JPS602374B2 - Highly corrosion resistant Zn alloy for hot-dip plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention is a method for hot-dip plating to obtain a material that has excellent corrosion resistance and does not peel or crack even when subjected to bending, by hot-dip plating the surface of a steel material. This invention relates to a highly corrosion-resistant Zn alloy for use.

In general, a method of hot-dip plating Zn or Zn alloy on the surface is known as an inexpensive and simple method for improving the corrosion resistance of steel materials, and there are many Zn alloys for hot-dip plating. Proposed.

It is true that these conventional hot-dip coatings of Zn alloys have provided steel materials with relatively good corrosion resistance, but they do not necessarily show sufficient corrosion resistance when placed in harsh usage environments. Furthermore, since a brittle Fe-based alloy layer is usually formed between the base material and the plating layer, when this is subjected to bending, it is unavoidable that the plating layer will peel or crack. . Therefore, from the above-mentioned viewpoints, the present inventors developed a hot-dip coating that exhibits excellent corrosion resistance even under harsh usage conditions and that does not cause peeling or cracking in the plated layer even when subjected to bending. As a result of research on Zn alloys for hot-dip plating, we found that when Zn contains Mh, Mn has a greater tendency to ionize than Zn.
Since Zn is preferentially dissolved, that is, it undergoes sacrificial corrosion, the corrosion resistance is improved, and Zn formed by bonding with Zn improves corrosion resistance.
Since the n-Mn alloy has good compatibility with Ti, the Ti content in Zn can be expanded, and Mn has the effect of uniformly distributing the Ti component, and also reduces the crystal grains of the alloy itself. In addition, the Zn alloy in which the Ti content is increased by the addition of Mn and the crystal grains are refined has extremely excellent corrosion resistance. Depending on the situation, additional Si
When it contains, the formation of the Fe-Zn alloy layer between the plating layer and the base material is significantly suppressed, and the peeling of the plating layer or cracking of the plating layer due to the Fe-Zn alloy layer during bending is prevented. They obtained the knowledge that the phenomenon that occurs is completely eliminated.

Therefore, the present invention was made based on the above findings, and the hot-dip plated Zn alloy was prepared with Ti: 0.1 to
1.2%, Mn: 0.05-0.6%, AI: 0.1-
Contains 1.6%, and if necessary, Si: 0.01~
0.4%, and the remaining Zn and unavoidable impurities (wt%). By hot-dip plating this Zn alloy on the surface of steel materials, it has a long-term durability under harsh corrosive environments. It is characterized in that it can be used stably for many years and can be bent without peeling off the plating layer or causing cracks.

Next, the reason why the composition range of the Zn alloy of the present invention is limited as described above will be explained.

'a} Ti The Ti component has the effect of imparting excellent corrosion resistance that satisfies even in severe corrosive environments, but when the content is 0.
If the content is less than 1%, the desired excellent corrosion resistance cannot be ensured, while if the content exceeds 1.2%, the plating workability will be impaired, so it is difficult to maintain the plating workability in a good state. To do this, the hot-dip plating temperature must be raised considerably, and as a result, the material to be plated dissolves in the plating bath and significantly disturbs the bath composition. %.

'b} Mn For the Mn component, as mentioned above, the degree of solidification of Ti in the Zn matrix is increased, and the crystal grains and partially dispersed precipitated Ti compound are made fine, and the Ti compound is uniformly distributed, This has the effect of improving corrosion resistance, but if the content is less than 0.05%, the desired effect cannot be obtained, while if the content exceeds 0.6%, the rutting property of the alloy will be extremely deteriorated. As the plating layer becomes more prone to cracking and peeling, its content should be reduced to 0.05 to 0.6%.
It was determined that

'c'AI The AI component suppresses the formation of a brittle Fe-Zn alloy layer between the surface of the substrate and the plating layer during hot-dip plating as described above, and thereby prevents the formation of the Fe-Zn alloy layer during bending. It has the effect of preventing peeling and cracking of the plated layer caused by the Zn-based alloy layer and mitigating the hardening of the plated layer due to Mn content, but if the content is less than 0.1%, the desired effect will not be achieved. On the other hand, if the content exceeds 1.6%, the corrosion resistance will decrease, so the content should be reduced to 0.6%.
It was set at 1 to 1.6%.

{'i)Si The Si component not only improves the fluidity of the plating bath to form a smooth and glossy plating layer, but also further suppresses the formation of the Fe-Zn alloy layer and dramatically improves corrosion resistance. Therefore, if these properties are particularly required, it is included as necessary. However, if the content is less than 0.01%, the desired effect of improving the above-mentioned effects cannot be obtained; on the other hand, if the content is less than 0.01%,
If the content exceeds 4%, the plating properties will be impaired, so the content was set at 0.01 to 0.4%.

Next, the Zn△gold of the present invention will be explained in comparison with the Zn△ gold example.

The present invention Zn having the component composition shown in Table 1 for each example
Alloys 1 to 12 and Zn were prepared for hot-dip plating, and then pretreated with a ZnC12-NH4CI-based flux in the hot-dip plating chamber in which the plating temperature was maintained at 460-480°C. One side thickness: 13〃 on the surface of the steel plate by soaking it for 5 seconds
The kite's plating layer was formed.

Next, the resulting Zn alloy plated steel sheet 1 of the present invention
~12 and secondary Zn-plated steel sheets, Fe-Zn
In addition to observing the presence or absence of a system alloy layer, JIS Z2371
A salt water mist test based on JIS Z2248 and a bending test based on JIS Z2248 were conducted.The salt water spray test measured the time until red rust appeared on the plated surface of the steel plate, and the bending test measured the state of the plating layer on the bent surface. Observe that there is no peeling or cracking in the plating layer.◎
The cases in which peeling and cracking were clearly observed in the plating layer were evaluated as x marks. These measurement results are also shown in Table 1. From the results shown in Table 1, the Zn alloy plated steel sheets 1 to 12 of the present invention all exhibit excellent corrosion resistance and have a plating layer with good adhesion that does not cause any peeling or cracking even when subjected to bending. On the other hand, in conventional Zn-plated steel sheets, Fe-Zn alloys are formed, and the corrosion resistance and adhesiveness of the finishing layer are extremely poor.

Furthermore, as seen in Zn alloy plated steel sheets 1 to 12 of the present invention, T
It is clear that the higher the i content, the better the corrosion resistance. Furthermore, it was confirmed that when the Zn alloy of the present invention was hot-dipped and further subjected to chromate treatment, the corrosion resistance was further improved.

As mentioned above, according to the highly corrosion-resistant Zn alloy for hot-dip plating of the present invention, excellent corrosion resistance can be ensured even under harsh usage conditions, especially by hot-dipping the surface of steel materials. , and has extremely good adhesion to the surface of steel materials, with almost no formation of a brittle Fe-Zn alloy layer, resulting in industrially useful effects such as no peeling or cracking of the plating layer during bending. It is possible.

Claims (1)

[Claims] 1 Ti: 0.1 to 1.2%, Mn: 0.05 to 0.6
%, Al: 0.1 to 1.6%, and the remainder consists of Zn and unavoidable impurities (weight %). 2 Ti: 0.1-1.2%, Mn: 0.05-0.6
%, Al: 0.1-1.6%, Si: 0.01-0.4
%, with the remainder consisting of Zn and unavoidable impurities (
1. A highly corrosion-resistant Zn alloy for hot-dip plating, characterized in that it has a high corrosion resistance (% by weight or more).