JP3594272B2

JP3594272B2 - High strength aluminum alloy for welding with excellent stress corrosion cracking resistance

Info

Publication number: JP3594272B2
Application number: JP12457396A
Authority: JP
Inventors: 富晴沖田; 康人中井
Original assignee: Furukawa Sky Aluminum Corp
Current assignee: Furukawa Sky Aluminum Corp
Priority date: 1995-06-14
Filing date: 1996-05-20
Publication date: 2004-11-24
Anticipated expiration: 2016-05-20
Also published as: JPH09279284A

Description

【０００１】
【産業上の利用分野】
本発明は、圧延材、押出材、鍛造材として溶接構造材に用いられる高力アルミニウム合金に関し、さらに詳しくは、４５０Ｎ／ｍｍ^２以上の引張強さが得られ、しかも耐応力腐食割れ性に優れた溶接用Ａｌ−Ｚｎ−Ｍｇ系高力アルミニウム合金に関するものである。
【０００２】
【従来の技術】
近年、建築、車両、船舶、航空機等においては、益々薄肉軽量化が進み、溶接可能でしかも、引張強さが４５０Ｎ／ｍｍ^２以上得られる高力アルミニウム合金の要求が高まって来ている。従来、これらの用途に対するアルミニウム合金としては、Ａｌ−Ｚｎ−Ｍｇ系合金やＡｌ−Ｚｎ−Ｍｇ−Ｃｕ合金が考えられてきた。
【０００３】
【発明が解決しようとする課題】
この種の高力アルミニウム合金は、Ｚｎ，Ｍｇ量を増加するに従って高強度になるが、それに伴って応力腐食割れ感受性や溶接割れ感受性が高くなる傾向があり、又、圧延、押出、鍛造等の熱間加工性も劣化してくる。
圧延、押出、鍛造等の成形が可能で、構造材に用いられる高力アルミニウム合金として代表的なものにＡ７０７５合金がある。該合金の引張強さは、４５０Ｎ／ｍｍ^２以上で、アルミニウム合金の中でも最高に属するが、溶接性が著しく劣り、接合はボルト締め、リベット等の機械的接合によらなければならない。又、該合金は、応力腐食割れ感受性が高いため、従来は本来最高強度が得られる熱処理であるＴ６処理では，応力腐食割れが起こる危険があるため、それよりさらに高い温度又は長い時間の焼き戻しを行い、組織を安定化させたＴ７処理で使用することが多い。
【０００４】
７０００系アルミニウム合金の中で、圧延、押出、鍛造等の成形が可能で、しかも溶接性、耐応力腐食割れ性に優れたアルミニウム合金としてはＡ７Ｎ０１が良く知られている。又、押出性の良好なＡ７００３も溶接性、耐応力腐食割れ性に優れたアルミニウム合金である。しかしながらこれらの合金では強度が４５０Ｎ／ｍｍ^２未満であり、更に強度を要する用途には適さなかった。上記のごとく従来の技術では、引張強さ４５０Ｎ／ｍｍ^２以上で、耐応力腐食割れ性、溶接性の全ての面で満足が得られ、しかも押出、圧延、鍛造等の成形性にも優れたアルミニウム合金を得ることは甚だ困難であった。
【０００５】
本発明は、従来の技術では解決できなかった、引張強さ４５０Ｎ／ｍｍ^２以上で、耐応力腐食割れ性、溶接性の全ての面で満足が得られ、しかも、押出、圧延、鍛造等の成形性にも優れた材料を提供することを目的とするものである。
【０００６】
【課題を解決するための手段】
本発明は上記の点に鑑み種々検討の結果、引張強さ４５０Ｎ／ｍｍ2 以上で、耐応力腐食割れ性、溶接性の全ての面で満足が得られ、しかも、押出、圧延、鍛造等の成形性にも優れた溶接用高力アルミニウム合金を開発したものである。即ち、本願請求項１の発明は、Ｚｎ４〜８重量％、Ｍｇ０．３〜３．０重量％、Ｓｃ０．０３〜３．０重量％、Ａｇ０．０３〜１．０重量％を含有し、かつ、Ｔｉ０．００５〜０．２重量％、Ｂ０．０００１〜０．０８重量％のうち少なくとも１種を含み、且つＭｎ０．０１〜１．５重量％、Ｃｒ０．０１〜０．６重量％、Ｖ０．０１〜０．５重量％、Ｎｉ０．０５〜３．０重量％、Ｍｏ０．０１〜０．５重量％のうち少なくとも１種を含有し、残部アルミニウムおよび不可避不純物からなり、限界押出速度が１ｍ／ｍｉｎ以上、引張強さ４５０Ｎ／ｍｍ² 以上、応力腐食割れ試験結果割れ発生迄の日数が３０日を越え、溶接割れ試験結果割れ長さが３０ｍｍ未満であることを特徴とする耐応力腐食割れ性、溶接性、成形性に優れた溶接用高力アルミニウム合金でいる。
【０００７】
また、本願請求項２の発明は、Ｚｎ４〜８重量％、Ｍｇ０．３〜３．０重量％、Ｓｃ０．０３〜３．０重量％、Ａｇ０．０３〜１．０重量％を含有し、かつ、Ｔｉ０．００５〜０．２重量％、Ｂ０．０００１〜０．０８重量％のうち少なくとも１種を含み、且つＭｎ０．０１〜１．５重量％、Ｃｒ０．０１〜０．６重量％、Ｖ０．０１〜０．５重量％、Ｎｉ０．０５〜３．０重量％、Ｍｏ０．０１〜０．５重量％のうち少なくとも１種を含有し、更にＣｕ０．３〜３．５重量％、Ｚｒ０．０１〜０．２５重量％、希土類元素（Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍのうち１種または２種以上）０．０３〜５．０重量％、のうち１種または２種以上を含有し、残部アルミニウムおよび不可避不純物からなり、限界押出速度が１ｍ／ｍｉｎ以上、引張強さ４５０Ｎ／ｍｍ² 以上、応力腐食割れ試験結果割れ発生迄の日数が３０日を越え溶接割れ試験結果割れ長さが３０ｍｍ未満であることを特徴とする耐応力腐食割れ性、溶接性、成形性に優れた溶接用高力アルミニウム合金できる。
【０００８】
【作用】
以下、本願発明の溶接用高力アルミニウム合金について、添加元素の役割とその含有量の限定理由を説明する。
Ｚｎは、本合金の強度向上に寄与し、４５０Ｎ／ｍｍ^２以上の引張強さを得るためには不可欠の元素である。Ｚｎが４重量％未満では十分な強度が得られず、８重量％を越えると耐応力腐食割れ性、溶接性、加工性が劣化する。従って、Ｚｎは４〜８重量％とするが、最も好ましい範囲は、５〜７．５重量％である。
【０００９】
Ｍｇは、Ｚｎと同様に本合金の強度向上に寄与し、４５０Ｎ／ｍｍ^２以上の引張強さを得るためには不可欠な元素である。Ｍｇが０．３重量％未満では十分な強度が得られず、３．０重量％を越えると耐応力腐食割れ性、溶接性、加工性が劣化する。従って、Ｍｇは０．３〜３．０重量％とするが、最も好ましい範囲は１．０〜２．８重量％である。
Ｓｃは、耐溶接割れ性や耐応力腐食割れ性を改善する効果があり、また、本合金の強度向上に寄与し、４５０Ｎ／ｍｍ^２以上の引張強さを得るためには不可欠な元素である。Ｓｃが０．０３重量％未満ではその効果が少なく、３．０重量％を越えて含有させると強度、加工性を劣化させる危険がある。従って、Ｓｃは０．０３〜３．０とするが、最も好ましい範囲は、０．１〜２．５重量％である。
【００１０】
Ｔｉ、及びＢは、組織を微細化し、溶接性を向上させる元素である。Ｔｉは、０．００５重量％未満ではその効果が少なく、０．２重量％を越えると巨大化合物が発生し、靱性、加工性が劣化する危険性がある。従って、Ｔｉは、０．００５〜０．２重量％とするが、最も好ましい範囲は、０．００８〜０．１重量％である。
Ｂは、０．０００１重量％未満では結晶粒微細化の効果が少なく、０．０８重量％を越えて含有されると、靱性、加工性を劣化させる危険がある。従って、Ｂは、０．０００１〜０．０８重量％とする。
【００１１】
Ｍｎ、Ｃｒ、Ｖ、Ｎｉ、Ｍｏは、それぞれ耐応力腐食割れ性を向上させるとともに強度の改善をはかる効果があり、１種または２種以上添加する。含有量がＭｎ：０．０１重量％未満、Ｃｒ：０．０１重量％未満、Ｖ：０．０１重量％未満、Ｎｉ：０．０５重量％未満、Ｍｏ：０．０１重量％未満では上記効果が無い。また、それぞれＭｎ：１．５重量％、Ｃｒ：０．６重量％、Ｖ：０．５重量％、Ｎｉ：３．０重量％、Ｍｏ：０．５重量％を越えて含有されると巨大晶出物が発生し、靱性、加工性を劣化させる等の危険がある。従って、Ｍｎは０．０１〜１．５重量％、Ｃｒは０．０１〜０．６重量％、Ｖは０．０１〜０．５重量％、Ｎｉは０．０５〜３．０重量％、Ｍｏは０．０１〜０．５重量％とするが、最も好ましい範囲は、Ｍｎ：０．１〜１．０重量％、Ｃｒ：０．０５〜０．４重量％、Ｖ：０．０５〜０．３重量％、Ｎｉ：０．１〜２．０重量％、Ｍｏ：０．０３〜０．３重量％である。
【００１２】
Ａｇは、耐応力腐食割れ性および強度を向上させる効果がある。Ａｇが０．０３重量％未満ではその効果が少なく、１．０重量％を越えると加工性、溶接性が劣化する。従って、Ａｇは０．０３〜１．０重量％とするが、最も好ましい範囲は、０．０５〜０．７重量％である。
Ｃｕは、耐応力腐食割れ性および強度を向上させる効果がある。Ｃｕが０．３重量％未満ではその効果が少なく、３．５重量％を越えると加工性、溶接性が劣化する。従って、Ｃｕは０．３〜３．５重量％とするが、最も好ましい範囲は、０．５〜３．０重量％である。
【００１３】
Ｚｒは、溶接性および強度を向上させる効果があり、Ｓｃ、と一緒に添加することによって強度は更に増大する。Ｚｒが０．０３重量％未満ではその効果が少なく、０．２５重量％を越えると強度、加工性が劣化する。従って、Ｚｒは０．０３〜０．２５重量％とするが、最も好ましい範囲は、０．０５〜０．２重量％である。
【００１４】
希土類元素は溶接性および強度を向上させる効果があり、Ｓｃ、Ｚｒと一緒に添加することによって硬化は更に増大する。希土類元素が０．０３重量％未満ではその効果が少なく、５．０重量％を越えると強度、加工性が劣化する。従って、希土類元素は０．０３〜５．０重量％とするが、最も好ましい範囲は、０．０５〜３．０重量％である。
【００１５】
尚、希土類元素としては、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍ等のうち１種または２種以上を用いることができ、これらのうちのいずれか１種の量、あるいは２種以上の合計量が０．０３〜５．０重量％の範囲内であればよい。これらのうち２種類以上を含む合金としては、例えばＣｅ、Ｌａを主成分とするミッシュメタル（通常Ｃｅ４５〜５０重量％、Ｌａ２０〜４０重量％、残部その他の希土類元素（Ｐｒ、Ｎｄ、Ｓｍ等）からなる）を用いることができる。上記希土類元素のうちのいずれか１種、或いはミッシュメタルは、いずれも同等の効果を示すが、希土類元素単体では高価であり、ミッシュメタルとして添加する方が経済的に有利である。
【００１６】
【実施例】
次に本発明の一実施例について説明する。表１〜４に示す組成の合金（参考例Ｎｏ．１〜３２、本発明合金Ｎｏ．３３〜３５、参考例Ｎｏ．３６〜４７、比較合金Ｎｏ．４８〜７６、および従来合金Ｎｏ．７７〜７９）を半連続水冷鋳造装置を用いて、押出用鋳塊（９インチ径）に鋳造した。この鋳塊を４７０℃で１２時間均質化処理した後、４３０℃に加熱し、それぞれ厚さ５ｍｍ、幅１００ｍｍの平角材に押出した。押出加工するに際して、前記平角材が表面欠陥や割れ発生が無く押出し得る最高押出速度（限界押出速度）をもって、各合金の押出性の良否を◎、○、×の３段階で評価し、その結果を表５〜８に示した。評価基準は下記の通りである。
◎・・押出速度がＡ７００３の限界押出速度（１８ｍ／ｍｉｎ）を越える。
○・・押出速度がＡ７０７５の限界押出速度（１ｍ／ｍｉｎ）以上で、Ａ７００３の限界押出速度以下。
×・・押出速度がＡ７０７５の限界押出速度未満。
【００１７】
各々の材料は押出後、４６０℃で１時間の溶体化処理後焼入し、１２０℃で２４時間の焼戻し処理を行った。
このようにして製造した材料について、引張試験、応力腐食割れ試験、および溶接割れ試験を行い、その結果を表５〜８に併記した。なお，試験方法は下記に示す通りである。
（１）引張試験
（ａ）試験片：ＪＩＳＺ２２０１の５号試験片
（ｂ）試験方法：アムスラー万能試験機を用いて、ＪＩＳＺ２２４１に基づき試験する。
（ｃ）測定値：引張強さを測定し、次の基準で判定する。
◎・・引張強さ５００Ｎ／ｍｍ^２以上
○・・引張強さ４５０Ｎ／ｍｍ^２以上で５００Ｎ／ｍｍ^２未満
×・・引張強さ４５０Ｎ／ｍｍ^２未満
【００１８】
（２）応力腐食割れ試験
（ａ）試験片：ＪＩＳＨ８７１１の１号試験片
（ｂ）試験方法：ＪＩＳＨ８７１１基づく。
応力負荷：１号試験片用ジグを用いて耐力の７５％を負荷
試験液、浸漬：３．５％ＮａＣｌ液、交互浸漬（周期：１０分浸漬、５０分乾燥）３０日間。
（ｃ）評価：応力腐食割れ発生の有無観察。
×・・・３０日以内に割れ発生。
○・・・３０日を越え６０日以内に割れ発生。
◎・・・６０日を越えても割れ発生せず。
【００１９】
（３）溶接割れ試験

【００２０】
【表１】

【００２１】
【表２】

【００２２】
【表３】

【００２３】
【表４】

【００２４】
【表５】

【００２５】
【表６】

【００２６】
【表７】

【００２７】
【表８】

【００２８】
表５〜６から明らかな様に、本発明合金Ｎｏ．３２〜３５はいずれも、押出加工性、強度、耐応力腐食割れ性、溶接性の全てにおいて優れている。一方、表７〜８から明らかな様に、比較合金Ｎｏ．４８〜７６、および従来合金Ｎｏ．７７〜７９は、上記特性の内のいずれかにおいて劣っている。
【００２９】
【発明の効果】
以上のように本発明の溶接用高力アルミニウム合金は、高強度で、耐応力腐食割れ性に優れており、しかも溶接性、熱間加工性にも優れており、溶接構造材の薄肉軽量化の要請に好適に対応し得る等、工業上顕著な効果を奏する。
【図面の簡単な説明】
【図１】フィッシュボーン形割れ試験片の形状（溶接後）を示す平面説明図。
１・・・・フィッシュボーン形割れ試験片
１ａ・・・溶接ビード
１ｂ・・・溶接割れ
１ｃ・・・割れ長さ
１ｄ・・・溶接方向
２・・・・切り込み[0001]
[Industrial applications]
The present invention relates to a high-strength aluminum alloy used for a welded structural material as a rolled material, an extruded material, and a forged material. More specifically, the present invention can provide a tensile strength of 450 N / mm ² or more and is excellent in stress corrosion cracking resistance. Al-Zn-Mg based high strength aluminum alloy for welding.
[0002]
[Prior art]
In recent years, in buildings, vehicles, ships, aircrafts, and the like, thinner and lighter weights have been increasingly promoted, and there has been an increasing demand for high-strength aluminum alloys that can be welded and have a tensile strength of 450 N / mm ² or more. Conventionally, Al-Zn-Mg-based alloys and Al-Zn-Mg-Cu alloys have been considered as aluminum alloys for these applications.
[0003]
[Problems to be solved by the invention]
This type of high-strength aluminum alloy has a higher strength as the amount of Zn and Mg increases, but tends to have higher stress corrosion cracking susceptibility and weld cracking susceptibility. Hot workability also deteriorates.
A7075 alloy is a typical example of a high-strength aluminum alloy that can be formed by rolling, extrusion, forging, or the like, and is used as a structural material. The tensile strength of the alloy is 450 N / mm ² or more and belongs to the highest among aluminum alloys. However, the weldability is remarkably poor, and the joining must be performed by mechanical joining such as bolting and rivets. In addition, since the alloy has high sensitivity to stress corrosion cracking, there is a risk that stress corrosion cracking may occur in the T6 treatment, which is conventionally a heat treatment that originally obtains the highest strength, so that tempering at a higher temperature or for a longer time is performed. And often used in T7 treatment to stabilize the tissue.
[0004]
Among the 7000 series aluminum alloys, A7N01 is well known as an aluminum alloy that can be formed by rolling, extrusion, forging, etc., and is excellent in weldability and stress corrosion cracking resistance. A7003, which has good extrudability, is also an aluminum alloy excellent in weldability and stress corrosion cracking resistance. However, these alloys had a strength of less than 450 N / mm ² and were not suitable for applications requiring further strength. As described above, according to the conventional technology, a tensile strength of 450 N / mm ² or more satisfies all aspects of stress corrosion cracking resistance and weldability, and also has excellent moldability such as extrusion, rolling, and forging. Obtaining an aluminum alloy was extremely difficult.
[0005]
The present invention has a tensile strength of 450 N / mm ² or more, which cannot be solved by conventional techniques, and is satisfactory in all aspects of stress corrosion cracking resistance and weldability. It is an object of the present invention to provide a material having excellent moldability.
[0006]
[Means for Solving the Problems]
In view of the above points, the present invention has been subjected to various studies, and as a result, it has a tensile strength of 450 N / mm2 or more, and is satisfactory in all aspects of stress corrosion cracking resistance and weldability. We have developed a high-strength aluminum alloy for welding that has excellent weldability. That is, the invention of claim 1 of the present application includes 4 to 8% by weight of Zn, 0.3 to 3.0% by weight of Mg, 0.03 to 3.0% by weight of Sc, and 0.03 to 1.0% by weight of Ag. And at least one of 0.005 to 0.2% by weight of Ti and 0.0001 to 0.08% by weight of Mn, and 0.01 to 1.5% by weight of Mn and Cr 0.01 -0.6% by weight, V 0.01-0.5% by weight, Ni 0.05-3.0% by weight, Mo 0.01-0.5% by weight, the balance being aluminum The critical extrusion speed is at least 1 m / min, the tensile strength is at least 450 N / mm ² , the number of days until the occurrence of cracks in the stress corrosion cracking test exceeds 30 days, and the crack length in the welding crack test is less than 30 mm Excellent in stress corrosion cracking resistance, weldability, and formability We are in contact for high-strength aluminum alloy.
[0007]
In addition, the invention of claim 2 of the present application includes 4 to 8% by weight of Zn, 0.3 to 3.0% by weight of Mg, 0.03 to 3.0% by weight of Sc, and 0.03 to 1.0% by weight of Ag. And at least one of 0.005 to 0.2% by weight of Ti and 0.0001 to 0.08% by weight of Mn, and 0.01 to 1.5% by weight of Mn and Cr 0.01 -0.6% by weight, V 0.01-0.5% by weight, Ni 0.05-3.0% by weight, Mo 0.01-0.5% by weight, and further Cu 0.3 to 3.5% by weight, Zr 0.01 to 0.25% by weight, rare earth element (one or more of La, Ce, Pr, Nd and Sm) 0.03 to 5.0% by weight %, One or more of the above, and the balance consists of aluminum and unavoidable impurities, and the limit extrusion speed is 1 m / min or more. , Tensile strength of 450 N / mm ² or more, the stress corrosion cracking resistance days 30 days beyond weld cracking test results crack length of up to stress corrosion cracking test results cracking is equal to or less than 30 mm, weldability A high strength aluminum alloy for welding with excellent formability.
[0008]
[Action]
Hereinafter, the role of the additive element and the reason for limiting the content of the high-strength aluminum alloy for welding of the present invention will be described.
Zn contributes to improving the strength of the present alloy and is an essential element for obtaining a tensile strength of 450 N / mm ² or more. If Zn is less than 4% by weight, sufficient strength cannot be obtained, and if it exceeds 8% by weight, stress corrosion cracking resistance, weldability and workability deteriorate. Therefore, Zn is 4 to 8% by weight, and the most preferable range is 5 to 7.5% by weight.
[0009]
Mg contributes to the improvement of the strength of the present alloy similarly to Zn, and is an indispensable element for obtaining a tensile strength of 450 N / mm ² or more. If Mg is less than 0.3% by weight, sufficient strength cannot be obtained, and if it exceeds 3.0% by weight, stress corrosion cracking resistance, weldability and workability deteriorate. Therefore, Mg is 0.3 to 3.0% by weight, and the most preferable range is 1.0 to 2.8% by weight.
Sc has an effect of improving weld cracking resistance and stress corrosion cracking resistance, and also contributes to improvement of the strength of the present alloy, and is an indispensable element for obtaining a tensile strength of 450 N / mm ² or more. . If Sc is less than 0.03% by weight, the effect is small, and if it exceeds 3.0% by weight, strength and workability may be deteriorated. Therefore, Sc is set to 0.03 to 3.0, and the most preferable range is 0.1 to 2.5% by weight.
[0010]
Ti and B are elements that refine the structure and improve the weldability. If Ti is less than 0.005% by weight, its effect is small, and if it exceeds 0.2% by weight, a giant compound is generated, and there is a risk that toughness and workability are deteriorated. Therefore, Ti is made 0.005 to 0.2% by weight, and the most preferable range is 0.008 to 0.1% by weight.
When B is less than 0.0001% by weight, the effect of refining the crystal grains is small, and when B is contained in excess of 0.08% by weight, there is a risk that toughness and workability are deteriorated. Therefore, B is set to 0.0001 to 0.08% by weight.
[0011]
Mn, Cr, V, Ni, and Mo each have an effect of improving stress corrosion cracking resistance and improving strength, and one or more of them are added. When the content is Mn: less than 0.01% by weight, Cr: less than 0.01% by weight, V: less than 0.01% by weight, Ni: less than 0.05% by weight, and Mo: less than 0.01% by weight, the above effect is obtained. There is no. In addition, if the content of Mn exceeds 1.5% by weight, Cr: 0.6% by weight, V: 0.5% by weight, Ni: 3.0% by weight, and Mo: 0.5% by weight, the content becomes huge. There is a danger that crystallized substances are generated and toughness and workability are deteriorated. Therefore, Mn is 0.01 to 1.5% by weight, Cr is 0.01 to 0.6% by weight, V is 0.01 to 0.5% by weight, Ni is 0.05 to 3.0% by weight, Mo is 0.01 to 0.5% by weight, but the most preferable ranges are Mn: 0.1 to 1.0% by weight, Cr: 0.05 to 0.4% by weight, and V: 0.05 to 0.5% by weight. 0.3% by weight, Ni: 0.1 to 2.0% by weight, Mo: 0.03 to 0.3% by weight.
[0012]
Ag has an effect of improving stress corrosion cracking resistance and strength. If the content of Ag is less than 0.03% by weight, the effect is small, and if the content exceeds 1.0% by weight, workability and weldability are deteriorated. Therefore, the content of Ag is set to 0.03 to 1.0% by weight, and the most preferable range is 0.05 to 0.7% by weight.
Cu has the effect of improving stress corrosion cracking resistance and strength. If Cu is less than 0.3% by weight, the effect is small, and if it exceeds 3.5% by weight, workability and weldability deteriorate. Therefore, Cu is set to 0.3 to 3.5% by weight, and the most preferable range is 0.5 to 3.0% by weight.
[0013]
Zr has the effect of improving weldability and strength, and the strength is further increased by adding Zr together with Sc. If Zr is less than 0.03% by weight, the effect is small, and if Zr exceeds 0.25% by weight, strength and workability deteriorate. Therefore, Zr is made 0.03 to 0.25% by weight, and the most preferable range is 0.05 to 0.2% by weight.
[0014]
Rare earth elements have the effect of improving weldability and strength, and the addition of Sc and Zr further increases the hardening. If the rare earth element is less than 0.03% by weight, the effect is small, and if it is more than 5.0% by weight, strength and workability deteriorate. Therefore, the rare earth element is used in an amount of 0.03 to 5.0% by weight, and the most preferable range is 0.05 to 3.0% by weight.
[0015]
As the rare earth element, one, two or more of La, Ce, Pr, Nd, Sm and the like can be used, and the amount of any one of these or the total amount of two or more of them can be used. What is necessary is just to be in the range of 0.03-5.0 weight%. As an alloy containing two or more of these, for example, a misch metal containing Ce and La as main components (usually 45 to 50% by weight of Ce, 20 to 40% by weight of La, and the rest other rare earth elements (Pr, Nd, Sm, etc.)) Consisting of). Any one of the above rare earth elements or a misch metal exhibits the same effect, but the rare earth element alone is expensive, and it is economically advantageous to add it as a misch metal.
[0016]
【Example】
Next, an embodiment of the present invention will be described. Alloys having compositions shown in Tables 1 to 4 ( Reference Examples Nos. 1 to 32, inventive alloys Nos. 33 to 35, reference examples Nos . 36 to 47 , comparative alloys Nos. 48 to 76, and conventional alloys Nos. 77 to 77) 79) was cast into an ingot for extrusion (9-inch diameter) using a semi-continuous water-cooled casting apparatus. The ingot was homogenized at 470 ° C. for 12 hours, heated to 430 ° C., and extruded into a rectangular material having a thickness of 5 mm and a width of 100 mm. At the time of extrusion, the extrudability of each alloy was evaluated on a three-point scale of ◎, 、, and × at the maximum extrusion speed (limit extrusion speed) at which the rectangular material could be extruded without surface defects or cracks. Are shown in Tables 5 to 8. The evaluation criteria are as follows.
A: The extrusion speed exceeds the limit extrusion speed of A7003 (18 m / min).
・ · The extrusion speed is equal to or higher than the limit extrusion speed of A7075 (1 m / min) and equal to or lower than the limit extrusion speed of A7003.
X: The extrusion speed is less than the limit extrusion speed of A7075.
[0017]
After extrusion, each material was quenched after solution treatment at 460 ° C. for 1 hour and tempered at 120 ° C. for 24 hours.
The materials thus produced were subjected to a tensile test, a stress corrosion cracking test, and a weld cracking test, and the results are shown in Tables 5 to 8. The test method is as shown below.
(1) Tensile test (a) Test piece: No. 5 test piece of JIS Z 2201 (b) Test method: A test is performed based on JIS Z 2241 using an Amsler universal testing machine.
(C) Measured value: The tensile strength is measured and determined according to the following criteria.
◎ less than ... tensile strength of 500N / mm ² or more ○ ·· tensile strength of 450N / mm ² or more × less than 500N / mm ² at ... tensile strength of 450N / mm ² [0018]
(2) Stress corrosion cracking test (a) Test piece: No. 1 test piece of JIS H 8711 (b) Test method: Based on JIS H 8711.
Stress loading: 75% of the proof stress was loaded using a No. 1 test piece jig, a test liquid, immersion: 3.5% NaCl solution, alternate immersion (period: 10 minutes immersion, 50 minutes drying) for 30 days.
(C) Evaluation: Observation of occurrence of stress corrosion cracking.
×: Cracks occurred within 30 days.
・・・: Cracking occurred within 30 days after exceeding 30 days.
・・・: No cracking occurred even after 60 days.
[0019]
(3) Weld crack test

[0020]
[Table 1]

[0021]
[Table 2]

[0022]
[Table 3]

[0023]
[Table 4]

[0024]
[Table 5]

[0025]
[Table 6]

[0026]
[Table 7]

[0027]
[Table 8]

[0028]
As is clear from Tables 5 and 6, the alloy No. of the present invention. All of Nos. 32 to 35 are excellent in extrudability, strength, stress corrosion cracking resistance, and weldability. On the other hand, as is clear from Tables 7 and 8, Comparative Alloy No. 48 to 76, and conventional alloy Nos. 77-79 are inferior in any of the above characteristics.
[0029]
【The invention's effect】
As described above, the high-strength aluminum alloy for welding of the present invention has high strength, excellent resistance to stress corrosion cracking, and also excellent weldability and hot workability. Industrially remarkable effects, such as being able to appropriately respond to the request of
[Brief description of the drawings]
FIG. 1 is an explanatory plan view showing the shape (after welding) of a fishbone-shaped cracked test piece.
1 ··· Fishbone type crack test piece 1a · · · Weld bead 1b · · · Weld crack 1c · · · Crack length 1d · · · Welding direction 2 ··· Cut

Claims

It contains 4 to 8% by weight of Zn, 0.3 to 3.0% by weight of Mg, 0.03 to 3.0% by weight of Sc, and 0.03 to 1.0% by weight of Ag, and 0.005 to 1.0% of Ti. 0.2% by weight, at least one of B 0.0001 to 0.08% by weight, Mn 0.01 to 1.5% by weight, Cr 0.01 to 0.6% by weight, V 0. 0.01 to 0.5% by weight, Ni 0.05 to 3.0% by weight, Mo 0.01 to 0.5% by weight, the balance consisting of aluminum and unavoidable impurities. Stress corrosion resistance, characterized in that the number of days until crack generation is more than 30 days, and the crack length is less than 30 mm as a result of welding crack test, at least 1 m / min, tensile strength 450 N / mm ² or more, stress corrosion crack test result. High strength aluminum alloy for welding with excellent cracking, weldability and formability.

It contains 4 to 8% by weight of Zn, 0.3 to 3.0% by weight of Mg, 0.03 to 3.0% by weight of Sc, and 0.03 to 1.0% by weight of Ag, and 0.005 to 1.0% of Ti. 0.2% by weight, at least one of B 0.0001 to 0.08% by weight, Mn 0.01 to 1.5% by weight, Cr 0.01 to 0.6% by weight, V 0. 0.01 to 0.5% by weight, Ni 0.05 to 3.0% by weight, Mo 0.01 to 0.5% by weight, at least one of Cu 0.3 to 3.5% by weight, Zr 0.01 to 0.25% by weight, rare earth element (one or more of La, Ce, Pr, Nd, Sm) 0.03 to 5.0% by weight, one or more of them , The balance consisting of aluminum and unavoidable impurities, the limit extrusion speed is 1 m / min or more, and the tensile strength is 450 N / mm ² or less. The stress corrosion cracking test results The days before crack occurrence exceeds 30 days Welding crack test results The crack length is less than 30 mm For welding excellent in stress corrosion cracking resistance, weldability and formability High strength aluminum alloy.