Influence of Calcium Additives on Stabilization of Solid Solutions of Mg-Al-System-Based Alloys

Investigations of decomposition kinetics and structure energy characteristics of multicomponent solid solutions of Mg-Al, Ca, X system are carried out to reveal a physical nature of their thermodynamic instability. As revealed, the Ca additives stabilize phase composition and concentration of alpha-Mg solid solution of the new alloys possessing high creep resistance at elevated temperatures. Thus, the interval of thermal stability of new experimental alloys is extended from 230 degrees C to 430 degrees C. The temperature factor describing electrical resistance (ER) changes normalized to room-temperature ER for each alloy on a linear section is the same for all investigated alloys of Mg-Al, Ca, X system, whereas an increment of ER of alloys is caused by formation of vacancies with activation energy of 0.8 eV typical for metallic magnesium. Decomposition of a-Mg solid solution oversaturated with vacancies and Al atoms during its ageing in the temperature range of 230 degrees C-300 degrees C proceeds with formation of Mg(17)Al(12-x)Ca(x) nanodispersed phase near phase interfaces. This process is controlled by diffusion of Al atoms with activation energy of 1.3 eV.