Microstructure And Mechanical Properties Of Mg-3Gd Alloy Fabricated By Large Strain Hot Rolling

Magnesium(Mg)alloys are the lightest structional materials and have potential applications in transportation,aerospace,electronic consumer and bio-materials areas.However,to date,their applications are still limited due to their low strength and poor formability.The purpose of this paper is to reveal the mechanisms that can result in superior combinations of high strength and ductility of Mg alloys and to fabricate such alloys.Deformed,heterogenous,and recrystallized Mg-3Gd(wt.%)samples are fabricated by large strain hot rolling and subsequent annealing.Mechanical behavior and properties are charactrrized by tensile tests(strength,ductility,strain rate sensitivity),plastic strain ratio,and cupping test.The microstructure and texture evolutions are characterized by Elctron Channel Contrast(ECC),Eletron Backscattered Diffraction(EBSD),X-ray Diffraction(XRD),and Transmission Electron Microscopy(TEM).The relationship among mechanical properties,texture,and microstructure are discussed.Strengthening mechanisms are analyzed and their contributions to stenrgth are quantified.The factors affecting the ductility and formability arediscussed.The main conclusions are summarized as follows:(1)Three kinds of microstructures are prepared by large strain hot rolling and annealing:1)a deformed state,2)two partially recrystallized heterougenous structures with different volume fractions of recrystallized grains,and 3)two recrystallized samples with a fine-grained and a coare-grained structures,respectively.Among these samples,the two samples with heterougenouss structures,and the fine-grained sample have superior combination of strength and ductility.Their yiled strength are 224,189,and 163MPa,and their uniform tensile elongation are 2%,10.8%,and 16.7%,respectively.The heterougenous samples have better tensile property but poor forming property than recrystallized samples.(2)After tensile deformation,the microstrucres of the above samples are not significantly changed with their textures show obvious evolutiont:1)The deformed sample has a strong basal texture;2)The{0002}pole figures of the samples of heterougenous structures and the fine-grained sample split from RD to TD after tensile deformation;3)The texture components of the fine-and coare-grained samples after tensile deformation are{0002}<10^<sub>1^<sub>0>and{0002},respectively.(3)Activation of non-basal dislocations is the critical factor for achieving good ductility,while the formability is enhanced by texture weakening.Boundary strengthening is the main strengening mechanism,which contributes to the strength more than solid solution strengthening and particle strengthening.There exists an additional strengthening of about 10%at mostof yiled strength in the samples of heterougenous structures.