Effect Of Solute Atoms On The Stacking Faults In Mg Solid Solution Alloys And The Investigation Of Dislocation Properties For Mg

Magnesium alloys as lightweight structural materials have been applied extensively inthe field such as automobile industries, microelectronics and aerospace owing to theirlow density, the highest strength/weight ratio, excellent electromagnetic shielding ability,and easy-recycling. However, the applications in the modern industries are still limitedbecause of the inferior ductility, lower strength and creep resistance at elevatedtemperature. In order to improve the mechanical properties, the material researchers havebeen done a lot of experimental studies, and found that the rare earth (RE) metals andtransition metals could improve the mechanical properties. And the mechanical propertiesof Magnesium alloys are closely related to the faults such as stacking fault anddislocation. Thus, it is necessary and urgent to study theoretically the effect of soluteatoms on stacking faults of Mg solid solution, and the investigation of dislocationproperties of Mg has an important directive significance to further improve thecombination properties. In this paper, we carried out first-principles calculations based ondensity functional theory to study on the effects of rare earth (RE) metals and specialtransition metal Zn on stacking faults and mechanical properties, and the dislocation coreproperties of pure Mg are also studied. The obtained main results are as follows:1. The effects of RE (RE=Pr, Nd, Gd, Tb, Dy) solute atoms on four basal stackingfaults of Mg solid solutions have been studied baded on density functional theory. Fromthe generalized stacking fault energy surface, both stable and unstable stacking faultenergies are reduced obviously with the addition of RE elements, and the effect becomesweak with increase of the atomic number of RE elements. Due to the decrease of faultenergies of I2stacking fault, the extended dislocation configuration tends to be stabilizedand the ductility could also be improved. Then the γis/γusvalues show that the addition ofRE elements is beneficial to promote the dissociation of dislocation into partials moreeasily. Finally, through the analysis of the electronic structure, it is found that thedecrease of SFEs originates from the charge transfer between the fault layers.2. First-principles calculations have been performed to investigate the effects of soluteatoms Zn and Y on I1and I2stacking faults in Mg-Y-Zn solid solution using densityfunctional theory. The calculated results show that single Y and singe Zn exhibit theopposite effect on the stable and unstable stacking fault energies. And the simultaneousaddition of Y and Zn decreases the stable and unstable stacking fault energiesdramatically. Then the I2stacking fault is studied in detail, it is found that the extended dislocation configuration tends to be stabilized and the ductility could also be improvedby the simultaneous addition of Y and Zn atoms. Then the γis/γusvalues show that thedissociation of dislocation into partials will happen more easily with the addition of Yand Zn atoms. Finally, the electronic structures reveal that the significant reduction ofSFEs originates from the stronger interaction between slip planes due to the formation ofcovalent bonds.3. Based on the GSFEs, a numerical approximation of dislocation cores is presentusing Peierls-Nabarro model to investigate core properties of various dislocations,namely,(0001)1010,(0001)1120and (1010)1120dislocations. Our resultsreveal a dislocations on both basal and prismatic slip planes can always dissociateinto two Shockley partials and basal slip is more easier than the prismatic slip. Moreover,the Peierls stresses and the Peierls energies are obtained for edge dislocation in basal andprismatic plane, and the obtained Peierls stresses are in good agreement withexperimental data.