JPH0765211B2 - Automotive bag closing structural member - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a structural member of an automobile, and more particularly to a bag closing structural member of an automobile made of a surface-treated steel sheet.

(Prior Art) In recent years, the problem of corrosion of a car body, in particular, a bag closing structural member such as a door, has been widely taken up. For example, the critical service life of perforated corrosion described below is
The target is 10 years. As a result, many automobile bag closing structural members have been proposed in recent years.

For example, conventionally, a typical example of a bag closing structure member for an automobile has been a Zn-plated steel sheet formed by a hot dipping method, but since further improvement in corrosion resistance has been required.
Zn is changing from a simple substance of Zn to a Zn alloy (Zn-Ni, Zn-Fe etc.), and its manufacturing method is from hot-dip plating to surface appearance,
Due to problems of press formability and unit weight accuracy, electroplating is being replaced.

By the way, what is considered to be one of the major causes of the perforated corrosion of outer shells of automobiles today is salt damage caused by a road surface anti-freezing agent removed on winter roads in cold regions such as North America and Canada. . In this case, the hem, such as the hood and door (hereinafter collectively referred to as "bag closing structural member"), is exposed to a particularly severe corrosive environment. The pooling, drying, wetting and cooling are repeated. In addition, a high concentration of organic substances is observed, and because it is used for automobiles, vibration is constantly applied, and the corrosion reaction is further accelerated.

Of course, this bag-closing structure member is for automobiles, so that press-molding such as work bending must be performed, and further electric welding, that is, spot welding must be possible.

(Problems to be Solved by the Invention) Generally, since various coatings are finally applied to an automobile body, its corrosion resistance depends not only on the corrosion resistance of each plating itself but also on the corrosion resistance of its top coating film. To be strengthened. Therefore, the corrosion resistance at the part where the coating film works well is improved so that there is almost no problem today, and moreover, the form of corrosion is so-called appearance rust, and even if the corrosion proceeds excessively, the coating film swells. It only happens.

However, in the case of the above-mentioned bag closing structural member, the coating is insufficient, or in an extreme case, it is not coated at all and is left as a bare material and exposed to the corrosive environment as described above. The form of corrosion at that time is called pitting corrosion, and is accelerated by repeating high-concentration chlorine ions, drying, wetting, and cooling.

For this reason, it has been proposed in recent years to use, for example, a Ni—Zn alloy plated material having excellent bare corrosion resistance instead of the galvanized material, but it has not always been satisfactory.

However, as the specifications for the corrosion resistance of the outer panel of the automobile body including the bag-closed structure part become stricter, it is demanded to take even better measures to improve the corrosion resistance even in the bag-closed part as described above. Came.

An object of the present invention is to provide an automobile bag closing structure member having excellent bare corrosion resistance.

Another object of the present invention is to provide an automobile bag closing structure member having excellent resistance to perforation and corrosion, and excellent press formability and weldability.

(Means for Solving the Problems) Here, the inventors of the present invention have conducted various studies in order to achieve the above-described object, and found that the conventional Zn or Zn-based alloy-plated steel sheet was further coated with Al. It was found that the bag-closing structural member for automobiles made of alloy electroplated laminated plated steel sheet has excellent corrosion resistance in the unpainted state, and also has excellent press formability and weldability.
The present invention has been completed.

Thus, the gist of the present invention is that the lower layer has a Zn coating amount of 1 to 100 g / m ² or a Zn content of 70% by weight or more.
n alloy plating layer and Al with a coating weight of 1 to 30 g / m ² as an upper layer provided on this Zn or Zn alloy plating layer
A bag closing structural member for an automobile made of a steel plate having an Al alloy plating layer with a content of 70 to 98% by weight.

Here, the plating base material is not particularly limited as long as it is one normally used for automobiles, but is preferably a high-strength steel plate. The plating treatment may be on both sides or one side. Furthermore, at least some of them are acceptable.

(Operation) In the present invention, the amount of each plating layer and the alloy composition are limited as described above, and the reason will be described below.

The plating of the lower layer is less than 1 g / m ² , sufficient corrosion resistance cannot be obtained, while when it exceeds 100 g / m ² , peeling of the plating layer is observed, so that the adhesion amount of the lower layer in the present invention is 1 to 1. Ten
It was set to 0 g / m ² . It is preferably 5 to 40 g / m ² .

This lower plated layer may be either Zn or zn alloy, but is generally said to have excellent corrosion resistance.
Zn-Ni based alloys and Zn-Fe based alloys are preferred.

The Al content of the upper layer is 70-98% by weight, and the amount of Al alloy plating deposited is 1
The reason for limiting to ~ 30 g / m ² is that if it is out of this range, the desired effect will not be obtained if it is too small, while if it is too large,
This is because the formability is deteriorated due to peeling of the plating layer.

This Al alloy is not particularly limited in its alloy system unless it goes against the gist of the present invention, for example, Al-Mn, Al-Ni, Al.
-Ti and the like are preferable, and an Al alloy containing at least one of Mn, Ni, and Ti of 2 to 30% by weight and Al of 70 to 98% by weight is preferable. The reason for limiting the Al content to 70 to 98% by weight is
This is because if it is less than 70%, not only the effect of improving the corrosion resistance due to the laminated plating is small, but also the workability of the plating film is poor and it becomes unsuitable for the bag closing process of automobiles. On the other hand, if the Al content exceeds 98% by weight, the above-mentioned members will be significantly corroded when salt water is accumulated in the bag-closed structure member, that is, when the member is immersed in salt water.

Next, in order to manufacture the bag closing structure member according to the present invention, it is preferable to use a so-called electroplating method, but in the case of Zn or Zn alloy plating, for example, a sulfuric acid acidic plating greed is used, and it is manufactured in the conventional manner. do it. On the other hand, in the case of an Al alloy, it is preferable to use a molten salt plating.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example In this example, a test piece as shown in the accompanying drawings was manufactured, a so-called bag-closed structure portion was reproduced, and the state of occurrence of red rust and the state of occurrence of perforated corrosion in this portion were investigated. In the test piece shown in the attached drawings, only the plated surface was bare, and all the shaded portions were sealed with epoxy paint.

Such a corrosion resistance test is called a cycle test, but it is particularly devised by the present inventors to reproduce a situation that is as close to the actual situation as possible. According to this, first, it was soaked in a 5% NaCl aqueous solution at 35 ° C for 2 hours, then dried at 70 ° C for 2 hours, and finally kept in a humid environment of 95% relative humidity and 50 ° C for 2 hours. As a cycle, this is repeated until surface red rust or pitting corrosion occurs, and the corrosion resistance is evaluated by the number of treatment cycles until that time.

This test method, unlike the conventional test method, is a reproduction of fairly severe corrosion conditions.
It can be said that if it withstands the cycle test, it is possible to guarantee the aforementioned pitting corrosion resistance for 10 years.

The test results are summarized in the table below. From the results shown in the table, single-layer plating is not enough, two-layer plating is required, and when both upper and lower layers are alloy-plated layers, the corrosion resistance is remarkably improved.

Regarding spot weldability and press formability,
There was nothing inferior to conventional Zn plating and Zn-Ni plating.

[Brief description of drawings]

The attached drawings are side views schematically showing the shapes of test pieces used in Examples of the present invention.

Continuation of the front page (56) References JP-A-54-112731 (JP, A) JP-A-60-52592 (JP, A) JP-A-51-5242 (JP, A)

Claims (1)

[Claims] 1. A Zn coating layer having a Zn coating amount of 1 to 100 g / m ² or a Zn alloy having a Zn content of 70% by weight or more on the lower layer, and an Zn coating amount of 1 to 30 g / M as an upper layer provided on the lower layer.
An Al alloy plating layer having an Al content of m ² of 70 to 98% by weight was provided,
An automobile bag closing structural member made of laminated plated steel sheets.