Effects Of ?-Mg₁₇Al₁₂ And TiB₂ Particle Phases On As-rolled Microstructural Evolution Of AZ80 Magnesium Alloy

AZ80 has shown great application potential for its higher comprehensive mechanical properties among Mg-Al series magnesium alloys.However,the higher Al content also result in the poor formability of AZ80.In research field,extrusion is the main deformation method used in AZ80 processing for the formability could be improved when three-dimensional compressive stress is applied.In comparison,rolling,as another important deformation method for magnesium alloys,can only provide pressing force in rolling reduction direction and twinning which may cause initial cracks always exists in AZ80 during hot rolling.Thus due to the difficulty in forming,only few investigation can be found about rolling process of AZ80.Based on this,in order to widespread application of AZ80 magnesium alloy,our investigation focus on the hot rolling process of AZ80 alloy.Time of homogenization treatment prior to hot rolling was studied in order to play the positive role of residual ? phase;Through investigating the optimal pass reduction process and the effect of adding ceramic particles,the microstructural evolution of as-rolled and as inter-stage annealed state was studied and the homogeneously distributed fully recrystallized fine grains were obtained.Some conclusion could be drawn from the investigations:Firstly,the as-cast AZ80 alloy was homogenized at 420? for different length of time and the controlled amounts,morphous and distribution of residual ?-Mg17Al12 phase prior to hot rolling was obtained.Coarse ? phase distributed along the grain boundaries could stimulate dynamic recrystallization through particle stimulated nucleation?PSN?mechanism and enhance the formation of fine grain band,Thus the distribution of the fine grain bands could be controlled by size and amounts of the residual ? phase The best comprehensive property was obtained with 12 h homogenization treatment.Based on the optimized homogenization process,rolling process with different pass reduction was discussed.It is found that grain size decreases with operation of rolling and inter-stage annealing,which makes more pass reduction could be followed.Compared with the small pass reduction process,more recrystallized fine grains could be obtained with large pass reduction.Also,less twining and a decrease of pole density of basal texture from 13.9 to 8.5 can be obtained with the optimized pass rolling reduction.In order to further obtain more recrystallized microstructure though PSN mechanism of hard particles,TiB₂ particles fabricated by SHS reaction of Al-Ti-B system was introduced into AZ80 alloy.Based on the optimized homogenization and rolling process,the effect of TiB₂ particles on microstructural evolution behavior was investigated.During multi-pass hot-rolling,the non-deformable TiB₂ particles could stimulate the nucleation of recrystallized grains through PSN mechanism in both rolling and annealing process.The PSN effect of hard TiB₂ particles are much stronger than the relatively soft ? particles,but the tiny ? particles separated from deformable residual ? phase may retard the growth of the nucleated grains.Thus with the combined effects of these two mechanisms,much larger scale of evenly distributed fine grains and less twinning could be observed during the whole microstructure evolution process in AZ80 alloy with TiB₂ particles addition,which also result in a decrease of pole density of the basal texture from 8.5 to 7.5 in as final rolled state.