Role of Cain hot compression behavior and microstructural stability of AlMg5 alloy during homogenization

Effects of a minor Ca addition on microstructural stability and dynamic restoration behavior of AlMg5 during hot deformation were investigated.They were studied using scanning electron microscopy(SEM),differential scanning calorimetry(DSC),electron backscatter diffraction(EBSD) analyses and transmission electron microscopy(TEM).JMatPro package was used for simulation of the solidification path of the alloys.The results show that the addition of Ca does not affect the microstructure and hot compression behavior of the as-cast samples.However,it prevents the drastic grain growth during homogenization.It is found that coarse grains of Ca-free alloy promote the dynamic recovery and slow down the dynamic recrystallization during hot compression.Also,the particle stimulated nucleation is suggested as the main nucleation mechanism of new recrystallized grains for hot compressed Ca-free alloy On the other hand,the microstructure of the hot compressed Ca-added alloy is greatly affected by the presence of Al4Ca intermetallics.The formation of Al4Ca phase is predicted by JMatPro and revealed by DSC,SEM and TEM studies.Finally,it is found that the presence of Al4Ca precipitates on the grain boundaries of Ca-added alloy prevents the growth of a(Al) by Zener pinning effect and results in the stability of microstructure during homogenization.

Effect of Ca addition on the microstructure and mechanical properties of heat-treated Mg-6.0Zn-1.2Y-0.7Zr alloy

In this study,the effects of Ca addition on the microstructure,thermal properties,and mechanical properties of a Mg-6.0Zn-1.2Y-0.7Zr(ZWK611)alloy at room temperature and 150℃ were investigated.With an increase in the Ca content,the ignition resistance of the ZWK611 alloy improved and the grains became finer.The as-cast ZWK611 alloy consisted mainly of the dendriticα-Mg matrix and I-phase(Mg_(3)Zn_(6)Y)at the grain boundaries.On the other hand,theτ-(Ca_(2)Mg_(6)Zn_(3))and I-phases were formed in the Ca-added ZWK611 alloy.The fraction of theτ-phase increased with an increase in the Ca content.After the solid-solution treatment,these phases remained partially at the grain boundaries of the Ca-added ZWK611 alloys and an additional W-phase(Mg_(3)Zn_(3)Y)was observed.The phases remaining at the grain boundaries restricted the grain growth through the grain boundary pinning effect.The aging treatment resulted in the formation of MgZn'precipitates in theα-Mg matrix of the alloys.These precipitates were more uniformly distributed in the Ca-added alloys than in the alloys without Ca.Thus,the heat treatment-induced precipitation improved the tensile and creep properties of the T6-treated alloys.The T6-treated ZWK611+0.7Ca alloy exhibited the best mechanical properties at room temperature and 150℃ among all the tested alloys.