Al-Mg-Si alloy member and method for manufacturing the same

Abstract

To provide an Al-Mg-Si alloy member that has sufficient strength as a structural member and can be deformed in any region when receiving external force and a method for producing the same, or more specifically, to provide an Al-Mg-Si alloy member that can be suitably used as an automotive structural member and a simple and efficient production method therefor.SOLUTION: An Al-Mg-Si alloy member has a friction stirring part, a heat-affected zone at the outer edge of the friction stirring part, and a base material part. The average particle size of precipitates in the most softened region of the heat-affected zone is 1.2 or more times as large as the average particle size of precipitates in the base material part.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an Al-Mg-Si alloy member and a method for producing the same, and more particularly to an Al-Mg-Si alloy member that can be suitably used as an automotive structural member and a simple and efficient method for producing the same. [Background technology]

[0002] Since high strength and reliability are required for structural members of automobiles and other vehicles, methods for partially strengthening such structural members are required as needed. In recent years, friction stir welding, a solid-state welding method, has been attracting attention as a method for modifying the surface of metal materials, and methods for partially strengthening and hardening metal members using this friction stir welding method are being investigated.

[0003] For example, Patent Document 1 (JP Patent Publication No. 11-050266) proposes a method for locally modifying a base material, which comprises placing a modifying material in an area of ​​the base material that requires modification, embedding a probe protruding from the rotor of a processing tool into the portion where the modifying material is placed while rotating, and moving the tool in this embedded state relatively along the portion where the modifying material is placed, thereby integrating the modifying material and the base material material through friction stirring caused by the rotation of the embedded probe.

[0004] The method of locally modifying a base material described in Patent Document 1 above does not create a substantial bonding interface in the modified area, preventing a decrease in durability due to interfacial peeling, etc., avoiding cracks caused by thermal effects and deterioration of quality, and enabling easy and low-cost processing.

[0005] Furthermore, Patent Document 2 (JP 2004-255440 A) proposes a surface modification method for light metal castings, in which a rotating shaft and rotor made of a material that is harder and has a higher melting point than the light metal casting are pressed against the surface of the light metal casting, and the rotating shaft and rotor are rotated to bring them into frictional contact with the surface of the light metal casting, and the heat generated by the frictional contact raises the temperature of the surface of the light metal casting to the plastic flow temperature range and stirs it, thereby refining the metal structure of the surface layer of the light metal casting, characterized in that when the metal structure is refined by friction stirring, an additive for modifying the metal structure is added to the metal structure.

[0006] In the surface modification method for light metal castings described in Patent Document 2, the surface structure of the light alloy casting is heated to a plastic flow temperature range by the frictional and stirring forces of the rotating shaft and rotor, softened or semi-molten, and stirred. Furthermore, coarse precipitate particles in the metal structure are crushed by frictional stirring in the plastic flow temperature range and refined while maintaining the cast alloy composition. At the same time, optional additives are supplied to the softened metal structure in the plastic flow temperature range, and the metal structure is refined by the frictional stirring action. The additives are then appropriately treated with or combined with the desired additives to provide desired effects. Therefore, not only can material properties be improved by refining the cast structure, but optional additives can also be added to the softened or semi-molten metal structure in the plastic flow temperature range. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-050266 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-255440 Summary of the Invention [Problem to be solved by the invention]

[0008] However, as mentioned above, high strength and reliability are required for structural components of automobiles and the like, and the methods described in Patent Documents 1 and 2 are primarily intended to partially increase the strength of metal materials.

[0009] Here, it is expected that reliability will be improved by removing defects and refining and homogenizing the structure through friction stirring, but structural members of automobiles and the like are important safety parts, and in the unlikely event that a large force is applied due to an accident, they are required to deform within the range assumed in the design. However, there is no simple and efficient method for deforming structural members within a desired range, and the methods described in Patent Documents 1 and 2 cannot achieve this.

[0010] In view of the above-mentioned problems in the prior art, an object of the present invention is to provide an Al-Mg-Si alloy member that has sufficient strength as a structural member and can be deformed in any desired region when an external force is applied, and a method for manufacturing the same. In particular, an object of the present invention is to provide an Al-Mg-Si alloy member that can be suitably used as an automotive structural member, and a simple and efficient method for manufacturing the same. [Means for solving the problem]

[0011] In order to achieve the above object, the inventors have conducted extensive research into friction stir processed parts formed on Al-Mg-Si alloy members, and as a result have found that it is extremely effective to strictly control the microstructure and hardness of the friction stir processed part, heat-affected zone and base material, thereby arriving at the present invention.

[0012] That is, the present invention provides: A friction stir welding joint has a friction stir portion, a heat-affected portion present at the outer edge of the friction stir welding joint, and a base material portion, the average grain size of the precipitates in the softest region in the heat-affected zone is 1.2 times or more the average grain size of the precipitates in the base material; The present invention provides an Al-Mg-Si alloy member characterized by the above.

[0013] In the Al-Mg-Si alloy member of the present invention, the Vickers hardness (H H ) is the maximum value of the Vickers hardness (H S ) than 10H V It is preferable that the temperature is lower than this.

[0014] In the Al-Mg-Si alloy member of the present invention, a friction stir zone is formed by friction stir processing, and a heat-affected zone is formed on the outer edge of the friction stir zone. Note that there are cases where a thermal processing affected zone, which is affected by heat and processing, is formed at the boundary between the friction stir zone and the heat-affected zone, but this is included in the heat-affected zone in the present invention. In addition, the hardness of the heat-affected zone is lower than that of the friction stir zone. Here, the hardness of the friction stir zone formed in the Al-Mg-Si alloy member is lower than that of the base material. Furthermore, depending on the composition of the Al-Mg-Si alloy member and the friction stirring conditions, a clear heat-affected zone (softened region) may not be formed, and the hardness gradually increases from the stir zone to the base material. However, in the Al-Mg-Si alloy member of the present invention, the maximum Vickers hardness (H S ) than 10H V It is preferable that a heat-affected zone, which is a region with the lowest softening point, is formed.

[0015] In the present invention, the hardness of the friction stir zone, heat-affected zone, and base material is evaluated by a horizontal hardness profile in a vertical section (a vertical section relative to the direction of friction stir processing) relative to the friction stir zone. In order to measure the hardness of the softest region, the interval between measurement positions in the horizontal direction should be 500 μm or less, and the measurement load should be adjusted appropriately. In addition, the maximum value of the Vickers hardness (H S ) may be determined by comparing the values ​​of at least two points (three points in total) at approximately the center and two points on the left and right of the friction stir zone in the obtained horizontal hardness profile.

[0016] In the Al-Mg-Si alloy member of the present invention, the average grain size of the precipitates in the softest region is 1.2 times or more the average grain size of the precipitates in the central region of the friction stir zone. Therefore, the Vickers hardness (H H ) is the maximum Vickers hardness (H S ) than 10H V The average grain size of the precipitates in the softest region is more preferably 1.2 to 3.0 times, and most preferably 1.5 to 2.0 times, the average grain size of the precipitates in the central region of the friction stir zone.

[0017] In the Al-Mg-Si alloy structural member of the present invention, the most softened region is preferably present in a region extending from the outer edge of the friction stir zone to 10 mm toward the base material. By having the most softened region in a region extending from the outer edge of the friction stir zone to 10 mm toward the base material, it is possible to accurately and easily determine the position where deformation occurs when external stress is applied.

[0018] In the Al-Mg-Si alloy member of the present invention, the Vickers hardness (H H ) is 50~80H V It is preferable that the Vickers hardness (H H ) for 50 hours V By setting the hardness to above 100%, the strength required for structural members can be ensured. On the other hand, the Vickers hardness (H H ) to 80H V By setting the value below, it is possible to reliably determine the position where deformation occurs when external stress is applied. H ) is more preferably in the range of 60 to 75H. V is.

[0019] In the Al-Mg-Si alloy member of the present invention, the Vickers hardness (H B It is preferable that the Vickers hardness (H BBy making the Vickers hardness (H ) of the base material 80HV or more, the strength required for a structural member can be ensured. B ) is 100HV or more, and the most preferable Vickers hardness of the base material (H B ) is 110HV or higher.

[0020] In addition, in the Al-Mg-Si alloy member of the present invention, Si:0.4~0.9% by mass, Cu:0.4% by mass over 0, Mg: 0.4 to 1.2 mass%, The total content of Si, Mg and Cu is preferably 1.3 mass % or more.

[0021] Si, Cu, and Mg are elements that significantly contribute to precipitation strengthening in Al-Mg-Si alloys, and by containing these elements within the above-mentioned ranges, sufficient strength can be imparted to the base material. On the other hand, the heat input during the formation of the friction stir zone causes the precipitates to redissolve and coarsen, resulting in the formation of an appropriate softened zone.

[0022] In the Al-Mg-Si alloy member of the present invention, the friction stir portion is preferably included in a friction stir welded portion. The friction stir portion can be formed by friction stir welding or a friction stir process, and by using friction stir welding, it is possible to simultaneously achieve the production (welding) of a structural member and the creation of a region that is selectively deformed when an external stress is applied (maximum softening region).

[0023] Furthermore, the Al-Mg-Si alloy member of the present invention is preferably a structural member for an automobile or a railway vehicle. These structural members require high strength and are particularly required to deform as designed when subjected to external stress, and the Al-Mg-Si alloy member of the present invention meets all of these requirements.

[0024] The present invention also provides a method for producing an Al-Mg-Si alloy member, comprising: a friction stir treatment step of subjecting an Al-Mg-Si alloy material to friction stir treatment; and an aging step of subjecting an Al-Mg-Si alloy material to natural aging and / or artificial aging for 24 hours or more.

[0025] The conditions for the friction stir treatment in the friction stir step are not particularly limited as long as they do not impair the effects of the present invention, and conditions for conventionally known friction stir welding or friction stir processes can be used. The treatment temperature can be controlled by the rotation speed, movement speed, pressing force, etc. of the friction stir tool (rotary tool), and the size and shape of the stir part can be controlled by the size and shape, etc. of the shoulder part of the friction stir tool and the probe part on the bottom surface of the friction stir tool.

[0026] Here, if the hardness of the resulting heat-affected zone is high, the hardness can be reduced by increasing the joining temperature by increasing the rotation speed of the friction stir tool, reducing the movement speed, increasing the pressing force, etc.

[0027] In the manufacturing method of the Al-Mg-Si alloy member of the present invention, an Al-Mg-Si alloy member consisting of a friction stir zone, a heat-affected zone, and a base material is obtained in the friction stir step, and then an aging step is carried out in which natural aging and / or artificial aging is carried out for 24 hours or more.This increases the hardness of the friction stir zone and softens the heat-affected zone, thereby increasing the difference in hardness between the friction stir zone and the heat-affected zone.

[0028] The natural aging time is more preferably 30 days or more. The artificial aging treatment conditions are preferably 160 to 200°C and 1 to 10 hours, and more preferably 170 to 190°C and 4 to 8 hours.

[0029] In addition, in the method for producing an Al-Mg-Si alloy member of the present invention, it is preferable to use an Al-Mg-Si alloy material containing Si: 0.4 to 0.9 mass%, Cu: more than 0.4 mass%, and Mg: 0.4 to 1.2 mass%, with the total content of Si, Mg, and Cu being 1.3 mass% or more.

[0030] Si, Cu, and Mg are elements that contribute significantly to precipitation strengthening in Al-Mg-Si alloys. By containing these elements within the above-mentioned ranges, sufficient strength can be imparted to the base material, while the heat input when forming the friction stir zone promotes re-solid solution and coarsening of the precipitates, allowing the formation of an appropriate softened zone. [Effects of the Invention]

[0031] According to the present invention, an Al-Mg-Si alloy member having sufficient strength as a structural member and capable of deforming in any region when an external force is applied, and a method for manufacturing the same can be provided. In particular, an Al-Mg-Si alloy member suitable for use as an automotive structural member and a simple and efficient method for manufacturing the same can be provided. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a schematic diagram of a cross-sectional macrostructure of an Al-Mg-Si alloy member according to the present invention. FIG. [Figure 2] 1 shows horizontal Vickers hardness profiles in cross sections perpendicular to the friction stir zone of the Al—Mg—Si alloy members obtained as Example 1 and Comparative Example 1. [Figure 3] 1 shows horizontal Vickers hardness profiles in cross sections perpendicular to the friction stir zone of the Al—Mg—Si alloy members obtained as Examples 1 to 4 and Comparative Example 2. [Figure 4] 10 shows the results of TEM observation of the central region of the friction stir zone of the Al—Mg—Si alloy member obtained as Example 4. [Figure 5] 1 shows the results of TEM observation of the most softened portion of the Al—Mg—Si alloy member obtained as Example 4. [Figure 6] 1 shows the results of TEM observation of the base material of the Al—Mg—Si alloy member obtained as Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0033] Representative embodiments of the Al-Mg-Si alloy member and its manufacturing method according to the present invention will be described in detail below with reference to the drawings, but the present invention is not limited to these. In the following description, identical or corresponding parts will be designated by the same reference numerals, and duplicated explanations may be omitted. Furthermore, since the drawings are intended to conceptually explain the present invention, the dimensions and ratios of the components shown may differ from those of the actual components.

[0034] 1. Al-Mg-Si alloy components (1) Structure and hardness distribution The cross-sectional macrostructure of the Al-Mg-Si alloy member of the present invention in a cross section perpendicular to the friction stir zone is shown in Figure 1. The hardness distribution corresponding to the cross-sectional macrostructure is also shown in the lower part of Figure 1. This hardness distribution is the hardness distribution along the dashed line of the cross section.

[0035] A friction stir zone 4 is formed in the Al-Mg-Si alloy member 2, and a heat-affected zone 6 exists on the outer edge of the friction stir zone 4, with the outside of that being a base material zone 8. While one friction stir treated region (friction stir zone 4 and its outer edge heat-affected zone 6) is shown in Figure 1, multiple friction stir treated regions may be formed, or the friction stir treated regions may be overlapped.

[0036] The friction stir portions 4 may be formed over the entire thickness direction of the Al-Mg-Si alloy member 2, or may be formed only on the surface. When friction stir welding is used, the friction stir portions 4 are basically formed over the entire thickness direction.

[0037] In the friction stir zone 4, the precipitates are redissolved, and the hardness is lower than that of the base material zone 8. In addition, the heat-affected zone 6 is softened by the coarsening of the acicular precipitates, and the acicular precipitates are redissolved and the coarse precipitates increase, forming a most softened region.

[0038] The Vickers hardness (H H ) is the maximum value of the Vickers hardness (H S ) than 10HV The Vickers hardness (H H ) difference is 10H V As a result, a clear and significant difference occurs in the deformation behavior, and when an external stress is applied, deformation starts from the softest part.

[0039] The average grain size of the precipitates in the softest region is 1.2 times or more the average grain size of the precipitates in the central region of the friction stir zone 4. Here, since a certain amount of measurement region is required for Vickers hardness measurement, the "softest region" is a concept that allows for a positional error of about 500 μm.

[0040] By making the average grain size of the precipitates in the softest region 1.2 times or more the average grain size of the precipitates in the central region of the friction stir zone 4, the Vickers hardness (H H ) is the maximum value of Vickers hardness (H S ) than 10H V The average particle size of the precipitates in the softest region is more preferably 1.2 to 3.0 times, and most preferably 1.5 to 2.0 times, the average particle size of the precipitates in the central region of the friction stir zone 4. The method for measuring the average particle size of the precipitates is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known methods may be used. For example, in the case of needle-shaped precipitates, their length may be measured by observation with a transmission electron microscope (TEM).

[0041] The most softened region is preferably present in a region extending from the outer edge of the friction stir zone 4 to 10 mm toward the base material 8. By having the most softened region in a region extending from the outer edge of the friction stir zone 4 to 10 mm toward the base material 8, it is possible to accurately and easily grasp the position where deformation occurs when external stress is applied.

[0042] Vickers hardness in the softest region (H H ) is 50~80H V It is preferable that the Vickers hardness (H H ) for 50 hours VBy setting the hardness to above 100%, the strength required for structural members can be ensured. On the other hand, the Vickers hardness (H H ) to 80H V By setting the following, it is possible to reliably determine the position where deformation occurs when external stress is applied. Here, the Vickers hardness (H H ) is 60~75H V It is more preferable to set the following.

[0043] In addition, the Vickers hardness (H B The Vickers hardness (H B By making the Vickers hardness (H ) of the base material portion 8 80 HV or more, the strength required for a structural member can be ensured. B ) is 100 HV or more, and the most preferable Vickers hardness (H B ) is 110HV or higher.

[0044] (2) Composition The Al-Mg-Si alloy member of the present invention has an optimized composition to impart high hardness (strength) to the base material 8 while forming an appropriate hardness distribution in the friction stir zone 4 and the heat-affected zone 6. Each component will be described in detail below.

[0045] (1) Essential additive elements Si:0.4~0.9% by mass The Si content is preferably 0.4 to 0.9 mass%. By setting the Si content to 0.4 mass% or more, solid solution strengthening and age hardening can be fully exhibited, and by setting the Si content to 0.9 mass% or less, it is possible to suppress a decrease in corrosion resistance and a decrease in ductility due to coarsening of crystallized particles and precipitates.

[0046] Cu:0.4% by mass over 0 The Cu content is preferably more than 0 and 0.4% by mass. Cu has the effect of increasing mechanical strength and fatigue strength by forming Al, Mg, Si, and Cu-based quaternary precipitates (Q phase or Q' phase). On the other hand, if the Cu content exceeds 0.4% by mass, there is a risk of reducing corrosion resistance.

[0047] Mg:0.4~1.2% by mass The Mg content is preferably 0.4 to 1.2% by mass. By setting the Mg content to 0.4% by mass or more, a sufficient amount of Mg-Si precipitates are formed, improving strength and fatigue properties, while by setting the Mg content to 1.2% by mass or less, the formation of coarse compounds that serve as starting points for fracture can be suppressed.

[0048] Total content of Si, Mg, and Cu: 1.3% by mass or more By setting the total content of Si, Mg, and Cu, which significantly contribute to precipitation strengthening, to 1.3 mass % or more, the Vickers hardness (H H ) is the maximum value of the Vickers hardness (H S ) than 10H V can be made even lower.

[0049] (2) Optional additive elements Various conventionally known elements can be used as additive elements for 6000 series aluminum alloys. The amount of the additive element may also be within the range specified for 6000 series aluminum alloys. Examples of additive elements include Mn, Cr, Zn, Fe, and Ti.

[0050] The method for producing an Al-Mg-Si alloy material having the above composition is not particularly limited as long as the effects of the present invention are not impaired, and an aluminum alloy material having a desired composition may be produced by any of various conventionally known methods.

[0051] 2. Manufacturing method of Al-Mg-Si alloy member The method for producing an Al-Mg-Si alloy member of the present invention provides an effective and simple method for producing the Al-Mg-Si alloy member of the present invention, and comprises a friction stir treatment step of subjecting an Al-Mg-Si alloy material to friction stir treatment, and an aging step of subjecting the material to natural aging and / or artificial aging for 24 hours or more. Each step will be described below.

[0052] (1)Friction stirring process This is a process for performing friction stir treatment on an Al-Mg-Si alloy material to form a friction stir zone 4 and a heat-affected zone 6. For the friction stir treatment, friction stir welding (FSW) or friction stir processing (FSP) can be used. Since friction stir welding and friction stir processing are basically similar friction stir processing techniques, the following explanation will focus on friction stir welding as a representative example.

[0053] Friction stir welding includes four modes (1) to (4) of joining, as well as combinations thereof: (1) joining in which the ends of metal plates are butted together to form a joint, and a rotating tool is moved while rotating along the longitudinal direction of the processed area to join the metal plates; (2) spot joining in which the ends of metal plates are butted together to form a joint, and a rotating tool is rotated at the joint without moving, (3) spot joining in which metal plates are overlapped at the joint, a rotating tool is inserted into the joint, and the rotating tool is rotated at that point without moving to join the metal plates; and (4) joining in which metal plates are overlapped at the joint, a rotating tool is inserted into the joint, and the rotating tool is moved while rotating along the longitudinal direction of the joint to join the metal plates.

[0054] The amount of heat input and temperature history introduced into the weld during friction stir welding can control the structure of the friction stir zone 4 and heat-affected zone 6 and the hardness distribution based on that structure. Furthermore, because Al-Mg-Si alloy materials are easy to friction stir process, a defect-free, good friction stir zone 4 can be formed over a wide range of processing conditions. Typical process parameters that determine the amount of heat input during friction stir welding include the rotational speed, travel speed, and press load of the rotating tool; the heat input can be increased by increasing the rotational speed, decreasing the travel speed, and increasing the press load.

[0055] The shape, size, and material of the rotary tool are not particularly limited as long as they do not impair the effects of the present invention, and various conventionally known rotary tools can be used. Furthermore, the control method for friction stir welding is also not particularly limited, and general friction stir welding methods such as position control and load control can be used.

[0056] (2) Aging process The aging process is a process for increasing the difference in hardness between the friction stir zone 4 formed in the friction stir process and the heat affected zone 6. Natural aging and / or artificial aging is used for the aging treatment.

[0057] Natural aging is performed for 24 hours or more, preferably 30 days or more. Suitable artificial aging conditions are 160 to 200°C and 1 to 10 hours, and more preferably 170 to 190°C and 4 to 8 hours.

[0058] Representative embodiments of the present invention have been described above, but the present invention is not limited to these, and various design modifications are possible, all of which are included in the technical scope of the present invention. [Example]

[0059] Example The Al-Mg-Si alloy materials having the compositions (mass%) shown in Table 1 as Examples 1 to 4 were cast and then extruded to obtain treated plates having a length of 6000 mm, a width of 54 mm, and a thickness of 4.5 mm. During the extrusion process, the materials were air-cooled at the die edge and then water-cooled, and then artificially aged at 180°C for 6 hours.

[0060] The resulting treated plates were then butted together and friction stir welded along the butted surfaces to obtain an Al-Mg-Si alloy member according to the present invention. A tool steel tool with a probe length of 3.3 mm and a shoulder diameter of 15 mm was used for friction stir welding, and the friction stir welding conditions were a plunge depth of 3.7 mm, a tool rotation speed of 1800 rpm, and a welding speed of 600 mm / min.

[0061] [Table 1]

[0062] Comparative Example Al-Mg-Si alloy members as comparative examples of the present invention were obtained in the same manner as in the examples, except that the compositions of the Al-Mg-Si alloy materials were set to the compositions (mass%) shown in Table 1 as Comparative Examples 1 and 2.

[0063] [evaluation] (1) Vickers hardness distribution Figure 2 shows the horizontal Vickers hardness profiles in cross sections perpendicular to the friction stir zone of the Al-Mg-Si alloy members obtained in Example 1 and Comparative Example 1. The positions where the Vickers hardness was measured are shown schematically in the upper part of Figure 2, with the measurement intervals being 0.5 mm in the range of 15 mm from the center of the measurement and 1.0 mm in the range of 15 to 20 mm, and the measurement load was 50 gf. Note that Figure 2 shows the results for one side of the center of the stir zone.

[0064] In the Al-Mg-Si alloy member of Example 1, the formation of a most-softened zone (heat-affected zone) was observed at the outer edge of the friction stir zone. The Vickers hardness of the most-softened zone was 70 Hv, while the maximum Vickers hardness in the central region of the friction stir zone was 80 Hv, meaning that the hardness of the most-softened zone was 10 Hv lower than that of the friction stir zone. The Vickers hardness of the base metal of the Al-Mg-Si alloy member of Example 1 was a high value of 110 to 120 Hv.

[0065] In contrast, in the Al-Mg-Si alloy member of Comparative Example 1, the hardness gradually increases from the friction stir zone to the base material, and no softened zone (heat-affected zone) is observed at the outer edge of the friction stir zone. The results of Example 1 and Comparative Example 1 show that by appropriately controlling the contents and total contents of Si, Mg, and Cu, which greatly contribute to precipitation strengthening, a softened zone is formed at the outer edge of the friction stir zone.

[0066] Fig. 3 shows the horizontal Vickers hardness profiles in cross sections perpendicular to the friction stir zone of the Al-Mg-Si alloy members obtained in Examples 1 to 4 and Comparative Example 2. The Vickers hardness measurement positions and conditions were the same as those in Fig. 2.

[0067] In the Al-Mg-Si alloy members obtained as Examples 1 to 4, the formation of a most-softened zone (heat-affected zone) was observed at the outer edge of the friction stir zone, and the hardness of the most-softened zone was 10 Hv or more lower than the hardness of the friction stir zone. On the other hand, in the Al-Mg-Si alloy member obtained as Comparative Example 2, the formation of a most-softened zone (heat-affected zone) was observed at the outer edge of the friction stir zone, but the decrease in hardness from the friction stir zone was only about 5 Hv.

[0068] (2) Observation of precipitates Precipitates in each region of the Al-Mg-Si alloy member obtained as Example 4 were observed by TEM observation. A Tecnai series G2-F20 manufactured by FEI was used for TEM observation. The observation results of the central region of the friction stir zone, the most softened zone, and the base material are shown in Figures 4, 5, and 6, respectively.

[0069] In the friction stir zone, no precipitates were observed at the TEM level, and the state was the same as after solution treatment. In the softest zone, the precipitates were noticeably coarsened, indicating an over-aged state. Furthermore, in the base material, fine precipitates were densely dispersed, similar to the state after T6 treatment. These changes in precipitates show good agreement with the Vickers hardness distribution shown in Figure 3. Furthermore, the average grain size of the precipitates in the softest zone was more than 1.2 times that of the precipitates in the central region of the friction stir zone. [Explanation of symbols]

[0070] 2. Al-Mg-Si alloy members, 4...friction stirrer, 6···Heat-affected zone, 8...Base metal part.

Claims

1. Si: 0.4 to 0.9% by mass, Cu: more than 0 0.4% by mass, Mg: 0.4 to 1.2 mass%, The total content of Si, Mg, and Cu is 1.3 mass% or more, A friction stir welding joint has a friction stir portion, a heat-affected portion present at the outer edge of the friction stir welding joint, and a base material portion, the average grain size of the precipitates in the softest region in the heat-affected zone is 1.2 times or more the average grain size of the precipitates in the base material portion, The Vickers hardness (H B ) is 80HV or more, The Vickers hardness (H H ) is the maximum value of the Vickers hardness (H S ) than 10H V or lower, The Al-Mg-Si alloy member is characterized by the above.

2. The most softened region exists in a region extending from the outer edge of the friction stir portion to a side of the base material by 10 mm, The Al-Mg-Si alloy member according to claim 1,

3. The Vickers hardness (H H ) is 50 to 80H V That is, The Al-Mg-Si alloy member according to claim 1 or 2,

4. The friction stir welding portion is included in a friction stir welding portion. The Al-Mg-Si alloy member according to any one of claims 1 to 3, characterized in that:

5. It is a structural component for an automobile or railway vehicle, The Al-Mg-Si alloy member according to any one of claims 1 to 4, characterized in that:

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