WO2021230080A1 - Aluminum alloy forging material and method for manufacturing same - Google Patents

Abstract

Provided are a 6000-series aluminum alloy forging material having high strength and exceptional toughness (excellent ductility), and an efficient method for manufacturing the same. This aluminum alloy forging material is characterized by being formed from a 6000-series aluminum alloy, having a Cu content of 0.2-1.0 wt.%, the composition of the 6000-series aluminum alloy satisfying relational expressions (1) and (2), and having deposits at the base metal crystal grain boundary, specifically Al-(Fe,Mn,Cr)-Si-type crystalline deposits at the base metal crystal grain boundary. (1) Si (at%)≥2Mg (at%) (2) 0.2≤surplus Si (wt%)+Mn (wt%)+Cr (wt%)≤1.7

Description

Aluminum alloy forged material and its manufacturing method

The present invention relates to an aluminum alloy forged material and a method for manufacturing the same, and particularly to an aluminum alloy forged material that can be suitably used for undercarriage parts for automobiles and the like, and a simple and efficient manufacturing method thereof.

The 6000 series aluminum alloy is an Al-Mg-Si based aluminum alloy to which Mg and Si are mainly added, and in addition to being excellent in moldability and corrosion resistance, it exhibits moderate age hardening and has good strength. Forged members are widely used as structural members for transportation equipment such as automobiles.

However, in recent years, _{there has been an increasing demand for weight reduction of transportation equipment for the purpose of improving fuel efficiency and reducing CO 2} emissions, and there is an urgent need for higher strength and toughness of 6000 series aluminum alloy forged members. In particular, when the 6000 series aluminum alloy forged member is used for undercarriage parts for automobiles, it is indispensable to impart high reliability.

On the other hand, for example, in Patent Document 1 (Japanese Unexamined Patent Publication No. 2017-155251), Si: 0.7 to 1.5%, Mg: 0.6 to 1.2%, Fe: 0 in mass%. Each contains 0.01 to 0.5%, and further, of Mn: 0.05 to 1.0%, Cr: 0.01 to 0.5%, and Zr: 0.01 to 0.2%. An aluminum alloy forged material containing one or more of the remaining Al and unavoidable impurities, which is measured by X-ray diffraction as the structure of the thickest part of the forged material on the observation surface at the center of the wall thickness. The dislocation density was in ^{the range of 1.0 × 10 14} to 5.0 × 10 ¹⁶ / m ^{2 on} average, and the tilt angle of the crystal grains with an orientation difference of 2 ° or more measured by the SEM-EBSD method was 2 to 2. It is characterized by an average ratio of 15 ° small tilt angle grain boundaries of 50% or more and an average number density of precipitates measurable by TEM at a magnification of 300,000 times of 5.0 × 10 ² / μm ³ or more. An aluminum alloy forged material having excellent strength and ductility is disclosed.

In the aluminum alloy forged material described in Patent Document 1, when the 6000 series aluminum alloy forged material is subjected to artificial aging treatment after being subjected to processing strain by warm processing to the forged material which has been solutionized and hardened. In addition, since both strength and ductility are improved (higher strength and higher ductility) than in the normal case where no processing strain is applied, artificial aging is performed in order to exert or guarantee the effect. It is said that the average dislocation density, the average ratio of small tilted grain boundaries, and the average number density of precipitates are defined as the structure at the center of the wall thickness of the thickest part of the forged material after the treatment.

Further, in Patent Document 2 (Japanese Unexamined Patent Publication No. 2008-163445), Mg: 0.5 to 1.25%, Si: 0.4 to 1.4%, Cu: 0.01 to 0 in mass%. .7%, Fe: 0.05 to 0.4%, Mn: 0.001 to 1.0%, Cr: 0.01 to 0.35%, Ti: 0.005 to 0.1%, respectively. , And Zr: regulated to less than 0.15%, and the balance is an aluminum alloy forged material composed of Al and unavoidable impurities. The crystallite density observed in the structure of the cross-sectional area where stress is generated is 1.5% or less in average area ratio, and each grain boundary observed in the structure of the cross-sectional area including the parting line generated during forging. Disclosed are automobile undercarriage parts, characterized in that the distance between the precipitates is 0.7 μm or more in average distance.

In the automobile undercarriage component described in Patent Document 2, the cross-sectional structure in the width direction of each specific portion of the rib and the web at the maximum stress generation portion in the rib, for example, of the automobile undercarriage component arm portion having a lightweight shape is provided. The components of the arm part of the automobile undercarriage after forging are adjusted and manufactured so that the widthwise cross-sectional structure of each specific part of the rib and the web at the part where the maximum stress is generated such as the rib is a predetermined structure. As a result, it is said that it is possible to suppress the coarsening of crystal grains in the rib portion and the web portion during forging, especially in the specific portion where the maximum stress is generated, in the weight-reduced automobile suspension component arm portion. There is.

Japanese Unexamined Patent Publication No. 2017-155251 Japanese Unexamined Patent Publication No. 2008-163445

The mechanical properties of the 6000 series aluminum alloy are affected by the precipitates at the grain boundaries and the crystal precipitates in the crystal grains. However, in the aluminum alloy forged material described in Patent Document 1, the precipitates in the crystal grains are basically used. Focusing only on, the influence of the precipitates at the grain boundaries, which greatly contributes to toughness (dexterity), is not taken into consideration.

Further, in the automobile undercarriage parts described in Patent Document 2, the spacing between the precipitates at the crystal grain boundaries is defined, but the size and shape of the precipitates are considered to be extremely important features in terms of metallographic structure. It has not been.

That is, it cannot be said that the precipitates at the grain boundaries and the crystal precipitates in the crystal grains are in a sufficiently optimum state from the viewpoint of achieving both strength and toughness at a high level for the 6000 series aluminum alloy forged material. ..

In view of the above problems in the prior art, an object of the present invention is to provide a 6000 series aluminum alloy forged material having high strength and excellent toughness (good ductility) and an efficient manufacturing method thereof. ..

As a result of intensive studies on the relationship between the composition of the 6000 series aluminum alloy forged material and the microstructure in order to achieve the above object, the present inventors added sufficient Si to form fine precipitates in the crystal grains. We have found that it is extremely effective to add appropriate amounts of Mn and Cr to refine the precipitates at the grain boundaries in addition to forming them, and have reached the present invention.

That is, the present invention
Made of 6000 series aluminum alloy
The Cu content is 0.2 to 1.0 wt%,
The composition of the 6000 series aluminum alloy satisfies the following relational formulas (1) and (2).
Having precipitates at the grain boundaries of the base metal and Al- (Fe, Mn, Cr) -Si-based crystal precipitates in the grain boundaries of the base metal.
Provided is an aluminum alloy forged material, which is characterized by.
Si (at%) ≧ 2Mg (at%) (1)
0.2 ≤ Excess Si (wt%) + Mn (wt%) + Cr (wt%) ≤ 1.7 (2)

In the aluminum alloy forged member of the present invention, _{by adding sufficient Si for the formation of Mg 2} Si, a fine and large amount of crystal precipitates are formed in the crystal grains. In addition, by setting the total content of excess Si, Mn and Cr to 0.2 to 1.7 wt%, Al- (Fe, Mn, Cr) -Si compounds are crystallized during casting and homogenized heat treatment is performed. In addition to precipitating Al- (Fe, Mn, Cr) -Si compounds during forging preheating to increase the strength of the aluminum alloy forged member, the precipitation of excess Si causes precipitates at the crystal grain boundaries. Has been refined. Here, the excess Si amount (wt%) can be calculated by "Si amount (wt%)-(Mg amount (wt%) /1.731".

In addition, the aluminum alloy forged material of the present invention contains 0.2 to 1.0 wt% of Cu, so that it is an Al, Mg, Si, Cu-based quaternary precipitate (Q phase or Q'phase). Good mechanical strength and fatigue strength are imparted by the formation of.

Further, in the aluminum alloy forged material of the present invention, it is preferable that the Si content is 0.5 to 1.4 wt% and the Mg content is 0.6 to 1.7 wt%. The more preferable Si content is 0.9 to 1.2 wt%, and the more preferable Mg content is 0.8 to 1.2 wt%.

When the Si content is 0.5 wt% or more, solid solution strengthening and aging hardening can be sufficiently exhibited, and when it is 1.4 wt% or less, the corrosion resistance is lowered and the crystallized material and the precipitate are coarse. It is possible to suppress the decrease in ductility caused by the formation. Further, by setting the Si content to 0.9 to 1.2 wt%, these effects can be obtained more reliably.

Further, by setting the Mg content to 0.6 wt% or more, a sufficient amount of Mg-Si-based precipitates can be formed, the strength and fatigue characteristics can be improved, and the Mg content can be 1.7 wt% or less. By doing so, it is possible to suppress the formation of a coarse compound that is the starting point of fracture. By setting the Mg content to 0.8 to 1.2 wt%, these effects can be obtained more reliably.

Further, in the aluminum alloy forged material of the present invention, it is preferable that the average particle size of the precipitate at the grain boundaries of the base metal is 50 nm or less. When the average particle size of the precipitates at the grain boundaries of the base metal is 50 nm or less, good ductility (toughness) can be imparted to the aluminum alloy forged material. Here, the average particle size of the precipitate may be calculated as a circle-equivalent diameter.

Further, in the aluminum alloy forged material of the present invention, it is preferable that the aspect ratio of the precipitate at the grain boundaries of the base material is 5 or less. By setting the aspect ratio of the precipitates at the grain boundaries of the base metal to 5 or less, the proportion of the precipitates occupying the grain boundaries of the base metal can be reduced, and the distance between the precipitates can be lengthened. As a result, good ductility (toughness) can be imparted to the aluminum alloy forged material.

Further, in the aluminum alloy forged material of the present invention, it is preferable that the width of the non-precipitation zone centered on the grain boundaries of the base metal is 100 nm or less. By setting the width of the non-precipitation zone at the grain boundaries of the base metal to 100 nm or less, high strength and good ductility can be imparted to the aluminum alloy forged material.

Further, in the aluminum alloy forged material of the present invention, it is preferable that the 0.2% proof stress is 350 MPa or more and the elongation is 10% or more. Since the aluminum alloy forged material has a 0.2% proof stress of 350 MPa or more and an elongation of 10% or more, it can be suitably used for structural members that require high reliability.

The present invention also provides an automobile undercarriage component made of the aluminum alloy forged material of the present invention. The aluminum alloy forged material of the present invention has good strength and ductility, and the undercarriage parts for automobiles of the present invention can be suitably used when high strength and reliability are required.

Further, the present invention
The method for producing an aluminum alloy forged material of the present invention.
The Cu content of the aluminum alloy forged material is 0.2 to 1.0 wt%.
Hot forging preheating process to preheat aluminum alloy material,
A hot forging step of hot forging the preheated aluminum alloy material obtained in the hot forging preheating step is included.
The preheating temperature in the hot forging preheating step is 300 to 550 ° C., and the preheating time is 1 to 3 hours.
The composition of the aluminum alloy satisfies the following relational expressions (1) and (2).
Also provided is a method for manufacturing an aluminum alloy forged material, which is characterized by the above.
Si (at%) ≧ 2Mg (at%) (1)
0.2 ≤ Excess Si (wt%) + Mn (wt%) + Cr (wt%) ≤ 1.7 (2)

In the method for producing an aluminum alloy forged material of the present invention, an Al- (Fe, Mn, Cr) -Si-based compound is subjected to a hot forging preheating step in which the preheating temperature is 300 to 550 ° C and the preheating time is 1 to 3 hours. In addition to increasing the strength of the aluminum alloy forged member, the precipitate at the crystal grain boundary is refined by consuming excess Si.

Further, in the method for producing an aluminum alloy forged material of the present invention, a homogenizing heat treatment step for the aluminum alloy material is provided before the hot forging preheating step, and the temperature of the homogenizing heat treatment step is set to 500 to 550 ° C. It is preferable that the holding time is 5 to 10 hours.

By subjecting the homogenization heat treatment at 500 to 550 ° C. for 5 to 10 hours, the Al- (Fe, Mn, Cr) -Si compound is more reliably precipitated, and the strength of the aluminum alloy forged member is increased. In addition, the precipitates at the crystal grain boundaries are refined by consuming excess Si.

According to the present invention, it is possible to provide a 6000 series aluminum alloy forged material having high strength and excellent toughness (good ductility) and an efficient manufacturing method thereof.

It is a schematic diagram of the microstructure of the aluminum alloy forged material of this invention. It is a TEM observation result in the vicinity of the grain boundary of the aluminum base material of the aluminum alloy forged material of Example 1. It is a TEM observation result in the aluminum base metal crystal grain of the aluminum alloy forged material of Example 1. It is a TEM-EDS spectrum of the crystal precipitate shown in FIG. It is a TEM observation result in the vicinity of the grain boundary of the aluminum base material of the aluminum alloy forged material of Comparative Example 5. It is a TEM observation result in the vicinity of the grain boundary of the aluminum base material of the aluminum alloy forged material of Comparative Example 1. It is a TEM observation result in the vicinity of the grain boundary of the aluminum base material of the aluminum alloy forged material of Comparative Example 4. It is a TEM observation result in the aluminum base metal crystal grain of the aluminum alloy forged material of the comparative example 5.

Hereinafter, typical embodiments of the aluminum alloy forged material of the present invention and the method for producing the same will be described in detail with reference to the drawings, but the present invention is not limited to these. In the following description, the same or corresponding parts may be designated by the same reference numerals, and duplicate description may be omitted. Further, since the drawings are for conceptually explaining the present invention, the dimensions of each component represented and their ratios may differ from the actual ones.

1. 1. Aluminum alloy forged material (1) Composition The aluminum alloy forged material is made of 6000 series aluminum alloy, and in order to impart high strength and toughness (dexterity) to the aluminum alloy forged material, the content of Si, Mg, Mn and Cr is particularly high. Is optimized. Hereinafter, each characteristic element of the aluminum alloy forged material of the present invention will be described.

Cu: 0.2-1.0 wt%
The Cu content is 0.2 to 1.0 wt%. Cu has an action of increasing mechanical strength and fatigue strength by forming Al, Mg, Si, and Cu-based quaternary precipitates (Q phase or Q'phase). If the Cu content is less than 0.2 wt%, these effects cannot be sufficiently obtained, and the proof stress of the aluminum alloy forged material cannot be 350 MPa or more. On the other hand, if the Cu content exceeds 1.0 wt%, the corrosion resistance may be lowered.

Si: 0.5-1.4 wt%
The Si content is preferably 0.5 to 1.4 wt%. When the Si content is 0.5 wt% or more, solid solution strengthening and aging hardening can be sufficiently exhibited, and when it is 1.4 wt% or less, the corrosion resistance is lowered and the crystallized material and the precipitate are coarse. It is possible to suppress the decrease in ductility caused by the formation. Further, the more preferable Si content is 0.9 to 1.2 wt%. By setting the Si content to 0.9 to 1.2 wt%, these effects can be obtained more reliably.

Mg: 0.6-1.7 wt%
The Mg content is preferably 0.6 to 1.7 wt%. By setting the Mg content to 0.6 wt% or more, a sufficient amount of Mg-Si-based precipitates can be formed, the strength and fatigue characteristics can be improved, and the Mg content is set to 1.7 wt% or less. This makes it possible to suppress the formation of a coarse compound that is the starting point of fracture. The more preferable Mg content is 0.8 to 1.2 wt%. By setting the Mg content to 0.8 to 1.2 wt%, these effects can be obtained more reliably.

Mn: 0.1-0.8 wt%
The Mn content is preferably 0.1 to 0.8 wt%. By setting the Mn content to 0.1 wt% or more, the strength of the aluminum alloy forged material can be increased by forming an Al- (Fe, Mn, Cr) -Si-based compound. Further, by setting the Mn content to 0.8 wt% or less, it is possible to suppress the formation of coarse Al— (Fe, Mn, Cr) -Si compounds that reduce toughness and ductility.

Cr: 0.1-0.8 wt%
The Cr content is preferably 0.1 to 0.8 wt%. By setting the Cr content to 0.1 wt% or more, the strength of the aluminum alloy forged material can be increased by forming an Al- (Fe, Mn, Cr) -Si-based compound. Further, by setting the Cr content to 0.8 wt% or less, it is possible to suppress the formation of coarse Al— (Fe, Mn, Cr) -Si compounds that reduce toughness and ductility.

Fe: 0.05-0.3 wt%
The Fe content is preferably 0.05 to 0.3 wt%. By setting the Fe content to 0.05 wt% or more, the strength of the aluminum alloy forged material can be increased by forming an Al- (Fe, Mn, Cr) -Si-based compound. Further, by setting the Fe content to 0.3 wt% or less, it is possible to suppress the formation of coarse Al— (Fe, Mn, Cr) -Si compounds that reduce toughness and ductility.

In addition, Cu, Zn, Ti and the like can be contained in the composition range specified as various 6000 series aluminum alloys (Al—Mg—Si based alloys).

Further, regarding the component elements of the aluminum alloy forged material of the present invention, it is necessary to satisfy the following two requirements.

(1) Si (at%) ≧ 2Mg (at%)
When Si and Mg satisfy Si (at%) ≧ 2Mg (at%) _{, sufficient Si is present for the formation of Mg 2} Si, and a large amount of crystal precipitates are formed in the crystal grains. be able to.

(2) 0.2 ≤ excess Si (wt%) + Mn (wt%) + Cr (wt%) ≤ 1.7
By setting the total content of excess Si, Mn and Cr to 0.2 to 1.7 wt%, Al- (Fe, Mn, Cr) -Si-based compounds are crystallized during casting and homogenized heat treatment is performed. In addition to precipitating Al- (Fe, Mn, Cr) -Si-based compounds during forging preheating to increase the strength of the aluminum alloy forged member, the precipitation of excess Si causes the precipitates at the crystal grain boundaries. Has been refined.

(2) Structure Figure 1 shows a schematic diagram of the fine structure of the forged aluminum alloy material of the present invention. In the aluminum alloy forged material of the present invention, the precipitate 6 is formed at the grain boundaries 4 of the aluminum base material 2. Further, extremely fine Al- (Fe, Mn, Cr) -Si-based crystal precipitates are dispersed in the crystal grains of the aluminum base material 2. It should be noted that what is present in the crystal grains is not limited to Al- (Fe, Mn, Cr) -Si-based crystal precipitates, and is generally known as, for example, an aging precipitation phase of an Al-Mg-Si-based alloy. The β phase and its precursor phase, the Q phase and its precursor phase and the like may be dispersed.

The average particle size of the precipitate 6 at the grain boundaries 4 is preferably 50 nm or less. When the average particle size of the precipitate 6 at the grain boundaries 4 is 50 nm or less, good ductility (toughness) can be imparted to the aluminum alloy forged material. The average particle size of the precipitate 6 is more preferably 40 nm or less, and most preferably 30 nm or less.

The aspect ratio of the precipitate 6 at the grain boundaries 4 is preferably 5 or less. By setting the aspect ratio of the precipitate 6 at the crystal grain boundaries 4 to 5 or less, the ratio of the precipitates 6 occupying the crystal grain boundaries 4 can be reduced, and the distance between the precipitates 6 can be increased. As a result, it is possible to suppress the propagation of the precipitate 6 and the growth of cracks, and it is possible to impart good ductility (toughness) to the aluminum alloy forged material. The more preferable aspect ratio of the precipitate 6 is 4 or less, and the most preferable aspect ratio is 3 or less.

Further, the width of the non-precipitation zone centered on the crystal grain boundaries 4 is preferably 100 nm or less. By setting the width of the non-precipitation zone at the grain boundaries 4 to 100 nm or less, high strength and good ductility can be imparted to the aluminum alloy forged material. The more preferable width of the non-precipitation zone is 90 nm or less, and the most preferable width is 80 nm or less.

The aluminum alloy forged material has the above composition and composition, and thus has excellent tensile properties. In the aluminum alloy forged material, it is preferable that the 0.2% proof stress is 350 MPa or more and the elongation is 10% or more. Since the aluminum alloy forged material 2 has a 0.2% proof stress of 350 MPa or more and an elongation of 10% or more, it can be suitably used for structural members that require high reliability. The more preferable 0.2% proof stress of the aluminum alloy forged material 2 is 360 MPa or more, and the most preferable 0.2% proof stress is 370 MPa or more. Further, the more preferable elongation of the aluminum alloy forged material 2 is 12% or more, and the most preferable elongation is 14% or more.

2. 2. Undercarriage parts for automobiles The undercarriage parts for automobiles of the present invention are undercarriage parts for automobiles made of the forged aluminum alloy of the present invention.

Specific examples of suspension parts for automobiles include upper arms, lower arms, transverse links, etc., which are suspension parts for automobiles.

3. 3. Method for Producing Aluminum Alloy Forged Material The method for producing an aluminum alloy forged material of the present invention provides an effective method for producing the aluminum alloy forged material of the present invention. In the method for producing an aluminum alloy forged material of the present invention, the Cu content of the aluminum alloy forged material is 0.2 to 1.0 wt%, and a hot forging preheating step for preheating the aluminum alloy material and a hot forging preheating step. It includes a hot forging step of hot forging the preheated aluminum alloy material obtained in 1. Further, the other steps are not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known steps used for producing a forged material of a 6000 series aluminum alloy may be used, if necessary. Just do it. Hereinafter, a process characteristic of the method for producing an aluminum alloy forged material of the present invention will be described.

(1) Homogenization heat treatment step As a pretreatment of the hot forging step including the hot forging preheating step, it is preferable to perform the homogenizing heat treatment on the aluminum alloy material to be hot forged. Further, the temperature of the homogenization heat treatment step is preferably 500 to 550 ° C., and the holding time is preferably 5 to 10 hours.

By subjecting the homogenization heat treatment at 500 to 550 ° C. for 5 to 10 hours, Al- (Fe, Mn, Cr) -Si-based compounds are more reliably precipitated in the crystal grains of the aluminum base material 2, and the aluminum alloy is formed. In addition to being able to increase the strength of the forged member, the precipitate 6 at the crystal grain boundary 4 can be made finer by consuming excess Si. As a result, the aspect ratio of the precipitate 6 can be reduced.

(2) Hot forging preheating process This is a process performed as a preliminary treatment for the hot forging process. By heat-treating the aluminum alloy material with a preheating temperature of 300 to 550 ° C and a preheating time of 1 to 3 hours, Al- (Fe, Mn, Cr) -Si system is used in the crystal grains of the aluminum base material 2. In addition to being able to precipitate the compound and increasing the strength of the aluminum alloy forged member, the precipitate 6 at the crystal grain boundary 4 can be made finer by consuming excess Si. As a result, the aspect ratio of the precipitate 6 can be reduced.

(3) Hot Forging Step The aluminum alloy material preheated by using various conventionally known forging methods may be hot forged to obtain a desired shape. Further, by making the final shape an upper arm, a lower arm, a transverse link, etc., which are suspension parts for automobiles, the undercarriage parts for automobiles of the present invention can be obtained.

(4) Solution heat treatment and aging treatment The strength of the entire forged part can be improved by subjecting the forged part to the final shape by hot forging to an appropriate solution heat treatment and aging treatment.

The conditions for the solution treatment and the aging treatment are not particularly limited, and various conventionally known solution treatments and aging treatments can be used as long as the effects of the present invention are not impaired. Since these optimum conditions depend on the type of aluminum alloy, the shape and size of the forged part, etc., it is appropriate to observe the structure and evaluate the mechanical properties of the forged part after solution treatment and aging treatment. It is preferable to select the conditions.

Although the typical embodiments of the present invention have been described above, the present invention is not limited to these, and various design changes are possible, and all of these design changes are included in the technical scope of the present invention. Will be.

<< Example >>
By the DC continuous casting method, aluminum alloy slabs having the compositions shown in Table 1 as Examples were obtained. The components in Table 1 are shown in wt%. Here, Table 1 shows the "excess Si (wt%)" related to the relational expression (1) and the relational expression (2) and the "excessive Si (wt%) + Mn (wt%) + Cr (excessive Si (wt%)) related to the relational expression (2). The value of wt%) ”is also shown. The aluminum alloys according to the examples all have excess Si and 0.2 to 1.0 wt% Cu, and 0.2 ≦ excess Si (wt%) + Mn (wt%) + Cr ( wt%) ≤ 1.7 is satisfied.

Next, the obtained slab was cut and forged to a forging rate of 60% after a hot forging preheating step at 350 ° C. or 500 ° C. for 2 hours to obtain an aluminum alloy forged material. Here, the case where the homogenization heat treatment was performed at 510 ° C. for 6 hours or 550 ° C. for 10 hours before the hot forging preheating step and the case where the homogenization heat treatment was not performed were examined.

Next, the obtained aluminum alloy forged material was subjected to a solution treatment at 550 ° C. for 2 hours, then water-cooled, and an aging treatment at 180 ° C. for 8 hours.

Table 2 shows the tensile properties and manufacturing conditions of each of the obtained forged aluminum alloy materials. As the tensile test piece, the No. 14A test piece described in JIS Z2241 is used, and the tensile speed conforms to JIS Z2241. bottom. As shown in Table 2, the aluminum alloy forged material of the present invention has a 0.2% proof stress of 350 MPa and an elongation of 10% or more.

In addition, for some aluminum alloy forged materials, the average value and aspect ratio of the equivalent circle diameters of the precipitates present at the grain boundaries of the aluminum base material were obtained. Specifically, with respect to the TEM observation photograph, the circle equivalent diameter and the aspect ratio of the precipitate were calculated using image processing software (Image-Pro Premier V9.0 manufactured by Media Cybernetic Inc. in the United States). The results obtained are shown in Table 2. It can be seen that in the aluminum alloy forged material of the present invention, the average value of the equivalent circle diameters of the precipitates present at the crystal grain boundaries is 50 μm or less, and the aspect ratio is 5 or less.

FIG. 2 shows the TEM observation results of the aluminum alloy forged material of Example 1 (homogenization heat treatment: 510 ° C., 6 h, hot forging preheating step: 500 ° C., 2 h) in the vicinity of the grain boundaries of the aluminum base material. A Tecnai series G2-F20 manufactured by FEI was used for TEM observation. Precipitates at the grain boundaries of the aluminum base material can be confirmed, and it can be seen that the precipitates are fine and granular. In addition, the precipitates are not in close contact with each other and are in an ideal state for imparting good toughness and ductility to the forged aluminum alloy. In addition, the width of the non-precipitation zone is 100 nm or less.

FIG. 3 shows the TEM observation results in the aluminum base metal crystal grains of the aluminum alloy forged material of Example 1 (homogenization heat treatment: 510 ° C., 6 h, hot forging preheating step: 500 ° C., 2 h). It can be confirmed that a large amount of fine crystal precipitates are dispersed in the crystal grains of the aluminum base material. The TEM-EDS spectrum of the crystal precipitate is shown in FIG. 4, and it was confirmed that the crystal precipitate contained an Al- (Fe, Mn, Cr) -Si-based crystal precipitate.

≪Comparison example≫
An aluminum alloy forged material was obtained in the same manner as in Examples except that an aluminum alloy slab having the composition shown in Table 1 as a comparative example was used. Moreover, the obtained aluminum alloy forged material was evaluated in the same manner as in Examples.

Table 3 shows the production conditions, tensile properties, and information on the precipitates present at the grain boundaries of the aluminum base metal, which were obtained as comparative examples. Table 3 also shows the results of obtaining the average value and aspect ratio of the equivalent circle diameters of the precipitates present at the grain boundaries of the aluminum base material for some aluminum alloy forged materials.

As shown in Table 3, the aluminum alloy forged material of the comparative example cannot achieve both strength and ductility at a high level. In Comparative Examples 1 to 4 having no excess Si, the absolute strength is insufficient, and the 0.2% proof stress is less than 350 MPa in each case. On the other hand, Comparative Example 5, which has excess Si but does not contain Mn and / or Cr, has poor ductility, and in each case, the elongation is less than 10%. Further, in Comparative Example 6 which contains Mn and Cr but does not have excess Si, the absolute strength is insufficient, and the 0.2% proof stress is less than 350 MPa in each case. ..

Regarding the precipitates present at the grain boundaries of the aluminum base material, coarsening and increase in aspect ratio are not observed when the excess Si is not present, but when the excess Si is present (Comparative Example 5). The average diameter equivalent to a circle is larger than 50 nm, and the aspect ratio is also larger than 5.

FIG. 5 shows the TEM observation results of the aluminum alloy forged material of Comparative Example 5 (homogenization heat treatment: 510 ° C., 6 h, hot forging preheating step: 500 ° C., 2 h) in the vicinity of the grain boundaries of the aluminum base material. Precipitates at the grain boundaries of the aluminum base material can be confirmed, and it can be seen that the precipitates are coarse and needle-shaped. In addition, the width of the non-precipitation zone is larger than that of the aluminum alloy forged material obtained in the examples.

FIG. 6 shows the TEM observation results of the aluminum alloy forged material of Comparative Example 1 (homogenization heat treatment: 510 ° C., 6 h, hot forging preheating step: 500 ° C., 2 h) in the vicinity of the grain boundaries of the aluminum base material. Precipitates at the grain boundaries of the aluminum base material can be confirmed, and it can be seen that the amount of the precipitates is smaller than that of the aluminum alloy forged material obtained in the examples.

FIG. 7 shows the TEM observation results of the aluminum alloy forged material of Comparative Example 4 (homogenization heat treatment: 510 ° C., 6 h, hot forging preheating step: 500 ° C., 2 h) in the vicinity of the grain boundaries of the aluminum base material. Precipitates at the grain boundaries of the aluminum base material can be confirmed, and it can be seen that the precipitates are finer than in the case of Comparative Example 1.

FIG. 8 shows the TEM observation results in the aluminum base metal crystal grains of the aluminum alloy forged material of Comparative Example 5 (homogenization heat treatment: 510 ° C., 6 h, hot forging preheating step: 500 ° C., 2 h). Dispersion of crystal precipitates is not clearly confirmed in the crystal grains of the aluminum base material.

Further, the aluminum alloy forged material of Comparative Example 7 has sufficient Si and satisfies the relationship of 0.2 ≤ excess Si (wt%) + Mn (wt%) + Cr (wt%) ≤ 1.7. The Cu content is less than 0.2 wt%, and the tensile strength and 0.2% proof stress are low values.

From the above results, in the aluminum alloy forged material of the present invention, a large amount of fine Al- (Fe, Mn, Cr) -Si-based crystal precipitates are dispersed in the crystal grains of the aluminum base material, and the precipitates in the crystal grains. It can be seen that the material has a fine and nearly granular shape, and as a result, it has high strength and excellent toughness (good ductility).

2 ... Aluminum base material,
4 ... Crystal grain boundaries,
6 ... Precipitate.

Claims (10)

Made of 6000 series aluminum alloy
The Cu content is 0.2 to 1.0 wt%,
The composition of the 6000 series aluminum alloy satisfies the following relational formulas (1) and (2).
Having precipitates at the grain boundaries of the base metal and Al- (Fe, Mn, Cr) -Si-based crystal precipitates in the grain boundaries of the base metal.
Aluminum alloy forged material featuring.
Si (at%) ≧ 2Mg (at%) (1)
0.2 ≤ Excess Si (wt%) + Mn (wt%) + Cr (wt%) ≤ 1.7 (2) The Si content is 0.5 to 1.4 wt%,
The Mg content is 0.6 to 1.7 wt%.
The aluminum alloy forged material according to claim 1. The Si content is 0.9-1.2 wt%,
The Mg content is 0.8 to 1.2 wt%.
The aluminum alloy forged material according to claim 1. The average particle size of the precipitate at the grain boundaries of the base metal is 50 nm or less.
The aluminum alloy forged material according to any one of claims 1 to 3. The aspect ratio of the precipitate at the grain boundaries of the base metal is 5 or less.
The aluminum alloy forged material according to any one of claims 1 to 4. The width of the non-precipitation zone centered on the grain boundaries of the base metal is 100 nm or less.
The aluminum alloy forged material according to any one of claims 1 to 5. 0.2% proof stress of 350 MPa or more and elongation of 10% or more.
The aluminum alloy forged material according to any one of claims 1 to 6. Composed of the aluminum alloy forged material according to any one of claims 1 to 7.
Undercarriage parts for automobiles featuring. The method for manufacturing an aluminum alloy forged material according to any one of claims 1 to 7.
The Cu content of the aluminum alloy forged material is 0.2 to 1.0 wt%.
Hot forging preheating process to preheat aluminum alloy material,
A hot forging step of hot forging the preheated aluminum alloy material obtained in the hot forging preheating step is included.
The preheating temperature in the hot forging preheating step is 300 to 550 ° C., and the preheating time is 1 to 3 hours.
The composition of the aluminum alloy satisfies the following relational expressions (1) and (2).
A method for manufacturing an aluminum alloy forged material.
Si (at%) ≧ 2Mg (at%) (1)
0.2 ≤ Excess Si (wt%) + Mn (wt%) + Cr (wt%) ≤ 1.7 (2) A homogenizing heat treatment step for the aluminum alloy material is provided before the hot forging preheating step.
The temperature of the homogenization heat treatment step shall be 500 to 550 ° C., and the holding time shall be 5 to 10 hours.
The method for manufacturing an aluminum alloy forged material according to claim 9.

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