For interior designers, the breakthrough in the high-quality electroplating of magnesium opens up new possibilities. This means that an interesting alternative to plastic materials is now available.
"The possibility of electroplating magnesium opens up completely new degrees of freedom for car designers," reports Werner Beneken, managing partner of HDO Druckguss- und Oberflächentechnik GmbH in Paderborn. After several years of development work, the company is now the first in the world to have a process-safe technology for finishing magnesium with high-quality galvanic surface coatings.
This breakthrough provides the developer with a highly welcome new material variant as an alternative to metallised plastics. Compared to this established material, magnesium has decisive advantages: its mechanical characteristic values, such as strength and modulus of elasticity, are significantly higher. In the case of electroplated magnesium, the adhesion strength and temperature resistance of the coating are significantly higher than in the case of electroplated engineering plastics due to the metal-metal bond. In addition, such magnesium parts are now sometimes cheaper to manufacture than those made of galvanised plastics. Magnesium components are manufactured using the die-casting process. This also gives the designer the option of designing load-bearing structural components with a noble, high-gloss surface finish.
Advantages of magnesium
"The decisive double advantage of magnesium is the combination of high strength and low weight," adds Bernhard Happe, Head of Sales and Development at HDO. For automotive developers, who are under constant pressure to reduce weight, this is a very important criterion. As the lightest metal used in large-scale production, magnesium weighs only 1.74 g/cm3. This is particularly attractive for parts in the upper part of the vehicle, since here as little mass as possible is required to keep the vehicle's centre of gravity low. In addition, magnesium has excellent castability, so that even very complex and large-area parts with thin walls can be produced without any problems. In comparison with plastics, it is also characterised by superior strength. Mechanically highly stressed structures, such as handles in the roof area, can be produced with magnesium in dimensions that would be unthinkable with plastic. This is also very much in line with new trends such as the integration of storage compartments in the roof area." Magnesium is also very attractive from a cost point of view," Happe reveals. When comparing prices, it is important to bear in mind that a magnesium part is usually much thinner-walled and thus often lighter than a plastic part of the same stability. Magnesium becomes even more attractive when the low disposal costs due to its excellent recyclability are taken into account.
Advance into the interior
"Magnesium has already spread rapidly in structural parts in cars," says Heinz Herberhold, head of process technology at HDO. Magnesium casting has been proving its worth for years in seat frames, door modules, gearstick consoles or dashboard holders. For visible parts, however, there have been only a few possible applications up to now because of the non-decorative surface. With the breakthrough achieved, a "career jump" into the domain of design elements with a noble high-gloss surface is now open to this useful construction material. The special feature of the development now presented is not that magnesium can be galvanised at all: This has been done before on a laboratory scale, but in practice this process has proven to be rather prone to failure. It is precisely this point that is the decisive factor in the new development: HDO now has a process technology with the help of which the requirements of the automotive industry can be fully met both in terms of batch sizes and process reliability. This is mainly due to HDO's advantage of being able to operate all processes itself and thus control them successfully.
"The essential process steps include aqueous degreasing as an alternative to the frequently used treatment with organic solvents as well as a special activation treatment," reveals Herberhold. The transition between the degreasing and activation stages takes place "wet in wet". In the activation treatment, the surface is freed from disturbing oxide layers. Then a wafer-thin metal layer is applied, which reduces the reactivity of the magnesium surface, which has a high affinity for oxygen, to such an extent that it does not immediately "seal itself off" again with an oxide layer. The parts are now ready for their further journey through the large, fully automatic electroplating plant of HDO GmbH, which consists of a total of 150 dip tanks, each with a capacity of between 4000 and 8000 litres. In further steps, first copper, nickel and finally chrome layers are deposited. For parts that are to be coated with other metals such as ruthenium or palladium instead of chrome, the application of the respective top layers takes place in separate plants.
Process chain decides
According to Happe, the real secret of HDO's success lies not only in the recipe for this or that electroplating bath, but in the careful coordination of all the individual steps in the process chain. Perfect surface quality stands or falls with the right parameters in the casting process. There, for example, defects can occur that are not visible on the raw casting but are very unattractive on the electroplated part. Grinding and polishing are also essential process steps that have a considerable influence on the success or failure of the galvanic coating. Anyone who tries to have magnesium castings cast, ground, polished and coated cheaply somewhere on a contract basis will sooner or later experience unpleasant surprises. The decisive know-how lies in the holistic optimisation of all essential process steps. That is why HDO attaches great importance to carrying out all processes that are crucial for success in-house.