JPS5852494A - Iron-zinc alloy plated steel material - Google Patents

Abstract

PURPOSE:To obtain steel materials having particularly high rust resistance, corrosion resistance, chemical convertibility, paintability, workability and weldability by forming the iron-zinc alloy plating on the steel materials for automobiles, household electrical appliances, etc. of two layers of respectively different alloy structures. CONSTITUTION:Steel materials having an iron-zinc solid soln. alloy layer of 0.5-7g/m<2> thickness and <=35wt% zinc content of an upper layer (surface) and an iron-zinc intermetallic compd. alloy layer of 5-25g/m<2> thickness consisting of >=1 kind among delta1, GAMMA, zeta, phases on a lower layer. These plating layers are obtained by plating the steel materials first with an insoluble anode at 60-200A/dm<2> current density and 40-80 deg.C bath temp. by using a sulfate bath of 0.4-0.9 Zn<++>/Fe<++> weight ratio in the bath, 100g/l total and within solubility limit on sulfate concn. of both metals, and 0.8-2.3pH. If the thickness of the layers is below the lower limit, corrosion resistance is insufficient, and if in excess of the upper limit, productivity, workability and weldability are degraded. Thereafter, the steel materials are plated under the similar conditions at 0.02-0.15 Zn<++>/Fe<++> weight ratio. Since the thickness of the layers is thin, formability and workability are good. Chemical convertibility is good at above the lower limit, and the generation of defects in the paint film is small.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an iron-zinc alloy plated steel material having an alloy plating layer having a two-layer structure of a solid solution alloy layer and an intermetallic compound alloy layer.

Steel is an important metal material because it has high strength, good workability, and can be supplied in large quantities, and is used in large quantities for automobiles, home appliances, etc. However, it has the disadvantage of being easily rusted and corroded, and more advanced properties are being required in terms of weldability, workability, chemical conversion treatment, paintability, etc. ◇For this reason, surface treatment of steel is extremely important. BACKGROUND ART Conventionally, steel materials have typically been galvanized, followed by chemical conversion treatment, and then coated with a paint such as electrodeposition paint. Regarding zinc plating, attempts have recently been made to further improve corrosion resistance, weldability, paintability, etc. by applying IFe-Zn alloy plating on steel materials by electroplating.

In the present invention, this iron (Pe)-zinc (, Zn) alloy plating is made into two layers each having a different alloy structure, and has particularly high rust prevention, corrosion resistance, chemical conversion treatment properties, paintability, workability, and weldability. The goal is to achieve the following goals:

That is, the present invention relates to Fe-Zn alloy plated steel material, and the upper layer (surface) has a thickness of α5 to 7 P/m.
A solid solution alloy layer with a Zn content of 35% by weight or less is provided as a lower layer (inner layer), an a1 phase, a ζ phase, and an inner layer of ζ phase.
5=25 y/m2 thick Fe-Zn consisting of seeds
In the present invention, which is characterized by having an alloy plating layer having a two-layer structure with an intermetallic compound layer applied thereto, the adhesion with the chemical conversion treatment layer and the paintability of electrodeposition are strengthened mainly in the upper layer. , mainly enhances corrosion protection in the lower layer. If only the upper layer is used, the anticorrosive effect is poor, and if only the lower layer is used, the chemical conversion treatment property is not sufficient.

In the present invention, firstly, δ is applied by electroplating onto a steel material as a base material.
An Fe-Zn based intermetallic compound alloy layer with a thickness of 5 to 25 f/m'' consisting of one or more of the l phase, F phase, and ζ phase and substantially free of the η phase is used as the lower layer. Let it form.

Such an intermetallic compound alloy layer can be used, for example, as a plating bath, when the weight ratio of zn++/Fe'' in the bath is 04 to 09.
% of both metals within the solubility limit, a sulfate bath with a pH of 08 to 2.3, a current density of 60 to 200 A/dm, and a bath temperature of 40 to 80%.
It can be formed by electroplating using an insoluble anode under conditions of .degree. Is the δ1 phase mainly? e
It has a composition of Zn, contains 6 to 93% by weight of Ba, and the ζ phase is mainly F'! l5zn21 and Fe3Z
n□. Zn is a mixed crystal containing 72-80% Zn, the ζ phase mainly has a composition of FeZn13, and Zn
It is said to contain 8 to 94.5% by weight of O&, and has excellent corrosion resistance.

However, if the thickness is less than 7 m2, the corrosion resistance effect cannot be achieved, and if the thickness exceeds 25 f/m, the merits of manufacturing by electroplating will not only decrease from the viewpoint of productivity, but also the processability and On the contrary, weldability deteriorates.Therefore, in the present invention, a thickness of 5 to 25 p/m2 is desirable.

On top of this lower layer with a thickness of α5~7 f/m2, Z
A Fe-Zn solid solution alloy layer having an n content of 35% by weight or less is formed.

Such a solid solution alloy layer can be formed, for example, when the plating bath has a Zn++/Pθ” weight ratio of 002 to α15,
The m-'aI salt concentration of both metals is 100 y/41 or more within the solubility limit, and the pH is α8-2. ．． Using a sulfate bath with a current density of 60-200 μm/dpn” and a bath temperature of 4.
Under conditions of 0-80°C.

It can be formed by electroplating using an insoluble anode. Compared to conventional Zn electroplating and We-Zn hot-dip plating, the solid solution alloy plating of the present invention causes fewer coating defects such as blisters on the electrodeposited coating, and also has a thinner coating layer. Therefore, it has good moldability and processability. The solid solution alloy layer is 05P/! If it is less than II2, the chemical conversion treatment property is not cakey and coating film defects such as blisters are likely to occur. Furthermore, the solid solution alloy layer itself may dissolve and disappear during chemical conversion treatment (it is possible that the solid solution alloy layer itself dissolves and disappears).Also, even if it exceeds the lid/m", the chemical conversion processability will not improve.α5~7P/m+a, preferably 1~4y/ms A range of is desirable.

In this way, the We-Zn alloy plating layer has a two-layer structure with a lower layer suitable for the base material and an upper layer suitable for chemical conversion treatment and electrodeposition coating, making it highly functional for modern steel materials such as automobiles. For example, when used in automobile steel materials, salt damage from snow melting salt sprinkled on roads and chipping damage from flying pebbles etc. may occur. There is.

The damage caused by salt is particularly severe, and in severe cases, the steel itself can become perforated within several years, posing a serious problem from a safety standpoint. For this reason, thick Z with high Zn content
Until recently, this problem has been dealt with by n-electroplating and Fe-Zn alloy hot-dip plating, but in this case, the suitability for chemical conversion treatment and electrodeposition coating is not good. In the present invention, two layers are used to meet the respective requirements.

The steel materials of the present invention are usually subjected to chemical conversion treatment, undercoating such as electrodeposition coating, and necessary surface coating before being used for each purpose.

Examples will be described in more detail below.

Examples 1 to 5 and Comparative Examples 1 to 5 Using α8mm spa as the material, alkaline electrolytic degreasing, water washing, cathodic electrolytic pickling, and water washing were performed according to the usual method. Examples 1 to 5 and Comparative Examples 1 to 4 For the plating bath, the bath composition is Fe8o, -7H2o 350 ri/2
, Zn80.・7H2O150p/L (NH,),
80.30f/It, pHL2, bath temperature 60℃
using a bath with a current density of 100 A/(111”
The lower layer was electroplated using a titanium substrate plated with platinum as an insoluble anode as a counter electrode. Regarding Comparative Example 5, the plating bath had a bath composition of Zn804.
・)HaO250ri/J! .

(HH,), 80.15ri/II, Ha, 80.100
Electroplating of the lower layer was carried out using a bath with a pH of 1 to 1, pH 12, and a bath temperature of 50° C., a current density of 40 A/(L! 11”), and a zinc plate as the anode for the counter electrode. Also,
The upper layer was solid solution alloy plated by the method described in the text. Both were adjusted by changing the plating time at the plating company. The plating amount and phase were confirmed by atomic absorption spectrometry and xIs diffraction, respectively.

The following evaluations were performed on the obtained samples.

Adhesion of the plating layer A white vinyl tape was attached to the plated surface, and 07 bending was performed with the mirror surface facing inside to measure the peeling of the rounded layer adhering to the tape (powdering test).

B. Phosphate treatability Phosphate treatment uses phosphoophyllite (Phogph).

phyllite, zn2Fe(po,)2)-based immersion treatment chemical, GrE? manufactured by Nippon Paint ■. -D
-2000, TiI4~18, AR18
~20, Zn 11000-200pp, Fe50
The sample was immersed for 120 seconds in a solution adjusted to ~1100 pp.

(1) Film Amount The phosphate film amount was determined by dissolving the film in a 2% by weight CrO3 solution.

(2) P ratio I asked for help.

0. Corrosion resistance after coating The sample plate after the above phosphate treatment was air baked at 120°C for 10 minutes, and Power Top U-30 manufactured by Nippon Paint ■ was cationically electrodeposited thereon. Samples at this stage were used for three evaluations: cross-cut peeling, red rust resistance, and red rust generation time. In addition, regarding water-resistant adhesion, Amirac TP-16R manufactured by Nippon Paint ■ was applied to the painted board that had been coated with the above cationic electrodeposition coating so that the dry film thickness was 20 μm.
Painted to a dry film thickness of 25 μm and baked at 140°C.
x 20 minutes), and then apply Nippon Paint's Amirac 030 as a topcoat to a dry film thickness of 30 coats (
The samples were evaluated.

(1) Water-resistant adhesion A top-coated plate is immersed in hot water at 40℃ for 240 hours, and after the immersion is finished, 10 2mm square base holes that reach the steel substrate are immediately formed.
The film was peeled off with cellophane tape in increments of 0, and the peeled area ratio was evaluated.

(2) Dry film thickness of cationic electrodeposition paint during cross-cut peeling 20 seconds
time, J Engineering 82371), and during its peeling (one side m
m).

(3) Red Rust Resistance On a plate coated with a cationic electrodeposition paint with a dry film thickness of 20 μm, the occurrence of red rust at the cross-cut portion was observed after a salt spray test (360 hours, J Engineering 82371).

(4) Time for red rust to develop A salt spray test (J Engineering 82371) was conducted on a board coated with a cationic electrodeposition paint with a dry film thickness of 5 μm without cross-cutting, and the time until red rust appeared was measured.

The above results are shown in Table 1.

Claims (1)

[Claims] 1- The upper layer has a thickness of α5 to P/- and has a zinc content of 35
Iron-zinc solid solution alloy layer with weight% or less, δl in the lower layer
5 to 25 consisting of at least one type of phase, ζ phase, and the inner layer of ζ phase
An iron-zinc alloy plated steel material having an alloy plating layer consisting of a two-layer structure with an iron-zinc intermetallic compound alloy layer of y/m" thickness.