Abstract:
The present invention provides a magnesium alloy used in manufacturing a seat frame for an automobile and a method for manufacturing the seat frame using the same. More specifically, this invention provides a novel extrusion technology as well as a bending technology for manufacturing an automobile seat frame using an extruded magnesium alloy with superior absorptivion against vibration and shock while also providing a 25-35% improvement in weight reduction over aluminum alloy products and a 60-70% improvement in weight reduction over conventional steel products.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority from Korean Application No. 2003-0101731, filed on Dec. 31, 2003.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a magnesium alloy used in manufacturing a seat frame for an automobile and a method for manufacturing the seat frame using the same.  
       BACKGROUND OF THE INVENTION  
       [0003]     In general, the seat frame for an automobile is designed to sufficiently support the passengers&#39; body weights. In particular, the materials and designs for the back rest frame are selected in terms of the safety of the passengers during a vehicle collision by considering the change in kinetic energy according to body shapes and vehicle movement. The materials that have been used in conventional vehicle seat frames are, as shown in  FIG. 5 , inexpensive steels and other auxiliary parts attached thereto. With the recent growing public concerns on efficient use of limited natural resources and environmental contamination control, light-weight seat frames manufactured using light-weight materials, such as aluminum alloy or magnesium alloy instead of the conventional heavy steel materials, have been drawing much public attention for achieving improved fuel efficiency. Aluminum alloy or magnesium alloy is soon expected to replace the conventional heavy steel materials that have been used in manufacturing many vehicle parts.  
         [0004]     As shown in  FIGS. 6 and 7 , there have been seat frames developed recently in which aluminum alloy extruded materials and magnesium alloy casting materials have been applied. As the conventional seat frames, which are made of steel, are much heavier than those manufactured by using light-weight materials such as an aluminum alloy or magnesium alloy, they have become a burden because of the long-felt need for efficient fuel consumption. Therefore, with the more recent strict regulations on fuel consumption efficiency and exhaust gas, globally renowned automobile manufacturers have made continuous efforts to develop seat frames using an aluminum alloy. As a result of early stage success, such seat frames show promise in near future applications. For example, a relatively light-weight seat frame is manufactured by using an aluminum alloy and by appropriately distributing a plurality of related members, and the seat frame exhibits sufficient strength to withstand against a vehicle collision. In another example, a seat frame is also manufactured by using aluminum alloy where the front, rear, left and right frames are molded into an integrated body via aluminum die casting. Although these aluminum alloy vehicle parts are more light-weight than the steel conventional parts, there have been attempts made to develop parts manufactured by using a magnesium casting material which is expected to be about 35% lighter than those produced with an aluminum alloy. However, magnesium casting material is manufactured via pressure casting, so the resulting product has relatively low strength and elongation when compared to those manufactured by an extrusion or plastic working process. This also raises the issue of how to provide safety for an entire structure.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention provides an extruded magnesium alloy for manufacturing a seat frame for a vehicle that is more light-weight by means of a novel extrusion technique as well as a bending technique developed by the present inventors.  
         [0006]     In one embodiment, the present invention provides a method for manufacturing a seat frame for a vehicle using the above-mentioned extruded magnesium alloy having superior light-weight over those manufactured with conventional steels, aluminum alloy extruded materials, magnesium alloy casting materials.  
         [0007]     Accordingly, the present invention provides a novel extrusion technology as well as a bending technology for manufacturing an automobile seat frame using an extruded magnesium alloy with superior vibration and shock absorption while also providing a 25-35% improvement in weight reduction over aluminum alloy products and a 60-70% improvement in weight reduction over conventional steel products.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The above and other objects and features of the present invention will become apparent from the following description of the invention, when taken in conjunction with the accompanying drawings, wherein:  
         [0009]      FIG. 1  shows an embodiment of an extruded magnesium alloy for a back frame of the present invention;  
         [0010]      FIG. 2  shows an embodiment of an extruded magnesium alloy for a reinforcing frame of the present invention;  
         [0011]      FIG. 3  shows an embodiment of a back frame manufactured by using an extruded magnesium alloy for a back frame of the present invention;  
         [0012]      FIG. 4  shows an embodiment of a seat frame manufactured by using an extruded magnesium alloy of the present invention;  
         [0013]      FIG. 5  shows an embodiment of a seat frame manufactured by using a conventional steel material;  
         [0014]      FIG. 6  shows an embodiment of a seat frame manufactured by using a conventional aluminum alloy extruded material; and  
         [0015]      FIG. 7  shows an embodiment of a seat frame manufactured by using a conventional magnesium alloy casting material. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0016]     The present invention includes a method for manufacturing a seat frame using magnesium alloy comprising: (a) manufacturing an extruded billet by melting AZ31 magnesium alloy by loading it into a stainless steel furnace at a predetermined temperature and then solidifying it by water-cooling; (b) manufacturing an extruded magnesium alloy having a certain shape from the extruded billet by adjusting the mold, container, and billet temperature; and (c) molding the extruded magnesium alloy into a shape of a seat frame via a bending process as well as a stretching process.  
         [0017]     As discussed further below, the present invention includes a method for manufacturing a magnesium alloy, which provides advantages in manufacturing a seat frame such as superior light-weight and vibration and shock absorption, thereby providing safe and comfortable seat frames for a vehicle.  
         [0018]     Hereinafter, such embodiments of the present invention are described in detail with reference to the accompanying drawings.  
         [0019]     The magnesium alloy used in the present invention comprises (a) magnesium as a major component; (b) AZ31 alloy comprising about 2.5 to 3.5 weight % of aluminum, about 0.6 to 1.4 weight % of zinc, and about 0.2 to 1.0 weight % of manganese; and (c) AZ61 alloy comprising about 5.8 to 7.2 weight % of aluminum, about 0.04 to 1.5 weight % of zinc, and about 0.15 to 0.5 weight % of manganese.  
         [0020]     In general, magnesium alloy has a crystal structure of close-packed hexagonal lattice (CPH), so it is relatively more difficult to produce through a plastic working process when compared to that of an aluminum alloy having a crystal structure of face-centered cubic lattice (FCC). Thus, the molding property of magnesium alloy is relatively deteriorated. However, the present invention has succeeded in manufacturing a sound magnesium alloy by means of a precise control over various processing variables, such as an optimum extrusion ratio, mold temperature, extrusion temperature and extrusion speed.  
         [0021]     Further, in the present invention, those extruded magnesium alloys suitable for parts of a back frame (A) and a reinforcing frame (B) for light-weight seats of a vehicle were manufactured by selecting suitable extrusion variables for magnesium alloys. The back frame (A) and reinforcing frame (B) are illustrated in  FIG. 4 .  
         [0022]      FIGS. 1 and 2  show the extruded magnesium alloy used in manufacturing parts for the back frame (A) and reinforcing frame (B) of the present invention. As shown in the  FIGS. 1 and 2 , suitable processing variables for magnesium alloys were selected in the present invention and thus enabled to manufacture a sound magnesium alloy with relatively complex shapes.  
         [0023]     In manufacturing the back frame (A), it is essential to go through with a bending process for forming an extruded magnesium alloy into a U-shape, I-shape, or a rectangular shape. However, as stated above, a magnesium alloy has a crystal structure of close-packed hexagonal lattice and thus has a very limited number of slip systems, thus making it very difficult for the plastic working process. Therefore, it is required that processing variables, such as selection of a suitable bending process, bending temperature, bending speed, and stretching pressure, be precisely controlled for performing the bending process of an extruded magnesium alloy.  FIG. 3  shows an embodiment of an extruded magnesium alloy for a light-weight seat prepared by the bending process.  
         [0024]     Hereinafter, preferred embodiments of the present invention are described in detail with reference to the following example. However, the following example is given for the purpose of illustration only, and it should not be construed as limiting the scope of the present invention.  
       EXAMPLE  
       [0025]     AZ31 magnesium alloy was loaded into a stainless steel furnace and heated to 700° C. to manufacture an extruded billet. To prevent oxidation of the surface of the base metal of magnesium alloy as well as the surface of the molten metal, a gas mixture of CO 2  and SF 6  was continuously sprayed and coated on the surface of molten metal and solidified by water-cooling after the base metal was completely melted.  
         [0026]     In order to eliminate any influences from structural inhomogeneity due to segregation during casting, manufactured casting materials were homogenized, and the extruded billet was manufactured using the homogenized casting materials. The mold, container, and billet temperatures at the time of extrusion molding were adjusted to a range of about 250- 450° C. and the speed of the ram was adjusted to a range of about 0.5-5 inch/min. The resulting sound extrusion magnesium alloy that was manufactured is shown in  FIGS. 1 and 2 .  
         [0027]     The above extruded magnesium alloy was then formed into a shape suitable for a back frame as shown in  FIG. 4  via a bending process. For the bending process, a stretching and bending machine capable of two-dimensional and three-dimensional bendings was used. As stated above, magnesium alloy is largely limited when forming shapes at room temperature due to its crystal structure of close-packed hexagonal lattice, and thus the bending process was performed by preheating the bending mold and the extruded magnesium alloy at a range of 150-350° C. Finally, the magnesium alloy was stretched under a pressure of 200-350 kg f  in order to prevent transformation due to a springback phenomenon that would result after the bending process and in order to secure dimensional stability. The final extruded magnesium alloy product manufactured from the above bending process is shown in  FIG. 3 .  
         [0028]     While the foregoing description represents various embodiments of the present invention, it will be appreciated that the foregoing description should not be deemed limiting since additions, variations, modifications and substitutions may be made without departing from the spirit and scope of the present invention. It will be clear to one of skill in the art that the present invention may be embodied in other forms, structures, arrangements, and proportions, and may use other elements, materials and components. The present disclosed embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims and not limited to the foregoing description.