JP2500010C

JP2500010C -

Info

Publication number: JP2500010C
Authority: JP
Original assignee: Mazda Motor Corp; Kobe Steel Ltd
Current assignee: Mazda Motor Corp; Kobe Steel Ltd
Publication date: 1998-03-04

Description

【発明の詳細な説明】【産業上の利用分野】本発明は、自動車用アルミニウム合金板に関し、より詳しくは、りん酸亜鉛処
理が塗装の下地として施されて、フード、フェンダー等の自動車用パネル材に適
用されるアルミニウム合金板並びにその制御方法に関する。【従来の技術及び発明が解決しようとする課題】自動車用のフードやフェンダー等のパネル材としては、近年、軽量化に対する
要請に応じアルミニウム板材が採用されつつあり、このようなアルミニウム板材
としてはＪＩＳＨ４０００に規定されているＡｌ−Ｍｇ系合金（５１８２等）が
使用される場合が多い。その場合、プレス成形が施されるため、絞りや曲げ加工
性が必要であることから、軟質材が用いられるのが一般的である。しかし、Ａｌ−Ｍｇ系合金は強度等で優れた特性を有しているが、りん酸亜鉛
処理性の点においては、必ずしも満足できるものではなく、りん酸亜鉛皮膜の均
一化、結晶の微細化等の改善が望まれていた。すなわち、りん酸亜鉛皮膜の生成のバラツキが大きかったり、結晶が粗大であ
ると、塗装後の耐食性は所望の品質が期待できず、更に、塗装外観に不具合を来
すことがあった。本発明はかかる問題点に鑑みてなされたものであって、りん酸亜鉛処理の際に
、りん酸亜鉛皮膜の生成速度が速く、しかも、均一でかつ、結晶が緻密なりん亜
鉛皮膜が得られると共に、りん酸亜鉛処理液を工夫することによって、りん酸亜
鉛処理後の塗装後の耐食性に優れたアルミニウム合金表面制御板を得ることができる自動車パネル用アルミニウム合金表面制御板の製造方法を提供することを目
的とする。【課題を解決するための手段】前記課題を解決するために、本発明者等は、Ａｌ−Ｍｇ系合金のりん酸亜鉛処
理性が良くない原因を究明すると共に、その対策について鋭意研究を重ねた。そ
の結果、りん酸亜鉛処理性は合金の表面性状と密接な関係にあることが判明した
。すなわち、Ｍｇを含有するアルミニウム合金の場合、特に加熱して軟質化した
場合は、その表面層にはＭｇが濃縮した酸化皮膜が生成することが知られている
が、この酸化皮膜は自動車材の塗装下地として実施されているりん酸亜鉛処理に
対して悪影響があることが判明した。そこで、本発明者等は、この原因究明の結果に基づいて酸化皮膜の悪影響を解
消する方策について種々研究を重ねた結果、表面層の性状を制御することによっ
てこの問題を解決できることを見い出し、ここに発明をなしたものである。本発明に係る自動車パネル用アルミニウム合金表面制御板の製造方法は、３．
５〜５％のＭｇを含有するアルミニウム合金板を、アルカリ系の水溶液を用いて
洗浄して、表面層のＭｇ／Ａｌ比を０．０３５〜０．５の範囲に制御し、次いで
、フリー弗素を７５〜８００ｐｐｍ含有するりん酸亜鉛浴でりん酸亜鉛処理する
ことを特徴とする。なお、本明細書で、組成をあらわす％は、重量％である。以下に本発明を更に詳述する。【作用】まず、本発明でアルミニウム合金中のＭｇ添加量を３．５〜５％の範囲とした
のは、自動車用パネル材としての強度、成形性及び耐食性を確保するためである
。Ｍｇ量が３．５％未満では必要な強度が得られず、また５％を超えると耐食性
が低下し或いは圧延が困難となって板材の製造が経済的に不利となる。なお、本発明において対象とするアルミニウム合金はＭｇを上記添加範囲で必
須成分とするが、本発明の目的乃至効果を阻害しない範囲内でＳｉ、Ｆｅ、Ｃｕ
、Ｍｎ、Ｃｒ、Ｚｎ、Ｔｉ等々を含んでいても差し支えない。例えば、Ｓｉ、Ｆ
ｅ、Ｍｎ、Ｃｒ、Ｚｎはそれぞれ０．２％程度まで、Ｃｕは０．５％程度まで、Ｔｉは０．１％までの添加が許容される。表面層のＭｇ／Ａｌ比が０．５を超えると、りん酸亜鉛皮膜の生成が不均一と
なり、更にりん酸亜鉛の結晶が粗大になって塗装材の耐糸錆性等、耐食性が低下
し、一方、Ｍｇ／Ａｌ比が０．０３５未満の場合には、りん酸亜鉛皮膜の生成速
度が遅くなる傾向が認められる。したがって、本発明においては表面層のＭｇ／
Ａｌ比を０．０３５〜０．５の範囲に制御するのである。なお、表面層のＭｇ／
Ａｌ比は光電子分光分析により測定できる。表面層のＭｇ／Ａｌ比を制御する方法としては、工業的な生産を考慮して、ア
ルカリ系水溶液による化学的な処理（洗浄）とする。アルカリ系水溶液としては
、例えば、りん酸ソーダ系水溶液等の弱アルカリ水溶液が挙げられる。硝酸等の
酸水溶液は、Ａｌ−Ｍｇ系合金に生成した酸化皮膜を除去する有効な処理液では
あるが、Ｍｇ／Ａｌ比を上記範囲に制御することは著しく困難である。なお、下地処理として適用されるりん酸亜鉛浴は、フリー弗素として７５〜８
００ｐｐｍ添加した浴である場合に本発明の効果が顕著である。７５ｐｐｍ未満
ではりん酸亜鉛の結晶は粗大になると共に所望の皮膜量が得られない。また、８
００ｐｐｍを超えると金属に対する溶解性が増大し、浴槽や配管材料を腐食し易
くなると共にアルミニウムの溶解が優先し、りん酸亜鉛皮膜の生成が困難となる
。フリー弗素はＨＦ、ＮａＦ或いはＫＦの形で添加できる。次に本発明の実施例を示す。【実施例１】【表１】表１に示す化学成分を有するアルミニウム合金を用いて常法により供試材（板
材）を作成した。但し、最終熱処理として３７０℃×３時間のバッチ焼鈍或いは
５５０℃×２０秒の連続焼鈍を施して軟質化した。各供試材の板厚を１ｍｍとし、７０ｍｍ×１５０ｍｍの矩形の板材を以下の条
件のりん酸亜鉛処理に供した。試験数１０枚のりん酸亜鉛皮膜の付着量、バラツ
キ（標準偏差）及び結晶の生成状態を走査電子顕微鏡によって観察した。〔りん酸亜鉛処理条件〕脱脂：弱アルカリ液（ｐＨ＝１０．５）、４０℃にて２分浸漬表面調整：コロイダルチタン水溶液１．５ｇ／１、室温にて１５秒浸漬りん酸亜鉛処理：りん酸亜鉛水溶液（全酸度２２ポイント、遊離酸度０．８ポ
イント、フリー弗素１５０ｐｐｍ）、４２℃にて２分浸漬なお、表面調整は、りん酸亜鉛皮膜結晶を微細化するために実施するものであ
り、本実施例で示した他に通常の鋼板用に用いられているものであれば適用可能
である。また、フリー弗素はＨＦの形で投入した。また、表面層のＭｇ／Ａｌ比は、光電子分光分析器（島津製作所製ＥＳＣＡ８
５０Ｍ）によりＭｇとＡｌのピーク高さを求めて、Ｍｇ／Ａｌ比を算出した。更に、耐食性は、りん酸亜鉛処理した供試材をカチオン電着（３０μｍ）後、
中塗り（４０μｍ）、上塗り（４０μｍ）した塗装板にカッターで十字傷を入れ
、次の条件で腐食試験を１０００時間実施し、最大糸錆長さ求めて評価した。〔腐食試験条件〕塩水噴霧（ＪＩＳＺ２３７１）２４時間 ↓ 純水浸漬１秒 ↓ 湿潤５０℃×８０％ＲＨ１０日 ↓ ５％食塩水浸漬１秒（湿潤→食塩水浸漬を繰り返す）これらの結果を表２に示す。【表２】表２より明らかなように、本発明材はいずれも、従来材や比較材に比べ、りん
酸亜鉛処理性が優れており、更に耐食性も優れている。【実施例２】りん酸亜鉛浴中のフリー弗素量を表３に示すように種々変え、他の条件は実施
例１と同様とし、表１に示した供試材についてりん酸亜鉛処理性及び耐食性を調
べた。その結果は、表３に示すとおり、本発明材は顕著な効果が得られているこ
とがわかる。【表３】 Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy plate for automobiles, and more particularly, to a panel for automobiles such as hoods and fenders, which is treated with zinc phosphate as a base for painting. The present invention relates to an aluminum alloy plate applied to a material and a control method thereof. 2. Description of the Related Art In recent years, aluminum sheets have been adopted as panel materials for automobile hoods, fenders and the like in response to a demand for weight reduction, and such an aluminum sheet material is JISH4000. Al-Mg based alloys (5182 and the like) specified in the above are often used. In that case, a soft material is generally used because press forming is performed and drawing and bending workability are required. However, although Al-Mg based alloys have excellent properties such as strength, they are not always satisfactory in terms of zinc phosphate treatability, and uniform zinc phosphate coatings and finer crystals. Improvement such as was desired. That is, if the dispersion of the formation of the zinc phosphate film is large or the crystal is coarse, the corrosion resistance after coating cannot be expected to have a desired quality, and further, the coating appearance may be inferior. The present invention has been made in view of such a problem, and in the case of zinc phosphate treatment, the rate of formation of the zinc phosphate film is high, and a uniform and crystal dense zinc film can be obtained. In addition, the present invention provides a method for manufacturing an aluminum alloy surface control plate for an automobile panel, which can obtain an aluminum alloy surface control plate excellent in corrosion resistance after coating after zinc phosphate treatment by devising a zinc phosphate treatment solution. The purpose is to: Means for Solving the Problems In order to solve the above problems, the present inventors have investigated the cause of poor zinc phosphate treatability of an Al—Mg based alloy, and conducted intensive research on the countermeasures. Was. As a result, it was found that the zinc phosphate treatability was closely related to the surface properties of the alloy. That is, in the case of an aluminum alloy containing Mg, particularly when it is softened by heating, it is known that an oxide film in which Mg is concentrated is formed on its surface layer. It has been found that there is an adverse effect on the zinc phosphate treatment performed as a coating base. Accordingly, the present inventors have conducted various studies on measures to eliminate the adverse effects of the oxide film based on the results of the investigation of the cause, and as a result, have found that this problem can be solved by controlling the properties of the surface layer. The invention has been made. The manufacturing method of the aluminum alloy surface control plate for an automobile panel according to the present invention is described in the section of 3.
An aluminum alloy plate containing 5 to 5% Mg is washed with an alkaline aqueous solution to control the Mg / Al ratio of the surface layer in the range of 0.035 to 0.5, and then free fluorine is added. Of zinc phosphate treatment in a zinc phosphate bath containing 75 to 800 ppm. In this specification,% representing the composition is% by weight. Hereinafter, the present invention will be described in more detail. First, the reason why the amount of Mg added to the aluminum alloy is set in the range of 3.5 to 5% in the present invention is to secure the strength, formability and corrosion resistance as a panel material for an automobile. If the Mg content is less than 3.5%, the required strength cannot be obtained, and if it exceeds 5%, the corrosion resistance is reduced or the rolling becomes difficult, and the production of the sheet material becomes economically disadvantageous. In the present invention, the target aluminum alloy contains Mg as an essential component in the above-mentioned addition range.
, Mn, Cr, Zn, Ti, and the like. For example, Si, F
Each of e, Mn, Cr, and Zn can be added up to about 0.2%, Cu can be added up to about 0.5%, and Ti can be added up to about 0.1%. If the Mg / Al ratio of the surface layer exceeds 0.5, the formation of the zinc phosphate film becomes non-uniform, and the zinc phosphate crystals become coarse, and the corrosion resistance, such as the rust resistance of the coating material, decreases. On the other hand, when the Mg / Al ratio is less than 0.035, the generation rate of the zinc phosphate film tends to be slow. Therefore, in the present invention, Mg /
The Al ratio is controlled in the range of 0.035 to 0.5. In addition, Mg /
The Al ratio can be measured by photoelectron spectroscopy. As a method of controlling the Mg / Al ratio of the surface layer, chemical treatment (cleaning) with an alkaline aqueous solution is performed in consideration of industrial production. Examples of the alkaline aqueous solution include a weak alkaline aqueous solution such as a sodium phosphate aqueous solution. An aqueous acid solution such as nitric acid is an effective treatment liquid for removing an oxide film formed on an Al-Mg-based alloy, but it is extremely difficult to control the Mg / Al ratio in the above range. The zinc phosphate bath applied as a base treatment is 75 to 8 as free fluorine.
The effect of the present invention is remarkable when the bath is added with 00 ppm. If it is less than 75 ppm, the zinc phosphate crystals become coarse and a desired coating amount cannot be obtained. Also, 8
If it exceeds 00 ppm, the solubility in metals increases, so that bathtubs and piping materials are easily corroded, and aluminum dissolution is prioritized, and it becomes difficult to form a zinc phosphate film. Free fluorine can be added in the form of HF, NaF or KF. Next, examples of the present invention will be described. [Example 1] A test material (plate material) was prepared by an ordinary method using an aluminum alloy having the chemical components shown in Table 1. However, as a final heat treatment, softening was performed by performing batch annealing at 370 ° C. × 3 hours or continuous annealing at 550 ° C. × 20 seconds. The thickness of each test material was 1 mm, and a rectangular plate material of 70 mm × 150 mm was subjected to a zinc phosphate treatment under the following conditions. The adhesion amount, variation (standard deviation), and the state of crystal formation of the ten samples of the zinc phosphate film were observed with a scanning electron microscope. [Zinc phosphate treatment conditions] Degreasing: Weak alkaline solution (pH = 10.5), immersion at 40 ° C for 2 minutes Surface adjustment: Colloidal titanium aqueous solution 1.5 g / 1, immersion at room temperature for 15 seconds Zinc phosphate treatment: Aqueous zinc phosphate solution (total acidity: 22 points, free acidity: 0.8 points, free fluorine: 150 ppm), immersed at 42 ° C for 2 minutes. Surface adjustment is performed to refine zinc phosphate film crystals. In addition, other than those shown in the present embodiment, any ones used for ordinary steel plates can be applied. Free fluorine was introduced in the form of HF. Further, the Mg / Al ratio of the surface layer is determined by a photoelectron spectrometer (ESCA8 manufactured by Shimadzu Corporation).
50M), the Mg / Al peak height was determined, and the Mg / Al ratio was calculated. Further, the corrosion resistance was determined by subjecting the test material treated with zinc phosphate to cationic electrodeposition (30 μm).
Cross-cuts were made with a cutter on the middle-coated (40 μm) and top-coated (40 μm) coated plates, and a corrosion test was carried out for 1000 hours under the following conditions to obtain and evaluate the maximum yarn rust length. [Corrosion test conditions] Salt spray (JIS Z2371) 24 hours ↓ 1 second immersion in pure water ↓ 10 days humidification 50 ° C x 80% RH ↓ 1 second immersion in 5% saline (wet → immersion in saline) Repeat these results It is shown in Table 2. [Table 2] As is clear from Table 2, all of the materials of the present invention have excellent zinc phosphate treatment properties and are also excellent in corrosion resistance as compared with conventional materials and comparative materials. Example 2 The amount of free fluorine in the zinc phosphate bath was variously changed as shown in Table 3, and other conditions were the same as in Example 1. The test materials shown in Table 1 were treated with zinc phosphate. The corrosion resistance was examined. The results show that, as shown in Table 3, the material of the present invention has a remarkable effect. [Table 3]

Claims

Claims: 1. An aluminum alloy plate containing 3.5 to 5% by weight of Mg is washed with an alkaline aqueous solution to reduce the Mg / Al ratio of the surface layer to 0.035. ~ 0.
5. A method for producing an aluminum alloy surface control plate for an automobile panel, wherein the control is performed in the range of 5 and then zinc phosphate treatment is performed in a zinc phosphate bath containing 75 to 800 ppm of free fluorine.