Study Of AZ91D Magnesium Alloy After Rolling Electric Pulse Annealing Process And Tissue Evolution

As the lightest metal structural material,magnesium alloy has great potential as an alternative material for lightweight structural parts in aerospace,3C digital,automotive manufacturing and other fields.Due to its special dense hexagonal close packed structure,magnesium alloy rolling deformation is difficult and the rolled sheet has serious anisotropy,and long time annealing treatment is required between rolling passes and after rolling,resulting in low productivity and high energy consumption of magnesium alloy rolling,and the production cost is greatly increased,which restricts the efficient and green development of magnesium alloy.In recent years,pulsed current has been widely used for material modification treatment,which has the advantages of high efficiency and environmental protection.In this paper,rolling experiments were carried out on cast and variegated AZ91D magnesium alloys,and the material was treated by conventional annealing and pulse current annealing to investigate the differences and commonalities in the evolution of the microstructure and mechanical properties of the material under different annealing processes,and to reveal the intrinsic mechanism of pulse current for material properties.Single pass simultaneous/asynchronous rolling experiments were carried out on cast AZ91D magnesium alloy after homogenisation,and the specimens were subjected to conventional and pulsed current annealing treatments.Compared with the conventional annealed specimens,the grain size of the pulsed current annealed specimens was refined to65.37μm,and the tensile strength was increased by 32.70%and elongation by 20.65%.The effect of pulsed current on the second phase and its elemental distribution under grain refinement was clarified by scanning observations and elemental surface sweeps.In order to investigate the influence of the initial morphology of the material on the rolling and post-rolling annealing of AZ91D magnesium alloy,single pass simultaneous/asynchronous rolling experiments were carried out on solid solution specimens of AZ91D magnesium alloy with variable morphology,and post-rolling specimens were subjected to conventional annealing and pulsed current annealing experiments to analyse the influence of the pulsed current treatment time on the post-rolling properties,material structure and microstructure.The results showed that 128 A/mm~2 and10 min were the best parameters for pulse current annealing after rolling,and the tensile strength of the specimens after pulse current annealing was 224.6 MPa and the elongation reached 7.4%.The number density of the second phase became smaller as the pulse current annealing time increased.Compared with conventional annealing,the peak weave of the basal surface was deflected towards the non-basal surface under pulsed current annealing,and the overall mechanical properties were better than those of conventional annealing.Through EBSD characterisation and derivation of equations such as Gibbs free energy and classical nucleation theory,the mechanism of the non-thermal effect of pulsed current on promoting second-phase dissolution,promoting grain boundary migration and twinning recrystallisation is analysed,and the mechanism of the effect of the non-thermal effect of pulsed current on grain boundary migration,second-phase dissolution and twinning behaviour is described.