Mag-Thor

Mag-Thor is the common name for a range of magnesium alloys containing thorium that are used in aerospace engineering. These alloys commonly contain manganese and zinc, but there are other combinations known. Some common alloys are named HK31, HM21, HM31, HZ32, ZH42, ZH62; where the "H" indicates that the alloy contains thorium. Magnesium alloy names are often given by two letters following by two numbers. The two letteres indicate the main elements present in the alloy where A = aluminum, Z = zinc, M = manganese, S = silicon, etc. the numbers tell percentage compositions of the two elements. So, AZ45 would indicate that there is 4% aluminum and 5% zinc in the alloy.

Magnesium-thorium alloys have been used in several military applications, particularly in missile construction. The most noted example of this is the CIM-10 Bomarc missile, which implemented thoriated magnesium in its construction. This is due to thoriated magnesium compounds being lightweight, having high strength, and creep resistance up to 350° C. But, these alloys are no longer used due to radiation concerns involving thorium's radioactivity. This has resulted in several missiles being removed from public display. Another concern for the thoriated magnesium alloys is the low melting point and rapid oxidation of the metal. This can result in dangerous flash fires during the production of the alloys. Additionally, thorium-free magnesium alloys have been developed that exhibit similar characteristics to mag-thor, causing currently used magnesium-thorium alloys to be cycled out of use.

Further reading

• US 3120435, Premo Chiotti, "Regeneration of Fission-Products-Containing Magnesium-Throium Alloys", issued Feb 4, 1964, assigned to United States Atomic Energy Commission 
• John J. McKetta. "Thorium and ThoriuM Compounds Supply-Demand Relationships" (Google Books excerpt). Encyclopedia of Chemical Processing and Design: Thermoplastics to Trays, Separation, Useful Capacity. http://books.google.com/books?id=ahNFGR1jMB4C&pg=PA81. 
• M. M. Avedesian, Hugh Baker (1999). "Metallographic and Fractographic Techniques and Microstructures" (Google Books excerpt). Magnesium and magnesium alloys. ASM International. pp. 28. ISBN 9780871706577. http://books.google.com/books?id=0wFMfJg57YMC&pg=PA28. 

External links

• Oak Ridge Associated Universities article on Mag-Thor alloys
• Safety Requirements For Handling And Fabrication Of Magnesium Alloys
• basic commercial magnesium alloys