aluminum sheet coil compete with steel

Steel has always been the main material in automobile manufacturing.But with the society to environmental protection and energy-saving voice increasingly high, the national fuel consumption policy tends to tighten, consumers also put forward higher requirements for vehicle safety, which has forced automakers to seek stronger and lighter vehicle building materials.The use of high-strength steel is expected to peak at nearly 15 per cent of vehicle weight by 2020, according to a report by the centre for automotive research.By 2040, that share will gradually fall to nearly 5 percent, when other lightweight materials will have a place in the automotive materials business.

With less than half the weight and better corrosion resistance than the raw material of steel, aluminum once posed a threat to automotive steel.However, due to the relatively high price of aluminum and the difficulty in manufacturing and maintenance processes, many auto manufacturers prefer to replace ordinary steel with high-strength carbon steel. Therefore, the game between steel and aluminum is played out.At the automotive and environmental forum held recently, experts in the industry such as wang li, chief researcher of baosteel research institute, zhu qiang, chair professor of southern university of science and technology, Chen shuming, professor of jilin university, zhang haitao and so on discussed the “steel and aluminum competition” in the round table.

Steel has great application potential and cost advantage

With the continuous development of automotive steel, automotive steel is not a few decades ago many people’s impression of low carbon steel, now automotive steel plate is thinning, but steel strength and corrosion resistance has been greatly improved.In order to meet the challenge of new materials, many steel production enterprises actively develop lightweight and high-strength steel that can compete with aluminum alloy and other materials.According to the figures, just 212 euros of extra cost per vehicle for high-strength steel is needed to achieve weight loss and fuel savings of about 5%.

What is the current situation and application potential of high-strength steel in China’s automobile market?Wang li analyzed this, he said that the current automotive steel in the continuous efforts to reduce the weight, “which used a lot of technology, one of the contribution is high strength steel.For the past 20 years or so, there has been an iisa project in which baosteel has been participating. If steel mills continue to use steel by developing new materials, what is the potential of steel?Through so many years of development, the last advice or technology to the auto plant, one is to develop a variety of advanced high-strength steel is still on the way, the second is to develop many advanced manufacturing technology, and at the same time introduced the concept of full life cycle.For example, the latest development of an electric concept car, the body weight reduction of up to 40%, it with high strength steel strength is higher, more than 1000 mpa of 40%, only 5% is soft steel, steel through the strength of this potential is still relatively large.

“From the sales data of baosteel, China’s self-owned brands accounted for 41% of the consumption of high-strength steel in 2017, and more than 28 million European, Japanese, American and Korean self-owned cars were sold. The materials provided by baosteel are relatively high-grade, and our national average level will be a little lower than this level.The application ratio of high strength steel reaches an average of 42-45% from our data last year, which should be relatively low, and 60-70% abroad. This gap is our potential.”

The competition between aluminum sheet and steel, aluminum’s outstanding advantage is low density, and to achieve body weight reduction, in keeping with the proportion of steel, the need to thin the steel plate.Whereas ordinary steel sheets are usually between 0.7 and 0.75mm thick, today’s super-strength sheets are only 0.65mm or thinner, and the new opel seferli’s bonnet is 0.6mm thick.

According to wang li, “if the specific gravity of steel is not changed, the weight can only be reduced to thinner, but the density can be adjusted. Now we have a new idea to do, which is to adjust the density of steel.The advantage of aluminum is the low density, the competition to a certain extent I can use your advantages to adjust my density.We raised the elastic modulus of steel, and now it’s in the lab.One point I want to make is that because steel itself remains unchanged on the basis of the existing industrial industry, there is still a lot of room for innovation. From this perspective, steel still has some vitality, as well as its market share.If the car sells for more than 200,000 yuan, it will use more materials. If the car sells for 100,000 yuan, it will still use steel.”

But the cost problem also becomes other material to replace the main body position of steel hard reason.Shu-ming Chen said, “under the trend of the automotive lightweighting, although now everyone doing light materials, such as aluminum alloy, magnesium alloy and other lightweight composite materials, high strength steel or in the main body position, but I think the main factors is the cost, I believe that if the cost of carbon fiber, carbon fiber will replace the likely, it’s not impossible, the key now cost is too high, steel at present also has very large cost advantage.”

In addition to the cost, within the strength range to meet the demand, the good and easy forming process also becomes the reason why steel is difficult to be replaced.”From a development point of view, the strength of the steel for the car is not very high. 1000 mpa is enough.High strength steel is now mainly carbon to strengthen, many have done 2200 mpa, but above 2200 mpa, will produce a mutation, or 2200-2500 mpa carbon to strengthen basically impossible.”I believe this steel will definitely have other materials to replace carbon, the strength will be higher and higher, but it is not necessarily used in the car, it may be used in other areas of high strength.For cars, we have a wide selection of steel under 1000 mpa, low cost and very good forming process, so it will be very difficult to replace steel in our country for a while.”

And from the structural properties of steel itself, it has a good repair.Zhu qiang pointed out that steel itself with phase transition has some advantages in some applications.”For automotive steel, because the steel has phase transitions, if it hits a pit, it can be easily repaired, which is relatively difficult for composites or aluminum.For example, aluminum alloy composite material, if a hole is broken, the basic repair is a whole piece of replacement, the cost is also high, this is the weakness of aluminum itself compared with steel.

Aluminum alloy development period encountered before the Wolf after the tiger

Figures show that it takes 725 kilograms of steel and cast iron and 350 kilograms of stamped steel to make an average mid-size car.By contrast, the weight of aluminium in a European car increased from 50kg in 1990 to 131.5kg in 2005, with most still used in engine internals and cylinder blocks and rising.Aluminium is also popular in cars because it is less than half the weight of iron, the material used to make steel, and has a better corrosion resistance than steel.

At present, the use of aluminum alloy to make the body of the model has been a lot of.Since its birth in 1994, the audi A8 has adopted the all-aluminum space frame body structure, and the Model S developed and manufactured by tesla also adopts the all-aluminum body.After the all-aluminum production line of chery jaguar land rover in changshu, jiangsu province was put into production, the first domestic car, the new jaguar XFL aluminum alloy material application rate reached 75%.The nobelis RC5754 high-strength aluminum alloy used in many of the jaguar XFL’s body parts has a yield of 105-145 Mpa, a tensile strength of 220 Mpa, and a good performance in strength, corrosion resistance, connectivity and molding rate.

“Now more and more aluminum is used for cars, especially for chassis parts, in addition to the body, now a lot of cars continue to walk this road.There are some problems with the all-aluminum frame, but they are being worked out.”Zhang haitao, a researcher at soochow university, said, “why use all-aluminum frames?The first cost is relatively low, the cost of a small car may be a few thousand yuan a frame, the most important is the section design is very complex, and aluminum bending and torsional stiffness is better than steel.

In addition, aluminum has better resource recovery and longer life cycle than steel.Zhu qiang said, “the recycling loss rate of aluminum is only 5 to 10 percent. If steel is rusted, it is very difficult to recover. Aluminum alloys have advantages in the long run.If the wheels with aluminum, now we have a consensus that aluminum alloy wheels must be better than steel, because steel is easy to touch rust, aluminum alloy scraping does not matter, this performance steel is no way to compare, aluminum alloy composite performance in this respect has a unique advantage.”In addition, the long life cycle is also important for the automotive industry, and every product has to be designed with the long life cycle in mind. Aluminum also has an advantage in this respect.”

Zhu qiang also pointed out that the composition of aluminum alloy is relatively complex, how to recycle the classification is also a problem.”For example, for the framework of die-casting, the two alloy plates can not be used together, they must be separated, it takes a lot of effort to connect them, and it takes a lot of effort to separate them. On the one hand, the recovery efficiency is not high, and on the other hand, it is not easy to manage.In addition, there are a lot of issues involved in aluminum recycling, such as reduced use, good aluminum recycling can be used to make something that is not important, what would have been good things end up with a low value.”

In terms of the fatigue properties of the materials, aluminum is more risky than steel, and processing is limited.”The fatigue performance of key components of vehicles is controlled not only by the properties of the materials themselves, but also by the defects of the materials.Aluminum oxidation capacity is very strong, these defects have a relatively large impact on the fatigue performance of components, very easy to go wrong.Steel does not oxidize as much and its defects have a relatively low impact on fatigue performance.”Zhu qiang said, “only with forging can not be complex components, forging must be processed, otherwise it can not meet the needs of structural design.Generally speaking, there are two kinds of forging, either giving up the structural optimization or reprocessing. However, once the surface of aluminum alloy is damaged, the fatigue performance will decline, and the cost will rise again.These are the problems that aluminum alloys need to overcome, and it is possible to replace steel after solving these problems.”

In the automotive chassis, aluminum has replaced some steel, but in recent years with the development of steel technology, chassis steel has introduced new solutions.Zhu qiang said, “now chassis with steel, we have developed several technology, one is the arm, we now to 780 mpa can now do steel triangle arm, it is less than 10 percent heavier than aluminum, much lower cost.There is also a link between the two wheels that is very heavy, and now we have developed a new technology that reduces the weight by 40 percent and solves the corrosion problem by using coatings, and the steel itself is improving.Now steel and aluminum are competing to promote each other, so there are more options for auto companies, and thus development.”

In fact, the current automotive aluminum has entered the stage before the Wolf after the tiger.The former steel manufacturers through continuous improvement of performance, now steel without nickel can achieve rust, while the latter magnesium alloy, carbon fiber and other materials with lower costs and improved performance, have formed an impact on the aluminum market.Zhu qiang pointed out, “aluminum alloy to do well can only be rapid development, because steel has been doing for so many years to replace it is difficult, aluminum must be industrialization as soon as possible, will not be easily replaced by later, the current automotive aluminum challenges and opportunities are co-existing.

Steel – aluminum hybrid body structure is the trend

At present, more and more automotive manufacturing engineers pay more attention to the hybrid application of lightweight materials. Their research and development focus is not only on the specific ratio of automotive steel and aluminum, but also on how to mix various materials correctly.Last year at the Frankfurt motor show debut at the new audi A8 has been of audi’s aluminum space frame type all body structure technology innovation and upgrade, abandoned the audi has always been proud of the whole aluminum body, aluminum alloy of slope to 58%, in addition to the identity of, in the body material added more composite materials, the body is nearly 51 kilogram heavier than cash model, by the cash A8 models of 236 kg “contrarian weight to 282 kg.

The new generation of audi A8 adopts aluminum alloy to build the overall frame of the body. To ensure the structural strength, aluminum castings are used in key joints and sheet metal parts are used on the body surface.In the cabin cage structure of the body, a large number of hot forming super high strength alloy steel, far more than the current A8 high strength steel only in the application of B column, the high strength steel material and 20 years ago compared to the steel, stiffness increased 5 times, weight reduced by 40%.Magnesium alloy is added to the body structure, and CFRP carbon fiber composite material is used in the rear of the car, which reduces the weight of the body from such details as the rear panel.

“In the future, aluminum will be used more and more in the whole car body, and there will be a lot of hybrid bodies. For example, audi A8 aluminum body also starts to make hybrid bodies, and now many domestic car companies are following suit.The main problem with steel and aluminum connections is corrosion resistance, with gluing, with tether, without welding.The upper body is made of steel and the lower body is made of aluminum.For example, the window frame of Beijing automobile is made of steel on top and aluminum on the bottom.Not that steel is bad, but I think it’s more promising to mix steel with aluminum.”Zhang haitao said.

In this regard, wang li also pointed out that in fact, as early as the 1940s when there was steel and aluminum competition, after many years of development, now the automotive materials have reached some consensus, is the right materials used in the right place.And steel itself is developing rapidly, with both competition and cooperation.And this competition is more beneficial to the development of automobile enterprises, because the existence of competition automobile enterprises can have more choices.Looking into the future, new energy vehicles may have higher requirements for lightweight.

Strategy of “independent brands must be lightweight, good steel with its potential is still not small, by means of joint venture brands with the proportion of high strength steel and it is very easy to achieve 10% of the white body weight loss, through the efforts of other vehicle drop 7% 8% is feasible, the identity of the proportion of the advanced technology can achieve body without change of more than 10%.””With some new technologies and techniques, more than 20 percent weight loss can be achieved.We have analyzed many models of our own brands, and the potential is still great. The gap is our motivation