Inhibiting effect of I-phase formation on the plastic instability of the duplex structured Mg-8Li-6Zn-1.2Y(in wt.%)alloy

In this work,the tensile behaviors of Mg-8%Li and Mg-8%Li-6%Zn-1.2%Y alloys at ambient temperature were investigated and compared.It revealed that the plastic instability of Mg-8%Li alloy was quite remarkable and the variation range of serrated flowing stress can reach5 MPa.For the Mg-8%Li-6%Zn-1.2%Y alloy,the formation of I-phase(Mg_(3)Zn_(6)Y)can simultaneously enhance the tensile strength and eliminate the plastic instability phenomenon,whilst its ductility was degraded.The in-situ tensile tests revealed that for the Mg-8%Li alloy,the severity and number of slip traces present in bothα-Mg andβ-Li matrix phases increased remarkably with the applied tensile strain.However,slip traces were quite fine inβ-Li matrix phase and could be clearly observed when the applied tensile strain exceeded 18%.Due to the incompatibility of plastic deformation occurred in two matrix phases,the induced strain concentration atα-Mg/β-Li interfaces caused their subsequent cracking.For the Mg-8%-6%Zn-1.2%Y alloy,the I-phase distributed atα-Mg/β-Li interfaces suppressed the plastic deformation ofα-Mg matrix phase and the tensile strain was dominated by theβ-Li matrix phase,resulting in the disappearance of plastic instability.Moreover,the plastic strain would preferentially concentrate at I-phase/β-Li interfaces and subsequently induced the cracking of I-phase.