Effect of Al₂Ca Precipitation on Plane Strain Deformation Behaviors of AZ61 Magnesium Alloy

Magnesium and its alloys have been paid attention as lightweight materials in various industrial fields. However, their low formability has been made them hard to applicate in industrial field. Even in the hot work such as extrusion or rolling, the occurrence of crystallographic texture makes strain anistropy and they become the reason to occurrence of crack or fracture. In order to improve poor formability, it is important to understand the texture control of magnesium and many studies has been conducted.<br/>Especially, addition of Ca as an alloying element has been known to improve the mechanical properties of magnesium alloys by restricting development of basal texture like RE(rare earth) elements does. It has been showed that alloying Ca or RE elements can affect to dynamic recrystallization by incuding particle stimulated nucleation (PSN) effect. This effect is able to make the grains which have new orientation from basal during hot deformation. However, its texture was maintained as a basal and it was insufficient to control the development of texture. Thus, further studies to control the texture formation related with the PSN effect are needed.<br/>In the previous study, One of the researchers investigated the characteristics of texture formation behavior of AZ80 magnesium alloy during high-temperature deformation. It was concluded that along with the strain rate the major mechanism of slip movement was changed. It was dislocation glide at high strain rate and solute dragg atmosphere at low strain rate. Due to this change of mechanism, The main texture component and its sharpness of AZ80 alloy was varied. Thus, in this study, the PSN mechanism was studied related with the different strain rate and its deformation mechanism variation using 1.5wt% Ca addition on AZ61 alloy.<br/>The commercial AZ61 and AZX611 which contains the 1.5wt% alloy were used as a starting material. they were hot rolled with the 25% redution at 673K. Rolled sheets were cut to 10×6.7×10 mm specimen. All of specimens were sealed in quartz tube with the Ar gas and annealed at the 773K for 4H. After annealing, the basal texture was formed to specimens. And then, high- temperature plane strain compression was conducted using channel die and under deformation condition that different strain rate with 5×10^-2s^-1 and 5×10^-3s^-1 at 723K. The compression direction was perpendicular to rolling direction of rolled sheet. They were quenched at the water after deformation. The behvior of texture formation and DRX was observed using SEM-EBSD after cutting specimen parallel to normal and transverse direction each.<br/>Due to Ca addition, Al₂Ca phase was formed in AZX611 and Ca was not soluted in matrix at all. AZX611 showed higher stress curves<br/>than AZ61 in the all deformation condition. By this deformation, dynamic recrystallization was occurred and the behaviors of DRX was continuous type in AZ61 and it was changed to discontinuous in AZX611 alloy. Also, occurrence of different texture formation behavior between both alloy was observed.