Production of Magnesium-Strontium Alloys Through Vacuum Metallothermic Process
- PDF / 1,924,877 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 39 Downloads / 207 Views
INTRODUCTION
MAGNESIUM (Mg) is a silvery white metal; it has two valance electrons, and its configuration is 1s2, 2s2, 2p6, 3s2. The residual 3s2 valance electron structure removes the Mg from the covalent bond structure, resulting in a structural material with the lowest average valence bond energy and with the lowest interatomic bond. The crystal structure of Mg is hexagonal-closed-packed (hcp).[1–8] Strontium (Sr) is one of the alkaline earth metals, and it belongs to group II of the periodic table with its atomic number 38. Strontium has allotropic transformation and it has three crystal structures: face-centered-cubic (up to 215 °C), hcp (from 215 °C to 605 °C), and body-centered-cubic (greater than 605 °C).[9,10] With respect to Hume–Rothery rules, it is possible to make Mg-Sr alloy. Because their ionic
MEHMET BUGDAYCI and AHMET TURAN are with the Chemical and Process Engineering Department, Yalova University, Yalova, 77200, Turkey. Contact email: mehmet.bugdayci@ yalova.edu.tr ONURALP YU¨CEL is with the Metallurgical and Materials Engineering Department, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Maslak, 34469, Istanbul, Turkey. Manuscript submitted July 2, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
balance is (Mg2, Sr+2), the difference between their atomic diameters is 3.2 pct, which is lower than the limitation of 15 pct.[11] The world’s demand for Mg increases about 10 pct annually because it has the lowest density (1.738 g/cm3) among all structural metals. However, the mechanical properties and processing performances of Mg alloys (such as AZ series alloys) are not still enough for some important parts in transportation and in aviation industries in which high strength is critical.[12] In order to improve high-strength Mg alloys, a lot of processes have been investigated in the world. Grain refinement is an alternative method to enhance the strength of metals.[13] The Sr is a grain refiner for particularly Al-Si alloys, and it is widely used in commercial scale for that purpose. Also, it is stated in the literature that it has a remarkable grain refinement effect for Mg alloys as well.[14,15] Apart from its grain refinement effect, Sr as an alloying element can decrease the ratio of microporosity and remarkably enhance the heat resistance and the creep properties of Mg alloys.[16,17] The Sr is added to Al or Mg alloys in the form of Sr-containing master alloy (such as containing 5, 10, or 15 pct Sr) because it prevents the burning loss of pure Sr metal addition.[15,18] Direct reaction, metallothermic reduction, vacuum thermal reduction, and electrolysis methods are main methods to produce Mg-Sr master alloys.[13]
The main primary production method of Mg metal is the Pidgeon process. The process is carried out to produce Mg metal from calcined dolomite (MgCaO2, MgOÆCaO) ores under vacuum atmosphere of approximately 100 Pa (1 mbar). FeSi (ferrosilicon) is used as reductant material in the conventional process. Moreover, it is reported that Al can be used as reduc
Data Loading...
