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Safety knowledge of galvanized sheet

Safety knowledge of galvanized sheet

Automobile body shell is mostly metal material, mainly with steel plate.

How does the steel plate of modern automobile prevent rust? Why do some cars claim to be rust resistant for more than 10 years? Galvanized sheet steel is widely used in automobiles because of its good corrosion resistance. In early experiments, it was found that when iron and zinc were placed in salt water without any wire connection, iron and zinc would rust, iron would give rise to red rust and zinc would give rise to "white rust"; If a wire is connected between the two, the iron will not rust and the zinc will give rise to "white rust", so that the zinc will protect the iron, this phenomenon is called sacrificial anode protection.

It is this phenomenon that engineers apply to the actual production, the production of galvanized steel. After research, when the amount of galvanized 350 g/square meter (single side), galvanized steel plate in the outdoor life (red rust), pastoral zone is about 15118 years, industrial zone is about 3 to 5 years, which is several times or even more than ten times longer than ordinary steel plate.

Since the 1970s, the car body steel plate is galvanized thin steel plate. When assembling, the galvanized surface is placed inside the car to improve the corrosion resistance of the body. The non-galvanized surface is placed outside the car and sprayed with paint. With the continuous improvement of corrosion resistance requirements of automobiles, galvanized steel plate continues to increase the weight of galvanized layer, but also the appearance of double galvanized steel plate.

But because the increase of galvanized weight will also make the electric energy consumption of galvanized greatly increase, resulting in the rise of material cost, so in the late 1970s there was a galvanized steel plate produced by hot dip galvanized process, known as hot galvanized steel plate. This galvanized steel plate with continuous hot dip galvanizing process: cold rolled plate (note *) → heating → cooling to galvanizing temperature → galvanizing → cooling → straightening.

In order to meet the various requirements of automobile galvanized steel plate, some manufacturers in galvanized steel production line for galvanized steel plate diffusion annealing and other special treatment, in order to form a "zinc-iron" alloy coating on the surface of the steel plate, which is characterized by better weldability and corrosion resistance than pure zinc coating plate. Later also appeared such as "zinc-aluminum-silicon", "zinc-aluminum-rhenium" and other alloyed hot galvanized steel plate, making the corrosion resistance of hot galvanized steel plate exponentially improved, and the combination of paint between long-term stability.

At present, galvanized steel plate has been widely used in cars. The thickness of galvanized steel plate is from 0.5 to 3.0 mm, and the body covering parts are mostly 0.6 to 0.8 mm galvanized steel plate. Most of the body parts of Audi car in Germany are galvanized steel plate (some of them are aluminum alloy plate), Buick car in the United States uses more than 80% of the steel plate is double-sided hot-dip galvanized steel plate, Shanghai Passat body of the outer cover parts using electric galvanizing process, the inner cover parts using hot-dip galvanizing process, which can make the body anti-rust shelf life as long as 11 years.

Material is an important factor affecting automobile quality. In modern automobile, body material accounts for a large part of the whole car material.

In order to improve the driving economy of cars and reduce the weight of cars is the goal of the world's major car manufacturers. In recent years, more and more cars are using non-steel materials such as aluminum or plastic as body parts. For example, Audi A2 body is made of aluminum, Nissan SUV "Qijun" is made of plastic front fender, and more passenger car bumpers are made of plastic. The growing use of non-steel materials for body parts poses an immediate threat to steel companies that are highly dependent on automotive manufacturing.

Therefore, the research and development of light and high strength automobile steel plate has become a hot spot in steel enterprises for many years. At present, ordinary mild steel plate is used most in automobile production.

Low carbon steel plate has good plastic machining performance, strength and stiffness can also meet the requirements of the automobile body, at the same time can meet the requirements of the body welding, so it is widely used in the automobile body. In order to meet the automobile manufacturing industry pursuit of lightweight requirements, iron and steel enterprises launched a series of high strength automobile steel plate.

This kind of high strength steel plate is obtained on the basis of low carbon steel plate by strengthening method, the tensile strength is greatly enhanced. With high strength characteristics, the mechanical properties of the vehicle body can be maintained even when the thickness is reduced, thus reducing the weight of the vehicle.

BH steel plate, for example, is pressed and formed under low strength conditions and then subjected to paint processing and heat treatment to improve its tensile strength. In contrast, the strength of steel plate produced in the past at 440MPa can be increased to 500MPa after using this processing technology.

Originally with a thickness of 1 mm steel plate to do the side plate, with high strength steel plate thickness only 0.8 mm. The use of high strength steel plate can also effectively improve the impact resistance of the car body, prevent the impact of the sand in the road due to the impact of dents, prolong the service life of the car.

High strength steel plate for vehicle should have the characteristics of high strength and good ductility. At present, there are BH steel (paint hardened steel), DP steel, TRIP steel, microalloy M steel, IF steel with high strength and no gap.

They are generally used for high strength, high collision resistance absorption energy, forming requirements of strict parts, such as wheel, reinforcing member, bumper, bumper, with the progress of performance and forming technology, high strength steel plate is used in the car, such as roof, door inside and outside the plate, engine cover, luggage cover, etc. Now many high - grade cars are made of high - strength steel plates.

High strength steel plate after more than 20 years of development and production in developed countries, most of the standardized and conventional production of series products, and widely used in the production of many automobile components. The average use rate of high-strength steel plates in Japanese automobiles was 25% in 1993 and 36% in 2000.

AISI organized 13 steel companies around the world to research and develop "Ultra-light body Research" (ULSAB). In March 1998, in Michigan, the United States, the high-strength steel body was exhibited. The high-strength steel body used in the body was about 86%, and its average weight was 25% less than that of the ordinary steel body, which was very attractive to automobile manufacturers. In January 1999, 34 of the world's largest steel companies jointly funded the launch of ULSAB-AVC, a high-strength steel body research and development project. Through the use of high-quality steel and new manufacturing technology, the vehicle can reduce weight and improve economy to meet the more stringent crash standards in 2004 and the implementation of Euro IV emission standards in 2005.

From here, it can be seen that the development of high-strength steel plate for vehicles is not just a matter of body material renewal, it is also about whether the vehicle can meet the new environmental and safety standards. The development and application of high strength steel plate is closely related to forming, coating and welding technology.

Stamping is the most important part of automobile manufacturing.


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