JPS59208061A - Steel material plated with zinc-aluminum alloy with superior resistance to stripping due to corrosion and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture the titled steel material by forming a layer of a molten alloy having a specified composition consisting of Al, Si, Mg and the balance essentially Zn by hot dipping, cooling the layer at a high cooling rate, and continuing cooling. CONSTITUTION:A steel material is dipped in a molten alloy consisting of, by weight, 5-24% Al, <=0.8% Si, <=0.5% Mg and the balance essentially Zn, and it is pulled up to form a layer on the surface. The layer is cooled at >=17 deg.C/sec cooling rate until it is practically solidified, and cooling is continued so that the layer is not reheated to a temp. above the solidifying point by the residual heat of the steel material.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Ikomei relates to a zinc-aluminum white core plated steel material with excellent corrosion resistance and its production.

1i11jrt, -72 Reminiu 1, alloy hot-dipped steel plate is secondary 1 (, II (11'), v), -1
, \il'l fig (,111; Mon [1., 11
The plating bath composition and its conversion fI+11 are described in Kokai 48-4045, 4fi-7181, 51-
25220, 56-17426 etc. 1 However, these zinc-aluminum alloy platings cannot be used in very severe corrosive environments such as the lf'j J'+' adjacent zone. Even with slight bending,
Easy to remove plating layer 1. li yoshi, again meishi J Near 1
It has been found that in some cases, there is a phenomenon in which the plating layer J'l/A occurs in a piecemeal manner even without applying the bending I'.

This phenomenon occurs in the microstructure of the cross section of the plating layer.
, Zn-li〉・chi phase corrodes preferentially! +I # (hereinafter, this phenomenon will be referred to as corrosion peeling).

Addition of the plating layer due to residual iron infusion due to poor plating pretreatment 1:! This is different from the case where the plating layer peels off due to the thick growth of a brittle metal compound at the interface between the plating and the steel car.
A:, 1. i'c In the course of investigating this corrosion peeling, I'1 of the corrosion inside the plating layer was investigated.
It was discovered that there is a relationship between the degree of electrical contact and the microstructure of the plating layer, and that corrosion peeling is suppressed when the microstructure reaches a certain 411 constant.

1113iS-aluminum plating layer], (ultimately can be thought of as a monolithic alloy of zinc-711/min) after being purified by CIt. -Aluminilla T・
In the case of α, α-A1 was crystallized as the first product, and as the temperature decreased, it became 1. In the case of hot-dip plating, the crystallization-precipitation reaction does not necessarily occur as shown in the phase diagram, as it is cooled at a relatively fast rate. . Therefore, the inventors 1-1:
A plated steel sheet is manufactured by changing the cooling rate of the plated layer after plating, and the microstructure of the plated layer is changed to 1ζ per rotation.
As a result of conducting a corrosion resistance test on the plated steel plate and investigating the corrosion situation, the plated steel plate was tested at 17°C/3! It has been found that when the product is cooled at a rate of 1, no corrosion peeling occurs. ,+,: The invention is based on such knowledge as 3. (A1.0.8 with 5-24Φ amount%)
During! , 1. , 0/or less Sl and 0.5 Φ-knee,
In the plating layer consisting of Mg and the remainder substantially Zn, corrosion J:;
111 (lead-aluminum alloy-plated steel material), which has been evaluated as 4a in the monthly corrosion publication, characterized by the fact that the propagation of corrosion at the interface between α-AI and Zn-Lynch phase is suppressed in one boundary 1. I will provide a.

E, the invention also has an A1.0.8 of 5 to 24 tons and 11%.
The steel material is immersed in a molten metal consisting of 1,000 ml of Sl, 0.5 tn% or more of Mg, the balance or Zn, and unavoidable small impurities.1. / te pull 4-keru・1
) at 7°C until solidified.
Cooling is carried out at a speed of 1-1+1-c for more than 1-sec, and the cooling is stopped so that the plating layer is not heated beyond the limit of its solidification range by the heat remaining in the 70-year-old raw steel material. 1111. has excellent corrosion and peeling resistance. ti%
〜Propose a method for making a robe made of aluminum alloy plated steel material.''1. The present invention has made it possible to manufacture aluminum plated products with improved corrosion and peeling resistance.

Curved lead-aluminum pot plating in one piece is 5 to 1゛244
1j, t, i+-%17) AI, 0.8% or more F'
(7) It has been carried out using an alloy bath consisting of less than 0.5% Mg and the balance essentially Zn and an unexploitable blunt material. In this composition range, the lead-aluminum alloy h'1 has uniform properties.

The invention will now be described in detail on the basis of experiments and examples.

q'S Figure 1 was produced using laboratory hot-dip plating equipment.
Weight 1:% Al, 0.5,000J1t% Si, 0
．． A plate with a thickness of 0.8 mm was coated using a plating bath consisting of 1°11 Mg, the balance 11ij lead, and unavoidable impurities.
Here are the results of an X-ray microanalyzer analysis of the cross section of the plating layer when it was plated on rimmed steel and cooled at a rate of 17°C/sec. The cross-sectional structure consists of a spherical primary α-AI and a Zn-Lynch phase that curves the curve, as shown in the secondary electric r-ray image in Figure 1 (A), or As seen in the AI (7) characteristic X-ray image shown in B) and the characteristic X-ray image of Zn shown in FIG. 1 (C), β contains almost no AI around α-A1. -Zn is precipitated.

, i! When the cooling rate is increased to 30°C/see,
The cross section 1flj*l weave becomes a net 1-1-shaped M[weave] as shown in the secondary electron beam image of FIG. 2(A). As seen in the characteristic X-ray image of A1 in 21st Δ(B) and the characteristic X-ray image of Zn in (C), the distribution shape jE of A1 and Zn around α-At is approximately equal to A1. The Zn-rich phase is filled with a uniformly distributed Zn-rich phase, as seen in Figure 1.
Znc7) segregation within the rich phase is 1! ! I can't stand it.

The plated steel machines were manufactured in the laboratory under various cooling conditions and were subjected to a 600-hour salt spray test (JI').
S Z-2371) After 2 (In, Sot7), 1
8o° Mizunoi 1111 Geka! ``Put cellophane tape on the bent part and remove the plating layer.''
The 4'Afn situation was observed. The degree of allr4+ is the third
As shown in the figure, the cellophane tape was rated 4-j, rr L and 1 on a four-level scale depending on the amount of the release plating layer. FIG. 4 shows the relationship between the cooling rate of the plating layer and the degree of corrosion peeling of the plating layer after the salt water spray test. As shown in the figure, the higher the cooling rate, the smaller the degree of corrosion flaking, which is 17°C.
At a cooling rate of /see or less, almost no corrosion 211 was observed. When we carefully observed the plating strength of a portion of a plated copper plate that had suffered severe corrosion and peeling under a microscope, we found that the β-Zn layer, which contains almost no A1, as shown in Figure 1, was selectively and heavily corroded. So, almost all α-A.

It was confirmed that the virus was spreading to the surrounding area. At present, there is no sufficient theoretical explanation for this phenomenon, or α
- Due to the precipitation of a β-Zn layer with a significantly low A1 concentration at the interface between the -AI' and Zn-Lynch phases, a local potential difference is created between α-At and β-Zn in a certain corrosive environment. It seems that the corrosion of β-Zn is vigorously promoted. Incidentally, in a plating layer where the cooling rate is high and precipitation of β-Zn containing almost no AI is observed around α-At, selective corrosion of the Zn-Lynch layer is said to propagate to the entire plating layer. No phenomenon was observed, and the corrosion progress was stopped by slight corrosion of the Z, n-Lynch phase near the surface of the layer. , Corrosion 11+ w+ The cooling rate until the plating layer substantially solidifies is 17°C/sec.
I discovered that by making the following -1-, I could get defense 11-. The cooling rate is controlled until the plating layer is substantially completely solidified, and the cooling is carried out so that the heat remaining in the base steel even after the plating process [1] does not cause it to heat up.
I need to get 6.

Based on the experimental results described above, test production was carried out on an actual production line scale. The results will be explained below as an example in 1.

Example In a conventional non-oxidizing furnace type continuous hot-dip plating line, a 0.8 mm thick (7) cold rolled steel strip was hot-dipped with 11 (lead-aluminum alloy). The composition of the plating bath was Al:
13 tons: 115%, Si: 0.3 tons 1%,
Mg: O1%, balance: Zn and inevitable impurities, and the bath temperature was 500°C.

The plating operation was as follows. FIG. 5 is a schematic diagram showing the structure around the Metsa pot. After immersing a steel strip l whose surface has been cleaned by scum reduction in a plating bath 2 and pulling it out, a scum wiper 3 is used to remove the plating layer. The thickness was adjusted to 20μ. Forced cooling of the plated copper strip was carried out in cooling box 4 by blowing air or water spray onto the plated steel strip, and the cooling rate was controlled by adjusting the pressure and quality of the air or wood spray. In this way (j4), the plated steel sheet was subjected to the A water spray frost test (t) described above. The results obtained are shown in FIG.゛.

As is clear from the figure, the cooling rate of the plating layer can be increased to 17°C/sac or more by blowing air or water over it.
It was found that the steel plate rated - had extremely slight corrosion flaking, and the effect of forced cooling on corrosion flaking was significant.

Example 2', (using the same continuous hot-dip plating line as Example 1,
Nso: 30. A cold-rolled steel strip of e mm was hot-dipped with a zinc-aluminum alloy. The composition of the plating bath is Al:5i
, i9%, S + : O, l
%ry%, Mg"O,'-'I': js
E%, ri(part Zn and υi<tIT 2) impurities, and the bath temperature was +850°C.

The work was reduced to Example 1 and plated with the company's C grade 1, v:1
il after tsu〉ll'l <i? at a divine cooling rate by spraying with air or water spray;
? It was cold JJI l. The rootlet that has been destroyed in this way is
The degree of %i (eclipse μq) of the plating layer after 114 shi, 600 ++lj- was investigated in the water jet test.The cooling rate of the plating layer was reduced to 17
The plated plate exposed to temperatures below °C/see corrodes and the plating layer 1. :+ It seems almost like a prisoner, Les, I:'r', 1lj
Is it the effect of 41? Jl is always making big things small.
This cuff), + according to 'lij Western atmosphere, 1' 1 meal 1; # border 1llj tj'r
- Fits aluminum - Prevents corrosion and peeling of the plating layer
, and its uses can be further expanded.

In addition, this method is rust 1;? It goes without saying that the plating of structures and wire rods can be applied only to the size of the wire.

[Brief explanation of the drawing]

εIs l 1A is a photograph (elephant) of an X-ray microanalyzer analysis of the lfi surface of the plating layer cooled at a cooling rate of 5°C/sec. (A) is a two-shot electron beam image, (B)
(C) is the characteristic X-ray image of AI, and (C) is the characteristic X-ray image of Zn. A (21< indicates the results of X-ray microanalyzer analysis of the cross section of the plating layer cooled at 30°C/see. sir
(C) shows a characteristic X-ray image of A1. 3rd (A is +13 water spray test 600 times after 600 plating intervals, 1 serving of plating layer) +'A2 water spray test 6
The relationship with the degree of peeling in the 180° damage bending peeling test after 00 hours is shown. Fig. 51.4 is a schematic diagram of the area around the plating bath of the rust (1? I11!) continuous plating line. Fig. 6 shows the cooling rate of the zinc-aluminum alloy plating layer produced in Example 1 and l) A water spray. The relationship with the degree of corrosion i1m after 600 hours of testing is shown. No. 7 IN shows the relationship between the cooling rate of the zinc-aluminum alloy plating layer produced in Example 2 and the degree of corrosion 'L11 separation after 600 hours of water spray test. Report 1 ``1 person'' 1 Shinsei Sabu Co., Ltd. representative PR 1゛ri'' - Masahiro Matsuzuki (et al.) 328 Figure 1 ('13.1 (C1: 1 Figure 2 (A) (B) ) 3 ml 4th mouth; Placement PL degree CAec) Case 6 mouth @ 7 figure Reiu z! <, cAec)

Claims (1)

[Claims] In a plating layer consisting of 15 to 24 tons of 111% Al, 0.8% or less Sl and 0.5000%; First product α-A
Since the β-Zn phase containing almost no AI does not precipitate around 1, α-Al and Zn-
Excellent anti-corrosion and flaking properties [11! Lead-aluminum alloy plated steel. A copper material is immersed in a molten metal consisting of 2.5 to 24 tons of AI%, 0.8 weight of 1% or less of Si, 0.5 tons of 7f or less of Mg, and the balance being Zn and unavoidable impurities. In the method of plating the surface of a steel material by pulling, pulling, and l-G, cooling is performed at a rate of 17°C/Sec or less until the plating layer is substantially solidified, and then the underlying copper material is Corrosion resistant 1.II characterized by cooling to 2°C so that the layer is not heated beyond its solidification range by the heat applied to it. f to a sex
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