JP5204793B2 - High strength aluminum alloy extruded material with excellent stress corrosion cracking resistance - Google Patents

High strength aluminum alloy extruded material with excellent stress corrosion cracking resistance Download PDF

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JP5204793B2
JP5204793B2 JP2010003996A JP2010003996A JP5204793B2 JP 5204793 B2 JP5204793 B2 JP 5204793B2 JP 2010003996 A JP2010003996 A JP 2010003996A JP 2010003996 A JP2010003996 A JP 2010003996A JP 5204793 B2 JP5204793 B2 JP 5204793B2
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aluminum alloy
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幸昌 宮田
伸二 吉原
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株式会社神戸製鋼所
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本発明は、耐応力腐食割れ性に優れた高強度アルミニウム合金押出材に関し、特にバンパーレインフォースやドアガードバーなどの自動車用構造材として好適に使用されるアルミニウム合金押出材に関する。   The present invention relates to a high-strength aluminum alloy extruded material excellent in stress corrosion cracking resistance, and more particularly to an aluminum alloy extruded material suitably used as a structural material for automobiles such as a bumper reinforcement and a door guard bar.
自動車の軽量化のため、バンパーレインフォース、ドアガードバーなどのエネルギー吸収部材として、Al−Zn−Mg系の高強度アルミニウム合金押出材(特許文献1,2参照)が用いられている。しかし、Al−Zn−Mg系アルミニウム合金押出材は、応力腐食割れ(以下、SCC)を起こす危険があり、これを防止するため、やむを得ず過時効処理を行って、耐力300N/mm2程度で使用されており、高強度合金としての特徴が薄れている。   In order to reduce the weight of automobiles, Al-Zn-Mg high-strength aluminum alloy extruded materials (see Patent Documents 1 and 2) are used as energy absorbing members such as bumper reinforcements and door guard bars. However, the Al-Zn-Mg-based aluminum alloy extruded material has a risk of causing stress corrosion cracking (hereinafter referred to as SCC). The characteristics as a high-strength alloy are weakened.
特開2002−327229号公報JP 2002-327229 A 特開平11−264044号公報Japanese Patent Laid-Open No. 11-264044
自動車の更なる軽量化のため、バンパーレインフォース等の自動車構造材に用いられるAl−Zn−Mg系合金押出材の高強度化が求められている。しかし、本系合金の高強度化を達成するためにZn及びMgを高濃度化すると、粒界析出物のMgZnが高密度に分布するため耐SCC性が低下し、自動車用構造材として適用できなくなる。同時に、押出性が低下して薄肉成形が困難となり、結果として軽量化効果を発揮できなくなる。
本発明は、このような従来技術の問題点に鑑みてなされたもので、高強度で耐SCC性に優れ、押出性にも優れたAl−Zn−Mg系アルミニウム合金押出材を提供することを目的とする。
In order to further reduce the weight of automobiles, it is required to increase the strength of Al—Zn—Mg alloy extruded materials used for automobile structural materials such as bumper reinforcement. However, when Zn and Mg are increased in concentration in order to achieve higher strength of this alloy, the grain boundary precipitate MgZn 2 is distributed at a high density, so that the SCC resistance is reduced and applied as a structural material for automobiles. become unable. At the same time, the extrudability deteriorates and thin-wall molding becomes difficult, and as a result, the effect of reducing the weight cannot be exhibited.
The present invention has been made in view of such problems of the prior art, and provides an Al—Zn—Mg-based aluminum alloy extruded material having high strength, excellent SCC resistance, and excellent extrudability. Objective.
Al−Zn−Mg系アルミニウム合金は、Zn及びMgからなる析出物MgZn2を高密度に分布させることで高強度を達成する合金である。本発明では、MgZnを過不足なく形成するZn及びMg量(MgZnの化学量論比)より過剰に添加されたMgが、高強度化に寄与することを利用した。MgをMgZnの化学量論比より過剰に添加することにより、MgZn量を抑えて高強度化することができ、これにより、Al−Zn−Mg系アルミニウム合金押出材を、耐SCC性を低下させることなく、高強度化することができる。その一方で、過剰Mg量が多すぎると押出性が悪化して押出速度が遅くなり、ダイクエンチ空冷(押出直後の押出材をオンラインで空冷すること、プレス焼き入れともいう)ができなくなる。さらに過剰Mgが増加するに伴って粒界析出物が微細かつ連続的になり、結局は耐SCC性を低下させる。従って、本発明では、押出性及び耐SCC性を低下させずに高強度化できる過剰Mgの限界量を見極めた。 The Al—Zn—Mg-based aluminum alloy is an alloy that achieves high strength by distributing precipitates MgZn 2 composed of Zn and Mg at a high density. In the present invention, it was utilized that Zn added in excess of the amount of Zn and Mg (stoichiometric ratio of MgZn 2 ) that forms MgZn 2 without excess or deficiency contributes to high strength. By adding Mg to excess over stoichiometric ratio of MgZn 2, it is possible to increase the strength of suppressing the MgZn 2 amount, thereby, the Al-Zn-Mg series aluminum alloy extruded material, the SCC resistance The strength can be increased without lowering. On the other hand, if the amount of excess Mg is too large, the extrudability deteriorates and the extrusion speed becomes slow, so that die quench air cooling (on-line cooling of the extruded material immediately after extrusion, also referred to as press quenching) cannot be performed. Further, as the excess Mg increases, the grain boundary precipitates become fine and continuous, eventually reducing the SCC resistance. Therefore, in the present invention, the limit amount of excess Mg that can be increased in strength without degrading extrudability and SCC resistance has been determined.
本発明に係るAl−Zn−Mg系アルミニウム合金押出材は、Mgの質量%を[Mg]、Znの質量%を[Zn]としたとき、[Mg]と[Zn]が下記(1)〜(3)式を満たし、
5.43≦[Zn]≦7.0・・・(1)
[Zn]/5.38+0.15≦[Mg]≦[Zn]/5.38+0.7・・・(2)
[Zn]+4.7[Mg]≦12・・・(3)
さらに、Cu:0.1〜0.6質量%,Ag:0.01〜0.15質量%の1種又は2種と、Ti:0.005〜0.05質量%と、Mn:0.1〜0.3質量%,Cr:0.05〜0.2質量%,Zr:0.05〜0.2質量%の1種又は2種以上を含み、残部Al及び不可避不純物からなる。
MgZnの化学量論比(質量比)は、[Mg]:[Zn]が1:5.38であるから、上記(2)式は、[Mg]がMgZnの化学量論比より0.15質量%以上過剰で、かつ過剰[Mg]が0.7質量%以下であることを意味する。
In the Al—Zn—Mg-based aluminum alloy extruded material according to the present invention, [Mg] and [Zn] are expressed by the following (1) to [Mg] when the Mg mass% is [Mg] and the Zn mass% is [Zn]. (3) is satisfied,
5.43 ≦ [Zn] ≦ 7.0 (1)
[Zn] /5.38+0.15≦ [Mg] ≦ [Zn] /5.38+0.7 (2)
[Zn] +4.7 [Mg] ≦ 12 (3)
Furthermore, Cu: 0.1-0.6 mass%, Ag: 0.01-0.15 mass% 1 type or 2 types, Ti: 0.005-0.05 mass%, Mn: 0.0. 1-0.3 mass%, Cr: 0.05-0.2 mass%, Zr: 0.05-0.2 mass% of 1 type (s) or 2 or more types are comprised, and it consists of remainder Al and an unavoidable impurity.
Since the stoichiometric ratio (mass ratio) of MgZn 2 is [Mg]: [Zn] is 1: 5.38, the above formula (2) indicates that [Mg] is 0 from the stoichiometric ratio of MgZn 2. .15% by mass or more and excess [Mg] is 0.7% by mass or less.
本発明のAl−Zn−Mg系アルミニウム合金押出材は、高強度で耐SCC性に優れている。そして、押出性に優れるため、ダイクエンチ空冷でT6材(溶体化処理後時効処理)にほぼ匹敵する高強度が得られ、また薄肉成形が可能である。本発明の高強度Al−Zn−Mg系アルミニウム合金押出材を適用することにより、バンパーリインフォースやドアガードバーなどの自動車構造部材のさらなる軽量化が可能となる。   The Al—Zn—Mg-based aluminum alloy extruded material of the present invention has high strength and excellent SCC resistance. And since it is excellent in extrudability, the die-quenching air cooling can provide high strength almost comparable to T6 material (aging treatment after solution treatment), and thin-wall molding is possible. By applying the high-strength Al—Zn—Mg-based aluminum alloy extruded material of the present invention, it is possible to further reduce the weight of automobile structural members such as bumper reinforcements and door guard bars.
本発明のAl−Zn−Mg系合金のZn及びMg量の範囲を示す図である。It is a figure which shows the range of Zn and Mg amount of the Al-Zn-Mg alloy of this invention. 実施例の押出材の断面形状を示す図である。It is a figure which shows the cross-sectional shape of the extrusion material of an Example. 実施例の押出材の断面組織の顕微鏡写真である。It is a microscope picture of the cross-sectional structure | tissue of the extrusion material of an Example.
以下、本発明に係るAl−Zn−Mg系アルミニウム合金押出材の組成等について詳細に説明する。
Zn;
Zn含有量が5.0質量%未満では強度が不足し、7.0質量%を超えると粒界析出物MgZnが増えてSCC感受性が鋭くなる。従って、Zn含有量は5.0〜7.0質量%とする。耐SCC性が特に重要視される場合、Zn含有量が比較的少ない領域、具体的には5.0〜6.3質量%が望ましく、さらに6.0質量%未満、さらに5.8質量%以下がより望ましい。一方、Zn含有量が6.3質量%を超えるときは、SCC感受性が鋭くなるのを抑えるため、後述するCu及びAgの両方を添加することが望ましい。
Hereinafter, the composition of the Al—Zn—Mg-based aluminum alloy extruded material according to the present invention will be described in detail.
Zn;
If the Zn content is less than 5.0% by mass, the strength is insufficient, and if it exceeds 7.0% by mass, the grain boundary precipitate MgZn 2 increases and the SCC sensitivity becomes sharp. Therefore, Zn content shall be 5.0-7.0 mass%. When SCC resistance is particularly important, the Zn content is relatively low, specifically 5.0 to 6.3% by mass, more preferably less than 6.0% by mass, and further 5.8% by mass. The following is more desirable. On the other hand, when Zn content exceeds 6.3 mass%, in order to suppress that SCC sensitivity becomes sharp, it is desirable to add both Cu and Ag mentioned later.
Mg;
MgはZnとともにMgZnを形成してAl−Zn−Mg系合金の強度を向上させる。その含有量は、Zn含有量との関係で、前記(2),(3)式のとおりに制限される。
Mg含有量がMgZn の化学量論比([Zn]/5.38)以下の領域ではMgZn量が減少して強度が不足する。Mg含有量が前記(2)式の下限値以上の領域(MgZnの化学量論比+0.15質量%以上の過剰Mg領域)になると、過剰Mgが高強度化に寄与するため、MgZn量を抑えたうえで高強度化が可能となる。しかし、過剰Mg量が0.7質量%を超えると押出性が低下し、ダイクエンチ空冷では高強度(対T6材比)が出ない。また、生産性が低下し、薄肉成形も困難になる。望ましくは過剰Mg量は0.6質量%以下である。
また、Zn及びMg含有量が前記(3)式の規定を超えると、粒界析出物が微細かつ連続的に形成され、耐SCC性が低下する。
Mg;
Mg forms MgZn 2 together with Zn to improve the strength of the Al—Zn—Mg alloy. The content is limited as shown in the above formulas (2) and (3) in relation to the Zn content.
In a region where the Mg content is less than the stoichiometric ratio of MgZn 2 ([Zn] /5.38), the amount of MgZn 2 decreases and the strength is insufficient. When Mg content is the (2) the lower limit value or more regions (stoichiometric ratio +0.15 wt% or more excess Mg region of MgZn 2) of, for excess Mg contributes to higher strength, MgZn 2 It is possible to increase the strength while suppressing the amount. However, when the excess Mg amount exceeds 0.7% by mass, the extrudability decreases, and die quench air cooling does not provide high strength (compared to T6 material). In addition, productivity is reduced and thin wall molding becomes difficult. Desirably, the excess Mg amount is 0.6% by mass or less.
Moreover, when Zn and Mg content exceeds the prescription | regulation of said (3) Formula, a grain-boundary precipitate will be formed finely and continuously, and SCC resistance will fall.
図1は、本発明に係るAl−Zn−Mg系合金のZn及びMg量の範囲を図示したものである。図中のプロット○は後述する表1のNo.1〜12、プロット●は同じく表1のNo.13〜18である。図1上において、前記(1)〜(3)式で規定される範囲は、実質的に、[Zn]=5.43、[Mg]=[Zn]/5.38+0.15、及び[Zn]+4.7[Mg]=12で囲まれた三角形の領域である。 FIG. 1 illustrates the range of Zn and Mg content of an Al—Zn—Mg alloy according to the present invention. Plot ◯ in the figure indicates No. in Table 1 described later. 1 to 12 and plot ● are No. 1 in Table 1. 13-18. In FIG. 1, the ranges defined by the equations (1) to (3) are substantially [Zn] = 5.43, [Mg] = [Zn] /5.38+0.15, and [Zn]. ] +4.7 [Mg] = 12.
Cu,Ag;
Cu及びAgはAl−Zn−Mg系合金の耐SCC性を向上させる作用があり、いずれか一方又は両方が添加される。
Cu含有量が0.1質量%未満、及びAg含有量が0.01質量%未満では、耐SCC性向上効果が小さい。一方、Cu含有量が0.6質量%を超えると押出性及び溶接性を低下させる。また、焼入れ感受性が鋭くなるため、空冷で焼入れができなくなる。Ag含有量は0.15%を超えて添加してもその効果が飽和する。従って、Cu含有量は0.1〜0.6質量%、Ag含有量は0.01〜0.15質量%とする。
Zn含有量が6.3質量%未満の場合は、CuとAgはいずれか一方の添加でもよいが、Zn含有量が6.3質量%を超える場合、耐SCC性の低下を抑えるためCuとAgの両方の添加が望ましい。
Cu, Ag;
Cu and Ag have the effect of improving the SCC resistance of the Al—Zn—Mg alloy, and either one or both are added.
When the Cu content is less than 0.1% by mass and the Ag content is less than 0.01% by mass, the effect of improving the SCC resistance is small. On the other hand, when Cu content exceeds 0.6 mass%, extrudability and weldability will be reduced. Moreover, since quenching sensitivity becomes sharp, it becomes impossible to quench by air cooling. Even if the Ag content exceeds 0.15%, the effect is saturated. Therefore, the Cu content is 0.1 to 0.6 mass%, and the Ag content is 0.01 to 0.15 mass%.
When the Zn content is less than 6.3% by mass, either Cu or Ag may be added. However, when the Zn content exceeds 6.3% by mass, Cu and Ag are used to suppress a decrease in SCC resistance. Both additions of Ag are desirable.
Ti;
Tiは、溶湯中にAlTiを形成させ、鋳塊の結晶粒を微細化する効果がある。Ti含有量が0.005質量%未満では結晶粒微細化効果が小さい。一方、Ti含有量が0.05質量%を超えると鋳塊中に粗大晶出物を形成させ、伸びを低下させる。従って、Ti含有量は0.005〜0.05質量%とする。
Ti;
Ti has the effect of forming Al 3 Ti in the molten metal and refining the crystal grains of the ingot. When the Ti content is less than 0.005% by mass, the effect of crystal grain refinement is small. On the other hand, if the Ti content exceeds 0.05% by mass, coarse crystals are formed in the ingot and the elongation is lowered. Therefore, Ti content shall be 0.005-0.05 mass%.
Mn,Cr,Zr;
Mn,Cr及びZrは均質化処理によってアルミニウム中に微細分散粒子として析出し、再結晶を抑制する効果があり、また再結晶を抑制することで耐SCC性を向上させることができるため、いずれか1種又は2種以上が添加される。Mn,Cr,Zrがいずれも0.1質量%、0.05質量%、0.05質量%より不足すると押出中に表面再結晶が厚く発生し、耐SCC性が低下する。一方、Mn,Cr,Zrがそれぞれ0.3質量%、0.2質量%、0.2質量%を超えると焼入れ感受性が鋭くなり、さらに粗大晶出物を形成するため伸びが低下する。従って、Mn,Cr,Zrの含有量はそれぞれ0.1〜0.3質量%,0.05〜0.2質量%,0.05〜0.2質量%とする。なお、Zrは焼き入れ感受性を鋭くする作用が比較的小さいため、Zr単独か、ZrとMn又はCrの一方又は両方を添加することが望ましい。
Mn, Cr, Zr;
Mn, Cr and Zr are precipitated as finely dispersed particles in aluminum by homogenization treatment, and have the effect of suppressing recrystallization, and SCC resistance can be improved by suppressing recrystallization. 1 type (s) or 2 or more types are added. If Mn, Cr, and Zr are all less than 0.1% by mass, 0.05% by mass, and 0.05% by mass, surface recrystallization occurs thickly during extrusion and SCC resistance decreases. On the other hand, when Mn, Cr, and Zr exceed 0.3% by mass, 0.2% by mass, and 0.2% by mass, respectively, the quenching sensitivity becomes sharp, and further, a coarse crystallized product is formed, resulting in a decrease in elongation. Therefore, the contents of Mn, Cr, and Zr are 0.1 to 0.3 mass%, 0.05 to 0.2 mass%, and 0.05 to 0.2 mass%, respectively. Since Zr has a relatively small effect of sharpening quenching sensitivity, it is desirable to add Zr alone, or one or both of Zr and Mn or Cr.
製造方法;
本発明に係るAl−Zn−Mg系アルミニウム合金押出材は、溶解してビレットを鋳造し、均質化処理した後、押出加工し、押出直後の押出材を空冷ダイクエンチし、続いて時効処理を行うことで、製造することができる。なお、空冷ダイクエンチにより焼き入れするには、押出速度が十分速い(押出性に優れている)ことが必要である。焼き入れするには高温状態(例えば450℃以上)から急冷することが必要であるが、押出速度が遅いと、オンラインで空冷されるまでに押出材の温度が低下して、十分焼きが入らない。このため時効処理しても高強度が出ず、T6材に比べて強度が大きく劣ることとなる。
一方、本発明に係るAl−Zn−Mg系アルミニウム合金押出材は、ダイクエンチに代えて、溶体化処理及び時効処理(T6材)することもできる。いずれの場合も、加工熱処理の各工程は通常の条件で行えばよい。なお、時効条件は65〜95℃で2〜6時間及び125〜165℃で7〜13時間の範囲(過時効領域を含む)から選択するとよい。
Production method;
The Al—Zn—Mg-based aluminum alloy extruded material according to the present invention is melted to cast a billet, homogenized, and then extruded, and the extruded material immediately after extrusion is air-cooled and die-quenched, followed by aging treatment Thus, it can be manufactured. In addition, in order to quench by air cooling die quenching, it is necessary that the extrusion speed is sufficiently high (extrudability is excellent). Quenching requires quenching from a high temperature state (for example, 450 ° C. or higher), but if the extrusion speed is slow, the temperature of the extruded material will drop before it is air-cooled online, and it will not quench sufficiently. . For this reason, even if an aging treatment is performed, no high strength is obtained, and the strength is greatly inferior to that of T6 material.
On the other hand, the Al—Zn—Mg-based aluminum alloy extruded material according to the present invention can be subjected to solution treatment and aging treatment (T6 material) instead of die quenching. In any case, each process of the heat treatment may be performed under normal conditions. The aging conditions may be selected from a range of 65 to 95 ° C. for 2 to 6 hours and 125 to 165 ° C. for 7 to 13 hours (including an overaging region).
表1に示す化学成分のAl−Zn−Mg系合金を常法により溶解し、それぞれ直径155mmのビレットを鋳造した。このビレットを470℃×6hで均質化処理した後ファン空冷し、再び450℃に加熱して図1に示す中空断面形状にポートホール押し出しした。押出材の断面の肉厚は1.5mmである。押出加工時の高温状態(450℃以上)からファン空冷によりダイクエンチし、200℃までの平均冷却速度は約160℃/minであった。
続いて各押出材から2本ずつの短尺材を切断採取し、一方の短尺材に対し90℃×3時間及び140℃×8時間の二段時効処理を施し、供試材(T5材)を得た。また、押出性評価のため、他方の短尺材を溶体化処理(450℃×1時間加熱後、水冷)した後、90℃×3時間及び140℃×8時間の二段時効処理を施して押出性評価の基準となるT6材を得た。
Al-Zn-Mg based alloys having chemical components shown in Table 1 were melted by a conventional method, and billets each having a diameter of 155 mm were cast. The billet was homogenized at 470 ° C. × 6 h, then air cooled by a fan, heated again to 450 ° C. and extruded into a hollow cross-sectional shape shown in FIG. The thickness of the cross section of the extruded material is 1.5 mm. The die was quenched from the high temperature state (450 ° C. or higher) during the extrusion process by fan air cooling, and the average cooling rate up to 200 ° C. was about 160 ° C./min.
Subsequently, two short materials were cut and collected from each extruded material, and one short material was subjected to a two-stage aging treatment of 90 ° C. × 3 hours and 140 ° C. × 8 hours, and a test material (T5 material) was obtained. Obtained. In addition, for the evaluation of extrudability, the other short material was subjected to a solution treatment (after heating at 450 ° C. × 1 hour, followed by water cooling), and then subjected to a two-stage aging treatment of 90 ° C. × 3 hours and 140 ° C. × 8 hours. T6 material used as the standard of property evaluation was obtained.
上記供試材及びT6材を用いて以下の試験を行った。その結果を表2に示す。
引張試験;
前記供試材(T5材)及びT6材からJIS13号B試験片を採取し、JIS−Z2241の引張試験法に従って、引張強さ、耐力及び伸びを測定した。表2に示す機械的性質は供試材(T5材)のものである。供試材(T5材)の引張強さ及び耐力が、T6材の90%以上を押出性○、80%以上90%未満を押出性△、80%未満を押出性×と評価し、耐力380N/mm以上かつ押出性△以上を合格とした。また、伸びについては12%以上を合格とした。
The following tests were conducted using the above-mentioned test materials and T6 materials. The results are shown in Table 2.
Tensile test;
JIS No. 13 B test specimens were collected from the test material (T5 material) and T6 material, and the tensile strength, proof stress and elongation were measured according to the tensile test method of JIS-Z2241. The mechanical properties shown in Table 2 are those of the test material (T5 material). The tensile strength and proof stress of the test material (T5 material) were evaluated as extrudability of 90% or more of T6 material, extrudability of 80% or more and less than 90%, extrudability x of less than 80%, and proof strength of 380N. / Mm 2 or more and extrudability Δ or more was considered acceptable. Moreover, about elongation, 12% or more was set as the pass.
SCC試験;
クロム酸促進法による耐応力腐食割れ試験を行った。各供試材から溶着部を避けて押出方向に平行に板状試験片を採取し、JIS−H8711に準じて押出方向に耐力比95%に相当する引張応力を負荷した状態で、90℃の試験溶液に最大10時間まで浸漬し、SCCを目視で観察した。なお、応力負荷はジグのボルト・ナットを締めることにより試験片の外表面に引張応力を発生させ、応力値はこの外表面に接着した歪みゲージによって測定した。また、試験溶液は蒸留水に酸化クロム36g、2クロム酸カリウム30g及び塩化ナトリウム3g(1リットル当たり)を加えて作製した。0.5時間毎にSCC発生の有無を観察し、10時間SCCが発生しなかったものを○、6時間以上10時間未満でSCCが発生したものを△、6時間までにSCCが発生したものを×と評価し、△以上を合格とした。
SCC test;
The stress corrosion cracking test by the chromic acid acceleration method was conducted. A plate-shaped test piece was collected from each specimen in parallel to the extrusion direction while avoiding the welded portion, and in the state where a tensile stress corresponding to a yield ratio of 95% was loaded in the extrusion direction according to JIS-H8711, It was immersed in the test solution for a maximum of 10 hours, and SCC was visually observed. In addition, the stress load generated tensile stress on the outer surface of the test piece by tightening the bolt and nut of the jig, and the stress value was measured with a strain gauge adhered to the outer surface. A test solution was prepared by adding 36 g of chromium oxide, 30 g of potassium dichromate and 3 g of sodium chloride (per liter) to distilled water. Observe the presence or absence of SCC every 0.5 hours, ○ if no SCC occurred for 10 hours, △ if SCC occurred in 6 hours or more but less than 10 hours, SCC occurred by 6 hours Was evaluated as x, and Δ or more was regarded as acceptable.
ミクロ組織;
SCC試験で△又は×と評価された供試材について、押出方向に平行に長さ20mmの試験材を採取し、非溶着部の押出平行断面をケラー液でエッチングした後、外側表面(中空材の外側表面に相当する部位)のミクロ組織を観察した。表面再結晶層の厚さが20μm以上の供試材は、表面再結晶層が厚いために耐SCC性が低下したと判断し、表2のミクロ組織の欄に×を付した。表面再結晶層厚さが20μm未満のものは、ミクロ組織自体には問題なしと判断し、表2のミクロ組織の欄に○を付した。なお、図3はNo.21の供試材のミクロ組織(顕微鏡写真)であり、表面再結晶層の厚みが両矢印で示され,粗大化した表面再結晶粒が観察される。
Microstructure;
About the test material evaluated as Δ or × in the SCC test, a test material having a length of 20 mm was collected in parallel to the extrusion direction, and the extruded parallel cross section of the non-welded portion was etched with a Keller solution, and then the outer surface (hollow material). The microstructure of the part corresponding to the outer surface of was observed. The test material having a surface recrystallized layer thickness of 20 μm or more was judged to have reduced SCC resistance due to the thick surface recrystallized layer, and “x” was given in the microstructure column of Table 2. When the surface recrystallized layer thickness was less than 20 μm, it was judged that there was no problem in the microstructure itself, and a circle was given in the column of microstructure in Table 2. Note that FIG. 21 is a microstructure (micrograph) of the specimen 21. The thickness of the surface recrystallized layer is indicated by a double arrow, and coarsened surface recrystallized grains are observed.
表2に示すように、No.1〜12(このうち本発明の規定範囲内の組成を有するものはNo.2,7,8)は、耐力及び伸びが大きく、同時に押出性と耐SCC性にも優れている。No.3はZn量が6.3質量%を超えているが、CuとAgの両方が添加されたことにより耐SCC性が優れる。No.10はZn量が6.3質量%を超え、Agの添加がないことにより、他の実施例に比べて耐SCC性がやや劣る。No.11は Cuの添加がない(0.01%以下)が、Agが添加されているため、耐SCC性が優れる。 As shown in Table 2, no . Nos. 1 to 12 (of which No. 2, 7 and 8 have compositions within the specified range of the present invention) have high yield strength and elongation, and at the same time are excellent in extrudability and SCC resistance. No. No. 3 has a Zn content exceeding 6.3% by mass, but is excellent in SCC resistance due to the addition of both Cu and Ag. No. No. 10 has a Zn content exceeding 6.3% by mass and no addition of Ag, so that the SCC resistance is slightly inferior to other examples. No. 11 has no addition of Cu (0.01% or less), but has excellent SCC resistance because Ag is added.
これに対し、No.13はZn量が下限未満であるためMgZn2量が少なく、強度が低い。No.14はZn量が7.0%を超えているため、CuとAgの両方が添加されているが、耐SCC性が低い。No.15は過剰Zn側(Mg含有量が前記(2)式の下限以下)であるためMgZn2量が少なく、強度が低い。No.16は過剰Mg量が多すぎる(Mg含有量が前記(2)式の上限超え)ため押出性が低く、さらにZn+4.7Mgが前記(3)式の上限を超えているため耐SCC性が低い。No.17は過剰Mg量が多すぎる(Mg含有量が前記(2)式の上限超え)ため押出性が低い。No.18はZn+4.7Mgが前記(3)式の上限を超えているため耐SCC性が低い。   In contrast, no. Since the amount of Zn is less than the lower limit, the amount of MgZn2 is small and the strength is low. No. Since the amount of Zn exceeds 7.0%, both Cu and Ag are added, but the SCC resistance is low. No. 15 is an excess Zn side (Mg content is lower than or equal to the lower limit of the formula (2)), so the amount of MgZn2 is small and the strength is low. No. No. 16 has too much excess Mg (Mg content exceeds the upper limit of the formula (2)), so the extrudability is low, and further Zn + 4.7 Mg exceeds the upper limit of the formula (3), so the SCC resistance is low. . No. No. 17 has an excessive amount of excess Mg (Mg content exceeds the upper limit of the formula (2)), so the extrudability is low. No. No. 18 has low SCC resistance because Zn + 4.7Mg exceeds the upper limit of the formula (3).
No.19はCu量及びAg量が下限未満であるため耐SCC性が低い。No.20はCu量が上限を超えているため押出性が低く、さらに焼入れ感受性が鋭く、空冷では焼き入れできず強度が低い。No.21はMn、Cr及びZrがいずれも下限未満であるため表面再結晶粒が粗大化し(図3参照)、耐SCC性が低い。No.19はZrが上限を超えているため粗大晶出物が形成し、伸びが低い。   No. No. 19 has low SCC resistance because the amount of Cu and the amount of Ag are less than the lower limit. No. No. 20 has a low extrudability due to the Cu amount exceeding the upper limit, and further has a sharp quenching sensitivity, which cannot be quenched by air cooling and has a low strength. No. Since Mn, Cr, and Zr are all below the lower limit, surface recrystallized grains are coarsened (see FIG. 3), and SCC resistance is low. No. In No. 19, since Zr exceeds the upper limit, coarse crystals are formed and elongation is low.

Claims (2)

  1. Mgの質量%を[Mg]、Znの質量%を[Zn]としたとき、[Mg]と[Zn]が下記3式を満たし、
    5.43≦[Zn]≦7.0
    [Zn]/5.38+0.15≦[Mg]≦[Zn]/5.38+0.7
    [Zn]+4.7[Mg]≦12
    さらに、Cu:0.1〜0.6質量%,Ag:0.01〜0.15質量%の1種又は2種と、Ti:0.005〜0.05質量%と、Mn:0.1〜0.3質量%,Cr:0.05〜0.2質量%,Zr:0.05〜0.2質量%の1種又は2種以上を含み、残部Al及び不可避不純物からなり、ダイクエンチ空冷及び時効処理を行ったことを特徴とする耐応力腐食割れ性に優れた自動車エネルギー吸収部材用高強度アルミニウム合金押出材。
    When the mass% of Mg is [Mg] and the mass% of Zn is [Zn], [Mg] and [Zn] satisfy the following three formulas,
    5.43 ≦ [Zn] ≦ 7.0
    [Zn] /5.38+0.15≦ [Mg] ≦ [Zn] /5.38+0.7
    [Zn] +4.7 [Mg] ≦ 12
    Furthermore, Cu: 0.1-0.6 mass%, Ag: 0.01-0.15 mass% 1 type or 2 types, Ti: 0.005-0.05 mass%, Mn: 0.0. 1 to 0.3 wt%, Cr: 0.05 to 0.2 mass%, Zr: include one or more of 0.05 to 0.2 wt%, Ri Do the balance Al and inevitable impurities, A high-strength aluminum alloy extruded material for automobile energy absorbing members excellent in stress corrosion cracking resistance, characterized by performing die quench air cooling and aging treatment .
  2. バンパーレインフォース用であることを特徴とする請求項1に記載された耐応力腐食割れ性に優れた自動車エネルギー吸収部材用高強度アルミニウム合金押出材。The high-strength aluminum alloy extruded material for automobile energy absorbing members excellent in stress corrosion cracking resistance according to claim 1, wherein the extruded material is used for bumper reinforcement.
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