ZA73镁合金热变形行为研究

Hot Tensile Deformation Behavior of ZA73 Magnesium Alloy

在应变速率为0.001s-1和0.1s-1、温度为150~300℃的条件下,采用热模拟对ZA73镁合金的高温拉伸变形行为进行了研究,并结合显微组织观察和挤压试验,分析确定了适合该合金的热加工工艺。结果表明：变形温度和应变速率是影响ZA73合金流变应力和塑性的关键参数,应变速率一定时,流变应力随温度的增加而降低;温度一定时,流变应力随应变速率的提高而增加。低应变速率下,温度高于200℃塑性反而降低;高应变速率下,合金的塑性随着温度的增加而提高,但在250℃时塑性出现反常变化。在200~250℃范围内变形时,铸态枝晶网状组织特征消失,第二相化合物呈颗粒状弥散分布于基体中,尺寸明显细化;300℃变形时,低应变速率下合金组织明显粗大。细小第二相粒子增多和组织粗化导致合金热塑性降低。较高的应变速率和较高的温度有利于合金的热变形。在350℃和较高应变速率（约0.1s-1）下,挤压棒材的抗拉强度达355MPa,延伸率仍保持19%,晶粒尺寸细化至3~6μm。

The hot tensile deformation behavior of ZA73 magnesium alloy were investigated in the temperature range of 150-300℃ and strain rates of 0.001s-1 and 0.1s-1,respectively,by thermo-mechanical simulation.The hot-forming processing parameters were then determined,combined with microstructural observation and real extrusion experiment.The results showed that the deformation temperature and strain rate are the key factors influencing the flow stress and plasticity.The flow stress decreases with the increase of temperature and the decrease of strain rate.At lower strain rate,the plasticity becomes worse when the deformation temperature is higher than 200℃.Comparatively,at higher strain rate,the plasticity improves with the temperature raising except at 250℃.Moreover,when deformed in the temperature range of 200-250℃,net-worked dendritic microstructural feature disappears,instead,the second phases disperse in the matrix in the form of particles of smaller size.The microstructure goes coarse when deformed at 300℃ under lower strain rate.It is concluded that the increase of the amount of small particles and the coarsening of microstructure lead to the deterioration of hot plasticity.Higher strain rate and temperature is considered to favour hot deformation.Bars were extruded at 350℃ under higher strain rate of about 0.1s-1.The tensile ultimate strength of the as-extruded bar reaches 355MPa,in the mean time maintaining a high elongation of 19%.In addition to,the grain size was refined to 3-6μm.