JPS6210483Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to the structure of a component made of a magnesium alloy, and particularly to the structure of its boss portion.

Although magnesium alloys are generally extremely lightweight, they have poor corrosion resistance, and are known to be particularly prone to stress corrosion cracking under stress.

For example, when a bolt is screwed into a boss part formed in a magnesium alloy part as a bolt fastening part or a bearing press-fit part, tensile stress is generated in the radial and circumferential directions when a bolt is screwed or a bearing is press-fitted. When exposed to a corrosive environment (salt-affected areas, humid areas, etc.) for a long period of time, corrosion and static stress act on the boss at the same time, which can cause stress corrosion cracking. To explain this using a bolt fastening part as an example, FIG. Since the threads of the screw holes formed in the screw holes and the threads of the bolts 3 are engaged with each other, tensile stress is generated in the boss portion 2 in the radial and circumferential directions as a reaction force of the tightening force against the fastener 4. acts. 1st
Figure B is a diagram showing the distribution of such tensile stress. However, as shown in FIG. 1B, since the conventional boss portion 2 has a simple cylindrical shape, its tensile stress increases toward the tip end, but it is difficult to tighten the fastener 4 with high torque. When the boss portion 2 is made thin, the maximum tensile stress generated in the boss portion 2 becomes larger than the critical stress that causes stress corrosion cracking within a certain period of time.
During use, stress corrosion cracking occurred at the tip of the boss 2 in some cases.

This idea was devised in view of the above circumstances, and its purpose is to provide a structure for magnesium alloy parts that does not cause stress corrosion cracking and can be made lighter as a whole. The outer diameter of the tip end of the boss into which the bolt is screwed is made larger than the outer diameter of the proximal end side while still being integral with the proximal end side, and the distal end side where stress corrosion cracking is likely to occur. The main point is that the tensile stress is configured to be below the critical stress.

Examples of this invention will be described below with reference to FIGS. 2 to 7.

FIG. 2 is a partial sectional view showing an embodiment of this invention, in which the magnesium alloy component 10 has a boss portion 11 projecting at a predetermined location.
1 is formed so that the outer diameter D on the distal end side is larger than the outer diameter d on the proximal end side, and the screw hole 15 is aligned with the central axis in order to attach the fastener 14 via the bolt 12 and washer 13. It is formed along the The reason why the tip end side is made larger in diameter is to reduce the tensile stress that occurs when the fastener 14 is tightened by the bolt 12. l is set so that the tensile stress generated when the bolt 12 is tightened to a required torque is below the critical stress that causes stress corrosion cracking.

When the bolt 12 is tightened to the required torque, the tensile stress in the radial and circumferential directions generated in the boss 11 is reduced by the curve shown in FIG. The stress is indicated by A, and therefore the tensile stress of the entire boss portion 11 is below the critical stress that causes stress corrosion cracking, so there is no risk of stress corrosion cracking occurring in the boss portion 11 shown in FIG. Furthermore, in the magnesium alloy component 10 provided with the boss portion 11 having the shape shown in FIG. The weight can be reduced as much as possible without causing any problems.

FIG. 4 is a partial sectional view showing another embodiment of this invention, in which the length l from the tip of the boss portion 21 is tapered to gradually increase in diameter toward the tip. The tensile stress when the bolt 12 is screwed into the boss part 21 with the required torque is
1 has a tapered shape, the stress is shown by curve B in FIG. Therefore, even in the magnesium alloy component 10 in which the boss portion 21 is formed in the shape shown in FIG. The weight can be reduced as much as possible.

As can be easily understood from the above embodiments, the tensile stress generated in the boss portions 11 and 21 when the bolt 12 is screwed in is greater toward the tip end, so the tensile stress can be absorbed by stress corrosion cracking. In order to reduce the resulting stress to below the critical stress, it is sufficient to increase the diameter of the tip end of the boss to increase its cross-sectional area. Therefore, the shape of the boss should be the shape shown in Figure 2 or Figure 4. For example, the shape of the tip portion may be approximately hemispherical, as in the case of the boss portion 31 shown in FIG. 5.

As is clear from the above explanation, according to the structure of the magnesium alloy part of this invention, the tip of the boss part, where a large tensile force is applied when the bolt is screwed in, is formed with a large diameter, so that the bolt can be screwed in with the required torque. Since the resulting tensile stress is reduced, stress corrosion cracking can be prevented, and since only the tip, where a large tensile force occurs, is made large in diameter, the entire part can be improved to the extent that stress corrosion cracking does not occur. The weight of can be reduced.

Furthermore, according to the structure of this invention, stress corrosion cracking can be prevented from occurring at the tip of the boss while the boss has an integral structure made of magnesium alloy. There is no need to attach it, so compared to attaching separate parts, there is no need for attachment or processing for attachment, and there are fewer parts, so stress corrosion cracking can be prevented without increasing costs. It has become possible to prevent this.

[Brief explanation of the drawing]

FIG. 1A is a partial sectional view showing the boss portion of a conventional magnesium alloy part, FIG. 1B is a line diagram showing the stress distribution, and FIG. 2 is a partial sectional view showing the first embodiment of this invention. Fig. 3 is a diagram showing the stress distribution in the first and second embodiments, Fig. 4 is a partial sectional view showing the second embodiment of this invention, and Fig. 5 is a third embodiment of this invention. FIG. 10... Magnesium alloy parts, 11, 21,
31, 41...boss part, 12...bolt, 43...
...Thread cutting washers.

Claims (1)

[Scope of utility model registration request] In magnesium alloy parts in which the boss part into which the bolt is screwed protrudes from the part body,
The boss portion is entirely made of magnesium alloy, and the outer diameter of the boss portion is set at the proximal end in order to keep the tensile stress generated in the boss portion below the critical stress that causes stress corrosion cracking. A structure of a magnesium alloy part characterized by a structure in which the diameter becomes larger on the tip side.