Effects of zinc concentration on the stretch formability of the rolled Mg Zn Ca alloys were investigated. The zinc addition more than 0.5 mass effectively modified the basal plane texture, which was characterized by the splitting basal pole toward the TD. The intensity of basal plane texture decreased with the increase in zinc concentration. The rolled Mg 1.5 massZn 0.1 massCa alloy showed significant stretch formability corresponding to the rolled aluminum alloys. On the other hand, the zinc addition more than 1.5 mass deteriorated the stretch formability of rolled Mg Zn Ca alloys. The deterioration of the stretch formability of rolled Mg Zn Ca alloys with high zinc concentration was suggested to be responsible for the solid solution hardening. It was suggested that not only the TD split texture but also the solid solution softening played an important role in the enhanced stretch formability of the rolled Mg Zn Ca alloys.
Stress corrosion cracking (SCC) and corrosion resistance of Mg-6 mass%Al-1 mass%Zn-1 mass%Ca (AZX612) extruded alloy were investigated by slow strain rate tensile tests (SSRT) in 0.01 M NaCl solution and immersion tests in 5 mass% NaCl solution, and compared with those of Mg-6 mass%-1 mass%Zn (AZ61) extruded alloy. In the SSRT in the salt solution, as-received AZX612 exhibited lower elongation and higher SCC susceptibility than those of as-received AZ61, indicating that calcium addition in Mg-Al alloy deteriorated SCC resistance. On the other hand, after solution treatment, improvement of elongation and SCC susceptibility occurred in both the alloys. Observation of surface profiles for AZX612 and AZ61 after the SSRT in salt solution revealed that corrosion pits on surface likely initiated SCC in both the alloys. The results of immersion tests showed the same tendency with those of SSRT in salt solution. It is suggested that SCC resistance of AZX612 and AZ61 was likely related to the microstructural change accompanied with calcium addition and solution treatment such as the change in distributions of Al 2 Ca phase and Al-rich phase.
Segregation behavior at grain boundary of Mg Zn Al Ca Sr alloys was calculated by using the grain boundary phase model based on the Hillert s 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 Ca 2 Mg 6 Zn 3 precipitation. The addition of Al and Zn in Mg Ca alloys promoted the Ca segregation. However, the Al addition in Mg Ca alloys signi cantly 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 coef cient 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 Ca 2 Mg 6 Zn 3 phase in the three phase region hcp, C14 and Ca 2 Mg 6 Zn 3 on the phase diagram.
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