Calculated grain boundary segregation in mg-zn-ca alloys and its correlation to the texture formation and formability of the alloys

Abstract

Segregation behavior at grain boundary of Mg-Zn（Al）-Ca （Sr）alloys was calculated by using the grain boundary phase model based on the Hillerts parallel tangential construction to Gibbs energy. The correlations between the calculated segregations and literature values of their maximum texture intensity and Erichsen value were investigated. The Zn addition in Mg-Ca alloys kept a certain Ca concentration in hcp phase regardless of Ca2Mg6Zn3 precipitation. The addition of Al and Zn in Mg-Ca alloys promoted the Ca segregation. However, the Al addition in Mg-Ca alloys significantly decreased Ca concentration in hcp phase due to precipitation of Al （Mg）-Ca compound phases. According to the comparison between the calculated segregation（Ca and Sr）and literature values of maximum texture intensity, the Ca and Sr segregation in grain boundary promoted a decrease of texture intensity of the alloys. The decrease of the texture intensity of Mg-Al-Ca and Mg-Zn-Sr alloys were relatively small because of the precipitates formation. The negative correlation coefficient of −0.85 was obtained between the calculated grain boundary segregation of Ca at the rolling temperature and the literature values of maximum texture intensity. It was estimated that the large amount of Ca segregation at grain boundary region in Mg-Zn-Ca alloys is obtained by rolling at just below the melting point of Ca2Mg6Zn3 phase in the three-phase region（hcp, C14 and Ca2Mg6Zn3）on the phase diagram.