JP2008150652A - Weldable aluminum alloy for forging having excellent stress corrosion cracking resistance, and forged part using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Al-Zn-Mg based weldable high strength aluminum material for forging having excellent stress corrosion cracking resistance, and, particularly, even in a state after welding, having excellent stress corrosion cracking resistance. <P>SOLUTION: The aluminum alloy for forging has a composition comprising 2.0 to 3.9% Zn and 0.1 to 3.5% Mg in such a manner that the total content of Zn+Mg lies within the range of 4.0 to 6.0%, further comprising 0.02 to 0.20% Cu, further comprising one or more kinds selected from 0.20 to 0.70% Mn, 0.10 to 0.30% Cr, 0.05 to 0.30% Zr and 0.01 to 0.10% V in such a manner that the total content of Mn, Cr, Zr and V is ≥0.25%, and further comprising one or more kinds selected from 0.01 to 0.20% Ti, 0.001 to 0.05% B and 0.01 to 0.5% C, and the balance substantially Al. The total content of Zn+Mg is preferably controlled to the range of 4.3 to 5.5%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a general welded structural member, a high-strength aluminum alloy for forging suitably used as a member or part that requires high strength in various fields, such as aircraft, railway vehicles, and automobiles, and forging using the alloy In particular, the present invention relates to an aluminum alloy for forging that is excellent in stress corrosion cracking resistance and can be welded, and a forged product.

  Conventionally, as forging aluminum alloys used for various structural materials or various parts that require high strength, Al-Zn-Mg-Cu alloys such as 7050 alloy, 7075 alloy, 7175 alloy, 7475 alloy, 7N01 alloy, etc. Alloys or Al—Zn—Mg alloys are often used.

  By the way, as for various structural materials and parts, the shape tends to become more complicated in recent years, and there is a strong demand for reduction in manufacturing cost. Therefore, free forging is used more frequently for forging than die forging. In addition, there are an increasing number of cases where welding is performed after forging. However, among the conventional forging alloys as described above, 7050 alloy, 7075 alloy, 7175 alloy, and 7475 alloy are all inferior in weldability, so that it is difficult to apply to applications for welding after forging. Therefore, when welding is required, the 7N01 alloy may be used at the expense of some strength.

Specifically, if the numerical value prescribed | regulated to JISH4140 aluminum and aluminum forging alloy (free forging material) is shown, in A7050FH-T7452 material, when the maximum thickness is 50-80 mm, tensile strength 495N / mm in the L direction ² or more, proof stress 420N / mm ² or more, whereas there is a stretch of 9% or more, in A7N01FH-T6 material, maximum thickness 150mm or less, tensile L direction strength 335n / mm ² or more, proof stress 275 N / mm ² As described above, the elongation is 10% or more, and both the tensile strength and the proof stress are reduced by about 30% as compared with the A7050FH-T7452 material.

  On the other hand, there is a case where an Al—Mg-based alloy (for example, 5083 alloy) that can be welded is used for the above-described applications, but the Al—Mg-based alloy is an Al—Zn—Mg—Cu-based alloy or Al—Zn—. Since the strength is considerably lower than that of the Mg-based alloy, it is necessary to increase the thickness in order to obtain a desired strength as a structural material or a component, which leads to an increase in weight.

Specifically, according to JIS H4140, for the A5083FH-O material, when the maximum thickness is 200 mm or less, the tensile strength in the L direction is 275 N / mm ² or more, the yield strength is 120 N / mm ² or more, and the elongation is 16% or more. Compared to the A7050FH-T7452 material, the tensile strength is reduced by about 40% and the proof stress is reduced by about 70%. Also, the tensile strength is reduced by about 20% compared to the A7N01FH-T6 material. It will be about 60% lower.

  Therefore, development of materials having high strength and capable of welding, particularly free forging, is strongly demanded as materials for structural materials and parts having various complicated shapes.

  On the other hand, in the case of Al-Zn-Mg-Cu alloy and Al-Zn-Mg alloy, which are generally called high strength materials, stress corrosion cracking is more likely to occur as the strength becomes higher. There is a problem of increasing. Conventionally, countermeasures that combine the addition of trace elements, the control of the shape and direction of the structure, heat treatment, and the like have been taken to deal with such a problem of stress corrosion cracking (see Non-Patent Document 1, for example).

Specifically, as an effect of trace elements, it is known that by adding Mn, Cr, Ti, Zr, V, etc., the crystal grains become fine and stress corrosion cracking susceptibility is reduced. Alloys containing these elements have already been put into practical use. In addition, as a control of the shape and direction of the structure, it is known that stress corrosion cracking susceptibility is eased by avoiding the recrystallized structure and forming a uniform fibrous structure (fiber structure) in the longitudinal direction. It is known that stress corrosion cracking resistance is improved by such a structure control in the case of both extruded and extruded materials (see, for example, Patent Document 1). Furthermore, as the heat treatment, a method in which the strength is slightly lowered and the susceptibility to stress corrosion cracking is generally reduced by mainly changing the aging condition to an overaging state (tempered T73, T74, etc.) (for example, non-aging). Patent Document 2). Also known is a method for preventing stress corrosion cracking susceptibility by controlling the crystal grain size (see, for example, Patent Document 2 and Patent Document 3).
Japanese Patent Laid-Open No. 11-6044 Japanese Patent Laid-Open No. 9-287046 JP-A-11-1737 "Structure and properties of aluminum", 1991, pp. 296-322, Japan Institute of Light Metals “Aluminium, 4”, 1968, pp. 403-411; Gruhl and H.M. Cordier

  Among the above-mentioned mitigation measures for stress corrosion cracking susceptibility to high strength materials such as Al-Zn-Mg-Cu alloys and Al-Zn-Mg alloys, the effect of trace added elements remains in the forged state. In addition, it is effective when a countermeasure for heat treatment is also performed after forging, and it is possible to obtain a forging material having good stress corrosion cracking resistance.

  However, when welding is performed on the forged material, the fine crystal grains obtained by the trace elements grow and become coarse due to heat input during welding, and the fibrous structure is partially divided. As a result, a recrystallized structure is formed, and the effect of improving the stress corrosion cracking resistance may be lost. Furthermore, since a T4 tempered region is formed in the vicinity of the welded portion, the over-aged state is canceled, and as a result, a product in which a portion having a portion excellent in stress corrosion cracking resistance and a portion inferior in resistance are mixed. There is a risk of becoming. Here, it is possible to perform heat treatment after welding, but there are many cases where heat treatment cannot be performed depending on the product shape and size, and therefore this cannot be a complete measure.

  Therefore, it is desired to develop a high-strength alloy material that does not change the susceptibility to stress corrosion cracking even if a recrystallized structure is generated by welding after forging, and if such an alloy material is realized, Application to various products becomes possible, and it becomes possible to manufacture structural members and parts having complicated shapes, and the application can be expanded.

  Here, a high-strength Al—Zn—Mg—Cu alloy or Al—Zn—Mg alloy (7050 alloy, 7075 alloy, 7175 alloy, 7475 alloy, etc.) is generally weldable as described above. Therefore, aluminum alloys for forging are strongly required to have at least A7N01FH-T6 level strength, weldability and excellent resistance to stress corrosion cracking. It has been.

  This invention was made against the background described above, and has at least A7NO1FH-T6 level strength as a forging alloy suitable for free forging, and can be welded after forging. To provide an Al-Zn-Mg alloy for forging that is excellent in corrosion cracking property and can maintain sufficient stress corrosion cracking resistance even if a recrystallized structure is generated by welding after forging. It is to be an issue. At the same time, a forged product obtained using the forging alloy is provided.

  As a result of various investigations in order to solve the above-mentioned problems, the present invention and the like are based on an Al-Zn-Mg alloy, and by appropriately controlling the addition amount of Zn, Mg, Cu, etc., the strength is improved. Without damaging, a high-strength aluminum alloy is obtained in which stress corrosion cracking hardly occurs even if a recrystallized structure is generated in any of the L direction, the LT direction, and the ST direction (the definition of each direction will be described later). I found out. In addition, forgings using alloys that have been appropriately adjusted in this way can be welded after forging, and the strength after welding is restored to 80% of the base metal due to natural aging for about one month. In addition, the present inventors have found that it has a stress corrosion cracking resistance equivalent to that of the base material and has made the present invention.

  Specifically, the forging aluminum alloy of the invention of claim 1 contains Zn 2.0 to 3.9%, Mg 0.1 to 3.5%, and the total content of Zn and Mg is 4.0 to 4.0. It is in the range of 6.0%, and further contains Cu 0.02 to 0.20%, Mn 0.20 to 0.70%, Cr 0.10 to 0.30%, Zr 0.05 to 0.30% , V0.01 to 0.10%, or one or more selected from V0.01 to 0.10%, and the total amount of Mn, Cr, Zr, and V is 0.25% or more, and Ti0.01 to Including one or more selected from 0.20%, B0.001 to 0.05%, and C0.01 to 0.5%, with the balance being made of Al and inevitable impurities To do.

  The forging aluminum alloy of the invention of claim 2 is the forging aluminum alloy of claim 1, wherein the total amount of Zn and Mg is further in the range of 4.3 to 5.5%. It is a feature.

  Furthermore, an aluminum alloy forged product according to the invention of claim 3 is an aluminum alloy forged product manufactured using the aluminum alloy for forging according to claim 1 or 2, and after the aluminum alloy forged product is welded, The tensile strength of the forged product weld material is recovered to 80% or more of the forged product base material by natural aging for months.

  Further, an aluminum alloy forged product according to the invention of claim 4 is an aluminum alloy forged product manufactured by using the aluminum alloy for forging according to claim 1 or 2, wherein the forged product is formed by welding the aluminum alloy forged product. The welding material is characterized by having a stress corrosion cracking resistance substantially equal to that of the forged product base material.

Further, the aluminum alloy forged product of the invention of claim 5 is an aluminum alloy forged product manufactured by using the aluminum alloy for forging according to claim 1 or 2, and after the aluminum alloy forged product is welded, The welded forging material subjected to natural aging for months has a tensile strength of 209 N / mm ² or more, a proof stress of 163 N / mm ² or more, and an elongation of 20% or more.

  According to the present invention, by appropriately adjusting the component composition of the Al—Zn—Mg alloy, it is excellent in resistance to stress corrosion cracking and can be welded. It is possible to provide an aluminum alloy for forging capable of maintaining sufficient stress corrosion cracking resistance and maintaining high strength even after welding. Therefore, the forging aluminum alloy of the present invention is widely used for general structural welding members, aircraft, railway vehicles, automobiles, and all other members and parts that require high strength as alloys for forging materials used by welding. It can be applied to meet diversifying product needs.

  First, the reason for adding the component elements in the forging aluminum alloy of the present invention will be described.

Zn:
Zn is an essential element for imparting strength to the material. That is, Zn is an element that maintains the strength of the forged material by forming an alloy phase by the precipitation effect and by combining with Mg. Here, when the Zn content is less than 2.0%, sufficient strength cannot be obtained. On the other hand, when the Zn content exceeds 3.9%, the strength is improved, but the stress corrosion cracking resistance is lowered. Therefore, the Zn addition amount range in the present invention is set to 2.0 to 3.9%. In addition, the desirable range of Zn amount for obtaining favorable stress corrosion cracking resistance while maintaining high strength as a structural member or component is 2.5 to 3.5%.

Mg:
Mg is also an element that imparts strength in the same manner as Zn, and contributes to the effect of precipitation and to maintain the strength of the forging material by combining with Zn to form an alloy phase. Here, if the Mg content is less than 0.1%, sufficient strength cannot be obtained. On the other hand, if it exceeds 3.5%, the strength is improved, but the stress corrosion cracking resistance is remarkably lowered. Therefore, the Mg addition amount range in this invention is set to 0.1 to 3.5%. In addition, the desirable range of Mg amount for obtaining good stress corrosion cracking resistance while maintaining high strength as a structural member or component is 0.5 to 3.0%.

Zn + Mg:
Since both Zn and Mg contribute to the strength as described above and at the same time affect the stress corrosion cracking resistance, the total amount of Zn and Mg is also regulated in the present invention. If the total amount of Zn and Mg is less than 4.0%, sufficient strength cannot be obtained. On the other hand, if it exceeds 6.0%, the strength is improved, but the stress corrosion cracking resistance is remarkably lowered. Therefore, in this invention, the total addition amount of Zn + Mg is defined as 4.0% or more and 6.0% or less. A desirable range of Zn + Mg for obtaining good stress corrosion cracking resistance while maintaining high strength as a structural member or component is 4.5% or more and 5.5% or less, and a more desirable range is 4.5 % Or more and 5.0% or less.

Cu:
Cu is an element that imparts strength, for example, by dissolving in an aluminum matrix and increasing the degree of supersaturation of the solute in the solid solution. If the Cu content is less than 0.02%, a sufficient strength improvement effect cannot be obtained. On the other hand, if it exceeds 0.2%, the strength is improved but the stress corrosion cracking resistance is remarkably lowered, and further, the weld cracking is further reduced. There is also a risk of generating. Therefore, in order to obtain good stress corrosion cracking resistance while maintaining high strength as a structural member or component, and to improve weldability, the Cu content needs to be in the range of 0.05 to 0.20%. is there.

Mn, Cr, Zr, V:
Mn, Cr, Zr, and V are elements that are effective in making the recrystallized grains finer and thus contribute to the improvement of the resistance to stress corrosion cracking. That is, these elements combine with aluminum to form Al-Mn, Al-Cr, Al-Zr, and Al-V compounds. These compounds contribute to recrystallized grain refinement and have stress corrosion cracking resistance. Improve. If each content is less than the lower limit (Mn 0.20%, Cr 0.10%, Zr 0.05%, V 0.01%), these effects cannot be obtained sufficiently, while the upper limit (Mn 0.70%, Cr 0.30). %, Zr 0.30%, V0.10%), a huge intermetallic compound is formed and causes a decrease in strength. Therefore, an upper limit and a lower limit of each content are determined. Here, in order to refine the recrystallized grains and improve the stress corrosion cracking resistance, one or more of these elements may be added. In addition, the upper limit of each addition amount of Cr, Zr, V is lower than the upper limit of the addition amount of Mn. If the addition amount of Cr, Zr, V is increased, the quenching sensitivity becomes more sensitive and the strength decreases. Because it invites. Here, the total amount of Mn, Cr, Zr, and V is also important. If the total amount of these elements is less than 0.25%, the effect of improving recrystallization grain refinement and stress corrosion cracking resistance can be sufficiently obtained. Therefore, the total addition amount of Mn + Cr + Zr + V is set to 0.25% or more. More preferably, the total amount of these is 0.40% or more.

Ti, B, C:
Ti is an element added for refinement of the cast structure in ordinary aluminum alloys. In the present invention, addition of Ti not only refines the cast structure, but also refines the recrystallized grains, and thus welds. It is also effective for later stress corrosion cracking resistance. In addition, B is an element that is often added together with Ti for refining the ingot structure. In the case of the present invention, addition of Ti not only makes the ingot structure fine, but also recrystallized grains. It also contributes to Furthermore, the effect of recrystallizing grains can be obtained by adding C together with Ti. Here, when Ti is less than 0.01%, B is less than 0.001%, and C is less than 0.01%, the effect of recrystallizing grains cannot be sufficiently obtained, while Ti is 0.20%, If B exceeds 0.05% and C exceeds 0.5%, the effect is not only saturated but also a coarse compound may be formed, where Ti is 0.01 to 0.20% and B is 0. 0.001 to 0.05% and C was in the range of 0.01 to 0.5%. Any one or more of these Ti, B, and C may be added. However, the effect of B can be maximized by adding together with Ti, and C can also be added together with Ti. Since the effect can be exhibited to the maximum, it is preferable to add B and C together with Ti.

  The remainder of each element as described above may basically be Al and inevitable impurities. A general aluminum alloy usually contains Fe and Si as inevitable impurities. These Fe and Si are not particularly problematic as long as they are about the amount of impurities contained in normally used bullion, and are not particularly positively added in the present invention. In a commonly used industrial purity 99.7% aluminum ingot, Fe is often contained in an amount of about 0.15% or less and Si of about 0.10% or less. In this invention, Fe of 0.20% or less, Si0 There is no particular problem up to about 15% or less.

  In the present invention, the forging aluminum alloy having the above component composition and the forged product using the same are defined. Here, as a method for forging an aluminum alloy, there are generally cold forging and hot forging, but the invention is not particularly limited. Since the former cold forging is forged at room temperature, the deformation resistance of the material is high, so it is necessary to increase the pressing force during forging, and therefore it is usually limited to a small size. On the other hand, hot forging is performed in a temperature range (about 300 to 500 ° C.) that is higher than the recrystallization temperature and lower than the solidus temperature, and can correspond to products of various sizes.

  Forged products are generally classified into free forged products and die forged products. Free forged products are forged on anvils using a hydraulic press or hammer, and the basic shapes are prisms, cylinders, disks, bars, rings, etc. It is usually used when manufacturing a forged product. On the other hand, the die forging is a method of manufacturing a product having a complicated shape using a mold, and is subdivided into a blocker type forging, a normal grade forging, and a precision grade forging. Each method forges to a shape close to the final shape, so multiple forgings and high dimensional accuracy dies are required. If the production quantity is small, the cost is high, but the metal flow can be processed without being divided. Therefore, there is an advantage that there is little reduction in mechanical properties.

  Next, the mechanical characteristics of the forged product will be described. In general, the mechanical properties of a forged product are affected by the forging ratio (also referred to as forging ratio or forging ratio) and metal flow. The forging ratio of the material in forging is always represented by the deformation ratio in the direction of maximum strain among the three main strains, and is usually indicated by the method defined in JIS G0701, “How to express the forging ratio of steel forging work”. There are many cases. In addition, since mechanical characteristics are improved as the forging ratio increases, molding with a high forging ratio is desired to obtain high characteristics. Here, in general, a material that has undergone plastic deformation by forging or the like causes anisotropy of mechanical properties due to metal flow. Mechanical strength and elongation are best in a direction parallel to the metal flow (L direction), and inferior in a direction perpendicular to the metal flow and parallel to the forging press direction (ST direction). Further, it exhibits intermediate properties in the direction perpendicular to the L direction and the ST direction (LT direction).

  In this invention, the manufacturing process of the forged product is not particularly limited, but the ingot obtained by a general casting method such as semi-continuous water-cooled casting is subjected to a homogenization treatment at a predetermined temperature, When cold forging is applied, forging is performed with a hydraulic press or hammer at room temperature. On the other hand, when hot forging is applied, the ingot is heated to about 300 to 500 ° C. And forging. In this case, heating and forging may be repeated several times depending on the size and shape of the product. Thereafter, in the case of a heat-treated alloy, a series of steps is completed by performing solution treatment, quenching, aging treatment, pre-shipment inspection, and the like. In the case of a non-heat-treatable alloy, a series of processes is completed by performing inspection before shipment after forging.

  In this invention, by appropriately controlling the alloy component composition of the material obtained using the general forging method as described above, even if it has a recrystallized structure in any of L, LT, ST direction, There was no stress corrosion cracking, and it was possible to secure the necessary strength for the structural members.

  Next, as an example of the present invention, various characteristics were investigated using a block-shaped forged material produced by free forging. The forging material manufacturing process and the survey results are shown below.

  First, the material manufacturing process for forging will be described.

  Alloy No. 1 in Table 1 and Table 2 1-No. After obtaining an ingot with an outer diameter of 345 mm and a length of 3000 mm by semi-continuous water-cooling casting using each alloy having the component composition shown in No. 48, homogenization treatment was performed at 460 ° C. for 26 hours, and ultrasonic flaw detection was conducted. The presence of internal defects was confirmed. Further, the outer diameter was cut to 320 mmφ, the surface oxide film and the like were removed, and the outer diameter was cut to 400 mm to produce a slab for forging. Furthermore, this slab was heated to 420 ° C. by induction overheating, and forged into a block shape having a cross-sectional dimension of 100 mm high × 200 mm wide × 1700 mm long. The training ratio was 6. Thereafter, solution treatment was performed at 460 ° C. for 4 hours, followed by quenching with warm water at 80 ° C., and T6 treatment by two-stage aging at 105 ° C. × 8 Hr + 155 ° C. × 16 Hr.

  The resulting block-shaped forged material (base material) was examined for mechanical properties as follows. That is, two test pieces based on JIS Z2201 were sampled from the block forging material in parallel from each metal flow (L, LT, ST) direction (see FIG. 1) from the center of the cross section, and JIS Z2241 Based on the above, a tensile test was carried out to determine tensile strength, proof stress, and elongation.

  Further, the crystal grain shape and crystal grain size of the block-like forged material (base material) were examined as follows. That is, a 20 mm square test piece was collected from the center of the block so that the structure of the L-LT, LT-ST, and L-ST cross sections could be observed, etched by the Barker method, and then crystallized with an optical microscope. While confirming the shape of the grains, five field images of a 100-fold structure photograph were taken, and the crystal grain size was determined from the photograph by a cutting method specified in JIS H0501, and the average value of the five fields of view was taken as the average crystal grain size.

Furthermore, the stress corrosion cracking resistance of the block-like forged material (base material) was evaluated as follows. That is, based on JIS H8711, the stress corrosion cracking resistance test by a constant load system (C ring test piece) was implemented. The test piece was sampled from the block-shaped forged material (n = 3), and the direction in which the maximum load was applied was defined as the ST direction (see FIG. 3). As a test method, a continuous dipping method in which the sample was dipped in a chromic phosphate test solution for a predetermined time was employed, and the presence or absence of cracks was visually evaluated. As a stress corrosion cracking test solution, a solution obtained by mixing 36 g of chromium oxide (anhydrous chromic acid), 30 g of potassium dioxide (potassium dichromate) and 3 g of sodium chloride in pure water obtained by ion exchange of 1 l (liter). The test piece was immersed in this test solution, and the presence or absence of cracks was confirmed every 15 minutes until 60 minutes. Thereafter, the presence or absence of cracks was observed every 30 minutes, and the test was conducted for a maximum of 420 minutes. The test was terminated when a crack occurred in at least one test piece. In addition, as stress applied to each test piece, two kinds of 75% (225 N / mm ² ) of the actual proof stress value of each material and 75% (225 N / mm ² ) of the actual proof stress value of the comparative material A7N01FD-T6 were adopted.

  Next, welding was performed using the forged material obtained as described above, and a weld crack test was performed on the welded material with a fishbone type weld crack test piece as shown in FIG. That is, five fishbone weld crack test pieces each having a predetermined thickness (66.8 mm × 105 mm) with a thickness of 3 mm were produced from the forged material described above. Then, by the TIG welding method, the test piece was tested under the conditions shown in Table 3 by two kinds of welding methods, that is, welding with no filler without using a filler material and welding with filler material A5356BY (φ2.4 mm). Welding was performed from the shallowest to the deepest. Weld crackability was evaluated by measuring the length of the generated crack with calipers. Evaluation criteria set the average value of five weld crack lengths as 0 to less than 75 mm, Δ to 75 to less than 100 mm, and 100 mm (total crack) as x.

  The mechanical properties of the weld material were examined as follows. That is, for the strength measurement method, a plate material was cut out from the block-shaped forged material described above, and a welding material was produced by I-groove 1-pass TIG welding (butting) (see FIG. 4). A5356BY (φ2.4 mm) was used as the filler material. After welding, natural aging was performed at room temperature (25 ° C.) for one month, and a tensile test based on JIS Z2241 was performed using a tensile test piece No. 13B based on JIS Z2201. The test pieces were each subjected to n = 3 tests with the weld beads attached.

  Next, the stress corrosion cracking resistance of the welded material was evaluated by a four-point bending test based on JISH8711 (see FIG. 5). Here, it is generally known that stress corrosion cracking is less likely to occur when the crystal structure is an unrecrystallized structure, but the forged material subjected to welding has a recrystallized structure part, Since stress corrosion cracking may occur, a stress corrosion cracking test was conducted on the welded material separately from the base metal.

As the load stress in the stress corrosion cracking test for the welded material, two kinds of stress were applied: 75% of the actual proof stress value and 75% (191 N / mm ² ) of the actual proof stress value of the comparative material A7N01FH-T6. The test was performed by immersing in a chromic phosphate test solution for a predetermined time to evaluate the presence or absence of cracks. As a stress corrosion cracking test solution, a solution obtained by mixing 36 g of chromium oxide (anhydrous chromic acid), 30 g of potassium dioxide (potassium dichromate) and 3 g of sodium chloride in pure water obtained by ion exchange of 1 l (liter). Using. The said test piece was immersed in this test liquid, and the presence or absence of the crack was confirmed every 15 minutes.

Further, as a stress corrosion cracking resistance test for the welded material, a constant strain uniaxial tensile test by an alternate dipping method based on JISH8711 was also performed in addition to the above test. The test solution was a 3.5% ± 0.1 mass% sodium chloride solution (PH 6.4 to 7.2), the test environment was a temperature of 25 ° C. ± 3 ° C., a relative humidity of 40 to 70%, and an alternate immersion cycle. Was a cycle of immersion in a test solution for 10 minutes and holding in the air for 50 minutes, and a test period of 30 days. The test piece was compliant with ASTM B557 (see FIG. 6). As the load applied, 75% (191 N / mm ² ) of the actual proof stress value of A7N01FH-T6 was applied as a tension by a bolt, and a constant strain method by a frame method was used (see FIG. 7). Cracks were confirmed 3 days after the start of the test, 1 week later, and thereafter every week thereafter, and cracks of 3 mm or more were determined as cracks.

  With regard to the materials shown in Tables 1 and 2, mechanical properties in the state of the base material (forged material), crystal grain shape and crystal grain size, and stress corrosion cracking resistance test results, and in the state of welding material Tables 4 to 7 show the fishbone weld cracking test, mechanical characteristics, and stress corrosion cracking resistance test results.

As is clear from these results, the stress corrosion cracking property of the material of the present invention is the state of the base material (forged material), and no stress corrosion cracking occurs even in the observation after 420 minutes. It was. Even in the state of the weld material, no stress corrosion cracking occurred after 2 hours in the accelerated test, and no cracking was observed even after 30 days in the constant strain uniaxial tensile test. Therefore, it is apparent that the material of the present invention is far improved compared to the conventional material, particularly with respect to stress corrosion cracking resistance. Regarding the mechanical properties, the tensile strength of the forged product welded material is the same as that of the conventional material as a high-strength material and the forged product welded material has a natural aging for one month after welding. It is apparent that the tensile strength is 209 N / mm ² or more, the proof stress is 163 N / mm ² or more, and the elongation is 20% or more.

  On the other hand, it is clear that any one or more performances are inferior in the comparative example in which the component composition is outside the range specified in the present invention.

It is an approximate perspective view for explaining the metal flow of a forged product. It is a rough perspective view which shows the extraction | collection condition of the C ring type stress corrosion cracking test piece in the stress corrosion cracking resistance test by the low load system applied in the Example. It is a top view which shows the fishbone type weld crack test piece used by the weld crack test applied in the Example. It is the top view and front view which show the welding material created in the Example. It is a rough front view which shows the test piece and the test method (four-point bending test method) of the stress corrosion cracking test of the welding material applied in the Example. It is a top view which shows the test piece of the stress corrosion cracking test based on ASTM B557 applied in the Example. FIG. 7 is a schematic plan view showing a stress corrosion cracking test method (constant strain uniaxial tensile test method) for the test piece (welding material) shown in FIG. 6.

Claims (5)

  Zn 2.0-3.9% (mass%, the same shall apply hereinafter), Mg 0.1-3.5%, and the total amount of Zn and Mg is within the range of 4.0-6.0%, Further, it contains Cu 0.02 to 0.20%, Mn 0.20 to 0.70%, Cr 0.10 to 0.30%, Zr 0.05 to 0.30%, V 0.01 to 0.10% It contains one or more selected from among them, and the total amount of Mn, Cr, Zr, and V is 0.25% or more, and Ti 0.01 to 0.20%, B0.001 to 0 .Excellent stress corrosion cracking resistance, characterized in that it contains one or more selected from 0.05% and C0.01-0.5%, and the balance consists of Al and inevitable impurities Weldable aluminum alloy for forging.   The welding aluminum alloy for forging according to claim 1, wherein the total amount of Zn and Mg is in the range of 4.3 to 5.5%. Possible forging aluminum alloy.   An aluminum alloy forged product manufactured using the forging aluminum alloy according to claim 1 or 2, wherein the tensile strength of the forged product weld material by natural aging for one month after welding the aluminum alloy forged product. Forged aluminum alloy, characterized in that it recovers to more than 80% of the base material of the forged product.   An aluminum alloy forged product manufactured using the forging aluminum alloy according to claim 1 or 2, wherein a forged product welded to the aluminum alloy forged product is substantially equivalent to a forged product base material. An aluminum alloy forged product characterized by having a stress corrosion cracking resistance. An aluminum alloy forged product manufactured using the forging aluminum alloy according to claim 1 or 2, wherein the forged product weld material has been subjected to natural aging for one month after welding the aluminum alloy forged product. A forged aluminum alloy having a tensile strength of 209 N / mm ² or more, a proof stress of 163 N / mm ² or more, and an elongation of 20% or more.

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