Choice between magnesium-alloy Classical aluminum is not just a matter of price, but a decision that affects the weight, dynamics and safety of the car. In today’s automotive industry, engineers are constantly looking for ways to reduce vehicle weight without losing strength, and these two metals are the main competitors in this race. Understanding their physical and chemical properties allows the owner of the car to make informed decisions when buying wheels or repairing body parts.
At first glance, both materials seem similar: they are lightweight, silvery gray and widely used in industry. However, chemical composition The structure of the crystal lattice dictates completely different rules of operation and maintenance. If you are faced with the choice of what is best for your SUV or sports car, you need to analyze the characteristics of each material in detail, so as not to overpay for unnecessary properties or, conversely, not to buy a fragile part.
In this article we will conduct an in-depth analysis that will help you understand the nuances of metallurgy in simple language. We will look at how these metals behave when impacted, how they react to reagents on the roads and what happens if you try to weld a cracked disc in a garage environment.
Physical properties and weight: where does the benefit lie?
The main advantage that immediately catches the eye when comparing is proportion. Magnesium is the lightest of all structural metals used in the automotive industry. Its density is approximately 1.74 g/cm3, which is almost 35% less than that of aluminum (2.7 g/cm3). For the motorist, this means that at the same volume, parts made of magnesium alloy will be significantly lighter.
However, lightness is not always synonymous with strength. Aluminum has a higher level of tensile in its pure form, but modern magnesium alloys with the addition of zinc, zirconium or rare earth elements can catch up and distill aluminum analogues in specific strength. This means that to achieve the same structural rigidity, the magnesium part can be made thicker, and it will still remain lighter than aluminum.
It is also important to consider the thermal characteristics. Thermal conductivity Aluminum is much higher, making it an ideal material for radiators and pistons where rapid heat removal is required. Magnesium in this regard is inferior, but has an excellent vibration-absorbing ability. That is why magnesium alloys are often used in elements subject to vibrations, for example, in motor crankcases or suspension brackets.
⚠️ Warning: Despite its lightness, pure magnesium is extremely unstable. In the automotive industry, extremely complex alloys are used, since the use of pure metal would lead to rapid destruction of the part from oxidation and low mechanical resistance.
The difference in weight directly affects the unsprung weight of the car. The weight reduction of the wheels even by 1 kg feels as if you removed 15-20 kg from the body. This improves acceleration, braking and handling, making the suspension more responsive to road bumps.
Strength and impact resistance
When the question arises of what is stronger, it is necessary to separate the static load and impact. Aluminum alloys, especially the 6061 and 7075 series, are renowned for their ability to withstand significant static loads without residual deformation. They have good ones. plasticityThis allows them to bend when hit hard rather than break instantly. This property often saves the hub knots from breaking down when they get into deep pits at high speed.
Magnesium alloys behave differently. They are more rigid and have a high modulus of elasticity, but their plasticity is lower. At extreme loads above the strength limit, aluminum will be more likely to remember, and magnesium can crack or split. This is a critical moment for those who often drive on broken roads or participate in rallying. However, in normal operating modes, magnesium demonstrates excellent performance. fatigueIt can withstand millions of vibration cycles without cracking.
It is worth noting that modern injection molding technologies allow you to create magnesium parts with complex geometry, which are not inferior in strength to aluminum analogues. The secret lies in the microstructure of the material and the correct selection of alloying additives. Engineers have learned to make magnesium less fragile, but the cost of such processing is much higher.
In the event of a real road accident or a severe impact on the curbs, the behavior of the materials will be as follows:
- 🚗 The aluminum disc is deformed, losing its tightness, but often retains the integrity of the structure, which allows you to reach the service (sometimes even with a swap).
- 🔨 The magnesium disc is prone to chipping and cracking in a critical impact, which can lead to instantaneous wheel loss and an emergency.
- 🛡️ The steel suspension elements to which the discs are attached may receive less momentum when hit through a magnesium disc due to the destruction of the disc itself, but the risk of wheel loss is higher.
When buying used cast discs, carefully examine the internal shelf. Cracks on magnesium alloys are often hidden under a layer of paint or varnish, while aluminum will give itself off as a characteristic dent.
Corrosion resistance and interaction with reagents
One of the weakest points of magnesium is its high chemicality. In the periodic table of elements, magnesium is left of aluminum, which makes it a stronger reducing agent. This means that it oxidizes much faster and reacts more readily with aggressive environments such as road reagents, salt solutions and acid rain. Without a quality protective coating, a magnesium part can begin to break down in one winter season.
Aluminum, in turn, has a unique property of self-defense. When in contact with air, it is instantly covered with the thinnest, but incredibly durable oxide film (see below).Al2O3). This film prevents further oxidation of the metal. That is why aluminum discs even with varnished for years do not rust, but only dim. Magnesium of such a film, capable of stopping corrosion under normal conditions, does not form.
A particular danger to magnesium alloys is galvanic. If the magnesium disk is fixed with steel bolts without special insulation, a galvanic pair will appear in the presence of an electrolyte (water with salt). Magnesium, as a more active metal, will begin to break down at a catastrophic rate, turning into powder around the fastening holes.
| Parameter | aluminum | Magnesium alloy |
|---|---|---|
| Oxidation rate | Low (self-defense) | High (requires coverage) |
| Reaction to salt | Sustainably | Critically vulnerable |
| galvanic pair | Average risk | High risk of destruction |
| Recovery | Easy to polish | Requires a complete repainting |
For owners of cars with magnesium components, washing the body and discs using reactive shampoos should be a regular procedure. The accumulation of dirt and reagents on the surface can locally damage the protective layer, triggering an irreversible process of corrosion.
⚠️ Warning: Never use acidic disc cleaners on magnesium products or on products with unknown alloy composition. The acid will react instantly with the metal, causing blackening and destruction of the structure, as well as the release of hydrogen.
Repairability: welding and restoration
The issue of repairing damaged elements is acute, given the cost of modern cast discs. Aluminum has proven itself to be sufficient. repairable. There are many specialized services where the method of argono-arc welding (TIG) restore the geometry of the discs, weld cracks and eliminate chips. The technology has been developed for decades and additives are available.
With magnesium, the situation is radically different. Magnesium alloy welding requires exceptional qualification, special protective gases (often helium mixtures) and a perfectly dry environment. The main problem is the high tendency of magnesium to ignite when heated. If the temperature of the welding bath exceeds a certain threshold, the metal will light up with a bright, dazzling flame, which is almost impossible to extinguish by conventional means (water will only increase the combustion).
Due to the complexity and danger of the process, most services simply refuse to take magnesium disks into operation, offering to buy new ones in return. Even if you can find a master, the cost of such welding can exceed the price of a new part. In addition, in the zone of thermal influence, the strength of the alloy drops sharply, and a repeated impact in this place is guaranteed to lead to destruction.
Why does magnesium burn so brightly?
When burned, magnesium releases a huge amount of energy and ultraviolet radiation. The flame temperature reaches 3000°C, which allows it to be used in incendiary bombs and fireworks. This is why welding requires complete isolation from oxygen.
If you choose a car with magnesium elements or discs made of this metal, you should immediately accept the idea that in case of serious damage, the part can only be recycled and replaced. Attempts to repair the garage can result in a fire.
Production technologies and cost
Manufacturing magnesium products is technologically more complicated and expensive. Magnesium extraction requires huge expenditures of electricity, as it is obtained by the method of electrolysis of molten salts. Aluminum, although energy-intensive in production, due to the established scale of industry and recycling costs much cheaper. This directly affects the final price of the product for the consumer.
The casting of magnesium alloys also has its own characteristics. Due to the high chemical activity, molten magnesium cannot be poured into ordinary sand molds or contacted with certain types of refractory refractory. It requires the use of special fluxes or casting in a vacuum/inert atmosphere, which makes the process more expensive. Aluminum is more “friendly” in this respect and allows for various casting technologies, from gravitational to high-pressure.
However, in the segment of premium automotive and aviation, the use of magnesium is justified. A 1 kg weight reduction in a car is equivalent to a reduction in fuel consumption and CO2 emissions, which, on a fleet scale, provides huge savings. Therefore, manufacturers are ready to overpay for magnesium crankcases, brackets and interior elements.
- 💰 Cost of raw materials: Magnesium is much more expensive than aluminum (the difference can reach 2-3 times depending on stock quotes).
- 🏭 Energy intensity: The production of 1 ton of magnesium requires more electricity than 1 ton of aluminum.
- ♻️ Recycling: Aluminum is more easily and cheaply recycled, losing a minimum of properties, whereas magnesium scrap is more difficult to work with due to the risks of ignition.
The high price of magnesium products is due not only to the cost of raw materials, but also to complex, dangerous casting and processing technologies that require special safety conditions.
Visual differences and marking
How do you tell magnesium from aluminum if you hold a part in your hand and it doesn’t have a marking? Visually they are very similar, but there are a number of signs. The surface of magnesium to the touch may seem slightly warmer and less slippery than that of aluminum. The color of magnesium often has a dimmer, grayish hue, while aluminum shines brighter.
The simplest but most devastating test is to test the spark. If you bring the detail to the sharpener, aluminum will give rare, rapidly fading sparks of white color. Magnesium will sparkle with bright white, dazzling sheaves. However, this method is not recommended for finished products, as sparks of magnesium can burn through clothing or cause a fire.
A safer method is weight assessment. If you have a reference aluminum part of the same volume, the magnesium part will be noticeably lighter. A magnet can also be used: neither aluminum nor magnesium is magnetized, but this will help eliminate steel. Often on the back of the spokes of the disks or on the crankcases is marked. Look for the signs:
- 🔍 Mg - indicates the magnesium content (e.g. AZ91D, AM60).
- 🔍 Al or ALU Aluminum alloy designation (e.g. A356, 6061).
- 🔍 TL To Leichtmetall, the German designation for light alloys, often indicates magnesium in combination with other letters.
There is also a "copper sulfur test." If you drop a solution of copper sulfur on a cleaned area of aluminum, the reaction will go slowly or not at all. On magnesium, the reaction will go instantly: copper will begin to precipitate on the surface with dark spots, as magnesium displaces copper from the solution.
⚠️ Attention: When conducting any chemical tests (cumulos, acid), be sure to use personal protective equipment and conduct an experiment on an inconspicuous part, so as not to spoil the appearance of an expensive product.
Final comparison and scope
To sum up, the choice between magnesium and aluminum depends on the specific tasks. For mass production of wheels, where the balance of price, strength and maintainability is important, aluminum He remains a leader without alternative. It forgives errors of operation, easily recovers and cheapens in production.
Magnesium is the lot of high-tech solutions, where every gram counts. Carters of gearboxes, elements of steering columns, seats in racing cars, instrument casings - this is his element. Here, it is not so much the impact toughness that is important, as the ability to extinguish vibrations and minimize weight.
For an ordinary motorist, acquaintance with magnesium is likely to be limited to the purchase of expensive forged wheels of the top level or repair of rare engine parts. Understanding the features of this metal will help to avoid errors in maintenance and washing, keeping parts intact for many years.
☑️ Check before buying a magnesium disc
Frequently Asked Questions (FAQ)
Can I paint magnesium discs with ordinary car enamel?
Technically possible, but surface preparation requires a special approach. Ordinary soils may not provide adhesion