MELTING AND HEAT TREATMENT PRACTICE FOR MAGNESIUM ALLOY CASTING GA9 TO IMPROVE MECHANICAL PROPERTIES FOR AEROSPACE AND AUTOMOBILES APPLICATIONS

摘要

Magnesium alloy (GA9) is used in various Housing and Casing applications of most of the Aerospace and Automobile machine components. The major alloying elements of this specification are 7.7 - 8.9 % Al, 0.1 - 1 % Zn and 0.1 - 0.6 % Mn. It has been established that the mechanical properties of the alloy are strongly dependent on aluminum and.zinc content in the alloy. Both aluminum and zinc introduce strength in the alloy but at the sacrifice of ductility. This phenomenon suggests that there exists a particular composition (within specification limits) which gives best combination of mechanical properties. However, the details of these are not available in open literature. In view of the above information, GA9 alloy with compositions in the lower range of the GA9 specification were selected and studied for mechanical properties. In order to achieve close tolerance in chemistry, the requisite alloy was fabricated. The prefabricated alloy thus prepared was subsequently re-melted and cast into test bars and castings. Degassing of GA9 melt is required to remove dissolved gases which are detrimental in obtaining the maximum mechanical properties. Effect of varying amounts of degasser on the mechanical properties has also been attempted in this study. To sum up, the re-melting of prefabricated alloy with optimum chemistry followed by degassing with 0.3 % degasser resulted in maximum strength and ductility of the alloy.