The Resrarch Of Microstructure And Mechanical Properties Of Mg-Li-Zn-Y Alloy

In this paper,Mg-7Li alloy,Mg-7Li-3Zn-6Y alloy and Mg-3Zn-6Y alloy were investigated by method of metallographic microscope(OM),scanning electron microscope(SEM),X-ray diffraction,differential scanning calorimetry(DSC)and the tensile tests were carried out the as-cast and extruded Mg-Li-Zn-Y alloy.Tensile deformation behavior and its dependence on strain rate of Mg-Li-Zn-Y alloy and the effects of heat treatment on the microstructure and properties of Mg-Li-Zn-Y alloy were investigated.The results showed that cast Mg-7Li alloys exhibited positive strain rate effect with the increase of strain rates.The fracture mechanism of alloys was the mixture mechanism of micro-voids aggregation fracture and intergranular fracture and cleavage fracture.Cast Mg-7Li alloys was consist of ? and ? phase,as well as ZnY and Mg12 YZn phase.Strength increased and plasticity reduced obviously after adding Zn and Y.The fracture mechanism of alloys was the mixture mechanism of intergranular fracture.Strength increased and plasticity has not changed of Mg-3Zn-6Y alloy,the fracture mechanism of alloys was the mixture mechanism of cleavage fracture.The LPSO phase was not formed in the microstructure of the Mg-7Li-3Zn-6Y alloy after solution treatment at 400 ?.When the solution temperature reached 450 ? and 500 ?,the LPSO phase was formed.The solution was dissolved at 450 ? for 8h,the hardness of alloy was the highest.The microstructure of Mg-3Zn-6Y alloy was in the form of elongated strip-like LPSO phase after solution treatment,and the properties of the alloy reach the best when the solution system was 470 ? × 8h.Compared with the solution treatment,the aging of the alloy after the formation of LPSO phase did not further improve the hardness of alloys,resulting in the hardness of the alloy was reduced.Dynamic recrystallization occured in Mg-7Li alloy during the hot extrusion process.And Zn and Y addition led to the grain refinement in Mg-7Li-3Zn-6Y alloy,and the size is about 5?m.Two alloys exhibited positive strain rate effect with the increase of strain rates,effect of plastic instability happened in two alloys and was restrained after adding Zn and Y.