JP3628434B2 - Drawing tube excellent in corrosion resistance and method for producing the same - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、内面の耐食性に優れる引抜きチューブを安価に製造する方法に関し、本発明により得られるチューブは熱交換器用チューブ等の内面の耐食性が必要とされる製品に好適である。
【０００２】
【従来の技術】
自動車用熱交換器の冷媒通路を構成するアルミニウム合金チューブは、例えばＪＩＳ−３００３合金製チューブ本体の内面に、ＪＩＳ−３００３合金より電気化学的に卑なＪＩＳ−７０７２合金が内張りされて内面の防食が図られている。
このようなチューブの製造方法には、圧延クラッド板を管状にロール成形しその縁端部を電縫加工する方法と、円筒状アルミニウム合金ビレットの内側に犠牲材となる円筒状内張材を嵌合した複合ビレットを熱間押出と引抜きにより製造する方法がある。
しかし、前記電縫加工法には、縁端部を溶接するため薄肉化に限界があり、溶接箇所は耐食性に劣り、さらにクラッド板の製造に高価な圧延設備を要するという問題がある。また前記嵌合式複合ビレットを用いる方法は、内張材のクラッド率のばらつきが大きく、所定のクラッド率を得ようとすると歩留まりが著しく低下し、また内張材には高度の寸法精度が要求されるため加工コストが嵩むという問題がある。
また、熱間押出成形したチューブ本体（芯材）の内面にＺｎを蒸着し、またはめっきする方法が考えられるが、蒸着法ではチューブ内面に十分なＺｎ量を安定して付着させる技術がなく、めっき法は内面にめっきするためチューブの長さが限られ生産性に劣り、いずれも実用性に欠ける。
【０００３】
【発明が解決しようとする課題】
この他、アルミニウム中空ビレットの内面にＺｎまたはＺｎ合金を溶射し、これを熱間で押出してパイプとする方法が特公昭５８−５１７７２号公報に開示されている。
この方法は安価であり、また太径の厚肉パイプの製造には有効であるが、熱交換器用チューブに代表されるような薄肉パイプの製造には適さない。その理由は、薄肉パイプを熱間押出法で直接製造するのは、熱間押出機のパワーが不足し、また肉部の厚さを十分精度良く出せないためである。
また前記公報の第４欄第２〜３行には、薄肉パイプの必要な場合は熱間押出成形後さらに引抜法で定寸に仕上げることが記載されているが、この記載にしたがって、実際に前記熱間押出後のパイプを引抜くと、溶射層が剥離し、さらにはこの剥離が原因で引抜き時にパイプが破断する場合があり、実用化できないものである。
本発明者等は、このような状況に鑑み鋭意研究を行い、溶射層と芯材との間に変形の緩衝層を形成することにより溶射層の剥離を防止できることを知見し、またビレット（芯材）に特定の合金を用いることにより溶射層の剥離を防止できることを知見し、さらに研究を進めて本発明を完成させるに至った。
本発明の目的は、内面の耐食性に優れる引抜きチューブを安価に製造する方法を提供することにある。
【０００６】
【課題を解決するための手段】
請求項１記載の発明は、円筒状アルミニウム合金ビレットの内面にZnまたはZn合金を溶射し、このビレットを管状に熱間押出し、次いでこの押出管を引抜加工するチューブの製造方法において、前記ZnまたはZn合金を溶射した円筒状アルミニウム合金ビレットに、前記熱間押出の終了よりも前に、350℃以上500℃以下の温度で1時間以上48時間以下の熱処理を施し、さらに肉厚が1mm以上10mm以下の引抜き途中の管材に300℃以上500℃以下の温度で30分以上24時間以下の熱処理を1回以上施すことを特徴とする耐食性に優れた引抜きチューブの製造方法である。
【０００７】
請求項２記載の発明は、ビレットの均質化処理の際のビレット加熱時にＺｎまたはＺｎ合金を溶射することを特徴とする請求項１に記載の耐食性に優れた引抜きチューブの製造方法である。
【０００８】
請求項３記載の発明は、ZnまたはZn合金を溶射した円筒状アルミニウム合金ビレットに施す熱処理を熱間押出の際のビレットの加熱を兼ねて施すことを特徴とする請求項１記載の耐食性に優れた引抜きチューブの製造方法である。
請求項４記載の発明は、熱間押出の際のビレット加熱時にZnまたはZn合金を溶射することを特徴とする請求項３記載の耐食性に優れた引抜きチューブの製造方法である。
【０００９】
請求項５記載の発明は、円筒状アルミニウム合金ビレットに0.05〜1.2wt%のSi、0.05〜1.2wt%のCu、0.05〜2.0wt%のFeを含有し、残部Alと不可避的不純物からなる円筒状アルミニウム合金ビレットを用い、かつ、前記円筒状アルミニウム合金ビレットの内面に溶射するZn合金としてAlを40wt%以下含有し、残部Znと不可避的不純物からなるZn-Al系合金を用いて、請求項１、２、３、４のいずれかに記載の耐食性に優れた引抜きチューブの製造方法を用いて製造されたことを特徴とする肉厚1mm以下の耐食性に優れた引抜きチューブである。
請求項６記載の発明は、円筒状アルミニウム合金ビレットに0.05〜1.2wt%のSi、0.05〜1.2wt%のCu、0.05〜2.0wt%のFeを含有し、2.0wt%以下のMn、2.0wt%以下のMg、2.0wt%以下のNi、0.3wt%以下のCr、0.3wt%以下のZr、0.3wt%以下のTi、0.3wt%以下のZnのうち1種または2種以上を含有し、残部Alと不可避的不純物からなる円筒状アルミニウム合金ビレットを用い、かつ、前記円筒状アルミニウム合金ビレットの内面に溶射するZn合金としてAlを40wt%以下含有し、残部Znと不可避的不純物からなるZn-Al系合金を用いて、請求項１、２、３、４のいずれかに記載の耐食性に優れた引抜きチューブの製造方法を用いて製造されたことを特徴とする肉厚1mm以下の耐食性に優れた引抜きチューブである。
【００１０】
【発明の実施の形態】
この発明を着想する前段階で、本発明者等は前記溶射層の剥離について種々検討し、剥離には２つのタイプがあることを見出した。
その１つは熱間押出時に生じる比較的小さな剥離で、この剥離は熱間押出パイプをそのまま使用する場合は殆ど問題にならない。特に特公昭５８−５１７７２号公報のように熱間押出パイプに熱処理を行えば、この剥離部分に周囲からＺｎが拡散するため全く問題にならない。
もう１つは、引抜きが進み管材（引抜管）の肉厚が薄くなると起きるもので、この剥離は溶射層（ＺｎまたはＺｎ合金層）と芯材（アルミニウム合金）との間の変形挙動が大きく異なるために起きる。剥離部分は耐食性が極端に低下し、剥離が生じたまま引抜きを続けると管材が破断することがある。前記の熱間押出時に生じる小さな剥離は、この引抜工程での溶射層の剥離の起点になるものである。
熱間押出後に引抜きを行う場合、製造コストの点から押出サイズはできるだけ引抜き後の製品サイズに近づけるが、前記の熱間押出時に生じる微小な剥離は、熱間押出比を上げて押出パイプの肉厚を薄くするほど生じ易くなる。
【００１１】
本発明はこのような剥離現象を踏まえて鋭意研究を進めて完成させるに至ったものである。
【００１３】
請求項１記載の発明は、内面に Zn または Zn 合金を溶射した円筒状アルミニウム合金ビレットに熱処理を施し、溶射層と芯材との間に拡散層を形成し、この拡散層に緩衝的機能を持たせて、引抜きにおける溶射層と芯材間の変形挙動の急激な変化に起因する溶射層の剥離を抑制し、さらに、引抜き時に生じる溶射層 (Zn または Zn 合金層 ) の剥離を、引抜き途中に熱処理を施すことにより抑制するものである。
この発明で、前記内面に Zn または Zn 合金を溶射した円筒状アルミニウム合金ビレットに施す熱処理の温度が 350 ℃未満で時間が１時間未満では、緩衝材となる層が十分に形成されず、熱処理温度が 500 ℃を超えると Zn の蒸発及び酸化が激しくなって十分な耐食性が得られず、また 48 時間を越える処理は加熱コストがかかり経済的でない。したがって前記ビレットの熱処理条件は 350 ℃以上 500 ℃以下の温度で１時間以上 48 時間以下に限定する。生産性と耐食性の点から 380 ℃以上 480 ℃以下で 3 時間以上 24 時間以下が特に望ましい条件である。
引抜き途中の熱処理は、肉厚が 1mm 以上 10mm 以下の管材に１回以上施して行われる。ここで熱処理を行うときの管材の肉厚を 1mm 以上 10mm 以下に限定した理由は、熱処理を 1mm 未満まで行わないと溶射層が剥離することがあり、また 10mm を超える厚さで熱処理を行っても、その後の引抜きで肉厚が薄くなると拡散層の厚さもだんだん薄くなりその効果が十分に得られなくなるためである。
熱処理の回数は、剥離を確実に防止するために 2 回以上行ってもよいが、経済的には少ない方が望ましい。熱処理は 300 ℃以上かつ 30 分以上で十分な厚さの拡散層が形成される。また 500 ℃を超えると Zn の蒸発及び酸化が激しくなり耐食性が低下する。また 24 時間を超える処理は加熱コストがかかり経済的でない上に Zn がチューブの内部にまで拡散して耐食性が逆に低下することがある。
したがって引抜き途中の管材に施す熱処理条件は 300 ℃以上 500 ℃以下の温度で 30 分以上 24 時間以下に限定するが、生産性と耐食性の点から 320 ℃以上 430 ℃以下で１時間以上４時間以下が望ましい。この熱処理は引抜き途中の管材の焼鈍を兼ねて行っても良い。
請求項１の発明は、ZnまたはZn合金を溶射した円筒状アルミニウム合金ビレットに熱処理を施したのち、さらに引抜き途中の管材に熱処理を施すもので、拡散層が厚く形成され、剥離がより確実に抑制される。
【００１４】
本発明において、熱処理で生じる拡散層も防食に役立つ。拡散層が形成された場合の腐食の進行は、表層のＺｎまたはＺｎ合金が犠牲防食層として先に溶解し、この層がなくなった後に拡散層が犠牲防食層として溶解する。
チューブをより成形性が要求される用途に用いるときは、チューブは最終焼鈍を行いＯ材等としても構わない。
このようにして製造されたチューブは、内面に犠牲防食層を有するため、特にチューブ内に冷媒を通す熱交換器用チューブ等として有用である。
【００１５】
円筒状アルミニウム合金ビレットは、アルミニウム合金の円柱ビレットを穴開け加工したり、押出により円筒状にしたり、最初から円筒状に鋳造することにより作製できる。ビレットの内面は機械的または化学的に処理し、溶射されるＺｎまたはＺｎ合金が付着し易くしておくことが望ましい。
【００１６】
円筒状アルミニウム合金ビレットの内面に溶射するＺｎまたはＺｎ合金の自然電位はアルミニウム合金ビレットの自然電位より ２００ｍＶ以上卑であることが望ましい。その理由は、溶射法で形成されるＺｎまたはＺｎ合金層の厚さは従来のクラッド法などに較べて薄いため、電位差が十分にないと防食効果が十分に発現しないためである。特には ３００ｍｖ以上卑であることが望ましい。さらに熱間押出時の成形性も考慮すると、純Ｚｎまたは Ｚｎ−Ａｌ系合金を溶射するのが望ましい。
溶射法としては、線爆溶射法が適しているが、火炎溶射法、プラズマ溶射法、ア−ク溶射法なども適用できる。
【００１７】
本発明において、溶射を熱間押出工程前に行う理由は、熱間押出時にアルミニウム合金とＺｎまたはＺｎ合金層を完全に拡散接合させるためである。
溶射はアルミニウム合金ビレットを加熱していない状態で行っても良い。それは、通常の溶射ではアルミニウム合金側を加熱していないとＺｎまたはＺｎ合金がアルミニウム合金に完全に接合しないが、本発明の場合は溶射後に行う熱間押出で完全に接合されるためである。
【００１８】
しかし、アルミニウム合金ビレットは加熱しておいた方がＺｎが付着し易く、溶射Ｚｎの歩留まりが高くなる。
アルミニウム合金ビレットを加熱して溶射を行う場合、溶射直後にそのまま拡散のための熱処理を行うとエネルギー的に効率が良い。逆にアルミニウム合金ビレットの均質化処理の際または熱間押出の際の加熱時等に、溶射を行うようにしてもエネルギー的に効率が良い。前記均質化処理での加熱とは均質化処理が完了してビレットを冷却する途中の状態も含める。
前述のように、熱間押出の際の加熱を利用して溶射や熱処理を行うと、通常行われている熱間押出の加熱時間である ０〜３０分と比較して加熱時間は長くなるが、全体的にエネルギーの節約が図れる。
【００１９】
溶射後の円筒状アルミニウム合金ビレットの熱間押出には、従来のアルミニウム合金管の熱間押出と同じ方法が適用できる。押出方法は直接押出でも間接押出でも構わない。
熱間押出された管材がチューブとして必要なサイズより大きい場合、そのサイズまで引抜きを行う。引抜きはパスの途中で中間焼鈍を入れるなど、従来と同じ方法で行えば良い。
【００２０】
本発明において、円筒状ビレットには、チューブの製造に適した熱間押出と引抜加工が可能な任意のアルミニウム合金が使用できる。その理由は、ＺｎまたはＺｎ合金（Ｚｎが５０ｗｔ％ 以上の合金）はどのようなアルミニウム合金よりも電気化学的に卑なため、どのようなアルミニウム合金に対しても防食効果を有するためである。具体的には、ＪＩＳ−３００３に代表される Ａｌ−Ｍｎ系合金、ＪＩＳ−１１００やＪＩＳ−１０５０に代表される純Ａｌ系合金、ＪＩＳ−６０６３に代表されるＡｌ−Ｍｇ−Ｓｉ系合金などが挙げられる。
【００２１】
請求項５及び６記載の発明は、ビレットに特定組成の合金を用いて溶射層の剥離を防止したものである。
以下に請求項５及び６記載の発明における合金の各添加元素の役割を述べる。
Siは強度上昇に寄与する。Siの量が0.05wt%未満ではその効果が十分でなく、1.2wt%を超えると合金の引抜き性が低下し、この発明のようなZnまたはZn-Al系合金を溶射した管材を引抜く場合、引抜き破断が生じ易くなる。したがって、Siは0.05wt%以上1.2wt%以下とするが、特に0.8wt%以下が良好な押出性が得られ望ましい。
【００２２】
Ｃｕはこの発明において最も重要な必須元素である。
ビレット内面にＺｎまたは Ｚｎ−Ａｌ系合金を溶射して押出した押出管をさらに引抜くと、溶射層（Ｚｎまたは Ｚｎ−Ａｌ系合金層）と管材（アルミニウム合金の引抜管）との間の変形挙動は大きく異なるので、引抜き工程が進み、管材の肉厚が薄くなると引抜き時に溶射層が管材から剥離してしまう。この剥離は溶射層が薄いほど生じ難くなるが、その代わり耐食性が低下する。ここでアルミニウム合金にＣｕを添加すると管材の変形抵抗が増し、溶射層の変形挙動に近づき剥離が生じ難くなる。さらにＣｕはアルミニウム合金の自然電位を高め、溶射層との電位差を増すために溶射層を薄くすることができる。Ｃｕは固溶状態で合金中に存在し強度向上にも寄与する。
Ｃｕの含有量は ０．０５ｗｔ％未満ではその効果が十分に得られず、１．２ｗｔ％を超えると合金の成形性が低下して引抜きが難しくなる。したがってＣｕの含有量は ０．０５ｗｔ％以上１．２ｗｔ％以下とするが、特には０．１ｗｔ％以上０．６ｗｔ％以下が望ましい。
【００２３】
Ｆｅは結晶粒を微細にし強度を高める作用を有する。その含有量は ０．０５ｗｔ％以下ではその効果が十分に得られず、２．０ｗｔ％を超えて添加した場合成形性が低下し、引抜き時に割れてしまう。したがってＦｅの含有量は０．０５〜２．０ｗｔ％とする。
【００２４】
２．０ｗｔ％以下のＭｎ、２．０ｗｔ％以下のＭｇ、２．０ｗｔ％以下のＮｉ、０．３ｗｔ％以下のＣｒ、０．３ｗｔ％以下のＺｒ、０．３ｗｔ％以下のＴｉ、０．３ｗｔ％以下のＺｎは強度や成形性を調整するために添加する任意添加元素である。Ｍｎ、Ｎｉ、Ｃｒ、Ｚｒ、Ｔｉを上限を超えて添加すると成形性が低下し、引抜き時に割れてしまう。またＭｇおよびＺｎを上限を超えて添加すると耐食性が低下する。
【００２５】
以上が本発明の芯材合金の成分であるが、鋳塊組織の微細化のために添加される Ｂや強度向上を目的として添加される Ｖ等、上記以外の元素はそれぞれ０．０５ｗｔ％ 以下であれば含有されていても構わない。
【００２６】
請求項５及び６記載の発明では、前記組成の円筒状アルミニウム合金ビレットの内面にZnまたは40wt%以下のアルミニウムを含有し残部Znと不可避不純物からなるZn-Al系合金を溶射し、このビレットに熱間押出を行い、さらに引抜きにより肉厚1mm以下のチューブに加工する。
この発明で、溶射するZn合金をAlを40wt%以下含有するAl-Zn系合金に限定した理由は、Alが40wt%を超えると前記組成のビレットに対して電位が十分に低くならず、本発明のような薄肉のチューブを製造する場合は十分な耐食性を確保できなくなるためである。
尚、本発明において、溶射するZnまたはZn合金は、不可避不純物が各々0.05wt%以下であれば含有されていても構わない。
【００２７】
熱間押出後の押出管は肉厚１ｍｍ以下のチューブとして必要なサイズまで引抜かれる。本発明では、引抜き中にＺｎ系合金層が剥がれ難いように芯材（ビレット）の組成を特定しているため、１ｍｍ以下の肉厚に十分引抜き可能である。引抜きは、途中で中間焼鈍を入れる等、従来通り行えばよい。
【００２８】
【実施例】
以下に本発明を実施例により具体的に説明する。
（実施例１）
ＪＩＳ−３００３またはＪＩＳ−１０５０のアルミニウム合金の円筒状ビレット （外径４００ｍｍ，内径８０ｍｍ， 長さ９９０ｍｍ）の内面にＺｎまたは Ｚｎ−Ａｌ合金を溶射し、これを熱間押出と引抜きにより肉厚 ０．９ｍｍの管材に加工した。次にこの管材を中間焼鈍を入れながら引抜いて外径３０ｍｍ、肉厚 ０．４ｍｍのチューブとした。熱間押出前のビレットの熱処理または／および引抜加工途中の管材の熱処理は適宜行った。前記円筒状ビレットは円柱ビレットを中ぐりし内面を平滑に切削加工して作製した。
【００２９】
（比較例１）
均質化処理後、Ｚｎ溶射を行わずに熱間押出し、次いで引抜きを行った。引抜き途中で熱処理は施さなかった。
【００３０】
（比較例２）
均質化処理後、Ｚｎ溶射を行ない、熱処理を施さずに熱間押出し、次いで引抜きを行った。引抜き途中で熱処理は施さなかった。
【００３１】
（従来例１）
ＪＩＳ−３００３合金板（芯材）の片面にＪＩＳ−７０７２合金板（内張材）を圧延によりクラッドした厚さ ０．４ｍｍのクラッド板をＪＩＳ−７０７２合金側を内側にして管状にロール成形し、この管状体の縁端部を電縫加工して外径３０ｍｍのチューブを作製した。クラッド板に占める内張材の断面積比は１０％とした。
【００３２】
得られたチューブを長さ５０ｍｍに切断し、これを長手方向に切り開いて板状に成形し、この板状体の外面（非Ｚｎ面）を樹脂でマスキングしてサンプルとした。
このサンプルをＯＹ水 （Ｃｌ１−３００ｐｐｍ、 ＳＯ４ ２−１００ｐｐｍ、Ｃｕ２＋１ｐｐｍ、Ｆｅ３＋３０ｐｐｍ）に浸漬し、８８℃での８時間保持と室温での１６時間保持を繰返すサイクル試験を最長５ヵ月間実施した。試験後のサンプルについて表面性状を調べた。
表面性状の結果は、５ヵ月の試験後において、貫通孔食のないものを○、貫通孔食があるものを×とした。尚、比較例２、３のものは、引抜き中に肉厚 ０．７ｍｍで破断したため、肉厚 ０．８ｍｍのチューブについて試験した。結果を、製造条件を併記して表１に示す。
【００３３】
【表１】
表１より明らかなように、本発明例品 （Ｎｏ．１〜８）は、いずれも５カ月間浸漬後も貫通孔食が発生しておらず、優れた耐食性を有している。
これに対して、比較例の Ｎｏ．９，１２はＺｎ溶射を行わなかったため、Ｎｏ．１０，１１は押出前と引抜き途中に熱処理を施さなかったため溶射層が剥離しいずれにも貫通孔食が発生した。従来品はクラッド板の製造に高価な圧延機を要しコスト高であった。
【００３５】
（実施例２）
表２のＮｏ．ａ〜ｇの組成のアルミニウム合金の円筒状ビレット （外径４００ｍｍ，内径８０ｍｍ， 長さ９９０ｍｍ）の内面に純Ｚｎまたは Ｚｎ−Ａｌ系合金を溶射し、これを熱間押出と引抜きにより外径３０ｍｍ、肉厚 ０．４ｍｍのチューブとした。引抜き途中、熱処理を適宜施した。前記円筒状ビレットは円柱ビレットを中ぐりし内面を平滑に切削加工して作製した。
【００３６】
（比較例４）
表２のＮｏ．ａ，ｅの組成のアルミニウム合金の円筒状ビレットを用い、純Ｚｎまたは Ｚｎ−Ａｌ系合金の溶射を行わなかった他は、実施例１と同じ方法により外径３０ｍｍ、肉厚 ０．４ｍｍのチューブを製造した。
【００３７】
（比較例５）
表２のＮｏ．ｈの組成のアルミニウム合金の円筒状ビレットを用いた他は、実施例１と同じ方法により外径３０ｍｍ、肉厚 ０．４ｍｍのチューブを製造した。
【００３８】
得られた各々のチューブについて実施例と同様にしてサイクル試験を行い、試験後のサンプルについて表面性状を調べた。表面性状の結果は、５ヵ月の試験後において、貫通孔食がなくかつ孔食が浅いものを◎、貫通孔食がなくかつ孔食がやや深いものを○、５ヵ月以内に貫通孔食が生じたものを×と表記した。
結果を、製造条件を併記して表３に示す。
【００３９】
【表２】
【表３】
表３より明らかなように、本発明例品 （Ｎｏ．１４ 〜２１） は、いずれも５カ月間浸漬後も貫通孔食は発生しなかった。これはチューブ本体にＣｕが含有されていてＺｎ系合金層の密着性が良好なためである。中でも引抜き途中に熱処理を施して拡散層を形成したもの（ Ｎｏ．１４，１６，１７，１９，２０，２１） は孔食が浅く耐食性が極めて優れている。
これに対して、比較例の Ｎｏ．２２，２４ はＺｎ溶射を行わなかったため、またＮｏ．２３ はビレットにＣｕが含有されていなく、又熱処理を施していないためＺｎ系合金層が剥離して、いずれにも貫通孔食が発生した。
【００４２】
【発明の効果】
以上に述べたように、本発明では、熱処理により溶射層と芯材との間に拡散層を形成することにより、あるいはビレット（芯材）の合金組成を特定することにより、引抜き時の溶射層の剥離を抑制したので、耐食性に優れるチューブが得られる。また高価な圧延設備や円筒状内張材を必要とせずチューブを安価に製造できる。依って工業上顕著な効果を奏する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a drawing tube having excellent corrosion resistance on the inner surface at a low cost, and the tube obtained by the present invention is suitable for products that require corrosion resistance on the inner surface such as a heat exchanger tube.
[0002]
[Prior art]
The aluminum alloy tube constituting the refrigerant passage of the automotive heat exchanger is, for example, an inner surface of a tube body made of JIS-3003 alloy, and JIS-7072 alloy, which is electrochemically lower than JIS-3003 alloy, is lined to prevent corrosion on the inner surface. Is planned.
In such a tube manufacturing method, a rolled clad plate is roll-formed into a tubular shape and the edge thereof is electro-sealed, and a cylindrical lining material as a sacrificial material is fitted inside a cylindrical aluminum alloy billet. There is a method for producing a combined composite billet by hot extrusion and drawing.
However, the electric seam processing method has a problem that the edge portion is welded, so that there is a limit to thinning, the welded portion is inferior in corrosion resistance, and expensive rolling equipment is required for manufacturing the clad plate. In addition, the method using the above-mentioned mating composite billet has a large variation in the cladding ratio of the lining material, and when trying to obtain a predetermined cladding ratio, the yield is remarkably reduced, and the lining material requires a high degree of dimensional accuracy. Therefore, there exists a problem that processing cost increases.
In addition, a method of vapor depositing or plating Zn on the inner surface of the tube body (core material) that has been hot-extruded is considered, but there is no technique for stably adhering a sufficient amount of Zn to the inner surface of the tube in the vapor deposition method. Since the plating method is for plating on the inner surface, the length of the tube is limited and the productivity is inferior, both of which lack practicality.
[0003]
[Problems to be solved by the invention]
In addition, Japanese Patent Publication No. 58-51772 discloses a method of spraying Zn or a Zn alloy on the inner surface of an aluminum hollow billet and extruding it hot to form a pipe.
This method is inexpensive and effective for manufacturing a thick pipe having a large diameter, but is not suitable for manufacturing a thin pipe represented by a heat exchanger tube. The reason is that the thin pipe is directly manufactured by the hot extrusion method because the power of the hot extruder is insufficient and the thickness of the meat portion cannot be obtained with sufficient accuracy.
In the fourth column, lines 2 to 3 of the above publication, if a thin pipe is necessary, it is described that after hot extrusion molding, it is further finished to a fixed size by a drawing method. When the pipe after hot extrusion is pulled out, the sprayed layer is peeled off. Further, due to this peeling, the pipe may be broken at the time of drawing out, which cannot be put into practical use.
The present inventors have conducted intensive research in view of such circumstances, and have found that the formation of a deformation buffer layer between the thermal spray layer and the core material can prevent the thermal spray layer from being peeled off, and the billet (core It has been found that the use of a specific alloy as the material can prevent the sprayed layer from being peeled off, and further research has been made to complete the present invention.
An object of the present invention is to provide a method for producing a drawing tube having excellent corrosion resistance on the inner surface at a low cost.
[0006]
[Means for Solving the Problems]
The invention according to claim 1 is a method of manufacturing a tube in which Zn or a Zn alloy is sprayed on the inner surface of a cylindrical aluminum alloy billet, the billet is hot extruded into a tube, and then the extruded tube is drawn. The cylindrical aluminum alloy billet sprayed with the Zn alloy is subjected to heat treatment at a temperature of 350 ° C. to 500 ° C. for 1 hour to 48 hours before the end of the hot extrusion, and the wall thickness is 1 mm to 10 mm. A method for producing a drawn tube having excellent corrosion resistance, characterized in that the following pipe material in the middle of drawing is subjected to heat treatment at a temperature of 300 ° C. to 500 ° C. for at least 30 minutes to 24 hours at least once.
[0007]
Invention of Claim 2 is a manufacturing method of the drawing tube excellent in corrosion resistance of Claim 1 characterized by spraying Zn or Zn alloy at the time of billet heating in the homogenization process of billet.
[0008]
According to a third aspect of the invention, excellent in corrosion resistance according to claim 1, wherein the heat treatment for applying a Zn or Zn alloy-sprayed cylindrical aluminum alloy billet also serves as the heating of the billet during the hot extrusion This is a method of manufacturing a drawn tube.
The invention described in claim 4 is the method for producing a drawn tube excellent in corrosion resistance according to claim 3 , wherein the Zn or Zn alloy is thermally sprayed during billet heating during hot extrusion.
[0009]
The invention according to claim 5 is a cylindrical aluminum alloy billet containing 0.05 to 1.2 wt% Si, 0.05 to 1.2 wt% Cu, 0.05 to 2.0 wt% Fe, the balance being Al and inevitable impurities. with Jo aluminum alloy billet, and Al as Zn alloy sprayed to the inner surface of the cylindrical aluminum alloy billet containing less 40 wt%, with Zn-Al alloy and the balance Zn and inevitable impurities, claim A drawing tube excellent in corrosion resistance having a thickness of 1 mm or less, characterized by being manufactured using the method for manufacturing a drawing tube excellent in corrosion resistance described in any one of 1 , 2 , 3 , and 4 .
The invention according to claim 6 contains 0.05 to 1.2 wt% Si, 0.05 to 1.2 wt% Cu, 0.05 to 2.0 wt% Fe, and 2.0 wt% or less of Mn, 2.0 wt% in the cylindrical aluminum alloy billet. 1% or more of Mg, 2.0 wt% or less of Ni, 0.3 wt% or less of Cr, 0.3 wt% or less of Zr, 0.3 wt% or less of Ti, 0.3 wt% or less of Ti, or 0.3 wt% or less of Zn. In addition, a cylindrical aluminum alloy billet composed of the balance Al and inevitable impurities is used, and the Zn alloy sprayed on the inner surface of the cylindrical aluminum alloy billet contains 40 wt% or less of Al, and the Zn composed of the balance Zn and inevitable impurities. Corrosion resistance of 1 mm or less in thickness, characterized in that it is manufactured by using the method of manufacturing a drawn tube having excellent corrosion resistance according to any one of claims 1, 2 , 3 , and 4 , using an Al alloy. Excellent drawing tube.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Prior to the idea of the present invention, the present inventors studied various types of peeling of the sprayed layer and found that there are two types of peeling.
One of them is a relatively small exfoliation that occurs during hot extrusion, and this exfoliation hardly poses a problem when the hot extrusion pipe is used as it is. In particular, when heat treatment is performed on a hot-extruded pipe as disclosed in Japanese Patent Publication No. 58-51772, there is no problem at all because Zn diffuses from the periphery into the peeled portion.
The other one occurs when drawing progresses and the wall thickness of the tube (drawn tube) decreases, and this delamination has a large deformation behavior between the thermal spray layer (Zn or Zn alloy layer) and the core material (aluminum alloy). It happens because it is different. The corrosion resistance of the peeled portion is extremely lowered, and the tube material may be broken if the drawing is continued while the peeling occurs. The small delamination that occurs during the hot extrusion is the starting point for delamination of the thermal spray layer in this drawing process.
When drawing after hot extrusion, the extrusion size is as close as possible to the product size after drawing from the viewpoint of manufacturing cost. However, the minute peeling that occurs during the above-mentioned hot extrusion increases the hot extrusion ratio and increases the thickness of the extruded pipe. The thinner the thickness, the more likely it is to occur.
[0011]
The present invention has been completed through extensive research based on such a peeling phenomenon.
[0013]
According to the first aspect of the present invention, a cylindrical aluminum alloy billet sprayed with Zn or a Zn alloy on the inner surface is subjected to a heat treatment, a diffusion layer is formed between the sprayed layer and the core material, and the buffer layer has a buffer function. To prevent the thermal spraying layer from peeling off due to abrupt changes in the deformation behavior between the thermal sprayed layer and the core during drawing, and to prevent the thermal spraying layer (Zn or Zn alloy layer ) from peeling during pulling. It suppresses by performing heat processing to.
In this invention, when the temperature of the heat treatment applied to the cylindrical aluminum alloy billet sprayed with Zn or Zn alloy on the inner surface is less than 350 ° C. and the time is less than 1 hour, the buffer layer is not sufficiently formed, and the heat treatment temperature If the temperature exceeds 500 ° C., the evaporation and oxidation of Zn become severe and sufficient corrosion resistance cannot be obtained, and the treatment exceeding 48 hours is expensive because of heating costs. Therefore, the heat treatment conditions for the billet are limited to a temperature of 350 ° C. or higher and 500 ° C. or lower for 1 hour or more and 48 hours or less. From the viewpoint of productivity and corrosion resistance, the conditions of 380 ° C. to 480 ° C. and 3 hours to 24 hours are particularly desirable conditions.
The heat treatment in the middle of drawing is performed once or more on a pipe material having a wall thickness of 1 mm or more and 10 mm or less. The reason for limiting the wall thickness of the pipe material to 1 mm or more and 10 mm or less when performing the heat treatment here is that the sprayed layer may peel off unless the heat treatment is performed to less than 1 mm , and the heat treatment is performed at a thickness exceeding 10 mm. However, if the thickness is reduced by subsequent drawing, the thickness of the diffusion layer is gradually reduced and the effect cannot be obtained sufficiently.
The number of heat treatments may be two or more in order to surely prevent peeling, but it is desirable that the number be reduced economically. A sufficiently thick diffusion layer is formed by heat treatment at 300 ° C. or higher and 30 minutes or longer. If the temperature exceeds 500 ° C., the evaporation and oxidation of Zn become severe and the corrosion resistance decreases. In addition, the treatment exceeding 24 hours is not economical because heating costs are added, and Zn may diffuse into the tube and the corrosion resistance may be lowered.
Therefore, the heat treatment conditions applied to the pipes during drawing are limited to 30 minutes to 24 hours at temperatures of 300 ° C to 500 ° C, but from the point of productivity and corrosion resistance, they are 320 ° C to 430 ° C for 1 hour to 4 hours. Is desirable. This heat treatment may be performed also for annealing the pipe material during drawing.
According to the first aspect of the present invention, the cylindrical aluminum alloy billet sprayed with Zn or Zn alloy is heat-treated, and then the pipe material in the middle of drawing is further heat-treated. It is suppressed.
[0014]
In the present invention, the diffusion layer produced by the heat treatment is also useful for preventing corrosion. When the diffusion layer is formed, the corrosion progresses when the surface Zn or Zn alloy is first dissolved as the sacrificial anticorrosion layer, and after this layer is removed, the diffusion layer is dissolved as the sacrificial anticorrosion layer.
When the tube is used for an application requiring more formability, the tube may be subjected to final annealing and used as an O material or the like.
The tube thus produced has a sacrificial anticorrosive layer on the inner surface, and is particularly useful as a heat exchanger tube or the like for passing a refrigerant through the tube.
[0015]
A cylindrical aluminum alloy billet can be produced by drilling a cylindrical billet of aluminum alloy, forming a cylindrical shape by extrusion, or casting into a cylindrical shape from the beginning. It is desirable that the inner surface of the billet be mechanically or chemically treated so that the sprayed Zn or Zn alloy is easily attached.
[0016]
The natural potential of Zn or Zn alloy sprayed on the inner surface of the cylindrical aluminum alloy billet is desirably 200 mV or more lower than the natural potential of the aluminum alloy billet. The reason is that the thickness of the Zn or Zn alloy layer formed by the thermal spraying method is thinner than that of the conventional cladding method and the like, and the anticorrosion effect is not sufficiently exhibited unless the potential difference is sufficient. In particular, it is desirable that it is 300 mv or more. Furthermore, considering the formability during hot extrusion, it is desirable to spray pure Zn or a Zn-Al alloy.
As the thermal spraying method, the line explosion thermal spraying method is suitable, but a flame thermal spraying method, a plasma thermal spraying method, an arc thermal spraying method and the like can also be applied.
[0017]
In the present invention, the reason why the thermal spraying is performed before the hot extrusion step is to completely diffuse and bond the aluminum alloy and the Zn or Zn alloy layer during the hot extrusion.
Thermal spraying may be performed in a state where the aluminum alloy billet is not heated. This is because Zn or Zn alloy is not completely bonded to the aluminum alloy unless the aluminum alloy side is heated in normal spraying, but in the present invention, it is completely bonded by hot extrusion performed after spraying.
[0018]
However, when the aluminum alloy billet is heated, Zn tends to adhere, and the yield of sprayed Zn increases.
When thermal spraying is performed by heating an aluminum alloy billet, energy efficiency is good if heat treatment for diffusion is performed as it is immediately after thermal spraying. On the contrary, it is energy efficient even if the thermal spraying is performed during the homogenization treatment of the aluminum alloy billet or during heating during the hot extrusion. The heating in the homogenization process includes a state in the middle of cooling the billet after the homogenization process is completed.
As described above, when thermal spraying or heat treatment is performed using heating during hot extrusion, the heating time is longer than 0 to 30 minutes, which is the heating time of hot extrusion that is normally performed. As a whole, energy can be saved.
[0019]
For the hot extrusion of the cylindrical aluminum alloy billet after thermal spraying, the same method as the conventional hot extrusion of an aluminum alloy tube can be applied. The extrusion method may be direct extrusion or indirect extrusion.
If the hot extruded tubing is larger than the size required for the tube, it is drawn to that size. Drawing may be performed by the same method as in the past, such as by performing intermediate annealing in the middle of the pass.
[0020]
In the present invention, any aluminum alloy capable of hot extrusion and drawing suitable for manufacturing a tube can be used for the cylindrical billet. The reason is that Zn or a Zn alloy (an alloy having Zn of 50 wt% or more) is electrochemically lower than any aluminum alloy, and therefore has a corrosion protection effect on any aluminum alloy. Specifically, Al-Mn alloys represented by JIS-3003, pure Al alloys represented by JIS-1100 and JIS-1050, Al-Mg-Si alloys represented by JIS-6063, etc. Can be mentioned.
[0021]
The inventions according to claims 5 and 6 prevent the thermal spraying layer from peeling off by using an alloy having a specific composition for the billet.
The role of each additive element of the alloy in the inventions of claims 5 and 6 will be described below.
Si contributes to an increase in strength. When the amount of Si is less than 0.05 wt%, the effect is not sufficient, and when it exceeds 1.2 wt%, the drawability of the alloy is reduced, and when pipes sprayed with Zn or Zn-Al alloy like this invention are drawn , Drawing breakage is likely to occur. Therefore, Si is 0.05 wt% or more and 1.2 wt% or less, but 0.8 wt% or less is particularly desirable because good extrudability is obtained.
[0022]
Cu is the most important essential element in the present invention.
Deformation between the sprayed layer (Zn or Zn-Al alloy layer) and the tube material (aluminum alloy drawn tube) when the extruded tube extruded by spraying Zn or Zn-Al alloy on the billet inner surface is further drawn Since the behavior differs greatly, if the drawing process proceeds and the thickness of the pipe material becomes thin, the sprayed layer peels off from the pipe material during drawing. This peeling is less likely to occur as the sprayed layer is thinner, but the corrosion resistance is reduced instead. Here, when Cu is added to the aluminum alloy, the deformation resistance of the pipe material increases, and the deformation behavior of the thermal spray layer is approached, so that the separation is less likely to occur. Further, Cu increases the natural potential of the aluminum alloy, and the sprayed layer can be made thinner in order to increase the potential difference from the sprayed layer. Cu exists in the alloy in a solid solution state and contributes to the improvement of strength.
If the Cu content is less than 0.05 wt%, the effect cannot be sufficiently obtained. If the Cu content exceeds 1.2 wt%, the formability of the alloy is lowered and drawing becomes difficult. Therefore, the Cu content is 0.05 wt% or more and 1.2 wt% or less, and particularly preferably 0.1 wt% or more and 0.6 wt% or less.
[0023]
Fe has the effect of increasing the strength by making the crystal grains fine. If the content is 0.05 wt% or less, the effect is not sufficiently obtained, and if it is added over 2.0 wt%, the moldability is lowered and cracking occurs during drawing. Therefore, the Fe content is 0.05 to 2.0 wt%.
[0024]
2.0 wt% or less Mn, 2.0 wt% or less Mg, 2.0 wt% or less Ni, 0.3 wt% or less Cr, 0.3 wt% or less Zr, 0.3 wt% or less Ti, Zn of 3 wt% or less is an optional additive element added to adjust strength and formability. If Mn, Ni, Cr, Zr, and Ti are added in excess of the upper limit, the formability is reduced and cracks occur during drawing. Moreover, corrosion resistance will fall when Mg and Zn are added exceeding an upper limit.
[0025]
The above are the components of the core alloy of the present invention. Elements other than the above, such as B added for refining the ingot structure and V added for the purpose of improving the strength, are each 0.05 wt% or less. If it is, it may be contained.
[0026]
According to the fifth and sixth aspects of the present invention, the inner surface of the cylindrical aluminum alloy billet having the above composition is sprayed with a Zn-Al alloy containing Zn or aluminum of 40 wt% or less and the balance being Zn and inevitable impurities. Hot extrusion is performed, and the tube is processed into a tube with a thickness of 1 mm or less by drawing.
In this invention, the reason why the Zn alloy to be sprayed is limited to the Al-Zn alloy containing 40 wt% or less of Al is that when the Al content exceeds 40 wt%, the potential is not sufficiently lowered with respect to the billet having the above composition. This is because when the thin tube as in the invention is manufactured, sufficient corrosion resistance cannot be secured.
In the present invention, the sprayed Zn or Zn alloy may be contained if the inevitable impurities are 0.05 wt% or less.
[0027]
The extruded tube after hot extrusion is drawn to a required size as a tube having a wall thickness of 1 mm or less. In the present invention, since the composition of the core material (billet) is specified so that the Zn-based alloy layer is difficult to peel off during drawing, it can be sufficiently drawn to a thickness of 1 mm or less. Drawing may be performed as usual, for example, with intermediate annealing in the middle.
[0028]
【Example】
Hereinafter, the present invention will be described specifically by way of examples.
(Example 1)
Zn or Zn-Al alloy is thermally sprayed on the inner surface of a cylindrical billet (outer diameter 400 mm, inner diameter 80 mm, length 990 mm) of JIS-3003 or JIS-1050, and this is thickened by hot extrusion and drawing 0 Processed into a 9 mm tube. Next, this tube material was pulled out while intermediate annealing was performed to obtain a tube having an outer diameter of 30 mm and a wall thickness of 0.4 mm. Heat treatment of the billet before hot extrusion and / or heat treatment of the pipe material during drawing was appropriately performed. The cylindrical billet was produced by boring a cylindrical billet and cutting the inner surface smoothly.
[0029]
(Comparative Example 1)
After the homogenization treatment, hot extrusion was performed without performing Zn spraying, followed by drawing. No heat treatment was performed during drawing.
[0030]
(Comparative Example 2)
After the homogenization treatment, Zn spraying was performed, hot extrusion was performed without heat treatment, and then drawing was performed. No heat treatment was performed during drawing.
[0031]
(Conventional example 1)
A JIS-7072 alloy plate (lining material) clad by rolling on one side of a JIS-3003 alloy plate (core material) is rolled into a tubular shape with a thickness of 0.4 mm, with the JIS-7072 alloy side facing inward. A tube having an outer diameter of 30 mm was produced by electro-sewing the edge of the tubular body. The cross-sectional area ratio of the lining material in the clad plate was 10%.
[0032]
The obtained tube was cut to a length of 50 mm, cut in the longitudinal direction and formed into a plate shape, and the outer surface (non-Zn surface) of this plate-like body was masked with a resin to prepare a sample.
This sample is immersed in OY water (Cl 1 -300 ppm, SO 4 2 -100 ppm, Cu 2+ 1 ppm, Fe 3+ 30 ppm), and a cycle test that repeats holding at 88 ° C. for 8 hours and holding at room temperature for 16 hours is a maximum of 5 cycles. Conducted for months. The surface property of the sample after the test was examined.
The results of the surface properties were evaluated as “◯” when there was no through pitting corrosion and “×” when there was through pitting corrosion after the 5-month test. Since Comparative Examples 2 and 3 were broken at a thickness of 0.7 mm during drawing, a tube having a thickness of 0.8 mm was tested. The results are shown in Table 1 together with the production conditions.
[0033]
[Table 1]
As is clear from Table 1, all of the products of the present invention (Nos. 1 to 8) have excellent corrosion resistance because no through-pitting corrosion occurs after immersion for 5 months.
In contrast, No. of the comparative example. Nos. 9 and 12 were not sprayed with Zn. In Nos. 10 and 11, heat treatment was not performed before extrusion or during drawing, so that the sprayed layer was peeled off, and through pitting corrosion occurred in both cases. The conventional product requires an expensive rolling mill for manufacturing the clad plate, and is expensive.
[0035]
(Example 2)
No. in Table 2 Pure Zn or Zn-Al alloy is sprayed on the inner surface of an aluminum alloy cylindrical billet (outer diameter 400 mm, inner diameter 80 mm, length 990 mm) of a to g, and the outer diameter is 30 mm by hot extrusion and drawing. The tube was 0.4 mm thick. During the drawing, heat treatment was appropriately performed. The cylindrical billet was produced by boring a cylindrical billet and cutting the inner surface smoothly.
[0036]
(Comparative Example 4)
No. in Table 2 A tube having an outer diameter of 30 mm and a wall thickness of 0.4 mm by the same method as in Example 1 except that a cylindrical billet of aluminum alloy having a composition of a and e was used and thermal spraying of pure Zn or Zn-Al alloy was not performed. Manufactured.
[0037]
(Comparative Example 5)
No. in Table 2 A tube having an outer diameter of 30 mm and a wall thickness of 0.4 mm was produced in the same manner as in Example 1 except that an aluminum alloy cylindrical billet having a composition h was used.
[0038]
Each obtained tube was subjected to a cycle test in the same manner as in the example, and the surface properties of the sample after the test were examined. The results of the surface texture are as follows: after 5 months of testing, no pitting corrosion and shallow pitting corrosion ◎, no through pitting corrosion and slightly deep pitting corrosion ○ Through pitting corrosion within 5 months The resulting product was marked with x.
The results are shown in Table 3 together with the production conditions.
[0039]
[Table 2]
[Table 3]
As is clear from Table 3, none of the present invention products (Nos. 14 to 21) generated through-pitting corrosion after immersion for 5 months. This is because Cu is contained in the tube body and the adhesion of the Zn-based alloy layer is good. Among them, those in which a diffusion layer is formed by heat treatment during drawing (No. 14, 16, 17, 19, 20, 21) have shallow pitting corrosion and extremely excellent corrosion resistance.
In contrast, No. of the comparative example. Nos. 22 and 24 were not sprayed with Zn. In No. 23, the billet contained no Cu and was not subjected to heat treatment, so that the Zn-based alloy layer was peeled off, and through pitting corrosion occurred in both cases.
[0042]
【The invention's effect】
As described above, in the present invention, the thermal spray layer during drawing is formed by forming a diffusion layer between the thermal spray layer and the core material by heat treatment or by specifying the alloy composition of the billet (core material). Since the exfoliation was suppressed, a tube having excellent corrosion resistance can be obtained. In addition, the tube can be manufactured at low cost without requiring expensive rolling equipment or a cylindrical lining material. Therefore, it has a remarkable industrial effect.
Claims (6)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP11364596A JP3628434B2 (en) | 1996-05-08 | 1996-05-08 | Drawing tube excellent in corrosion resistance and method for producing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP11364596A JP3628434B2 (en) | 1996-05-08 | 1996-05-08 | Drawing tube excellent in corrosion resistance and method for producing the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH09296263A JPH09296263A (en) | 1997-11-18 |
| JP3628434B2 true JP3628434B2 (en) | 2005-03-09 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP11364596A Expired - Fee Related JP3628434B2 (en) | 1996-05-08 | 1996-05-08 | Drawing tube excellent in corrosion resistance and method for producing the same |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3628434B2 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2005066570A1 (en) * | 2004-01-09 | 2005-07-21 | Showa Denko K.K. | Heat exchanger, method for manufacturing the same, and heat exchanging tube |
| EP1716266B1 (en) * | 2004-02-12 | 2011-12-21 | Showa Denko K.K. | Tube for use in heat exchanger, method for manufacturing said tube, and heat exchanger |
| JP6329924B2 (en) * | 2015-06-19 | 2018-05-23 | 三菱アルミニウム株式会社 | Aluminum alloy tube and heat exchanger core for heat exchanger |
-
1996
- 1996-05-08 JP JP11364596A patent/JP3628434B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH09296263A (en) | 1997-11-18 |
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