What material should a car be made of to be "advanced"?

I don't know if it is because of the "credit" of some media "peers" who are keen on frying old rice. The controversy about body materials has recently become the focus of many hot discussions again.

This time, Mercedes-Benz bears the brunt. Although the current Mercedes-Benz E-Class has been on the market for nearly four years, the door cover "aluminum for steel", which was heated up at the beginning of the replacement, has long been an old calendar, but it still can't stop the enthusiasm of the people who eat melons. In addition, even in the criticism of Mercedes-Benz "good friend" BMW, the domestic BMW 3 Series was exposed, and the hood and front fender were changed from aluminum alloy materials of overseas models to steel materials.

Is aluminum alloy really "advanced" than steel in the choice of body material?

Steel is one of the oldest and most widely used materials in the history of human industry. From the day the car was born, steel was the main material of the car. The history of aluminum alloy used in automobile manufacturing is much shorter. This lightweight material originally from the aviation industry (of course, like cars, composite materials have begun to replace it in recent years) was used by Jaguar in the 1930s. "All-aluminum body" was born in 1994, after Audi A8 officially launched ASF body structure.

If we want to make a simple comparison between steel and aluminum alloy, the simplest physical properties are as follows: the tensile strength of aluminum alloy exceeds that of steel, but its toughness is far less than that of steel, and their specific gravity is different. The aluminum alloy with the same volume is nearly half lighter than steel.

Modern cars, especially high-end cars that emphasize performance and luxury, all use aluminum alloy to save precious weight. Lightweight plays an important role in automobile performance, which affects fuel consumption, braking ability, maximum speed, acceleration performance and even cornering dynamic performance. In the field of racing cars and modified cars, there is a saying that "horsepower is less than 10 kg is better"; The reduction of vehicle mass 10% can improve fuel efficiency by about 6% to 8%, which is a very impressive data. This shows the importance of automobile lightweight.

Using lighter aluminum alloy can save more weight. In the eyes of many people, aluminum alloy is "more advanced". But making a car is not that simple.

The tensile strength of aluminum alloy exceeds that of steel, but its toughness is much worse than that of steel. Simply put, aluminum alloy is harder but more brittle, while steel is softer but more ductile. When a collision accident occurs, under the condition that the stress limit of structural members is also exceeded, the steel will resist the Japanese war step by step, and its elasticity can offset part of the impact force; Aluminum alloy will collapse instantly and "surrender" directly.

In a famous car accident that year, the all-aluminum Audi R8 was smashed to pieces. ...

More importantly, this defect is almost insurmountable for aluminum alloys. Some people may say, since aluminum alloy is much lighter than steel, can we make aluminum alloy thicker than steel with the same weight? Don't! With the increase of thickness, the yield strength of aluminum alloy will decrease, and the thicker the aluminum alloy, the easier it is to break into two pieces directly under the impact force!

In addition, compared with steel, aluminum alloy has the disadvantages of poor weldability and high processing cost. You know, the cost is not only for automobile manufacturers-aluminum alloy with poor toughness can hardly be repaired with sheet metal in the event of collision, but needs to be replaced as a whole.

When it comes to all-aluminum body, we will think of the two names mentioned above: Audi and Jaguar, but Jaguar XFL's all-aluminum body "only" uses 75% aluminum alloy, not100% as most people think; Audi is also gradually reducing the proportion of aluminum alloy in high-end models.

Audi replaced aluminum alloy and added carbon fiber reinforced composite-if you insist, titanium alloy and carbon fiber composite are "more advanced" materials than aluminum alloy. For example, the density of carbon fiber composites is lower than that of aluminum alloy, and the tensile strength can easily reach above 3500Mpa, which is about 8- 10 times that of aluminum alloy and steel; Titanium alloy can achieve high hardness and high toughness at the same time, which has the advantages of aluminum alloy and steel.

So, why don't cars use these two "more advanced" materials in large quantities? Cost, cost, or cost. Due to the high cost, carbon fiber and titanium alloy are only used by a few models in a few places. The toughness of carbon fiber is also poor and almost impossible to maintain. A slight touch will have a huge replacement cost, so only a few supercars such as BMW i8, Koenigsegg and Lamborghini will use this material. In addition to the high price, titanium alloy has the disadvantages of poor formability and poor weldability. Only monsters like NSX and Bugattica Long Xing are willing to use a little on engine crankshafts or brake calipers.

In short, aluminum alloy, steel, carbon fiber and titanium alloy all have different characteristics and different "values". There is no absolute "high and low" between them, but each has its own strengths.

In fact, with the development of automobiles, all kinds of new materials are blooming. For example, on the Li number, nylon was used (you read it right! A lower main swing arm made of the same material as your girlfriend's stockings; Volvo, which has always been keen on environmental protection, even cooperated with a company called Bcomp's, trying to make semi-structural interior parts by reorganizing plastics recovered from the sea (as the name suggests, waste plastics salvaged from the sea).

In fact, it doesn't matter which material is more "advanced" for cars. What is most suitable and practical is the best.

This article comes from car home, the author of the car manufacturer, and does not represent car home's position.