Study On Microstructure Refining Mechanism And Properties Of AZ Wrought Magnesium Alloys Inoculated By Oxidation

Deformation is an important route to improve the strength and toughness of magnesium alloys.However,the lack of magnesium slip system and poor formability limit their wider application.The refinement of as-cast microstructure can significantly shorten the homogenization processing time and improve the plastic forming property of magnesium ingots.In the present study,Mg-Al based alloys(AZ31B and AZ80)were inoculated by oxides to achieve microstructure refinement.The refining effects of?-Mg and?-Mg₁₇Al₁₂ in the AZ serial alloys were mainly studied by adding oxidized powders prepared by igniting different type and amount of Mg-RE alloy scrap.Also,the influences of inoculation and refinement on homogenizing annealing process and rolling performance were further studied.Based on organizational observation and theoretical analysis,the influence mechanism was discussed.The?-Mg grains of AZ31B alloy can be effectively refined by different oxidized powders of Mg-RE alloy scrap.The optimal addition amount of Mg-30Gd(Sm)and Mg-20Ce(La)are3.0 wt.%and 2.0 wt.%,respectively.Compared with the same amount of Mg-20La master alloy,the oxidized powders of 2.0 wt.%Mg-20La alloy scrap have better grain refinement effect.Grain refining ratio reaches 67%with better mechanical properties.The tensile strength and elongation are increased by 58.7%and 74.8%,respectively.The refining mechanism is attributed to the synergistic refinement caused by Mg O heterogeneous nucleation and compositional undercooling of RE.Moreover,the oxidized powders of Mg-20La alloy scrap can effectively refine the coarse?-Mg₁₇Al₁₂ phase in AZ80 and Mg-12Al alloy,and reduce the generation of?-Mg₁₇Al₁₂.The optimal addition amount is 3.0 wt.%.The reason is that La element consumes Al atoms in the matrix to reduce the?-Mg₁₇Al₁₂ phase.Also,La atom can adsorb on the dendritic tip of?-Mg₁₇Al₁₂,inhibiting the growth of?-Mg₁₇Al₁₂ phase.After?-Mg₁₇Al₁₂ phase refinement,the tensile strength and elongation of the alloy increase by 26.5%and 38.5%,respectively.The effect of inoculation by oxidized powders of Mg-RE alloy scrap on the homogenization process of AZ80 alloy is significant.After microstructure refinement,the homogenization annealing time of the alloy at 400?is shortened from 14h to 8h and the efficiency is increased by 43%.The ultimate rolling deformation ratios of AZ31B alloy and AZ80 alloy are increased from 35%to 65%and 50%,respectively.Moreover,the mechanical properties are also greatly improved.The mechanism is that the fine grains promote the initiation of the(10^<sub>11)slip system on the cone of AZ magnesium alloy.Moreover,the crushed Al₁₁La₃ particles promote the dynamic recrystallization process during the rolling process and inhibit the growth of recrystallized grains.As a result,twinning deformation is reduced,improving the plastic deformation ability of the alloy.The present study provided a new technique,i.e.,the oxide powder from magnesium scrap are designed as the inoculant for grain refinement.The oxide powder of Mg-La scrap can effectively refine the microstructure of AZ serial magnesium alloy and improve the plastic forming ability and mechanical properties.The study can provide important reference value and theoretical guiding significance on the utilization of oxide inclusions for grain refinement and the forming process development of wrought magnesium alloy with a high performance.