Definition

Magnesium alloys have good mechanical strength characteristics, modulus of elasticity and low density ( 1.7 g/cm3 ), and an intense strength/density ratio. These properties give magnesium a wide use in structural applications. Magnesium also has good electrical and thermal conductivity and absorption to elastic vibrations.

Its melting point is low, around 650 °C. It has good machinability and can be forged, extruded, rolled, and cast. Its crystalline structure is hexagonal. Magnesium has good corrosion resistance in non-aggressive atmospheres but is susceptible to corrosion in marine environments.

Classification  Of Magnesium Alloys

After their designation, magnesium alloys are classified by ASTM (American Society of Testing and Materials) and divided into three parts. The first part, composed of two letters, indicates the two main alloying elements. The second part, with two numbers, shows the percentage of these two elements. If two alloys have the same characteristics, the third part designates a sequential number in order of patent. The fourth and last part indicates the thermal or mechanical treatment used. The unified numbering system (UNS) reserves the designations from M10001 to M19999 for magnesium alloys.

Classification System

The ASTM classification system has the defined designations as indicated below.

First Part (Alloy Elements)

• A: Aluminum
• B: Bismuth
• C: Copper
• D: Cadmium
• E: Rare Earths
• F: Iron
• G: Magnesium
• H: Thorium
• K: Zirconium
• L: Lithium
• M: Manganese
• N: nickel
• Q: Lead Q: Silver
• A: Chrome
• S: Silicon
• T: tin
• W: Yttrium
• Y: Antimony
• Z: Zinc

Second Part:

Indicates The Amount Of The Two Main Alloying Elements

Part Three: Distinguish Alloys With The Same Alloying Element Content

• A: first ASTM-registered alloy
• B: second ASTM-registered alloy
• C: third ASTM registered alloy
• D: high purity

alloy · E: high corrosion resistance

alloy · X1: non-ASTM registered alloy

Fourth Part: Indicates Condition Of Heat Or Mechanical Treatment

• • • F: untreated
    • O: annealed
    • H10 and H11: lightly work hardened
    • H23, H24, and H26: work hardened and partially annealed
    • T4: solubilization heat treatment
    • T5: artificially aged
    • T6: solubilization heat treatment and artificially aged
    • T8: solubilization heat treatment, cold worked, and artificially aged

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Example:

Alloy AZ91A-T6

• AZ: means that aluminum and zinc are the two main alloying elements
• 91: indicates the percentages of aluminum (9%) and zinc (1%) present in the alloy
• A: indicates that this alloy was the first to be registered in the ASTM with these amounts of aluminum and zinc
• T6: indicates that the alloy underwent solubilization heat treatment and was artificially aged

Applications

Magnesium alloys are widely use in the aeronautical industry in engine components, fuselage, and landing gear, for example. It also finds application in the automotive industry (gearboxes, wheels, steering columns), the military industry (missiles), and some electrical and electronic components.

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