The increasing use of light alloys owing to their high performance makes magnesium alloys very attractive for the use in automotive and biomedical applications.However,it is well known that magnesium and its alloys ha...The increasing use of light alloys owing to their high performance makes magnesium alloys very attractive for the use in automotive and biomedical applications.However,it is well known that magnesium and its alloys have poor corrosion resistance in different atmospheric and aqueous environments.As a means of improving corrosion resistance through the microstructure modification,electron beam processing(EBP)was applied on the as-cast AZ91 magnesium alloy.To evaluate the microstructure influence on the corrosion-resistant,the EB processed samples underwent a solution heat treatment and an artificial aging heat treatment.Four different obtained microstructures were investigated by standard microscopy and electrochemical corrosion tests to evaluate the microstructure and its effects on the corrosion resistance of AZ91 alloy.The EBPed specimens show a significant microstructure refinement and homogenous distribution ofβ-phase at the grain boundaries surrounded by supersaturatedα-Mg which acts as a barrier against corrosion.The electrochemical corrosion test of the samples immersed in 3.5 wt%NaCl after 4 weeks indicates that the EBP improves the corrosion resistance of the alloy due to the nobler corrosion potential of supersaturated a-Mg and more stable protective hydroxide films compared to the heat-treated and as-cast conditions.展开更多
Together with the mechanical properties,the degradation rate is an important factor for biodegradable implants.The ZKX50 Mg alloy is a suitable candidate to be used as a biodegradable implant due to its favorable bioc...Together with the mechanical properties,the degradation rate is an important factor for biodegradable implants.The ZKX50 Mg alloy is a suitable candidate to be used as a biodegradable implant due to its favorable biocompatibility and mechanical properties.Current research investigates the degradation rate and corrosion behavior of the ZKX50 as a function of the microstructure constituents and their morphology.Since grain refinement is the main strengthening mechanism for the ZKX50,the effect of the microstructure refinement on the corrosion rate was studied by applying electron beam processing(EBP)and friction stir processing(FSP)on the ZKX50 cast alloy.To study the effect of the microstructure constituents and their morphology a subsequent solution heat treatment(HT)was applied to the processed samples.The results show that the EBP and FSP lead to a uniform and remarkably refined microstructure of the ZKX50 alloy and homogeneous distribution of the intermetallic phases.The results of electrochemical corrosion tests together with the microstructure characterization show that microgalvanic corrosion is the predominant mechanism that occurs between the Ca2Mg6Zn3 intermetallic phase andα-Mg matrix.According to the results attained through the electrochemical tests,the EBPed-HT ZKX50 alloy shows higher corrosion resistance compared to all other conditions immersed in 0.5 wt.%NaCl solution.The dissolution and spheroidizing of Ca2Mg6Zn3 particles during the solution heat treatment provides higher corrosion resistance mainly by decreasing the microgalvanic corrosion.The microstructure of the heat-treated samples does not show a significant grain coarsening which can degrade the enhancement of the mechanical properties achieved by the EBP and FSP.展开更多
The prediction of microstructure constituents and their morphologies is of great importance for the evaluation of material properties and design of advanced materials.There have been considerable efforts to model and ...The prediction of microstructure constituents and their morphologies is of great importance for the evaluation of material properties and design of advanced materials.There have been considerable efforts to model and simulate microstructure evolution using a wide spectrum of models and simulation approaches.This paper initially reviews the atomistic and mesoscale simulation approaches for microstructure evolution,emphasizing their advantages and disadvantages.Atomistic approaches,such as molecular dynamics,are restricted by the scale of the studied system because they are computationally expensive.Continuum mesoscale simulation approaches,such as phase field,cellular automata,and Monte Carlo,have inconsistent phenomenological equations,each of which only describes one aspect of microstructure evolution.To provide comprehensive insight into microstructure evolution,a unified model that is capable of equally evaluating the nucleation and growth processes is required.In this paper,a physics-based model is proposed that incorporates statistical mechanics,the energy conservation law,and the force equilibrium concept to include all aspects of microstructure evolution.A compatible simulation approach is also described to simulate microstructure evolution during thermomechanical treatments.Furthermore,the microstructure evolution of AISI 304 austenitic steel during isothermal heat treatment and fusion welding is simulated and discussed.The use of fundamental physical rules instead of phenomenological equations,together with the real spatial and temporal scales of the proposed model,facilitates the comparison of the simulation results with experimental results.To examine the accuracy of the proposed simulation approach,the isothermal heat treatment simulation results are compared with experimental data over a broad region of temperatures and time periods.展开更多
文摘The increasing use of light alloys owing to their high performance makes magnesium alloys very attractive for the use in automotive and biomedical applications.However,it is well known that magnesium and its alloys have poor corrosion resistance in different atmospheric and aqueous environments.As a means of improving corrosion resistance through the microstructure modification,electron beam processing(EBP)was applied on the as-cast AZ91 magnesium alloy.To evaluate the microstructure influence on the corrosion-resistant,the EB processed samples underwent a solution heat treatment and an artificial aging heat treatment.Four different obtained microstructures were investigated by standard microscopy and electrochemical corrosion tests to evaluate the microstructure and its effects on the corrosion resistance of AZ91 alloy.The EBPed specimens show a significant microstructure refinement and homogenous distribution ofβ-phase at the grain boundaries surrounded by supersaturatedα-Mg which acts as a barrier against corrosion.The electrochemical corrosion test of the samples immersed in 3.5 wt%NaCl after 4 weeks indicates that the EBP improves the corrosion resistance of the alloy due to the nobler corrosion potential of supersaturated a-Mg and more stable protective hydroxide films compared to the heat-treated and as-cast conditions.
文摘Together with the mechanical properties,the degradation rate is an important factor for biodegradable implants.The ZKX50 Mg alloy is a suitable candidate to be used as a biodegradable implant due to its favorable biocompatibility and mechanical properties.Current research investigates the degradation rate and corrosion behavior of the ZKX50 as a function of the microstructure constituents and their morphology.Since grain refinement is the main strengthening mechanism for the ZKX50,the effect of the microstructure refinement on the corrosion rate was studied by applying electron beam processing(EBP)and friction stir processing(FSP)on the ZKX50 cast alloy.To study the effect of the microstructure constituents and their morphology a subsequent solution heat treatment(HT)was applied to the processed samples.The results show that the EBP and FSP lead to a uniform and remarkably refined microstructure of the ZKX50 alloy and homogeneous distribution of the intermetallic phases.The results of electrochemical corrosion tests together with the microstructure characterization show that microgalvanic corrosion is the predominant mechanism that occurs between the Ca2Mg6Zn3 intermetallic phase andα-Mg matrix.According to the results attained through the electrochemical tests,the EBPed-HT ZKX50 alloy shows higher corrosion resistance compared to all other conditions immersed in 0.5 wt.%NaCl solution.The dissolution and spheroidizing of Ca2Mg6Zn3 particles during the solution heat treatment provides higher corrosion resistance mainly by decreasing the microgalvanic corrosion.The microstructure of the heat-treated samples does not show a significant grain coarsening which can degrade the enhancement of the mechanical properties achieved by the EBP and FSP.
文摘The prediction of microstructure constituents and their morphologies is of great importance for the evaluation of material properties and design of advanced materials.There have been considerable efforts to model and simulate microstructure evolution using a wide spectrum of models and simulation approaches.This paper initially reviews the atomistic and mesoscale simulation approaches for microstructure evolution,emphasizing their advantages and disadvantages.Atomistic approaches,such as molecular dynamics,are restricted by the scale of the studied system because they are computationally expensive.Continuum mesoscale simulation approaches,such as phase field,cellular automata,and Monte Carlo,have inconsistent phenomenological equations,each of which only describes one aspect of microstructure evolution.To provide comprehensive insight into microstructure evolution,a unified model that is capable of equally evaluating the nucleation and growth processes is required.In this paper,a physics-based model is proposed that incorporates statistical mechanics,the energy conservation law,and the force equilibrium concept to include all aspects of microstructure evolution.A compatible simulation approach is also described to simulate microstructure evolution during thermomechanical treatments.Furthermore,the microstructure evolution of AISI 304 austenitic steel during isothermal heat treatment and fusion welding is simulated and discussed.The use of fundamental physical rules instead of phenomenological equations,together with the real spatial and temporal scales of the proposed model,facilitates the comparison of the simulation results with experimental results.To examine the accuracy of the proposed simulation approach,the isothermal heat treatment simulation results are compared with experimental data over a broad region of temperatures and time periods.
