Enhancing superplasticity of LA103Z magnesium-lithium alloy by friction stir processing
Hot rolled LA103Z magnesium-lithium alloy sheets were modified by friction stir processing(FSP).The superplastic deformation behavior of FSP-LA103Z Mg-Li alloy at the temperatures of 200-350℃and strain rates of 5×10-4-1×10-2 s-1 was studied,and the superplastic deformation mechanism was revealed.The results show that,when the deformation temperature is 300℃and the strain rate is 1×10-3 s-1,the elongation of FSP-LA103Z Mg-Li alloy is about 430%,the stress-strain curve is flow stress stable,the strain rate sensitivity coefficient m under this condition is 0.55.During superplastic deformation of FSP-LA103Z Mg-Li alloy,β-Li grains grow and rearrange,and their grain boundaries are distorted.The α-Mg phases precipitate,fracture and grow up,as equiaxed or spherical grains,uniformly distribute in grain boundaries,and partially repolymerize.Solid solution precipitation of AlLi promotes dislocation slip and coordinates intracrystalline deformation.At the early stage of deformation,β-Li dominated deformation,and fine α-Mg phases inhibite β-Li growth.In the later stage of deformation,α-Mg phases dominate the deformation,and β-Li grains are arranged regularly along the tensile direction,which makes the increase of β/β interface resistance unfavorable to deformation.At this time,α/β interface slip and α-Mg grain rotation coordinate deformation,with the cavity nucleation,growth and merger,eventually lead to fracture.
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