Study On The Discharge Performance Mechanism Of AZ31 Magnesium Alloy Enhanced By Rolling And Electropulsing Coupling

With the escalation of energy and environmental issues,Mg-air batteries are considered ideal energy storage devices due to their high theoretical discharge voltage and specific capacity.However,the self-corrosion behavior of magnesium and its alloys during the discharge process,uneven dissolution,and the formation of discharge products on their surface lead to low discharge voltage and anode efficiency.These issues significantly limit the further development of Mg-air batteries.This study is based on the understanding that grain size,grain orientation,and homogenization degree are crucial factors influencing the anode discharge performance of magnesium alloys.The research proposes a strategic approach involving extensive plastic deformation to refine grain size,followed by subsequent heat treatment and electric pulse processing to further control grain orientation and homogenization degree.This article focuses on the AZ31 magnesium alloy,investigating in-depth the influence of rolling processes on the electrochemical and discharge behaviors of AZ31 magnesium alloy.The research explores the fundamental mechanisms of how the microstructure affects discharge performance.By employing annealing heat treatment and pulsed current processing techniques to control the microstructure of magnesium alloy subjected to extensive plastic deformation,the study investigates the qualitative and quantitative relationships between pulsed current parameters,microstructure,and discharge performance of magnesium alloy.A comparative analysis of the effects of annealing heat treatment and pulsed current processing on the discharge performance of deformed magnesium alloy is conducted,revealing the enhancement mechanism of magnesium alloy anode discharge performance achieved through pulsed current processing.The main research contents and conclusions are as follows:（1）Under the conditions of rolling speed at 0.1 m/s,rolling temperature at 350℃,and total deformation of 60%,various rolling experiments（2-5 passes）were conducted on the cast AZ31 magnesium alloy to study the impact of different rolling passes on its microstructure and discharge behavior.The results indicate that multiple rolling passes promote recrystallization and refinement.After 4 rolling passes,the alloy exhibits a higher degree of recrystallization,evident grain refinement,and optimal discharge activity.Additionally,the corrosion products are loose,which facilitates the self-detachment of discharge products and reduces anode polarization.By employing the optimal rolling parameters corresponding to the best discharge performance mentioned earlier,further exploration was conducted by changing the rolling paths（6 types）and speed rates to investigate the variations in discharge activity.The results indicate that all six alterations in rolling paths have a positive effect on the discharge performance of AZ31 magnesium alloy.Among these,the magnesium alloy exhibits optimal anode efficiency after being rolled through the A2 path（cross-way method）.This is because the magnesium alloy under this path has a lower breakdown potential.During discharge,the passivation film of this alloy is easily ruptured,facilitating the reaction between the electrolyte and the unreacted magnesium matrix,thereby enhancing its discharge performance.Particularly,at a current density of 10 mA·cm^-2,its anode efficiency increased by 25%compared to the as-cast state.Through comparative experiments with four speed rates（0.9,1,1.1,and 1.2）,it was observed that at a speed rates of 1.2,the degree of grain refinement is most significant,with a grain size reaching 5.76μm.The substantially increased grain boundaries greatly enhance the alloy’s discharge activity.At a current density of 10 mA·cm^-2,the anode efficiency increased by 28%compared to the as-cast state.However,with a further increase in speed rates,the passivation film thickens,weakening the discharge activity.（2）To enhance the homogenization of the as-rolled AZ31 magnesium alloy and improve its discharge performance,annealing treatments were carried out at temperatures ranging from 260℃ to 380℃ and for durations of 30 to 120 minutes on the deformed AZ31 magnesium alloy rolled through the A2 path.The results show that annealing treatment at 350℃ for 30minutes led to the formation of annealing twins,promoting the uniform dissolution of grains around the twins.At a current density of 10 mA·cm^-2,the anode efficiency of the AZ31magnesium alloy reached 57.6%.At the same temperature,when the annealing time was extended to 60 minutes,the discharge performance of the alloy further improved,reaching 58.9%at a current density of 10 mA·cm^-2.This improvement is attributed to the uniform distribution of grains within the alloy and the orientation of some grains towards the（10 10）and（2110）basal planes.The resulting discharge product film is thin and easily ruptured,facilitating the contact between the electrolyte and the magnesium matrix.（3）To enhance the discharge performance of the as-rolled magnesium alloy,experiments were conducted at a pulse frequency of 500 Hz,effective pulse currents ranging from 60A to 240A,and pulse durations from 2.5 to 10 minutes on the AZ31 magnesium alloy rolled through the A2 path.The results indicate that a pulse duration of 5 minutes and effective pulse currents between 60A and 120A effectively improve the discharge performance of the magnesium alloy.Specifically,the magnesium alloy exhibits optimal discharge performance under the treatment of 120A effective pulse current,reaching an anode efficiency of 58.9%.With pulse parameters of 60A for 10 minutes,a fully recrystallized microstructure with an average grain size of approximately 5.57μm was obtained.This treatment also induced structural changes in theβ-Mg₁₇Al₁₂phase within the alloy,transitioning from dendritic to spherical shapes and evenly dispersed throughout the material.As a result,excellent discharge performance was achieved,with an average discharge voltage of 1.088V and an anode efficiency of 61.4%at a current density of 10 mA·cm^-2.Through the research of this paper,the comprehensive mechanism and the best preparation process of improving the discharge performance of magnesium alloy under the combined action of rolling deformation,annealing heat treatment and electric pulse treatment are obtained.The grain size,orientation and second phase of magnesium alloy anode for magnesium air battery were obtained,which provided theoretical and technical support for the improvement of comprehensive performance and industrial application of magnesium alloy anode.