变形条件对挤压态ZA21镁合金热变形和腐蚀行为的影响

Effect of Deformation Condition on Hot Deformation and Corrosion Behavior of As-extruded ZA21 Magnesium Alloy

研究了变形温度、应变速率和变形量对挤压态ZA21镁合金的热变形行为及组织演变的影响规律,建立了热加工图,并对失稳区、安全区和最佳加工区试样进行浸泡失重和电化学试验,研究不同区域内ZA21镁合金的腐蚀行为。结果表明:在高温低应变速率时,ZA21镁合金的动态软化机制以动态回复为主,低温高应变速率时,以动态再结晶为主;最佳加工区温度为300~350℃、应变速率为0.001~0.01s^-1,这主要与完全动态再结晶的产生有关;在同一加工工艺下,随变形量增加,ZA21镁合金自腐蚀电位明显正移,自腐蚀电流密度明显下降,当变形量增加至60%时,自腐蚀电流密度降低了3~4个数量级,这主要是因为晶粒细化导致合金表面形成了更加致密的氧化膜;但加工失稳区试样的微观组织存在楔形裂纹和明显孔洞,所以腐蚀速率相对较大。

The effects of deformation temperature,strain rate and deformation amount on the hot deformation behavior and microstructure of as-extruded ZA21 magnesium alloy were investigated.The processing map was established,and the immersion mass loss and electrochemical tests were carried out on the unstable zone,the safe zone and the best processing zone to study the corrosion behavior of ZA21 magnesium alloy in different regions.The results show that the dynamic softening mechanism of ZA21 magnesium alloy is mainly dynamic recovery at high temperature and low strain rate,while dynamic recrystallization is dominant at low temperature and high strain rate.The optimum processing temperature is 300~350℃,and the strain rate is 0.001~0.01 s^-1,which is mainly related to the generation of complete dynamic recrystallization.Under the same processing technology,with the increase of deformation,the self-corrosion potential of ZA21 magnesium alloy obviously positively shifts,and the self-corrosion current density significantly decreases.When the amount of deformation increases to 60%,the self-corrosion current density can decrease by 3~4 orders of magnitude.This is mainly because the grain refinement leads to a denser oxide film on the surface of the alloy.However,the microstructure of the samples in the processing instability zone has wedge cracks and obvious pores,so the corrosion rate is relatively large.