Thermodynamic characterization of solidification and defects that occur in Mg-alloy AM60

The AM60 alloy was thermodynamically examined using chemical analysis, thermodynamic calculation made by ThermoCalc program, ?in situ? thermal analysis and differential scanning calorimetry (DSC), whereas the microstructure constituents were confirmed using optical and scanning electron microscopy (SEM). At the eutectic temperature of 437 ?C the equilibrium solubility of Al in Mg is 12.6 wt. % Al. On the boundaries of the primary Mg grains the intermetallic compound of Al12Mg17 is precipitating according to the solvus line of the Mg-Al phase diagram. Solidification of the AM60 alloy has been investigated using ?in situ? simple thermal analysis. The investigation of solidification has been taking place by evaluation of the cooling curves in connection with metallographic examinations, differential scanning calorimetry and thermodynamic calculations. All defects, nonmetallic inclusions and intermetallic compounds that occur in investigated AM60 alloy were identified.

Structural Relaxation by Precipitation in Al-Li I. Growth Kinetics of Precipitates

Changes in electrical resistance measured by the four probe method was adopted as a structure sensitive physical property used to trace changes in the atomic microstructure below and above the δ'-solvus line in the Al-Li binary alloys. The kinetics of the growth and dissolution of δ' phase (Al3Li) and the formation of δ phase (AlLi), below and above δ'-solvus line, during the coarsening process were studied by isochronal and isothermal investigations. The diffusional growth of δ'-phase, below the δ'-solvus line, was found to be activated by 0.24 eV. Interpretation of the results showed that this energy involved two events during the coarsening process. The first event seemed to be a breakdown of the bonding between the vacancy-Lithium pair and the second event involved the transport of Li atoms to Al-particles to coarsen δ'; (Al3Li) particles. Furthermore, the study of the temperature dependence of electrical resistance of the stable phases δ' and δ of Al-Li alloys was found to be accompanied by difference in the temperature coefficient of the electrical resistance and was attributed to the change in structure of the two phases considered.