Superdyma is an alloying (zn-11al3mg-0.2si) hot-dip galvanized steel sheet with high corrosion resistance and alloying (zn-11al3mg-0.2si) by adding Al, Mg and Si to Zn. In recent years, due to the improvement of environmental protection awareness, first
of all in the field of home appliances to promote chrome free products, in building materials products, the requirements of chromium free products are also increasing. According to the public building engineering standards issued by the Ministry of
land and transportation of Japan, chromium free may be used as building material products in 2016. In this context, Nippon Steel Sumikin has developed a variety of chrome free post-treatment films suitable for superdyma to meet the new requirements
of environmental protection.
1. Structure of chromium free post treated galvanized steel sheet
Superdyma s a kind of steel plate with special treatment layer attached on the alloyed coating. The coating structure is shown in Fig. 1. The special treatment layer is a treatment
layer with corrosion inhibitor added to the special film with corrosion factor shielding function, so it has both corrosion factor shielding function and self-healing function, and can replace chromate film. According to the different service conditions
of the coated steel plate, the inorganic / organic components and corrosion inhibitor components of the chrome free post-treatment coating were optimized, and two kinds of non chrome post-treatment coatings were developed: one was QN type skin film with
the same corrosion resistance as the traditional chromate coating, and the main component was inorganic compounds; The other is qfk type film with excellent corrosion resistance and processability and mainly composed of organic compounds.
method for properties of chrome free aftertreatment film
Table 1 shows the condition of the steel plate used for the film performance test without chrome treatment. The original plate is superdyma (the coating amount is 90g / m2). The original plate
is treated by QN and qfk without chromium respectively. The traditional chromate post-treatment steel plate is used as the contrast steel plate for test.
2.1 corrosion resistance
The end of the sample was sealed, and the corrosion test was
carried out on the plane part of the sample by salt spray test (JISZ2371), and the corrosion resistance was evaluated according to the area of white rust. In addition, outdoor exposure test was conducted in gonggu island. The end and back of the sample
were sealed, and the exposed corrosion test was carried out with the specimen facing south and inclining 45 degrees. The corrosion resistance was evaluated according to the area ratio of white rust.
The dynamic friction coefficient is one of the indexes to judge the formability of steel plate. The dynamic friction coefficient of steel plate was measured by heidon-14 dynamic friction coefficient tester. The sliding piece
is a stainless steel ball with a diameter of 10 mm and a load of 1.0 n. The sliding speed of steel ball is 150 mm / min, and the dynamic friction coefficient shall be determined according to the steel ball.
In addition, in order to evaluate the
sliding property of the steel plate plane during die stamping, the dynamic friction coefficient in the steel plate drawing test was measured. The test steel plate was clamped with a plane die made of SKD11 and the contact area was 30mm × 25mm. The clamping
force was 0.5kn. The sample is drawn at the speed of 200 mm / min, and the friction coefficient is determined according to the drawing process.
The interlayer resistance and contact resistance (grounding) of the test materials
were measured. The interlayer resistance was measured according to jisc2550, the test voltage was 0.5V, and the test pressure was 2n / mm2. The contact resistance measurement method is four probe method.