Basic Knowledge - Article Series Part 2
Light Metal Alloys: Spotlight Magnesium
Weight plays an increasingly important role in the design of components. This also boosts the importance of magnesium, because the material not only excels as the lightest metallic construction material, but also offers numerous other advantages for series production.
In the eyes of experts, magnesium is an underestimated material. This notion is also supported by statistics: While in 2017 aluminum accounted for 19,076,000 tons of global castings production, magnesium only amounted to 197,000 tons1. Magnesium is the lightest metallic construction material and, in terms of mass, is the lightest alloy used in modern die casting processes. This characteristic has not gone unnoticed by the automotive industry either. With the industry looking for ever lighter structural components, a significant increase in magnesium in the material structure of vehicles is to be expected. Whereas in 2010 magnesium had a share of 9 %, by 2030 it is expected to have risen to 17 %2, almost doubling this figure. Its low weight is certainly one important reason for the increasing popularity of magnesium, but the low-cost production also makes the material interesting for industrial applications. Apart from that, the seventh most common element on earth can even be extracted from seawater and is available in almost unlimited quantities.
What are Magnesium Alloys?
A magnesium alloy is present if, in addition to the main component magnesium, other metals are also included. As a rule, alloys are produced by melting the individual elements together and then cooling them. According to the alphanumeric designation system (ASTM), magnesium alloys can be divided into the following groups: M (magnesium, manganese), AM (magnesium, aluminum, manganese), AZ (magnesium, aluminum, zinc, manganese), K (magnesium, zirconium), ZK (magnesium, zinc, zirconium), ZE (magnesium, zinc, zirconium, rare earth), EZ (magnesium, rare earth, zirconium), QE (magnesium, silver, rare earth, zirconium), WE (magnesium, yttrium, rare earth, zirconium), ZC (magnesium, zinc, copper, manganese), AS (magnesium, aluminum, silicon, manganese), AJ (magnesium, aluminum, strontium). The advantage of these composite materials over pure magnesium is mainly in their improved mechanical properties and increased corrosion resistance.
What are the Characteristics of Magnesium Alloys?
As one of the lightest and most flexible metals, magnesium and its alloys play an important role in die casting, but they are also used in sand and gravity die casting. The properties of these composites vary with their composition. For instance, the share of aluminum in magnesium die casting alloys is always at least 4 % in order to improve castability. In this way, magnesium alloys can be cast into almost any shape - even thin-walled and complex structures can be realized. However, the use of a specific alloy also depends on the temperature, as it affects the metallurgical structure of magnesium. The following alloys are especially import for casting.
- AZ91: Suitable for die casting, gravity die casting and sand casting. This composite material also exhibits good strength and features outstanding corrosion resistance and castability. The combination of these properties makes the material the most commonly used die casting alloy and allows the parts to be used at room temperature.
- AM50/AM60: These alloys are well-suited for die casting due to their good casting properties. They also feature high ductility, tensile strength and energy absorption. The parts made of these alloys can also be used at room temperature.
- AS21/AS41, AE42 and AJ52/AJ62: In this case, the good creep properties are the main advantage, though use is also possible at higher temperatures.
- AE44: Known for excellent casting properties and high ductility, this alloy is suitable for high temperature applications.
- AS31: features high mechanical strength and good creep properties at temperatures up to 150 ºC.
- SC1, WE43, WE54, QE22, Elektron21: These alloys are typically used in sand and gravity die casting. Due to the high temperature ranges, only aluminum-free materials can be used with these alloys.
Physical Properties of Magnesium Alloys
Magnesium alloys have a density of 1.7-2.0 g/cm3, which is about 30 % below that of aluminum. This characteristic is especially important in aircraft and vehicle construction. As far as thermal conductivity is concerned, the use of magnesium has long been associated with a fire hazard. However, this assumption has been refuted for modern alloys, with elements such as calcium and yttrium reducing the flammability of magnesium. Its electrical conductivity varies depending on the composition of the components, but is generally within a very favorable range.
Areas of Application
Due to the potential of magnesium for lightweight design, magnesium castings will increasingly be used in multi-material construction. Magnesium is highly relevant for the construction of modern vehicles. The advantages of alloy components are their light weight, aerodynamic properties and smoothness. Compared to steel and aluminum, magnesium components can save approx. 55 % and 25 - 40 % of weight respectively. If, for example, the doors and tailgates are made of magnesium and aluminum instead of steel, this can reduce the weight by approx. 40 - 50 kg.
The aerospace industry benefits above all from its insulating properties and long durability, which resist external influences. The material is also capable of increasing the flexibility and durability of fuel transfer systems, fuel injectors and engine housings in commercial aircraft. Another means of transport that receives increased attention in connection with magnesium is a children's bicycle. A Chinese manufacturer uses such alloys mainly for the frame, the wheel circle, the front fork and other parts of the bike, which makes the vehicle very light and shock-absorbing. This year, the International Magnesium Association awarded a prize in the "Commercial Cast Product" category for this technological development.
Protective housings made of magnesium alloys are also used in telephones, laptops, tablets and televisions. Although these alloys provide high conductivity, they also offer excellent shielding against electromagnetic and radio interference. In addition, magnesium alloys are 100 % recyclable and could become the sustainable standard for most portable electronic enclosures due to their availability. Apart from other consumer products such as cases or household items, magnesium alloys are also used in medical implants. Magnesium in the form of alloys offers great potential in numerous industries.
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