Microstructure and mechanical properties of AZ31-Mg_2Si in situ composite fabricated by repetitive upsetting

AZ31-4.6% Mg2Si （mass fraction） composite was prepared by conventional casting method. Repetitive upsetting （RU） was applied to severely deforming the as-cast composite at 400 ℃ for 1, 3, and 5 passes. Finite element analysis of the material flow indicates that deformation concentrates in the bottom region of the sample after 1 pass, and much more uniform deformation is obtained after 5 passes. During multi-pass RU process, both dendritic and Chinese script type Mg2Si phases are broken up into smaller particles owing to the shear stress forced by the matrix. With the increasing number of RU passes, finer grain size and more homogeneous distribution of Mg2Si particles are obtained along with significant enhancement in both strength and ductility. AZ31-4.6%Mg2Si composite exhibits tensile strength of 284 MPa and elongation of 9.8%after 5 RU passes at 400 ℃ compared with the initial 128 MPa and 5.4%of original AZ31-4.6%Mg2Si composite.

Microstructural evolution and mechanical properties of Mg-9.8Gd-2.7Y-0.4Zr alloy produced by repetitive upsetting

A newly developed severe plastic deformation （SPD） technique, i.e. repetitive upsetting （RU）, is employed to improve the strength and ductility of a Mg-Gd-Y-Zr alloy. During the RU processing, dynamic recrystallization occurs in the Mg alloy, which leads to a significant grain refinement from 11.2 p.m to 2.8 μm. The yield strength （YS）, ultimate tensile strength （UTS） and elongation increase simultaneously with increasing RU passes. The microstructural evolution is affected by processing temperatures. Dynamic recrystallization prevails at low temperatures, while dynamic recovery is the main effect factor at high temperatures. Texture characteristics gradually become random during multiple passes of RU processing, which reduces the tension-compression asymmetry of the Mg-Gd-Y-Zr alloy. 2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.

Microstructural Evolution and Anisotropic Weakening Mechanism of ZK60 Magnesium Alloy Processed by Isothermal Repetitive Upsetting Extrusion

The isothermal repetitive upsetting extrusion(RUE)was implemented to process ZK60 magnesium alloy at 380℃.Then,the relationship between the microstructural characters,including grain refinement and texture evolution,and the mechanical performance of the alloy was investigated.Results showed that after 3 passes of RUE,the average grain size was refined from 115.0 to 26.5μm,which was mainly caused by the continuous dynamic recrystallization and discontinuous dynamic recrystallization.Meanwhile,the elongation of the alloy increased from 13.8 to 21.6%,and the superplasticity(142%)of the alloy has been achieved in the following high temperature tensile test,which is very beneficial for the further processing of the alloy into components.In particular,the alloy formed a distinctive texture distributed between<2-1-11>and<2-1-14>,which was greatly related to the Schmid factor of extrusion direction(ED)and transverse direction(TD).This texture changed the initiation ability of basal and prismatic slip in both directions and inhibited the initiation of partial tensile twinning in TD;thus,the anisotropy in both directions was weakened.As expected,the tensile yield strength difference decreased from25.9 to 3.4 MPa,but it was used as the cost of tensile yield strength in ED.

Effect of homogenization on the microstructure and mechanical properties of the repetitive-upsetting processed AZ91D alloy

The current research investigates the effect of homogenization on the microstructure and mechanical properties of the AZ91 D alloy processed by repetitive upsetting（RU）. Results show that during RU processing, the initial large Mg;Al;particles in the as-cast specimen accelerate the dynamic recrystallization（DRX） due to the particle stimulating nucleation（PSN） mechanism. With the progress of RU,the inherent large strain breaks the large second phases into small fragments, which indicates the PSN gradually disappears, while the pinning effect becomes obvious. As for the homogenized specimen, a pre-heat treatment leads to the absence of Mg;Al;particles but a uniform distribution of Al atoms in the Mg alloy. Though the subsequent RU promotes the precipitation of Mg;Al;particles, the relatively small particle size and the uniform distribution are more favorable to act as obstacles for grain growth than contributors to PSN. Finally, a more homogeneous and refined microstructure is obtained in the specimen with prior homogenization than the as-cast one.