  and a rear cross part  22  extending in the crosswise direction of the vehicle, front arm parts  23 ,  24  extending from both ends of the front cross part  21 , rear arm parts  25 ,  26  extending from both ends of the rear cross part  22 , and a left longitudinal part  27  and a right longitudinal part  28  extending in the longitudinal direction of the vehicle and connecting with the front cross part  21  and the rear cross part  22 , as shown in  FIG. 7 . 
     The front cross part  21  and the rear cross part  22 , the front arm parts  23 ,  24  and the rear arm parts  25 ,  26 , and the left longitudinal part  27  and the right longitudinal part  28  are cast members based on an aluminum alloy. 
     The front cross part  21  is a channel shape that opens downward, as shown in  FIG. 8 . A channel has a large hollow portion and can be made lightweight. However, the strength of a hollow cross-section is less than that of a solid cross-section. In terms of strength, the bending stress of the widthwise center part is at the maximum. 
     As a countermeasure, a reinforcing plate  29  is added to the widthwise center part of the front cross part  21 , as shown in  FIG. 7 . 
     The reinforcing plate  29  is a wrought material formed of one of aluminum or an aluminum alloy. The reinforcing plate  29  is brought against and welded to the front cross part  21  with the aim of covering the downward opening of the front cross part  21 , which is a cast member, as shown in  FIG. 8 . In other words, the end part of the reinforcing plate  29  is the joint shape shown in  FIG. 2 , and is joined to the front cross part  21 . 
     The center part is reinforced by the reinforcing plate  29  in the same manner as the front cross part  22 , and the left and right longitudinal parts  27 ,  28  shown in  FIG. 7 . 
     The weld joint of the present invention is appropriate for a subframe of a vehicle, but may be used in other weld structures. 
     INDUSTRIAL APPLICABILITY 
     The weld joint of the present invention is appropriate for a subframe of a vehicle. 
     Legend 
       10  Structure 
       11  Cast member 
       12  Wrought material 
       12   a  End part of wrought material 
       13  Inserting portion 
       14  Slope 
       15  Bead 
     L Root space 
     T Wrought material thickness 
     θ Groove angle