JPS6033892B2 - Zinc alloy for hot-dip plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zinc alloy for hot-dip plating, and more particularly to a Zn-Yamaichi Si-based hot-dip plating alloy that has excellent corrosion resistance and adhesion.

In recent years, the use of galvanized products made by galvanizing steel materials has been expanding rapidly, and along with this, there has been a demand for plating alloys with higher corrosion resistance and adhesion.

In particular, since weight reduction by reducing the plate thickness of structural steel materials is achieved by the corrosion resistance of the plating alloy, there is a demand for a plating alloy with further improved corrosion resistance. As a method to improve the corrosion resistance of galvanized products, there is a general method of increasing the amount of zinc deposited, and adding elements such as AI, Pb, Sn, Ti, and Si, which are said to be effective in corrosion resistance, to zinc alloys for plating. A method has been proposed in which it is added to However, in the case of hot-dip plating, there is a problem with the stability of the alloy composition in the plating bath, and the drawback is that corrosion resistance and adhesion vary. In order to improve these drawbacks, a Zn--N--Si hot-dip plating alloy consisting of 55 wt% N, 31.5 wt% Si, and the remainder of Zn has been adopted. However, the metal alloy has a high plating temperature and cannot be plated in an oxidizing atmosphere, so it has drawbacks in terms of workability and equipment. As a method of lowering the plating temperature, an alloy in which the N content is reduced to 1 t% or less has been proposed. For example, N: 5 to 20 wt%,
A hot-dip plating alloy consisting of Si: 5 wt% or less and the remainder Zn is disclosed in JP-A-50-104731, and N: 2 to 2.
0wt%, Si: 0.001-0.5wt%, Sn: 0
．． JP-A-54-23033 discloses an alloy for plating consisting of 0.01 to 0.1 M% and the remainder Zn. However, in the former case, the corrosion resistance of the plated film obtained is insufficient, and in the latter case, although the plated film has excellent insect resistance, it peels off during processing such as bending, and the adhesion and processing I have a sexual problem. An object of the present invention is to provide a Zn-AI-Si alloy for hot-dip plating that has excellent workability, corrosion resistance, and adhesion.

The present inventors have stated that ``In order to achieve the above-mentioned purpose, as a result of intensive research, it was found that when the ratio of Sj to Sj is within a certain range, it is possible to bring out the effect of Sj as a corrosion-resistant element;
It was discovered that the effect was further doubled by adding g, and the present invention was completed.

The present invention provides a Zn-N-Si hot-dip plating alloy,
The composition of the peak and Si expressed in weight% is expressed by the relational expression '1}N=3
．． 50 Six (2 to 10)...{1} (However, N
<8.00.1<Si<1.25.

), and is characterized by containing Mg: 0.01 wt% or more and less than 0.05 wt% and unavoidable impurities.

In the present invention, when the relationship between M and Si of the Zn-AI-Si alloy falls within the range of the above relational expression {1), it exhibits excellent insect resistance as shown in FIG. Relational expression {1-Si
When the value in parentheses is less than 2, the insect resistance of the resulting plating film tends to gradually decrease, and when it exceeds 10,
This is not preferable because the oxidizing property increases rapidly. However, A
I is -8. If it exceeds t%, the viscosity of the plating increases and the solidification temperature range increases, which is undesirable because thermal separation tends to occur due to long-term holding. Preferably, it is 5 wt% or less. Furthermore, if the amount of Si added exceeds 1.25 wt%, the plating temperature will increase, which is not preferable. moreover,
Addition of Mg has the effect of preventing intergranular corrosion caused by Pb, Cd, Sn, etc. contained as unavoidable impurities in Zn-AI alloy, and although it varies depending on their content, at least 0.01 wt% is added. 0.05 wt% is sufficient. As shown in the examples and FIG. 1, the plating film using the hot-dip plating alloy of the present invention exhibits extremely excellent corrosion resistance, with a corrosion loss of 0.15 nights/force hr or less in the salt water fog test. It also has excellent adhesion.

Furthermore, the plating operation using the hot-dip plating alloy of the present invention has the advantage that it can be performed in the atmosphere at a low temperature of 480 oo or less. The present invention provides a Zn-N-Si hot-dip plating alloy that has excellent corrosion resistance, adhesion, and workability, and has extremely great industrial significance. Hereinafter, the present invention will be explained in more detail with reference to Examples.

However, the scope of the present invention is not limited by the following examples. Example A cold-rolled steel plate having a plate thickness of 0.3 ribs was degreased using a 6 wt % caustic soda aqueous solution, pickled with 6 wt % hydrochloric acid, and then washed with water.

Next, a 1% NH4CI-ZnC12 aqueous solution [N
H4CI/ZnC12=3/1 (M)], the steel plate was soaked and dried in an electric furnace. The steel plate has the AI shown in Table 1.
The Zn alloy having the relationship between
A plated steel plate was obtained.

The obtained plated steel sheet was subjected to a salt spray test and a repeated bending test.

The results are shown in Table 1. Salt water fog test is JISZ-2
371, after 72 hours of salt water mist, the rust immersed in a 5wt% ammonium acetate aqueous solution at a temperature of 50°C for 2 seconds was removed, and the corrosion rate (unit/hour) was determined from the weight difference. Calculated. In the repeated bending test, the number of times it was bent 90 degrees until the plating film peeled off was determined. Comparative Example A steel plate treated in the same manner as in Example was immersed in a Zn alloy solution having the composition shown in Table 1 for 10 seconds and then pulled up to obtain a plated steel plate.

Table 1 shows the results of a salt water mist test and a repeated bending test under the same conditions as in the examples. In Table 1, X represents the value when expressed as AI Go 3.50 Sixx.

[Brief explanation of drawings]

Fig. 1 When the relationship between 1 and Si is expressed by the relational expression AI = 3.5 x Six x, in the relationship curve between x and corrosion rate (unit/hour), 1 is Sj = 0.25wt%, 2 is
Si=0.5wt%, 3 represents Si=1.25wt%.

Claims (1)

[Claims] 1. In a Zn-Al-Si hot-dip plating alloy, the composition of Al and Si expressed in weight percent satisfies the relational expression (1) Al=3.
5+Si×(2-10)...(1) (However, Al<8
．． 00.1<Si<1.25. ), and contains Mg: 0.01 wt% or more and less than 0.05 wt% and unavoidable impurities.