|M.Sc Student||Vainberg Uri|
|Subject||Microstructure and Properties of Aged Vs Crept|
|Department||Department of Materials Science and Engineering||Supervisors||Professor Emeritus Menachem Bamberger|
|Dr. Shaul Avraham|
|Full Thesis text|
Mg-alloys are highly applicable in the automotive and aerospace industries due to their high specific mechanical properties. The Mg-Al-Zn-Sn-RE alloy design was motivated by the formation of Al-RE intermetallics at the grain boundaries (GB) and Mg2Sn precipitates inside the α-Mg matrix. The presence of precipitates at the GB can inhibit GB sliding, while the precipitation inside the α-Mg matrix grains inhibits the dislocation climb which is responsible for bulk creep.
Thermodynamic simulations were used for optimal composition and process parameters derivation. Mg-Al-Zn-Sn alloys with additions of Nd and Ce were examined in terms of creep resistance and microstructure development during aging and creep. The evolution of the microstructure was monitored by Scanning Electron Microscopy and X-ray diffraction. Mechanical properties were examined by creep testing and Vickers micro-hardness measurements.
Mg-Al-Zn-Sn-Ce alloy of previous work was compared with the present work Mg-Al-Zn-Sn-Nd alloy. It was found that the Ce alloy is superior to Nd alloy in terms of creep resistance. This result is despite the fact that the two alloys underwent the same process, which concludes that not all Rare Earth elements can be treated the same way. It was also found that the main creep mechanism of the Nd alloys is dislocation climb with a strength factor of 7.
A directional growth of the MgZn2 precipitates was found in the crept specimens in contrast to the aged counterparts, as well as possible dislocation slip-lines in the crept samples grains. From that we conclude that the application of external stress has a major impact on the precipitation process and a major impact on the microstructure development in Mg-Al-Zn-Sn-Nd alloys.