JPS6032700B2 - 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 particularly to a zinc alloy that exhibits excellent intergranular corrosion resistance when used for hot-dip plating the surface of a steel material.

Conventionally, the zinc alloy used for melt-coating the surface of steel materials is generally about 0.2% by weight (hereinafter referred to as %).
A zinc alloy is known that has a standard composition in which about 0.2% of AI is added to distilled zinc containing Pb of 0.2% (all means weight %), and it has good results in terms of corrosion resistance and aesthetics. However, recently, steel materials that have been hot-dip plated using the conventional zinc alloys have frequently encountered problems due to intergranular corrosion.

In other words, in minimum spangle products manufactured on a continuous galvanizing line using the conventional zinc alloy mentioned above, a peeling phenomenon occurs in the plating film during the bending process several months after production. It has been revealed that this is caused by intergranular corrosion. From the above-mentioned viewpoints, the present inventors have discovered that when hot-dip plating is applied to the surface of a steel material, it has good corrosion resistance and aesthetic appearance, and particularly excellent intergranular corrosion resistance. In order to develop a zinc alloy for hot-dip plating that does not cause peeling of the plating film when processed, it is necessary to suppress the development of a brittle Zn-Fe alloy layer on the surface, especially when hot-dip galvanizing steel materials. From, 0
．． It is essential to contain about 2% AI, and about 0.03% F from the steel material to be plated in the plating bath.
Since e is eluted, approximately 0.03% of Fe is added as an impurity.
We focused on a zinc alloy containing approximately 0.2% of nails as an alloy component, and conducted various studies to impart excellent intergranular corrosion resistance to this zinc alloy. , when Mn is contained in the range of 0.01 to less than 0.1%, it has extremely excellent intergranular corrosion resistance,
Moreover, in the Mh-containing zinc alloy, it was found that the intergranular corrosion resistance due to the Mn content was not impaired even if the AI content was increased to a range of 0.05 to 2.0%. It was. Therefore, the present invention was made based on the above findings, and it is possible to reduce the brittle Zn-Fe alloy layer formed on the plated surface of the steel material to be plated by containing 0.05 to 2.0% of AI. Suppresses development and 0.01
The zinc alloy for hot-dip plating is characterized by ensuring excellent intergranular corrosion resistance by containing less than ~0.1% Mn.

Next, in the zinc alloy for hot-dip plating of this invention, A
The reason why the contents of I and Mn are limited as described above will be explained.

[a} As mentioned above, the mountain AI component has the effect of suppressing the development of the brittle Zn-Fe alloy layer that is formed on the plated surface of the steel material to be plated, but the content is 0.05%. If the content exceeds 2.0%, the desired effect cannot be obtained in the above action, and on the other hand, even if the content exceeds 2.0%, no further improvement effect can be obtained due to the action. It was set as 0%.

'b} If the Mn content is less than 0.01%, the desired excellent intergranular corrosion resistance cannot be secured;
．． If the content is 1% or more, the oxidation of the molten alloy in the plating area will be accelerated and the amount of oxides produced will increase, so the content was limited to 0.01 to less than 0.1%.

In addition, in the zinc alloy of this invention, the contents of Pb, Cd, and Sn as inevitable impurities are each 0.
．． If it exceeds 0.02%, intergranular corrosion resistance will rapidly deteriorate, so Pb, Cd, and
The allowable upper limits of Sn and Sn must each be 0.02%.

Next, the zinc alloy of the present invention will be explained using examples and comparing with comparative examples.

Examples Each of the zinc alloy finishing baths having the composition shown in Table 1 and containing 0.02% or less of each of Pb, Cd, and Sn as unavoidable impurities was prepared, and then plated. Gakufu: The plating bath having a temperature of 460°C,
Zinc alloys 1 to 7 of the present invention and comparative zinc alloy 1 each having a thickness of 50 mm on one side were applied to the surface of the steel plate by dipping a steel plate having a thickness of 0.6 skin treated with ZnC12-NACI flux for 20 seconds. A plating layer consisting of 4 to 4 plating layers was formed, respectively.

Next, the resulting hot-dip plated steel sheets having the respective plating layers of the present invention zinc alloys 1 to 7 and comparative zinc alloys 1 to 4 were heated at a temperature of 70°C and a relative humidity of 98%.
A wet test was conducted under the conditions of test time: 10 feeding hours, and the intergranular corrosion depth in the plating layer was measured.

The measurement results are shown in Table 1. Also, for comparison purposes,
The above conventional zinc alloy (Zn-0.2% Yamaichi 0.2% Pb
Table 1 also shows the results of a wet test under the same conditions for a steel plate hot-dip plated under the same conditions. -Table 1 As is clear from the results shown in Table 1, the plating layers of Comparative Zinc Alloys 1 to 3 that do not contain Mn, and even if they do contain Mn, fall outside the scope of the present invention, the desired In contrast, the plating layers of zinc alloys 1 to 7 of the present invention all have excellent resistance to intergranular corrosion. Indicates intergranular corrosion.

Further, as seen in Comparative Zinc Alloy 4, even if Mm is contained at a higher value than the range of the present invention, there is no further improvement in intergranular corrosion resistance. As mentioned above, the zinc alloy of the present invention exhibits extremely excellent intergranular corrosion resistance especially when used for hot-dip plating of steel materials. As for the material, there is no peeling of the plating layer caused by intergranular corrosion of the plating layer during bending, etc., so its reliability is extremely high, and it also extends the service life of steel materials over a long period of time. This brings about industrially useful effects such as the ability to secure

Claims (1)

[Claims] 1 Al: 0.05 to 2%, Mn: 0.01 to less than 0.1%, the remainder consists of Zn and unavoidable impurities, and the unavoidable impurities are Pb, Cd, A zinc alloy for hot-dip plating with excellent intergranular corrosion resistance, characterized by having a composition in which the content of Sn and Sn is 0.02% or less (weight %).