Friends who often pay attention to the car circle should have found that aluminum, as a body material, its topic is no worse than the three major parts of the engine, gearbox and chassis. If a new car uses an aluminum alloy body, the manufacturer not only has to blow several pages of PPT, but also usually pulls the body in white to the auto show, 4S store, shopping mall blindly. In addition to manufacturers, consumers' attention to aluminum is also not low, whoever dares to use a piece of aluminum less than the overseas version of the new car, netizens will indignantly raise the keyboard and occupy the forum in minutes. So the question is, how much stronger can aluminum be than steel? In addition to lightness, what other unique things are there in aluminum? Why do good cars have a soft spot for aluminum? Please read on!
Compared to the steel used on cheap models, the biggest advantage of aluminum alloy is that it is light enough! It should be known that the density of steel is 7.8g/cm, while the density of aluminum is only 2.7g/cm. This means that under the same volume, the weight of aluminum is only about one-third of that of steel, and even lighter than the 4.5g/cm of titanium alloy that everyone remembers as ultra-light.
Therefore, the use of aluminum alloy materials on the body, or the replacement of the original steel body coverings including doors, hoods, fenders and other parts into aluminum, the purpose is to reduce weight. In the current domestic market, the BMW 5 Series can be said to be a representative model with aluminum coverings. Here we may wish to make a comparison, with the same level of the 5 series of domestic Mercedes-Benz E-class because of the cover parts "aluminum for steel", so the minimum quality of the car reached 1780kg, while the same lowest 5 series is only 1705kg, equivalent to the E-class naturally than the 5 series to pull more than a person weighing 150 pounds!
The benefits of using aluminium alloys for vehicles to reduce weight are numerous. At the driving level, the lighter the car, the less inertia it has, so whether it is accelerating, decelerating, or cornering, the less resistance the vehicle will have to change its current state, and the response speed can be improved. This will also make those who spend a lot of money to buy a good car feel that his car is "easier to drive" than those cheap cars.
In addition, the lighter weight can significantly reduce the fuel consumption of the vehicle. According to experiments by international research institutions, for every 100kg reduction in the quality of automobile maintenance, the fuel consumption of vehicles can be reduced by 0.3 to 0.6L, which is undoubtedly of great significance for today's strict and "inhumane" fuel consumption and emission regulations.
The yellow line is the height of the vehicle's center of gravity
In addition to reducing inertia and fuel consumption, the use of lighter aluminium alloy overlays can also reduce the height of the vehicle's center of gravity and optimize the front and rear counterweights. As shown in the figure above, the center of gravity height of the general fuel vehicle is about 550mm-580mm (the height of the yellow line in the above figure), so if you can reduce the weight of the part above the height, such as the hood and roof, it is equivalent to reducing the height of the vehicle's center of gravity. The lower the center of gravity of the vehicle, the smaller the roll caused by the vehicle when it turns, and the better the driver's subjective handling feeling. In addition, for some models with heavier fronts, after replacing the body coverings such as hoods and fenders of the front of the car with aluminum alloy materials, the load bearing of the front axle of the vehicle can also be reduced to a certain extent, thereby playing a role in optimizing the front and rear counterweights of the vehicle.
Range Rover all-aluminium body
In addition to body coverings, more and more luxury brands have begun to use aluminum alloys to replace the original steel on the body-in-white to reduce the weight of the car as much as possible. For example, the fourth-generation Range Rover is 420 kilograms lighter than the third-generation Range Rover using a steel body after using an all-aluminum body and a large number of aluminum alloy coverings, which is equivalent to subtracting 5 adult men with 170 kilograms!
Cadillac CT6 body in white
Of course, because the cost of all-aluminum bodies is too high, most luxury cars only use the method of increasing the proportion of in-white aluminum alloy materials to reduce weight. For example, cadillac CT6, by increasing the proportion of aluminum alloy to 64% on the body in white, plus the use of various aluminum alloy coverings, greatly reduced the weight of the vehicle, and finally helped the car length of 5 meters 2, the size of the standard axle Mercedes-Benz S-class as large as the full-size car will be the maintenance quality control at 1663kg, which is about 100kg lighter than the smaller domestic long-axis Mercedes-Benz E-class!
When it comes to the models that need to reduce weight through aluminum alloys the most, it is undoubtedly an electric vehicle that has gradually become mainstream. This is because for every 10% weight of an electric vehicle, the vehicle's power consumption increases by 5.5%. Let's take an example of an electric vehicle with an aluminum alloy body, a curb weight of 1800kg, and a range of 500km. Since the steel body is usually 200kg heavier than the aluminum alloy body, if the body of this electric vehicle is replaced by steel, its weight will reach 2000kg. Correspondingly, the cruising range will be reduced from the original 500km to 472.5km. At this time, if the steel body electric vehicle wants to make up for the lost endurance by increasing the battery capacity, then the car needs to increase the battery capacity by 4.5Kw·h to re-achieve 500km endurance, which is equivalent to spending about 6,000 yuan more for the battery.
Although the 6,000 pieces are counted, the steel body + additional battery scheme can still save thousands of production costs compared with the aluminum body with the same mileage. But for consumers who buy more than 200,000 and pursue the experience of electric vehicles, the better energy consumption performance of a car in the entire use cycle, as well as the attraction of better driving texture, is definitely greater than the difference of thousands of dollars. This is just like if the mid-range fuel vehicle wants to become a hit, more competition is the product power, rather than who is cheaper than whose terminal price is thousands of pieces. And because in the maximum endurance version of the high-end electric vehicle, the battery pack will use up the space as much as possible, so there is no extra battery space left for the steel body to catch up with the aluminum alloy body life. This is the reason why slightly more expensive electric vehicles will spare no effort to increase the proportion of aluminum alloys on the body.
In addition to the body and coverings, the walking part of the vehicle is also a place where aluminum alloys can shine. Among them, the most obvious effect after changing to aluminum alloy material is the various swing arms of the suspension. This is mainly because the suspension swing arm as a spring mass becomes lighter, and its motion inertia will also be reduced, so it will be easier to be pushed when moving. When encountering bumps in the road, it can dissolve the bumps and return to position at a faster speed, improving the tire's adhesion to the ground on the bumpy road.
Better tire grounding not only makes the vehicle more controllable in bumpy sections, but also effectively improves the comfort of the vehicle when passing through the bumps. This is because when the wheels are bounced up by bumps, the vehicle will have a downward movement trend due to the loss of support. At this time, if the wheel can quickly return to position under the drive of the suspension swing arm with less inertia, the shorter the time the wheel will leave the ground, and the sooner it can support the vehicle, shorten the distance of the vehicle falling down, and thus reduce the pitch of the vehicle when it passes the bump.
For enhancing body rigidity, the simplest and most effective way is to pile up the material. For example, the addition of tie rods to create triangles, and the use of thicker diameter frames to increase torsional rigidity. However, no matter which scheme is adopted, it will inevitably lead to an increase in metal materials. At this time, the material advantages of aluminum alloys are revealed. Although in order to achieve the same strength, the aluminum alloy is 40% more than the volume of steel, but because the weight of the aluminum alloy is only one-third of the steel under the same volume, it can be calculated that at the volume of the same strength, the weight of the aluminum alloy is only 40% of the steel. With the advantage of more than double the strength of the unit, the body-in-white body using aluminum alloy material can be "unscrupulously" stacked, and finally the steel body can be crushed in terms of anti-torsional rigidity.
Taking the All-Aluminum body of the WEILAI ES8 as an example, it uses ultra-hard 7 Series aluminum alloy in the front part of the car to ensure the rigidity of the front of the car and improve the responsiveness of the vehicle to the steering wheel. In the rear and B-pillar positions, the ES8 uses 6000 series aluminum, which is more widely used in automobiles and has better fatigue resistance, to avoid deformation of the frame due to bumps in long-term use. In the rear window position, the ES8 uses a 5000 series aluminum alloy that is not prone to deformation to improve the vehicle's anti-rear-end ability. Finally, under the combined work of 5000, 6000 and 7000 series aluminum alloys, the torsional rigidity of the NIO ES8 body reached 31100Nm/°, and if the battery is added, it can reach 44140Nm/°, even exceeding the 39130Nm/° of Lexus flagship supercar LFA. More importantly, under such excellent data, the naked weight of the in-white body of the NIO ES8 is only 335kg.
Volvo XC90 body material
In order to give everyone a better idea of this set of data, we found the Volvo XC90, which is similar in size to the ES8 and is also a medium and large SUV, for a comparison. As can be seen from the above figure, XC90 only uses aluminum alloy (green area on the figure) in the anti-collision beam and tower top position, and the rest is steel, so its in-white body weight reaches an exaggerated 401.3kg, which is 65kg heavier than the all-aluminum WEILAI ES8, which is equivalent to 20% more weight. Under such a weight gap, the anti-torsional rigidity of XC90 is only 25000Nm/°, which is 6100Nm/° lower than that of ES8 without batteries, which is equivalent to XC90's torsional rigidity difference of 20% under the premise of 20% more body-in-white weight. This also confirms the above statement that at the same strength of the volume, the weight of the aluminum alloy is only 40% of the steel. It can be seen that aluminum alloy can indeed make the body in white have higher torsional rigidity under the premise of lighter weight, and provide better handling feeling.
As we all know, the listen-to-pack version of a drink such as Coca-Cola is made of aluminum. So no matter which direction we put pressure on it, the bottle will easily collapse. This softer, elastic, and even a certain ductility of the characteristics also gives the aluminum alloy the ability to better use its own deformation to absorb energy.
According to experiments, aluminum absorbs twice as much energy in a collision as steel of the same weight. This also means that if two identical cars, one uses aluminum alloy at the longitudinal beam responsible for the collision at the front of the car, and one uses steel, then at the same collision speed, the model using the aluminum alloy stringer will have a better energy absorption effect due to the stringer, so the impact of the A column will be significantly smaller than that of the model with steel for the stringer.
However, it is precisely because of the soft nature of aluminum alloy that it is not suitable for application in A-pillar, B-pillar, which need to be firm at all times. What's more, with the advancement of steel manufacturing technology, it is now possible to create ultra-high-strength thermoformed steel with 1800MPa. Because the strength of this ultra-high-strength thermoformed steel has reached 4 times that of the aluminum alloy, but the weight is not 4 times that of the aluminum alloy, even if the aluminum alloy is stacked, the effect is not as good as the ultra-high-strength thermoformed steel.
The new Audi A8 steel-aluminum hybrid body
Then, according to the characteristics of aluminum is more suitable for energy absorption and ultra-high-strength thermoformed steel is stronger, we can infer what kind of body material distribution should be used in a model with excellent crash performance. For example, in the front and rear of the car, which are responsible for collapse and have a large collapse space, the body should use aluminum alloy materials with better energy absorption effect to minimize the impact transmitted to the cockpit. In the A-pillar and B-pillar positions, which are responsible for supporting the living space for the occupants of the car in a violent collision, ultra-high-strength thermoformed steel that is not easy to deform should be used. In fact, models such as the Mercedes-Benz S-Class, the new Audi A8 and cadillac CT6 have adopted this body design concept to ensure the safety of the occupants in the car in the event of a collision.
The all-aluminum body of the previous-generation Audi A8
Among the above-mentioned cars, the new Audi A8 confirms the rationality of the steel and aluminum hybrid body structure with a "punch in the face". You know, the all-aluminum body of the previous generation of Audi A8 is Audi's proud work, and the hype of the all-aluminum body when the new car is listed is not absent. But just when the new generation of Audi A8 was listed in 2017, this car turned to the camp of steel and aluminum hybrid body... It can be seen that if the collision performance of the all-aluminum body is proud enough, then Audi naturally has no reason to ban the all-aluminum body!
Although car manufacturers will use double-sided galvanized steel plates with very good anti-rust effect as cover parts for steel bodies, for many friends in the northeast, the snow melting agent sprinkled by the municipal department after snow will still cause certain corrosion to the coverings in various parts of the vehicle, which will cause the surface of the steel plate to rust, which will lose strength. Compared with steel plates, aluminum alloys do not have such concerns, because they can react with oxygen in the air to form a dense film of alumina, which in turn prevents the aluminum alloy from continuing to react with the outside world. Therefore, compared with steel plates, the corrosion resistance of aluminum alloys is obviously better.
As for the chassis corrosion resistance that many friends care about, although the chassis corrosion resistance of the aluminum alloy body is also better, because the manufacturer attaches great importance to the chassis, which was once the hardest hit area of rust, most models will be sprayed with anti-corrosion chassis armor during production. In this way, even if everyone's car is a steel body, there is no need to worry too much about the anti-rust ability of the chassis.
A recognized good thing has not been popularized, and there is often only one reason, that is, it is expensive, and aluminum alloys are no exception. In the current market environment, the price of a ton of steel is about 5,000 yuan, and the price of a ton of aluminum is about 20,000 yuan, which is 4 times that of steel, which is a product of this size for automobiles, and the cost of aluminum alloy and steel will naturally be far apart.
Jaguar XE body-in-white
In addition to the price gap of raw materials, the processing of aluminum is also much more arduous (money) than steel. Since the melting point of aluminum is only 660 ° C, and the melting point of steel is around 1400 ° C, if the resistance welding of the welded steel plate is used to process the aluminum, the aluminum will instantly become liquid and lose its shape. Therefore, aluminum plate welding can only use expensive aluminum welding, cold metal transition arc welding, and laser welding. In addition, because the heat expansion ratio of aluminum and other metals is not the same, when connecting aluminum and other metals, it is also necessary to use a large number of extremely expensive structural adhesives or rivets to fix them to avoid the fracture problem of the two metals when the ambient temperature changes. For example, the Jaguar XE, which uses an all-aluminum body, uses more than 2,000 rivets to stitch the bodywork.
In addition to the high manufacturing cost of the aluminum body, the user's later use cost is also not low. Because aluminum is as difficult to repair as it is to weld, once the body collides, whether it is a class II repair shop or a 4S shop on the side of the road, it is usually directly recommended that the owner replace the parts, rather than sheet metal spray paint. Then this part of the extra cost will either be borne directly by the owner himself, or he can only pass on part of the cost to the insurance company by paying a higher insurance premium.
Why do good cars use aluminum? I believe that everyone must know the mystery after reading this article. But for the mainstream family cars within 200,000 that everyone buys every day, aluminum is not a mainstream material, after all, it is too expensive to reduce the price of the vehicle, and the high repair cost is even more difficult for ordinary family cars to accept. Therefore, even if good cars and luxury cars like to use aluminum, it does not mean that cars that do not use aluminum are not good cars, after all, for the people, the product force is balanced, and the car with high cost performance is a good car that belongs to the people.