JPS58181855A - Production of steel plate hot-dipped in aluminum base composite - Google Patents

Abstract

PURPOSE:To obtain a planted steel plate excellent in corrosion resistance, wet corrosion resistance and suitability to chemical conversion treatment, by immersing a steel plate in an Al base composite plating bath having a specific composition containing Zn and Si to which Mg, Mn, Cr and a Misch metal are added in a proper amount. CONSTITUTION:One kind or more 0.01-1.0% Mg, 0.01-0.5% Mn, 0.01-0.5% Cr and 0.01-2.0% Misch metal are added to an Al base Al-Zn alloy bath containing 1-30% Zn and 1-12% Si and, according to necessity, 0.01-0.5% Sb is further added to form a hot dipping bath material. This hot dipping bath material is heated to about 620-670 deg.C and, after a pretreated steel plate is immersed in the heated hot dipping bath to carry out plating, the adhered amount is controlled to pref., 30g/m<2> (single surface) or less by a gas squeezing method to prepare a steel plate hot-dipped in an aluminum base composite excellent in corrosion resistance, heat resistance and wet corrosion resistance and good for chemical conversion treatment and processability.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing a hot-dip galvanized steel sheet in which the steel sheet is subjected to trap pretreatment, then immersed in a plating bath, and then bath-dip plated, and then coated in an aluminum-based alloy bath. This relates to a method for obtaining products with excellent corrosion resistance, moisture corrosion resistance, and chemical conversion treatment.

The conventionally used I! Most of the 1m aluminum-plated steel sheets are plated in a bath of 11650 U or more by cooling Si for suppressing the alloy layer in an Al bath.

This hot-dip aluminized steel plate is f8! m Galvanized steel sheet and Zn-AI alloy II! It has particularly superior corrosion resistance and heat resistance compared to IIm-plated steel sheets, and is widely used in building materials such as roofs and walls, parts for home appliances, and automobile parts that especially require these properties.

However, in the case of hot-dip aluminized steel sheets, the suppression of the alloy layer by Si addition is insufficient, so a hard (and brittle) Fe-AI alloy is formed at the interface between the plating layer and the steel base, and the It does not have enough workability to withstand processing.Also, in terms of corrosion resistance, L-type does not have cathodic corrosion protection, so it is easy to cause cracks in the plating layer due to processing, and pinholes occur during aging and plating. It has the disadvantage that red rust occurs.

On the other hand, as a way to obtain a product without such defects, A1
A method of plating with a base alloy bath containing 5 to 25% Zn and 3 to 12% Si is known (% Kosho 46
-4045). This method has better workability compared to the method for producing bath-dipped aluminized steel sheets.
The bending workability of the plating layer and the corrosion resistance of the bent parts have also improved. But Cl io/
Pitting corrosion of the mating layer progresses rapidly in the atmosphere, and it is used for automobile underbody parts that are subject to salt damage (C had problems).

The present invention may have the above-mentioned drawbacks, but it may not be suitable for use as a moisture-corrosion-resistant material for automobile mufflers, an appropriate material for alcohol-based fuel tanks, or highly corrosion-resistant surface treatment, which has been in strong demand in recent years as part of the diversification of AI-paced hot-dipped steel sheets. There is also a method for manufacturing bath-melted steel sheets that is suitable for use as a material for steel sheets.

Automobile mufflers undergo repeated wet-dry cycles with large temperature differences, and alcohol-based fuels contain water, so materials that have excellent corrosion resistance, heat resistance, and moisture corrosion resistance are required.

In addition, surface-treated steel sheets are required to have excellent chemical conversion treatment properties, high corrosion resistance, and no pinholes even if the surface weight is as thin as 30 V/piece or less.

In order to eliminate the above-mentioned drawbacks and meet the stiffness requirements, the present inventors have conducted various studies and found that In'
A1 with 0% or less, Si Y 1%8112% or less
Based AI-Zn alloy bath K Mg, Mn %C
Ill also of r and Mitsushmetal. is 2 or more 'kMgo, 01~10%, MrIo01~0.5%
, CrO, 01~0.5%, Mi7'y:L) Tal 0.01~2.0% ~ stock added, or this bath 6c
I found out that it is best to use a bath containing 5% sbyo, ot~O.

The reasons for limiting the plating bath composition of the present invention will be described below.

(1) Zn Zn can be plated 11 by coexistence with Si! In addition to suppressing the development of the Fe-AI@gold layer by lowering U, it also improves the corrosion resistance of the processed part by cathodic corrosion protection, and furthermore prevents the formation of beer/small beads even with a thin basis weight. In order to obtain this effect, it is necessary to add more than 1%. However, if it exceeds 30%, the crystals in the mating layer will have less area for the primary α-AI phase and β-Zn. It forms a eutectoid structure with the phase, which may impair the properties of the AI plating.For this reason, the Zn content is set to more than 1% and less than 30%.

(2) Perhaps the cooling is performed to suppress the development of the Fe-Al alloy layer in the Si plating layer, but its effect is not observed at 1% or more. If the temperature exceeds 12%, the effect of suppressing the alloy layer will not increase even if the amount added is increased when the bath is warm, and the formation power of the AI-8i eutectic structure will become significant and the formation of the plating layer will be reduced. Quality characteristics deteriorate. This f should be more than 11% and less than 12% f:.

(3) Mg Mg crystallizes near the β-Zn phase during layer solidification and α
- Suppress the contact corrosion between the AI phase and β-Zn phase, accelerate the progress of pitting corrosion, and provide stable Mg on the surface of the plating layer.
Is the plating layer formed by forming an oxide film? Protects and improves eating tolerance. However, such an effect can be obtained with Mg when Mg'a-o, ol5 or more is added, and 00
If it is less than 1%, it is unsatisfactory.

On the other hand, if the amount added exceeds 10%, it is easily oxidized on the bath surface and becomes a large amount of dross, leading to an increase in costs due to a reduction in Mg yield (and at the same time, fluctuations in the bath composition become large, making it difficult to control the bath composition). Also, in terms of appearance, blackened Mg oxide is formed on the surface of the plating layer.Furthermore, Mg-8i gold metal compound is formed in the plating layer. (1) Corrosion resistance and workability will decrease. (1) F Mg should be 001 to LO%.

(4) Mn and Cr Mn and Cr improve the corrosion resistance of the A1 alloy, but their effect is reduced in the coexistence of Zn. Corrosion resistance will be improved in the coexistence of more than 1% and less than 30% Zn in IJ. When adding 0.01% or more each of Mn and Cr, it was necessary to add more than 0.01% each.On the other hand, if Mn and Cr were added in excess of 0.5% each, the outside appearance of the product would be poor (0.01% and the upper bath temperature would also rise). This results in a decrease in YP performance and also promotes the development of the alloy layer.For this reason, both Cr and Cr are each 0.01 to 0.
It was set at 5%.

(5) Minosh Metal Minoshu Metal is uniformly dispersed within α-AI crystal grains and further refines the crystal grains, thereby improving corrosion resistance and bending processability. It also has the effect of suppressing the generation of pinholes in products with a thin coating, and greatly improves corrosion resistance by adding it in combination with Mg. The effective amount of this additive is 0.01% or more, but even if it is added at 20%, it will turn into dross on the plated yukata surface, lowering the effective yield and increasing costs (and making it difficult to control the bath composition). Because of this, the upper limit is 20% and 1.

(6) 5b sb improves chemical conversion treatment properties (chromate treatment properties, painting pretreatment properties, etc.) and prevents blistering of the paint film when painted. However, when sb is added alone, it promotes pitting corrosion and reduces corrosion resistance. Therefore, in the present invention, it is intended to improve chemical conversion treatment properties by adding a combination of corrosion resistance improving elements such as Mg and Mn.

The improvement in chemical conversion treatment property due to sb is recognized when the amount is 0.01% or more, and the increase in the amount added improves T, but on the contrary, the corrosion resistance deteriorates. No improvement in corrosion resistance can be expected. Additionally, the sb turns into dross on the surface of the plating bath, and the bath composition fluctuates rapidly due to a decrease in yield, making bath management difficult. Therefore, sb is 0
01 to 0.5%.

In the present invention, plating is carried out by a known plating process using the bath as described above. In other words, the steel plate is pretreated to make the surface of the steel plate suitable for hot-dip plating, and then immersed in a bath for plating.

In the case of the present invention, there are no particular limitations regarding the relationship with the bath components.

The bath temperature during plating is 1. When n is large, it should be low, and it should be in the range of about 620C to 670C.

After plating, adjust the amount of adhesion. This adjustment of the adhesion amount is usually carried out by the gas squeezing method, and in the case of the present invention, the thinness KyA of 30 t/m' (one side) or less can be adjusted using the current gas squeezing method.

After adjusting the adhesion 11, the appearance can be adjusted by cooling to a regular spangle (or by rapidly cooling with water droplet spray to a minimized 'snow metal') (・0 to 1 yen
The invention will be explained by examples.

Sosho Example I L Wiping material 0, 61111 thickness x 150 width unannealed rimmed steel strip 2
Metsujo conditions ■Before plating + ll dull ■Atmosphere gas AX gas (Hz75%, N!25%)
■Plating temperature (4) Rhino heat 40 to 60 seconds ■Adjustment of adhering particles Gas squeezing method using combustion exhaust gas ■Cooling after plating Cooling 3 Post-treatment ■Chromate treatment, oiling treatment...no ■Temper rolling...・No 4, Test method 4, 1 Workability ■Adhesion... Adhesive bending and impact test) (20 bond inch) fk Sellotape peeling method.

■Bending workability: Observe the occurrence of cracks in the closely bent portion using a looper (x50-100).

Judgment criteria Small...There is a small rack.

Medium...Ranked as coarse.

There is a rise in the large and coarse ranks and the mating layer.

4.2 Corrosion resistance σ) Salt spray test (according to JIS-Z~2371) (1) Start time of red rust occurrence and change in appearance after 2000 hours (H) Corrosion weight loss after 10 days■ Cathodic protection (sacrificial corrosion) property A concentration cell is formed by coupling Fe (base steel) to the mating layer and the potential is measured.

(1) Corrosive liquid... (a) Tap water (b) 1/6000 M Na C1 (PH=5.8
) (II) v Soaking time...48 hours ■Muffler wet corrosion (1) Corrosion liquid NH4Cl +N84So4+N) 4m + water (11) Method In 50U of corrosive liquid [Immerse for 30 seconds, then 80t? Operation 40 of drying for 20 minutes in an atmosphere of
This cycle is defined as one cycle.

(Processed flat part of 11# sample material, 2 bent part N Rate of occurrence of red rust 4.3 Heat resistance Change in surface appearance after heating for 1000 hours in 400C atmosphere and alloy layer in plating layer 0) Judgment Criteria Table for Observation of Generated Dye Cross-sectional Structure
The quality and characteristics of conventional products are shown in the bath composition and boiling table.

When each characteristic 1 shown in Table IK is considered, the following K is obtained.

(1) Workability The workability of the product of the present invention is almost the same as that of a hot-dip plated steel sheet made of AI-Zn-8i alloy, and the alloy layer is thinner and workability is better than that of a hot-dip aluminium-coated steel sheet.

Further, addition of Mg within the scope of the present invention does not affect workability.

(2) Corrosion Resistance ■ Salt Spray Test The time and rate of red rust occurrence for products of the present invention with Mg added were as follows. f-containing (/I
612).

This tendency is the same in terms of corrosion loss, and it can be seen that the material has excellent corrosion resistance. This is due to the addition of Mg.
It is thought that this is because pitting corrosion, which is a fatal defect in base alloy coated steel sheets, is suppressed.

Table 2 shows excitations other than Mg, C'', Misosmetal and sb.
This figure shows the corrosion resistance when adding .

As in the case of Mg addition, pigeons were placed in the AI-Zn-Si bath.
Corrosion resistance is improved when Cr and minosmetal are added alone. However, Mythosmetal is slightly inferior to other elements. For this reason, in the case of minosu metal, it is preferable to add it in combination with pigeon.

When sb is added as shown in the comparison,
Decrease corrosion resistance. Therefore, it is necessary to add sb in combination with dove, dove, Cr, and miso metal.

■ Cathode corrosion resistance (sacrificial corrosion resistance) The addition of Mg fA does not impair the cathode corrosion resistance of Zn, and it has cathodic corrosion resistance even in Na Cl water Sa.

■ Moist corrosion In a wet corrosion test simulating corrosion caused by condensed water on an automobile muffler, the rate of occurrence of red rust on processed parts was significantly lower than that of conventional products, demonstrating excellent moisture corrosion resistance.

(2) Heat resistance Although the product of the present invention contains a large amount of Zny, it has the heat resistance of a molten aluminum steel sheet lid. Heat resistance improves in this way when Mg is not added (/
The heat resistance is improved compared to 1611.412 >, and the improvement in heat resistance is small when the amount of Mg added is small (4
1) is thought to suppress the interdiffusion of Mgf/iFe-Zn from the point that it improves with increasing (/Vi2).

Example 2 Using the bath of the present invention under the same pretreatment and plating conditions as Example 1, a light weight product was manufactured by setting the gas tie dyeing so that the coating amount on one side was 3017 mm or less. The treatment after adjusting the adhesion amount was carried out under the following conditions.

■ Cooling after plating ■ Air cooling (air pressure 3.0 -) ■ Air Minx method water cooling (air pressure 3.0 Air/ait, water pressure 301)
■ Skip/bath of temper-rolled dull skin Elongation rate t6±0.2% ■ Chromic acid treatment (processing solution... Allozin $1000 (ID treatment conditions... 65C 12 seconds immersion ■ Test method (1) Corrosion resistance...Correspondence between red rust occurrence and time by salt spray test (ID pinhole test...wet test (70C, 9g
% & Force Presence of dotted red cap after 1000 hours Table 3 shows the results of this test.
Although it is improved by fA m K, the improvement is even greater when sb is added.

In addition, pier holes do not occur when Zn is low or when pigeon is added alone. However, in the latter case, the occurrence of pinholes can be suppressed by combining with Mitsushmetal.

As described above, the product manufactured according to the present invention has excellent pitting corrosion resistance in a salt water atmosphere, and therefore can be used as an automobile underbody member for salt damage resistance.

It also has excellent processability, excellent corrosion resistance and moisture corrosion resistance in processed parts, and heat resistance, so it can be used for automobile mufflers and alcohol fuel tanks.

Furthermore, the chemical conversion treatment property of the Sb-added material is improved, and since no pinholes occur even when the coating weight is reduced, it can be used as a highly corrosion-resistant surface-treated steel sheet circumferential cable material, in combination with the corrosion resistance of the mating layer.

patent applicant Japan #r Steel Co., Ltd. representative person Mitsuru Shindo Continuation of page 1 0 shots clear person Yasushi Miyoshi 2-1-17 Sakurajima, Konohana-ku, Osaka City No. 1 Nisshin Steel Co., Ltd. Hanshin Manufacturing Inside the office

Claims (4)

[Claims] (1) In a method for producing #dip-plated steel sheets, in which a steel sheet is pretreated, immersed in a plating bath for plating, and then the coating amount is controlled a, the plating bath contains more than 1% of Zn and no more than 30% of Si. AI-based Al containing more than 1% but less than 12%
- Pvlg O, 01~L of one or more of the following: - Pvlg O, 01~L in a Zn alloy bath.
0%, Mn01ol~0.5%, Cro, ox~o,
A method for producing an aluminum-based hot-dip plated steel sheet, characterized by using a bath to which 0.01 to 2.0% of mimetal is added. (2) The method for manufacturing an aluminum paste composite hot-dip plated steel sheet according to claim 1, characterized in that the amount of adhesion is controlled to 30H (one side) or less. (3) In a method for producing a hot-dipped steel sheet, in which a steel sheet is pretreated and then immersed in a plating bath for plating, and then the coating amount is controlled, the plating bath contains more than 1% of Zn and no more than 30% of Si; A1-based AI containing more than 1% and less than 12%
-Zn alloy bath [Mg. One or two of Mn, Cr and minosmetal
More than species YMg0.01~L□%, Mn0.01~05%
, Cr001~05%, Mi7, :L) Tal00
Addition of 1 to 2.0% increases the amount of K [Sb from 001 to 0].
．． A method for producing an aluminum-based hot-dip plated steel sheet, characterized by using a bath containing 5% additive. (4) The method for producing an aluminum paste composite hot-dip plated steel sheet according to claim 3, wherein the coating amount Y is controlled to be less than or equal to 30 Vtt/ (one side).