Effect Of Electro Plastic Effect On Microstructure And Properties Of FSP AZ31 Magnesium Alloy

With the progress of global industrialization and the rapid development of world economy,energy crisis is becoming more and more serious.People have paid more attentions on energy saving and emission reduction.Magnesium and magnesium alloys are widely used in electrommunication products,aerospace,automobiles,weapons and other fields due to their rich storage,high ratio of strength,low elastic modulus,strong electromagnetic interference,excellent damping performance and non-pollution.But owning to its hexagonal close-packed structure,the actuated slip system under the room temperature deformation is relatively less accompanied with the uneasy coordinated deformation,the low strength and poor plasticity,which limits the further application of magnesium alloy.When high-energy pulse current was applied to the material,the electro-plasticity effect will occur,resulting in the decrease of the deformation resistance and the increase of the plasticity?elongation?under the current stimulation.In this paper,the modified X52 vertical milling machine was used as a friction stir processing equipment to perform the friction stir processing on the as-rolled AZ31 magnesium alloy.The optimal combination parameters for the FSP AZ31 magnesium alloy with the excellent electro-plastic effect were pulse time 8min,pulse frequency 100Hz and pulse current density 0.87×10⁷A·m^-2.After the treatment of the FSP AZ31 magnesium alloy was treated under this condition,the influence of the electric plasticity effect caused by the high energy pulse current on the microstructure and mechanical properties of AZ31 magnesium alloy was analyzed.The results showed that the grain size in the SZ was refined from 3.17?m to 2.12?m.After high energy pulse treatment,the room-temperature mechanical properties of FSP AZ31magnesium alloy were improved obviously,and the increase range of tensile strength,yield strength and elongation rate in TD direction was 24.7%,18.5%and 134.3%,respectively.The increase range of tensile strength and elongation rate in PD direction were26.7%and 4.13%,and the yield strength basically remained the same.The mechanical properties of FSP AZ31and Pulsed FSP AZ31 magnesium alloys processed along the TD and PD directions were anisotropic.The fracture morphology of Pulsed FSP AZ31 magnesium alloy showed a large number of deep dimples corresponding to ductile fracture.While the fracture morphology of the FSP AZ31 magnesium alloy had some small and shallow dimples elongated along a certain direction corresponding to a mixed fracture of quasi-cleavage and ductile fracture,which indicated that the plasticity and toughness of the pulsed FSP AZ31 magnesium alloy were superior to that of the FSP AZ31 magnesium alloy.The boundaries migration of both the large and low angle grain in FSP AZ31 magnesium alloy were accelerated High-energy pulse treatment.The grain orientation of the FSP AZ31magnesium alloy changed obviously forming a tilted texture.And the texture intensity weakened and the degree of recrystallization increased.The XRD results showed that no new phase formation occurred in the pulse processing,but the number and intensity of the diffraction peaks changed obviously.Through the migration of small-angle grain boundaries in the grain shear zone of the stirred zone of FSP AZ31 magnesium alloy was promoted by the high-energy pulse processing,resulting in the formation of sub-crystal structure,the grain size was significantly refined,and the elongation had a significant increase.