In an industry atmosphere where car reviewers wished to have magnets as standard equipment, Li Xiang's sentence that aluminum is not a high-end thing sounded a bit harsh at the time. When the Ideal L9 was just launched in July, the steel swing arm of its rear suspension was painted with silver makeup, which attracted an unwarranted suspicion of pretending to be aluminum. Adhering to the usual hard-hearted style, Li Xiang is also justifiable: First, silver is an anti-corrosion coating, we didn't want to pretend to be aluminum and did not advertise it as aluminum; second, aluminum is not a high-end thing, and this piece is not intended to be used. Aluminum; Third, it is recommended that relevant netizens replace all the steel bars in their houses with aluminum.
On the one hand, it is not uncommon for the steel parts of the chassis to be painted with silver anti-corrosion paint, and it is unfair to install the aluminum board. Aluminum has the advanced level of aluminum, and steel has the reason for steel.
In some places, it makes sense to use iron
On the certain hand, you have probably read the content of the car reviewer holding a long pole with a magnet at the end to see if it is aluminum or iron. In fact, it is not only limited to the suspension swing arm aluminum or not aluminum, this is a question, an old topic that has been wandering in the automotive world for many years and never dissipated.
When it comes to aluminum, the most well-known characteristic is that it is light. When aluminum is used for body parts, it often means less weight than steel parts, so an all-aluminum body was once widely sought after. When aluminum is used for suspension components, in addition to making the vehicle lighter, it also reduces the unsprung mass, which also contributes to chassis performance.
Just earlier this year, the Japanese magazine "Motor Fan" published such a story: In September 2020, when the second-generation Toyota 86 / Subaru BRZ was approaching mass production, Toyoda Akio suddenly stopped the development of the new-generation 86 work because, as Toyota's chief test driver, he was dissatisfied with his driving feel.
Because of the well-known relationship, after negotiating with Subaru, Subaru engineers proposed to replace the new aluminum steering knuckle shared with the new BRZ on Toyota's new 86 and replace it separately with the iron steering knuckle on the previous model. As a result, Akio Toyoda was satisfied after trying it himself, and even the famous Japanese driver Nobuki Taniguchi believed that the new 86 with iron steering knuckles had a better driving feel.
Akio Toyoda's preference for the metaphysical feel brought by iron components may be partly due to the higher component stiffness of cast iron steering knuckles, and partly due to the difference in weight distribution between cast iron steering knuckles and cast aluminum steering knuckles. This is just a special case, but if you look at the suspension structure of mainstream passenger cars, it is easy to find that the Cullinan, which has reached the true 5 million + also has iron suspension links/swing arms.
In the suspension system, aluminum may indeed have a weight reduction effect on a single component, but the use of some iron components in the pursuit of system optimization is not necessary to directly lead to criticism, and it needs to be analyzed in combination with specific situations. In particular, suspension components are more limited in volume and shape than body components, and aluminum components may not necessarily achieve the required high stiffness and high strength through greater thickness/volume.
Only aluminum is respected, it is past tense
At the beginning of this century, the all-aluminum body was once regarded as the development direction of body technology, but now only a few car companies are still insisting, especially since many executive-level flagship sedans are no longer 100% aluminum bodies, and the reason is difficult. It simply comes down to cost savings.
Taking the body as an example, the main function of aluminum is to reduce weight and increase stiffness. High school science students have learned that the density of aluminum is 2.7*10³kg/m³, while the density of steel is about 7.85*10³kg/m³ (ignoring the slight differences between different alloys). From our day-to-day thinking, aluminum seems to be much lighter than steel.
But the account is not calculated like this, and the light is not like this. Density measures the weight under the same volume, but the overall strength (or upper limit of strength) of aluminum alloy materials is much lower than that of steel. The tensile strength (UTS) of the commonly used 6-series aluminum alloys is about 300MPa, which is only slightly higher than the most common low-carbon steel among steels and is incomparable with various ultra-high-strength sheets of steel.
However, because the density of aluminum alloy is only 1/3 of that of steel, aluminum parts can use a much larger material thickness/volume to compensate for the disadvantage of material strength, so that the structural strength of the part can be improved to the level it should be. Compared with general high-strength steel, aluminum can obtain higher strength under the same mass, or reduce the weight under the same strength, so there is an impression of aluminum = light.
At the end of the last century and the beginning of this century, the application of ultra-high-strength steel (UTS>1370MPa) for vehicles was still very limited (data said that it was about 5% in 2000). The strength of the 7-series hot-formed aluminum commonly used in the aviation field can reach 600MPa. Although it is rare, expensive, and difficult to process, for high-end models dedicated to brand building, such as Audi at that time, using all aluminum to achieve the best body performance is valuable.
With the emergence and spread of ultra-high-strength steel with a tensile strength of more than 1500MPa, expensive high-strength aluminum can no longer easily recover its strength through the thickness, so car companies have changed the key parts of high-end models to ultra-high-strength steel. Aluminum bodies are gradually becoming rare.
Aluminum alloy still plays an important role in the body, especially the high-end body. On the one hand, it is the lightweight advantage of non-critical parts, and on the other hand, it is the stiffness advantage brought by the thicker aluminum material. And because of the material properties of aluminum, the cast aluminum process eventually became a concentrated expression of these two advantages.
Of course, the actual situation is much more complicated than the above description. For example, depending on the shape of the components, when steel, aluminum, and other materials are used for beam-shaped and plate-shaped components, there are different mathematical relationships between the density, thickness, stiffness, and modulus, and the pros and cons of various materials will be different. Aluminum is not necessarily an advantage. Not to mention that there are huge cost differences between different materials. In the face of such intricate relationships, pure materialism is obviously unworkable.
What exactly do people want when they want aluminum?
The material price difference between aluminum and iron, especially the material price difference between the left and right connecting rods, obviously cannot be interpreted as cost-saving. Just staring at a certain part is aluminum or iron, which is caught in the misunderstanding of the leopard.
From a local point of view, it is true that aluminum is not a high-end thing. You may even pick out a few iron products in the suspension of Bentley and Rolls-Royce. On the whole, there is indeed a general rule that more expensive models have a higher proportion of aluminum.
But aluminum and aluminum are also different. You may not believe it when you say it. You can buy an all-aluminum body model for only tens of thousands of yuan, Chery Little Ant. And its all-aluminum body is obviously different from the all-aluminum body of the Polestar 5. The advantages and disadvantages of steel and aluminum are considered as a whole, and when judging individuals, specific problems need to be analyzed in detail.
The pursuit of better body performance and better chassis performance is the reasonable demand of consumers. The problem is that if you just stay on iron or aluminum, it will only be counterproductive. Many people are given whether a single component is made of iron, and it is directly deduced how good the performance and conscience are, and take the opportunity to fish in troubled waters.
Avoiding looking only at aluminum is not because aluminum is not high-end, but because a single and simplified evaluation criterion such as high-end or not will only become a new tool for cutting leeks.