Magnesium alloys, as one of the lightest commercially used structural materials, are traditionally used in aircraft and spacecraft applications. Magnesium alloys also have high speciﬁc strength and elastic stiffness, good machinability and excellent damping capacity.
Current trends to reduce energy consumption lead to efforts to minimize both total weight and the weight of moving part of vehicles. Therefore, lately, to an increasing rate, wrought magnesium alloys in automotive applications are considered, which can significantly decrease the weight of vehicles. Magnesium alloys are also used for manufacture of housings of many portable electronic devices, such as, cellular phones or notebooks, not only for the material lightness but also for the easiness of recycling and good electromagnetic shielding capabilities. These replace castings with wrought products, including complex shape precision forgings.
The Mg alloy systems are divided into Al-containing and Al-free compositions.
The most frequently used alloys are those based on the Mg-Al system, such as Mg-Al-Zn (referred to as AZ) and Mg-Al-Mn (AM series). Their weak creep resistance is related to the occurrence of a low-melting Mg17Al12 phase, rendering such materials unsuited for applications above 120°C. The Mg-Al-RE (AE series), Mg-Al-Ca-Sr (AXJ series), and Mg-Al-Sr (AJ series) have better creep resistance, since their microstructure is characterized by the presence of second phases from system Al-RE, Al-Sr or Al-Ca at the grain boundaries which are stable compounds with a relatively high melting point. The maximum operating temperature of these alloys do not exceed 180°C.
The basic systems for Al-free magnesium alloys are Zr-containing alloys such as Mg-Zn-Zr (ZK series), Mg-Nd-Y-Zr (WE series), Mg-Ag-Nd-Zr (QE series), Mg-Gd-Nd-Zr (Elektron 21), Mg-Zn-RE-Zr (ZE series), Mg-Th-Zr. These alloys are predicted mainly to gravity casting and their maximum operating temperature approaches 300°C. Among these alloys, ZRE1 magnesium alloy exhibits good creep properties up to 200°C. This alloy containing zinc, rare earth metals and zirconium. Zinc is usually used in combination with aluminum, zirconium, rare earths, or thorium to produce precipitation-hardenable magnesium alloys having good strength. Zinc also helps overcome the harmful corrosive eﬀect of iron and nickel impurities that might be present in the magnesium alloy. Rare earth metals are added either as 'mischmetal compound' to reduce synthesis costs.
Additions of the rare earth elements drastically improve ductility and increase the strength at elevated temperatures. They also reduce weld cracking and porosity because they narrow the freezing range of the alloys. Zirconium has a string grain-reﬁning eﬀect on magnesium alloys. The Elektron ZRE1 alloy exhibits excellent casting characteristics with components being both pressure tight and weldable.
The main Mg alloy classes are
• Mg-Al casting alloys
• Mg-Al-Zn casting alloys
• Mg-Zn and Mg-Zn-Cu casting alloys
• Mg-Zn-Zr and Mg-RE-Zn-Zr casting alloy
• High temperature Mg casting alloys
• Wrought Mg alloys
Alloy Symbol Key for Magnesium Alloys:
Letters plus numbers indicate the alloying elements added to Mg in weight % and rounded to the nearest whole number. For example AZ31 indicates the alloy Mg-3Al-1Zn.
|Code Letter||Alloying Element|
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