JP2017140632A - Manufacturing method of aluminum forging member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an aluminum forging member capable of improving stress-corrosion cracking resistance (SCC resistance) by setting P/L to be inclined to a press-fitting direction of a bush press fitting part when manufacturing the aluminum forging member which has a product main body part and a bush press-fitting part, a forging direction upon the forging of the product main body part and a press-fitting direction for the bush press fitting part being different from each other (not parallel).SOLUTION: After performing blockage forging of a product main body part from raw material, a direction of an intermediate material made by performing blockage forging of the product main body part is changed and a forging direction when performing the forging (burr-producing forging) of bush press-fitting part is made even with the press-fitting direction of the bush press fitting part.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for producing an aluminum forged member, and more particularly to a method for producing an aluminum forged member having improved stress corrosion cracking resistance.

  In recent years, in the automobile field, the application of aluminum forging materials to undercarriage parts such as upper arms and lower arms has been expanding in order to reduce weight and improve handling stability and riding comfort.

  As the aluminum forging material that constitutes the undercarriage parts for automobiles, aluminum alloys such as 6000 series (Al-Si-Mg series alloys) with a balance between corrosion resistance and strength are mainly used, and continuous casting or extrusion After hot forging a material made of an aluminum alloy produced by processing, a predetermined strength is imparted through solution treatment, quenching treatment, aging treatment, and the like, and then processed into a part shape.

  Based on these processes, proposals have already been made to improve strength by optimizing material components and refining the crystal structure after forging heat treatment (suppressing recrystallization coarsening).

  For example, in Patent Document 1, compared to a general 6000 series aluminum alloy (for example, A6061 alloy), the matrix is strengthened by adding a large amount of precipitation elements Si and Cu, and further Mn and Cr are added. It has been proposed to increase the forging temperature to refine the crystal structure and improve the strength.

  However, even in aluminum forging members made of forged aluminum materials as described above, depending on the heat treatment conditions and direction of forging flow, stress corrosion cracking (hereinafter referred to as SCC: Stress Corrosion Cracking) There is a concern that the sensitivity of In particular, in the aluminum forged member, because the direction of the crystal grains is easily aligned in the vicinity of the forging parting line (also referred to as a parting line, hereinafter referred to as P / L: Parting Line), for example, used as an undercarriage part for automobiles, If the tensile stress generated by bush press-fitting acts in the direction perpendicular to P / L, SCC may occur. More specifically, in the vicinity of the P / L formed during forging (the part where burrs are generated), the structure is not uniform when viewed in cross-section, and the crystal grains are elongated in the direction toward the P / L. Therefore, when the bush is press-fitted, stress concentrates on the P / L part. However, if the tensile stress generated by the bush press-fitting works in a direction perpendicular to P / L, stress concentration tends to occur. This increases the possibility of SCC.

  For example, in a steering knuckle for automobiles, an iron collar may be press-fitted at a fastening portion with a tie rod, but in a steering knuckle manufactured by a conventional forging process, the press-fitting direction of the collar (or bush) and forging The direction of P / L formed at the time of molding is parallel (in other words, P / L is formed in the direction along the color press-fitting direction), and the tensile stress generated by the press-fitting of the collar is Acts in the direction of peeling P / L. That is, in the conventional forging process, the direction of P / L may be a condition that increases the sensitivity of SCC as described above, and when the load stress on the part exceeds the SCC lower limit allowable stress of the material The SCC may occur (see also Patent Document 2 below).

  As a measure to reduce such SCC sensitivity, overaging treatment (T7 treatment) may be additionally performed, but as a contradiction, the strength is lower than the peak aging condition, so the material should have The original strength cannot be expressed.

  In the automotive field, in order to meet the need for further weight reduction, the application of 7000 series aluminum alloys (Al-Zn-Mg series alloys), for example, beyond the scope of 6000 series aluminum alloys is also considered. However, 7000 series aluminum alloys are known to be more sensitive to SCC than 6000 series aluminum alloys, and their application to automotive undercarriage parts with severe corrosive environments is limited.

  With respect to the above problems, in Patent Document 3, in a suspension arm formed by machining a forged suspension member, a parting line (P / L) in the ball joint portion is formed on the side surfaces of the ball joint portion and the arm portion. Disposing near the center in the thickness direction is disclosed.

Japanese Patent Laying-Open No. 2015-193903 JP 2004-175262 A Japanese Patent Laying-Open No. 2005-082140

  However, in the prior art described in Patent Document 3, the forging direction of the entire suspension arm as a product and the insertion direction of the stud bolt with respect to the ball joint portion as a bush press-fitting portion provided in the product are set in substantially the same direction. For example, like the above-described steering knuckle for automobiles, the product itself is the main part (occupying most of the product), and the bush press-fitting portion provided with a hole into which the bush or the like is press-fitted When the forging direction of the product main body and the press-fitting direction with respect to the bush press-fitting part (the hole provided in) are different (not parallel), how can P / L be the press-fitting direction of the bush press-fitting part? No mention is made as to whether or not to match.

  The present invention has been made in view of the above-described problems, and has a product main body portion and a bush press-fit portion, and a forging direction when forging the product main body portion and a press-fit direction with respect to the bush press-fit portion are different (parallel). In the production of aluminum forged members, P / L is inclined with respect to the press-fitting direction of the bush press-fitting part, so that the forged aluminum members can improve the stress corrosion cracking resistance (SCC resistance). An object is to provide a manufacturing method.

  In order to achieve the above object, a method for producing an aluminum forged member according to the present invention comprises a product body part and a bush press-fit part from a material made of an aluminum alloy, the forging direction when forging the product body part, and the A manufacturing method for manufacturing an aluminum forged member that is not parallel to a press-fitting direction with respect to a hole provided in a bush press-fitting portion, wherein the product main body portion of the aluminum forged member is closed and forged from the material, By changing the direction of the intermediate material in which the product main body is closed and forged, pressure is applied to the bush press-fit portion corresponding to the bush press-fit portion of the intermediate material in the same direction as the press-fit direction of the bush press-fit portion. A second step of performing deburring and forging, and a hole is formed in the bush press-fitted portion subjected to deburring and forging in the press-fitting direction to form the bush press-fitting portion. And third step, a fourth step of pressing the bush into the hole of the bush press-fitting portion, the method comprising.

  According to the present invention, after forging the product body portion from the material, the direction of the intermediate material in which the product body portion is closed forged is changed, and the forging direction when forging the bush press-fit portion (burring forging) is performed. Since it is aligned with the press-fitting direction of the bush press-fit portion, the P / L at the bush press-fit portion is inclined with respect to the press-fit direction of the bush press-fit portion. Therefore, stress concentration is less likely to occur in the P / L portion, and as a result, the influence of SCC is reduced and the SCC resistance can be improved.

It is the flowchart explaining embodiment of the manufacturing method of the aluminum forge member of this invention. It is explanatory drawing which demonstrated typically embodiment of the manufacturing method of the aluminum forge member of this invention. (A) is the expansion perspective view which expanded and showed the bush press-fit part of the aluminum forge member manufactured by the manufacturing method of the aluminum forge member of this invention, (B) was manufactured by the conventional manufacturing method It is the expansion perspective view which expanded and showed the bush press-fit part of the aluminum forge member.

  Hereinafter, an embodiment of a method for producing an aluminum forged member of the present invention will be described with reference to the drawings.

  In the following, a steering knuckle having a knuckle arm part (bush press-fitting part) with a through-hole into which a bush and a collar are press-fitted, which is a kind of undercarriage part for automobiles, is mainly used as an aluminum forging member. The method of manufacturing will be explained. As the aluminum forged member to be manufactured, the main part (occupying most) of the product main body and the hole into which the bush or collar is press-fitted (may be penetrated or penetrated) Of course, the above-mentioned thing is not limited as long as it is provided with a bush press-fitting portion provided with a (not necessarily required).

  FIG. 1 is a flowchart illustrating an embodiment of a method for manufacturing an aluminum forged member of the present invention, and FIG. 2 is an explanatory diagram schematically illustrating an embodiment of a method for manufacturing an aluminum forged member of the present invention. .

  The method for producing an aluminum forged member according to the present invention includes, for example, an aging precipitation type aluminum of 6000 series (Al-Si-Mg series alloy) or 7000 series (Al-Zn-Mg series alloy) having a Cu addition amount of 0.30% or more. From the aluminum alloy which is an alloy, it has a main part of the product (which occupies most) and a knuckle arm part (bush press-fitting part) in which a bush or collar is press-fitted, and a product main part This is a method of manufacturing a steering knuckle for an automobile in which the forging direction when forging the steel and the press-fitting direction with respect to the through hole provided in the knuckle arm part (bush press-fitting part) are not parallel (different).

  As shown in FIG. 1 and FIG. 2, the manufacturing method of the aluminum forged member (steering knuckle) basically includes a material forming step S1, a homogenizing heat treatment step S2, a heating step S3, and a crushing step S4. Closed forging step S5, reheating step S6, deburring forging step S7, trimming step S8, solution treatment step S9, quenching step S10, aging treatment step (artificial aging treatment step for obtaining maximum strength) S11, hole drilling process S12, and press-fit process S13 are included.

  In addition, as needed, you may include a surface treatment process, a degassing process, etc. in each above described process.

  Among the above-described steps, a material forming step (a step of forming a material made of an aluminum alloy (aged precipitation type aluminum alloy) by melting / casting or extruding) S1, a homogenization heat treatment step (homogenizing heat treatment of the material) Step) S2, heating step (step of heating the homogenized heat-treated material (for example, heating to 500 ° C. or higher and melting start temperature or lower)) S3, crushing step (pressure in a predetermined direction with respect to the heated material) To form a predetermined shape (shape suitable for forging in the subsequent process) S4, solution treatment, which is a T6 step performed to obtain the necessary strength, toughness, and corrosion resistance of the aluminum forging material Since the processing step S9, the quenching step S10, and the aging treatment step S11 are substantially the same as the conventionally known steps, the other steps (S5 to S8) are described below. S12, S13) will be described in detail.

(Closed forging process S5)
The closed forging step S5 is a step of hot forging the forging material heated in the heating step S3 and formed into a predetermined shape in the crushing step S4. In the closed forging step S5, the material heated in the heating step S3 (particularly, the portion corresponding to the product main body portion) is closed forged, and the product main body portion of the aluminum forged member is forged from the raw material. To do.

(Reheating step S6)
In the reheating step S6, the intermediate material in which the product main body is forged by the closed forging step S5 is reheated (for example, heated to 500 ° C. or more and the melting start temperature or less).

(Burring forging process S7)
The deburring and forging step S7 is a step of hot forging the intermediate material heated in the reheating step S6. In the deburring and forging step S7, the direction of the intermediate material heated in the reheating step S6 is changed (here, the intermediate material (workpiece) is rotated 90 degrees), and the bush press-fitting portion of the intermediate material Deburring forging for applying pressure in the same direction as the press-fitting direction of the bush press-fitting portion is performed on the bush press-fitting portion (here, the portion other than the product main body portion) corresponding to the (knuckle arm portion).

(Trimming step S8)
In the trimming step S8, forging burrs are removed from the bush press-fitting portion of the intermediate material subjected to the deburring and forging, and then the T6 step (solution treatment step S9, quenching step S10, and aging treatment step S11) is performed. .

(Drilling process S12)
In the hole machining step S12, a hole (here, a through hole) is formed in the bush press-fitted portion of the intermediate material that has been subjected to the T6 step (solution treatment step S9, quenching step S10, and aging treatment step S11). ) To form a bush press-fit portion (knuckle arm portion) of the aluminum forged member (steering knuckle).

(Press-fit process S13)
In the press-fitting step S13, a bush (or collar) is press-fitted into a hole formed in the bush press-fitting part (knuckle arm part).

  By passing through the above-mentioned steps, specifically, after forging the product body from the material, the direction of the intermediate material for which the product body is closed and forged is changed, and the bush press-fitting part is forged (deburring forging ) By aligning the forging direction at the time of molding with the press-fitting direction of the bush press-fitting part, the P / L at the bush press-fitting part is inclined with respect to the press-fitting direction of the bush press-fitting part (here, it becomes orthogonal) (See also FIG. 3). Therefore, stress concentration is less likely to occur in the P / L portion, and as a result, the influence of SCC is reduced and the SCC resistance can be improved.

[Experiment and results of measuring stress corrosion cracking resistance (SCC resistance) of specimen]
The present inventors made four test bodies (Examples 1 and 2 and Comparative Examples 1 and 2) having different compositions and production methods, and performed SCC resistance measurement on each test body.

<Chemical component composition of each specimen>
Table 1 below is a list showing the chemical composition of each test specimen (Examples 1 and 2 and Comparative Examples 1 and 2). Here, Example 1 and Comparative Example 1 (material A) correspond to AA6110 alloy, and Example 2 and Comparative Example 2 (material B) correspond to A7075 alloy.

<Manufacturing method of each specimen>
The inventors have melted and cast an aluminum alloy having the chemical composition shown in Table 1 to form an ingot (forging material), and from the material, the closed forging process and the burrs described with reference to FIGS. Steering knuckles (Example 1 and Example 2) were manufactured by a manufacturing method including a forging step and the like. In addition, the present inventors melted and cast an aluminum alloy having the chemical composition shown in Table 1 to form an ingot (forging material), and from that material, a conventional manufacturing method (specifically, as described above) Among the manufacturing methods of the present invention, the steering knuckle (Comparative Example 1, comparison) is performed by omitting the reheating step, the deburring forging step, and the trimming step, and forging the bush press-fit portion together with the product main body in the closed forging step. Example 2) was prepared.

  Table 2 below is a list showing the T6 treatment conditions for each specimen (Examples 1 and 2 and Comparative Examples 1 and 2).

<Tensile test with each specimen and its result>
The present inventors conducted a tensile test on each specimen in accordance with the provisions of JIS Z2241, and measured the tensile strength, 0.2% proof stress, and elongation of each specimen.

  As a result of the tensile test, the specimens of Example 1 and Comparative Example 1 both have a tensile strength of 390 MPa, a 0.2% proof stress of 370 MPa, and an elongation of 10%. The tensile strength was 560 MPa, the 0.2% proof stress was 510 MPa, and the elongation was 10%. That is, the tensile strength, 0.2% proof stress, and elongation were the same in the specimens of Example 1 and Comparative Example 1, and in the specimens of Example 2 and Comparative Example 2.

<Measurement test of stress corrosion cracking resistance (SCC resistance) by each specimen and results>
The present inventors cut out a C-shaped test piece (C-ring test piece) from the knuckle arm portion of the steering knuckle of each specimen (specifically, each specimen after the T6 step and before the drilling step). Then, in accordance with JIS H8711, a stress corrosion cracking test using a salt water alternate dipping method was performed.

  Table 3 below is a list showing the measurement results of the SCC resistance of each specimen. In Table 3, when a 60 day evaluation was performed for each load stress, the case where no crack (stress corrosion cracking: SCC) occurred was OK (○), and the case where a crack occurred was NG (×). Is shown.

  As a result of the stress corrosion cracking test, in the specimen of Comparative Example 1, the forging flow was in the worst direction (see FIG. 3B), so SCC was generated at a stress load of 200 MPa or more. On the other hand, in the test body of Example 1, the forging flow was in the direction of low SCC sensitivity (see FIG. 3A), and SCC did not occur even at 340 MPa (corresponding to about 90% of the proof stress).

  Moreover, in the test body of Comparative Example 2, SCC occurred regardless of the load stress. On the other hand, in the test body of Example 2, no SCC occurred at a load stress of 220 MPa or less. In the test body of Example 2, the occurrence of SCC can be further suppressed by optimizing the thickness and shape and lowering the input to the parts, and can also be applied to materials with higher SCC sensitivity. Conceivable.

  From this experimental result, after forging the product main body part from the material, change the direction of the intermediate material for which the product main body part is closed forged, and change the forging direction when forging the bush press-fitting part (deburring forging). It was demonstrated that the SCC resistance can be improved while maintaining the tensile strength by aligning with the press-fitting direction of the press-fitting part.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

S1 ... Raw material forming step, S2 ... Homogenizing heat treatment step, S3 ... Heating step, S4 ... Crushing step, S5 ... Closure forging step, S6 ... Reheating step, S7 ... Deburring forging step, S8 ... Trimming step, S9 ... Solution , Treatment process, S10 ... quenching process, S11 ... aging treatment process, S12 ... hole drilling process, S13 ... press-fitting process

Claims (1)

An aluminum forging member comprising a material body made of an aluminum alloy and having a product body portion and a bush press-fit portion, wherein the forging direction when forging the product body portion and the press-fit direction with respect to the holes provided in the bush press-fit portion are not parallel A manufacturing method for manufacturing
A first step of closing and forging the product body portion of the aluminum forging member from the material;
By changing the direction of the intermediate material in which the product main body is closed and forged, pressure is applied to the bush press-fit portion corresponding to the bush press-fit portion of the intermediate material in the same direction as the press-fit direction of the bush press-fit portion. A second step of performing deburring and forging;
A third step of forming a bush press-fitting portion by opening a hole in the press-fitting direction in the bush press-fitting portion subjected to deburring forging;
And a fourth step of press-fitting a bush into the hole of the bush press-fitting part.

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