JP2010174274A - Surface processing method of aluminum casting product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface processing method of aluminum casting product capable of removing a casting defect due to friction stir processing without damaging an effect imparted by heat treatment such as improvement of fatigue strength and without bringing about elongation of processing time. <P>SOLUTION: In the surface processing method of aluminum casting product, an aluminum casting product is made to be an object to be processed, and the prescribed heat treatment and the friction stir processing for reforming a surface part of the object to be processed by stirring in the non-fusion state caused by frictional heat, by inserting the prescribed rotation tool to the surface part of the object to be processed while rotating the prescribed rotation tool are performed. Therein, a solution heat treatment (S20) and an aging treatment (S40) are performed as the heat treatment, and the friction stir processing (S30) is performed between the solution heat treatment (S20) and the aging treatment (S40). <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a surface treatment method for an aluminum casting by friction stir processing.

  Conventionally, as a surface treatment for a cast product (casting) such as an aluminum alloy, a friction stir processing is performed. Friction stirring is a surface that is stirred and modified without melting the surface of the object to be processed by friction heat generated when a predetermined rotating tool is inserted into the surface of the object to be processed in a rotating state. It is processing.

  According to the friction stir processing, defects in the cast product are removed and the strength is improved. However, when the object to be treated is an aluminum heat-treated alloy that has been subjected to a predetermined heat treatment, the effect of the heat treatment may be reduced due to the influence of the heat (friction heat) of the friction stir treatment. On the other hand, Patent Document 1 proposes a surface treatment method in which heat treatment is further performed after the friction stir treatment.

  That is, in the surface treatment method disclosed in Patent Document 1, a casting defect is removed by friction stir treatment after a so-called T6 treatment (solution treatment and aging treatment) is performed as a heat treatment on an aluminum cast product. Thereafter, the T6 process is performed again.

  However, according to the surface treatment method disclosed in Patent Document 1, there are the following problems, and a sufficient effect cannot be obtained. That is, when a heat treatment that is a high-temperature treatment is performed after the friction stirring treatment, the crystal grains become coarse due to recrystallization. From this, for example, when the T6 treatment is performed as the heat treatment after the friction stirring treatment, the fatigue strength equivalent to that of the normal T6 treatment cannot be obtained. In addition, since it is necessary to perform heat treatment that requires a considerable amount of time twice before and after the friction stir treatment, the heat treatment takes twice as long as usual, so that the treatment time becomes longer.

JP 2001-181809 A

  The present invention has been made in view of the problems as described above, and the problem to be solved is that the effect of heat treatment such as improvement of fatigue strength is not impaired, and the processing time is prolonged. An object of the present invention is to provide a surface treatment method for an aluminum casting that can eliminate casting defects by friction stir processing.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

  That is, in claim 1, an aluminum casting is a processing target, and the surface portion is subjected to frictional heat by inserting a predetermined heat treatment and a predetermined rotary tool into the surface portion of the processing target in a rotating state. A surface treatment method of an aluminum cast product that performs a friction stir treatment that is stirred and modified in a non-molten state, wherein the heat treatment includes a solution treatment and an aging treatment, and the solution treatment and the aging treatment. In the meantime, the friction stir processing is performed.

As effects of the present invention, the following effects can be obtained.
That is, according to the present invention, casting defects can be removed by the friction stir processing without impairing the effects of heat treatment such as improvement of fatigue strength and without increasing the processing time.

Explanatory drawing about a friction stirring process. The flowchart which shows the surface treatment method which concerns on one Embodiment of this invention. The figure which shows an example of the test result of a stress life.

  The present invention relates to a surface treatment method in which an aluminum cast product (hereinafter referred to as “aluminum cast product”) is a treatment target (hereinafter referred to as “workpiece”), and between casting and aging treatment as a heat treatment. By performing the friction stir processing for removing the defect of the product, it is intended to prevent the effect of the heat treatment from being reduced due to the heat effect or the like accompanying the friction stir processing. Embodiments of the present invention will be described below.

  The surface treatment method (hereinafter simply referred to as “surface treatment method”) for an aluminum cast product according to the present embodiment uses an aluminum cast product such as an aluminum alloy cast as a workpiece. Specifically, the surface treatment method according to the present embodiment is performed, for example, on a part of the surface of a cylinder head constituting an automobile engine, or on the surface of a part such as a piston or a brake disk constituting the automobile engine. . Therefore, the surface treatment method according to the present embodiment is performed in the process of manufacturing a workpiece such as a cylinder head, for example.

  In the surface treatment method according to the present embodiment, predetermined heat treatment and friction stirring treatment are performed on the workpiece. The friction agitation process is a process for removing defects in the aluminum casting product and improving the strength, and is performed using a predetermined rotary tool.

  Specifically, as shown in FIG. 1, the friction stir processing is performed by inserting the rotary tool 20 into the surface portion (hereinafter referred to as “work surface portion”) 11 of the workpiece 10 while rotating the rotary tool 20. The part 11 is modified by stirring in a non-molten state with frictional heat.

  The rotary tool 20 is provided in the friction stir processing apparatus, and is driven to rotate by a predetermined driving means similarly provided in the friction stir processing apparatus. In the friction stir processing apparatus, a jig for positioning and holding the workpiece 10 is provided.

  As shown in FIG. 1, the rotary tool 20 is composed of a substantially cylindrical shaft member, and is configured to be rotatable with a motor or the like by a predetermined driving means (see arrow A1). The rotary tool 20 has a protruding probe 22 that is a small-diameter portion on an end surface portion 21 on one side thereof.

  The rotary tool 20 is rotated and moved along the processing area in the workpiece surface portion 11 in a state where the probe 22 is pressed so as to be pushed into the workpiece surface portion 11 (see arrow A2). For this reason, in the friction stir processing apparatus, the rotary tool 20 and the workpiece 10 are provided so as to be relatively movable in a predetermined direction along the processing region in the workpiece surface portion 11 by a predetermined driving means or the like.

  In this way, by moving on the work surface portion 11 while rotating while the rotary tool 20 is pressed, the contact portion of the rotary tool 20 with respect to the work surface portion 11, that is, the end face portion 21 and the probe on the work surface portion 11. Frictional heat and stirring action occur at 22 contact portions. Due to the frictional heat and the stirring action of the rotary tool 20, the contact portion of the rotary tool 20 with respect to the workpiece surface portion 11 and the area in the vicinity thereof are softened, and plastic flow occurs in the area portion. The portion where the plastic flow has occurred is modified by being stirred in a non-molten state, and the modified layer 12 is formed.

  According to such a friction stir processing, the metal structure of the workpiece surface portion 11 is refined, defects such as a cast hole are removed, and the strength of the workpiece surface portion 11 is improved. Note that the rotary tool 20 may not have the probe 22. In this case, the end surface portion 21 becomes a contact portion with respect to the workpiece surface portion 11 of the rotary tool 20, and frictional heat and a stirring action for forming the modified layer 12 are obtained at the contact portion.

  In the surface treatment method of the present embodiment, solution treatment and aging treatment are performed as the predetermined heat treatment. The solution treatment is a solution treatment for a non-ferrous metal such as an aluminum alloy as in the workpiece 10 of the present embodiment, and the alloy element is dissolved (melted) by heating the metal to a predetermined temperature. ) After that, it is a process (quenching process) for rapidly cooling the alloy element to form a solid solution (solution).

  Therefore, in the solution treatment of the present embodiment, the workpiece 10 is placed in a solution treatment furnace (furnace for performing the solution treatment), and a predetermined solution temperature (for example, about 500 ° C.) for about several hours. ) Is kept heated. And the workpiece | work 10 after a heating is made into a solution by being rapidly cooled by being immersed in the water tank for hardening which stores boiling water etc.

  The aging treatment is a treatment for precipitating and hardening a solid solution alloy element by holding the metal after the solution treatment at a relatively low temperature with respect to the solution treatment temperature.

  Therefore, in the aging treatment of the present embodiment, the workpiece 10 after the solution treatment is placed in an aging treatment furnace (furnace for performing the aging treatment), and a predetermined temperature (for example, about 200 ° C.) for about several hours. ) Is kept heated. As a result, the alloy element that has been dissolved by the solution treatment is precipitated, and the workpiece surface portion 11 is cured.

  As described above, the solution treatment and the aging treatment as the heat treatment are performed on the workpiece 10, so that effects such as improvement of fatigue strength and hardness of the workpiece surface portion 11 can be obtained.

  And in the surface treatment method of this embodiment, a friction stirring process is performed between the solution treatment and aging treatment which are performed on the workpiece 10. That is, as described above, after the solution treatment as the heat treatment applied to the workpiece 10 is performed, the friction stir processing for removing the defect is performed, and after the friction stir processing, the aging treatment as the heat treatment is performed. Done.

  The case where the surface treatment method of the present embodiment is applied in the manufacturing process of the cylinder head (when the workpiece 10 is a cylinder head) will be described with reference to the flowchart shown in FIG. As shown in FIG. 2, in the manufacturing process of the cylinder head, first, the cylinder head is cast from an aluminum alloy by a casting machine (S10). Thereby, the cylinder head which is an aluminum casting as the workpiece | work 10 in the surface treatment method of this embodiment is obtained.

  Next, a solution treatment is performed on the cylinder head as the workpiece 10 (S20). That is, the cast cylinder head is placed in a solution treatment furnace and heated for a predetermined time, and then immersed in a quenching water tank and rapidly cooled, whereby the cylinder head is subjected to a solution treatment.

  Subsequently, a friction stirring process is performed on the cylinder head after the solution treatment (S30). That is, as shown in FIG. 1, a friction stir processing for forming the modified layer 12 is performed on a predetermined region in the work surface portion 11 of the cylinder head by the friction stir processing apparatus including the rotary tool 20.

  Next, an aging process is performed on the cylinder head after the friction stirring process (S40). That is, the cylinder head on which the modified layer 12 is formed by the friction stirring process is placed in an aging furnace and heated at a relatively low temperature for a predetermined time, whereby the cylinder head is subjected to an aging process.

  Then, the cylinder head after the aging treatment is machined (S50). That is, machining such as finishing is performed by a predetermined processing machine on the cylinder head subjected to the solution treatment and aging treatment as the heat treatment and the friction stir treatment.

  According to the surface treatment method of the present embodiment described above, casting defects are removed by friction stir treatment without impairing the effects of heat treatment such as improvement of fatigue strength and without causing a prolonged treatment time. be able to.

  That is, when the friction stir treatment is performed after the heat treatment (solution treatment and aging treatment) is performed, the effect of the heat treatment such as improvement of fatigue strength may be reduced due to the thermal effect of the friction stir processing. In this regard, according to the surface treatment method of the present embodiment, the friction stir treatment is performed between the solution treatment and the aging treatment as the heat treatment, thereby preventing the heat treatment effect from being reduced due to the heat effect of the friction stir treatment. Is done.

  In addition, when a heat treatment including a solution treatment and an aging treatment is performed after the friction stir processing, a heat treatment (solution treatment) that is a high-temperature treatment is performed after the friction stir processing. As the roughness of the steel increases, it becomes difficult to ensure fatigue strength. In this regard, according to the surface treatment method of the present embodiment, after the friction stir treatment, only the aging treatment, which is a low-temperature heat treatment as compared with the solution treatment, is performed, so that the crystal grains are coarsened by recrystallization. Is prevented, and the fatigue strength is improved by removing the casting defects by the friction stir processing.

  In addition, according to the surface treatment method of the present embodiment, since the solution treatment and the aging treatment as the heat treatment are performed only once, the treatment time is not prolonged due to an increase in the number of heat treatment steps. .

  By the way, in the surface treatment method according to the present embodiment, it is preferable that the friction stirring treatment as described above is performed in water. In the friction stir processing in water, in the friction stir processing apparatus including the rotary tool 20 and the like, a water tank having a size capable of dipping and soaking at least a part of the work surface portion 11 in the work 10 is provided. That is, according to the friction stirring process in water, the frictional heat and stirring caused by the rotating rotary tool 20 being pressed against the work surface part 11 in a state where the contact part of the rotary tool 20 with the work surface part 11 exists in the water. The effect is obtained.

  As the friction stirring process in water, for example, the process by the rotary tool 20 is performed in a state where the workpiece 10 is submerged in the water tank. Further, as water stored in the water tank, for example, room temperature water or predetermined temperature hot water is used.

  As described above, when the friction stir processing is performed in water, the portion affected by the heat (friction heat) of the friction stir processing is reduced, and the cooling rate is also increased in the heat affected portion. For this reason, about the workpiece | work surface part 11, the characteristic equivalent to solution formation can be acquired by the quenching effect.

  FIG. 3 shows an example of a stress life test result (fatigue test result) for a test piece (product of this example) subjected to surface treatment by the surface treatment method according to the present invention as an example of the present invention. In the graph shown in FIG. 3, the vertical axis indicates the stress amplitude (MPa), and the horizontal axis indicates the number of breaks (the number of repetitions until breakage).

  In this test, the following test piece (comparative example product) was used as a comparative example for the product of this example. The comparative product 1 is obtained by performing a friction stir treatment as a surface treatment and then performing a solution treatment and an aging treatment as a heat treatment (friction stirring treatment → solution treatment → aging treatment). The comparative example product 2 is a cast product having a casting defect (cast defect product). The comparative example product 3 is a cast product without casting defects (a product without casting defects).

  According to the test results, the 10 million times fatigue strength was about 70 MPa for Comparative Example Product 1, about 52 MPa for Comparative Example Product 2, and about 80 MPa for Comparative Example Product 3. On the other hand, in the product of this example, a value of 100 MPa or more was obtained for the 10 million times fatigue strength.

  As can be seen from the test results, according to the surface treatment method of the present invention, casting defects can be removed by friction stir processing, and heat treatment (solution treatment and aging treatment) is performed after the friction stir processing. A sufficiently high fatigue strength can also be obtained in comparison with a cast product and a product without casting defects.

10 Workpieces (processing target)
11 Workpiece surface (surface)
20 Rotating tools

Claims (1)

An aluminum casting is a target to be processed, and a predetermined heat treatment and a predetermined rotary tool are inserted into the surface portion of the processing target while rotating, and the surface portion is agitated in a non-molten state by frictional heat and modified. A surface treatment method for an aluminum casting product that performs a friction stir treatment.
As the heat treatment, solution treatment and aging treatment are performed,
A surface treatment method for an aluminum cast product, characterized in that the friction stir treatment is performed between the solution treatment and the aging treatment.

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