FIRST-PRINCIPLES STUDY OF STACKING FAULT ENERGY AND DEFORMATION TWIN\par ENERGY IN Al-Mg ALLOYS

By using first-principles method based on the density functional theory(DFT), the stacking fault energy(SFE)and deformation twin energy(DTE)for the(111)[112]slip system of pure Al metal and Al-Mg alloys were investigated.The dependence of these SFE and DTE on solid-solution Mg content and its accupation were specifically analyzed.Two major approximations were made in the process of calculation,which were local density approximation(LDA)and generalized gradient approximation(GGA-PW91),respectively.The calculated SFE values by using GGA-PW91 exhibit an excellent agreement with corresponding experimental measurements.For pure Al metal,the calculated SFE values are greater than those of DTE.Moreover,it is found that under the same deformation conditions,the DTE in pure Al and Al-Mg alloys increase monotonically with the increase of deformation twin thickness.In addition,the calculated results shows that 6-layer twin possesses the lowest DTE,which is probably due to its mirror symmetry structure.Also noteworthy, our calculations reveal a noticeable decreased tendency of SFE and DTE with Mg content increasing,while Mg occupying on stacking fault and twin boundary most likely increases SFE and DTE.There are no considerably detected effects of Mg atomic occupancy variation in Al-Mg alloy on its cohesive energy and formation energy.