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The title of the original text: "Aluminum" authoritarianism, what's wrong? | | Technology flow "|

In an industry atmosphere in which car critics wanted to carry standard magnets with them, Li thought that "aluminum is not a high-end thing" sounded a bit harsh at that time. Shortly after its launch in July, the ideal L9 attracted unwarranted suspicion of "pretending to be aluminum" because of its rear suspension steel swing arm painted with "silver makeup".

Adhering to the usual hard style, Li wants to be justified: first, silver is an anticorrosive coating and does not pretend to be aluminum or advertise it; second, aluminum is not something high-end, so this piece does not intend to use aluminum; third, it is suggested that relevant netizens replace all the steel bars in their houses with aluminum.

On the one hand, it is not uncommon for chassis steel parts to be painted with silver anticorrosive paint, and the "aluminum" board is wronged; on the other hand, the so-called analogy between house steel and car aluminum is indeed of no comparable value. Aluminum is as advanced as aluminum, and steel is reasonable.

In some places, when iron is reasonable in a certain hand, you have probably brushed the content of "the car critic has a long pole with an end magnet in his hand to poke and rub to see if it is aluminum or iron." In fact, it is not limited to the suspension arm swing-aluminum or not aluminum, this is a problem, an age-old topic that has wandered in the automobile world for many years.

When it comes to aluminum, the most well-known feature is light. When aluminum is used in car body parts, it often means less weight than steel parts, so "all-aluminum body" was once widely sought after. When aluminum is used in suspension parts, it not only reduces the off-spring mass of the whole vehicle, but also helps the 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 nearing mass production, Akio Toyoda suddenly halted the research and development of the new generation 86 because he, as Toyota's chief test driver, was dissatisfied with his driving feel.

Because of the well-known relationship, after discussions with Subaru, Subaru engineers proposed to replace the new aluminum steering knuckle shared with the new BRZ on Toyota New 86 to the iron steering knuckle on the previous generation model separately. As a result, Akio Toyoda was satisfied after he tried it, and even Nobuhui Taniguchi, a well-known Japanese driver, thought that the new 86 with iron steering knuckle had a better driving feeling.

Akio Toyoda's preference for iron parts may be due in part to the higher stiffness of the cast iron steering knuckle and partly to the difference in weight distribution between the cast iron steering knuckle and the cast aluminum steering knuckle. This is only a special case, but if you take an inventory of the suspension structure of mainstream passenger cars, it is also easy to find that there is no shortage of iron suspension connecting rods / swing arms on the "True 5 million +" Curinan.

In the suspension system, aluminum may indeed have a weight loss 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, but needs to be analyzed according to the specific situation. In particular, suspension parts are more limited by volume and shape than car body parts, so aluminum parts may not be able to achieve the required high stiffness and strength through larger thickness / volume.

Only aluminum is respected, the past is the past.

At the beginning of this century, all-aluminum body was once regarded as the development direction of body technology, but now only a small number of car companies still insist, especially many administrative flagship cars are no longer 100% aluminum body, the reason is difficult to simply attributed to "cost savings".

Take the car body as an example, the main function of aluminum is to reduce weight and improve stiffness. High school science students have learned that the density of aluminum is 2.7 × 10 ³kg / m ³, while the density of steel is about 7.85 × 10 ³³kg / m ³(ignoring slight differences in different alloys). From our daily thinking, aluminum seems to be much lighter than steel.

But the account is not calculated in this way, and light is not how it comes from. Density measures the weight of the same volume, but the overall strength (or upper limit of strength) of aluminum alloy is much lower than that of steel. The commonly used tensile strength (UTS) of 6 series aluminum alloy is about 300MPa, which is only slightly higher than that of the most common low carbon steel and can not be compared with all kinds of ultra-high strength steels.

However, because the density of aluminum alloy is only as high as that of steel, aluminum components can use much larger material thickness / volume to make up for the disadvantage in material strength and improve the structural strength of the parts to their due level. Compared with ordinary high-strength steel, aluminum can obtain higher strength under the same mass, or reduce weight under the same strength, so it has the impression of "aluminum = light".

Today's "all-aluminum body" is no longer 100% aluminum. At the end of the last century and the beginning of this century, the application of automotive ultra-high strength steel (UTS > 1370MPa) is still very limited (according to some figures, about 5% in 2000). The strength of 7-series hot-formed aluminum commonly used in aviation can reach 600MPa, which is rare, expensive and difficult to process, but for high-end models dedicated to brand building, such as Audi at that time, it is valuable to use all-aluminum to achieve the best body performance.

With the emergence and diffusion of ultra-high strength steel with tensile strength higher than 1500MPa, expensive high-strength aluminum can no longer recover strength easily through thickness, so car companies have changed the key parts of high-end models to ultra-high-strength steel, and all-aluminum body is gradually rare.

Aluminum alloy still plays an important role in the car body, especially in the high-end car body, on the one hand, it is the lightweight advantage of non-critical parts, on the other hand, it is the stiffness advantage brought by the larger thickness of aluminum. And because of the material characteristics of aluminum, the casting aluminum process has finally become the concentrated embodiment of these two advantages.

Of course, the actual situation is much more complicated than the above description. For example, according to the different shape of parts, when using steel, aluminum and other materials, there are different mathematical relations between density, thickness, stiffness and modulus, and the advantages and disadvantages of various materials will be different. Aluminum does not necessarily have advantages. Not to mention the huge cost differences between different materials.

In the face of such a complex relationship, it is obvious that materialism alone will not work.

When people want aluminum, what exactly do they want? the material price difference between aluminum and iron, especially the material price difference between the left and right connecting rods, obviously cannot be explained as "cost saving". Only staring at a certain part is aluminum or iron, this is caught in the misunderstanding of peeping leopards.

From a local point of view, it makes sense that aluminum is not a high-end product, and even you may pick out a few iron products from the Bentley and Rolls-Royce suspensions. On the whole, there is 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, you can buy an all-aluminum alloy car body model, Chery Little Ant, for tens of thousands of yuan. And its all-aluminum body is obviously different from the all-aluminum body of Polar Star 5. The advantages and disadvantages between steel and aluminum are considered as a whole, and specific problems need to be analyzed when judging individuals.

The pursuit of better body performance, better chassis performance, this is the reasonable demand of consumers. The problem is that if we just stay on "iron or aluminum", it will only be counterproductive: it will give many people a direct derivation of the performance and conscience of whether a single component is made of iron, and take advantage of the opportunity to fish in troubled waters to make a profit.

Avoid looking forward to aluminum is not because "aluminum is not high-grade", but because "high-grade" such a single, simplified criteria, will only become a new tool for cutting leeks.

This article comes from the official account of Wechat: autocarweekly (ID:autocarweekly), author: ao'hu

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