Tensile fracture of as-cast and hot rolled Mg-Zn-Y alloy with long-period stacking phase

摘要

An experimental Mg97Zn1Y2（molar fraction,%）alloy was produced by rolling the as-cast alloy.The microstructure of the alloy is composed of theα-Mg（also marked as 2H-Mg with reference to long-period stacking structure according to hexagonal close packed structure）and long-period stacking（LPS）phase.Tensile tests of Mg97Zn1Y2 alloy in comparison with pure Mg were conducted.The fracture morphologies of the tensile specimens were characterized and the microstructures near fracture surface were observed.The results show that the rolled Mg97Zn1Y2 alloy shows a mixed fracture mode including dimples indicating a ductile fracture pattern and a small fraction of cleavage planes indicating a brittle fracture pattern,which is different from the single brittle fracture of the as-cast alloy.In addition,the plastic deformation is mainly from dislocations induced strain with small strengthening effect during plastic deformation in the as-cast Mg97Zn1Y2 alloy,and the strain hardening rate is similar to that of the as-cast pure magnesium.The deformation mechanism of Mg97Zn1Y2 alloy is different from that of the pure magnesium according to a metallographical observation that whether twins are found or not.The strengthening effect hardly exists in the rolled Mg97Zn1Y2 alloy under the same dislocations induced strain,which is different from that of the as-cast alloy with moderate strengthening effect.