MAGNESIUM AND ITS ALLOYS Moiz Ullah Baig (MM-036), Saad Arif (MM-026), Haris Iqbal (MM-020) & Omar Siddiqi (MM-004) Materials Engineering Department INTRODUCTION The word ‘Magnesium’ is derived from the Greek word ‘Magnesia’. It is a white silvery metal, dis- covered by Joseph Black in 1755 at Edinburgh, England. It is the 6 th most abundant element on earth and about 2.4% of earth crust contains magnesium. PROPERTIES Crystal Structure: Hexagonal Closed Packed Atomic Number: 12 Atomic Mass: 24.3 Configuration: [Ne] 3s 2 Group: Alkaline Earth Metal Melting Point: 651 °C Boiling Point: 1100 °C Density: 1.738 gm./cm 3 Specific Gravity: 1.738 Burns in air with an intense white light, produces a lot of heat. Group: II-A Period: III APPLICATIONS Aircraft parts As desulfurizers and deoxidizers As anode in ship hulls and ballast tanks to protect from corrosion Automotive parts Bicycles and sports goods Laptops and cellphones Bohr’s Model MAGNESIUM ALLOYS Magnesium is the metal for the 21 st century. Mg-alloys are being considered as one of the most versatile material choices amongst the structural materials that exhibit both energy efficiency and environmental benefits. Mg-based materials (alloys and composites) have enormous and unlimited potential to replace aluminum, steel and structural plastics in diverse industrial and commercial sectors. Magnesium alloys have a relatively high strength-to-weight ratio, with some commercial alloys attaining strengths as high as 380 MPa. High energy absorption means good damping of noise and vibration, as well as impact and dent resistance. Mg– Zn Binary Alloy Mg-Al Binary Alloy Zinc renders more solid solution strengthening than an equal atomic percent of other alloying elements. They have a strong age hardening response. By these advantages, high strength alloys can be developed. EFFECT OF ZIRCONIA The addition of Zirconia (Zr) enhances the homogeneity of microstructure by making grains round. As a result more zinc can dissolve and contribute positively to the strength of alloy. Solubility: 6.2% at eutectic temperature i.e. 341 °C Solubility: 12.6% at eutectic temperature i.e. 437 °C It is one of the oldest and most commonly used alloys. Addition of aluminum reduces the grain sizes and makes dendrites finer and more developed. Aluminum increase hardness, strength and has minor effect on density. EFFECT OF STRONTIUM The effects of strontium (Sr) on microstructure are found to be very apparent. Addition of Sr makes lamellar structure which are distributed along the grain boundaries and make better creep resistant alloy. JOINING OF ALLOYS Magnesium and magnesium alloys may be joined by most of the common fusion and mechanical fastening methods. Fusion methods include, Shielded-metal arc welding Gas welding Electric resistance seam and spot welding. While mechanical fastening methods include, Riveting Bolting Adhesive bonding. ADVANTAGES DISADVANTAGES Good machinability Good creep resistance to 120 °C High thermal conductivity Easily gas-shield arc-welded High tendency to galvanic corrosion when contact with dissimilar metals and electrolyte. Difficult to deform by cold working High Cost REFERENCES Introduction to Physical Metallurgy 2nd Edition—Sidney H Avner Materials and Process in Manufacturing 10 th Edition—Paul DeGarrmo http://www.totalmateria.com/Article78.htm http://www.intlmag.org/magnesiumapps/overview.cfm https://www.forging.org/design/47-magnesium-alloys http://www.rsc.org/periodic-table/element/12/magnesium http://www.hindawi.com/journals/jma/2014/704283 https://www.jstage.jst.go.jp/article/matertrans/49/6/49_MOV2007315 http://www.foundryworld.com/uploadfile/20094161419781 http://ir.lib.uwo.ca/etd/816/ https://researchspace.auckland.ac.nz/handle/2292/22223 Magnesium alloys are in use around the world in a variety of different applications. It is preferred material when looking for weight reduction without compromising overall strength.