热机械加工对EW75镁合金组织与性能的影响

采用金相显微镜、扫描电镜和拉伸试验机等手段,研究了恒温多向锻造工艺对EW75镁合金显微组织和力学性能的影响,并分析了动态再结晶机制。结果表明,500和470℃锻造态EW75镁合金薄板都发生了动态再结晶,而440和410℃锻造态EW75镁合金薄板中可见大量细小颗粒状析出相,未见明显动态再结晶组织,且在平行于锻压方向上,可见原始晶粒形貌以及颗粒状析出相,而在垂直于锻压方向上,可见明显加工变形流线。470℃锻造态EW75镁合金薄板发生了完全动态再结晶,平均晶粒尺寸约为15μm,且合金中动态再结晶晶粒大部分为大角度晶界。经过锻造处理后的EW75镁合金薄板的强塑性相较于固溶态均有明显提升,随着锻造温度的降低,EW75镁合金薄板的抗拉强度和规定塑性延伸强度都呈现逐渐上升的趋势,而断后伸长率则表现为先增加后减小的特征。在470℃锻造时,EW75镁合金薄板具有最好的塑性,这主要与完全再结晶协调塑性变形以及较大的晶粒间取向差有助于晶面滑移有关。

Effect of thermomechanical process on microstructure and properties for EW75 magnesium alloy

The effect of constant temperature multi-direction forging process on the microstructure and mechanical properties of EW75 magnesium alloy was studied by means of metallographic microscope,scanning electron microscope and tensile testing machine,and the dynamic recrystallization mechanism was analyzed.The results show that dynamic recrystallization occurs in the forged EW75 magnesium alloy sheets at 500 and 470℃,while there are a large number of fine granular precipitates observed in the forged EW75 magnesium alloy sheets at 440 and 410℃,and no obvious dynamic recrystallization microstructure is observed.The original grain morphology and granular precipitates can be seen in the specimen parallelled to the forging direction,while the deformation streamline can be seen in the specimen perpendicular to the forging direction.Complete dynamic recrystallization takes place in the forged EW75 magnesium alloy sheet at470℃,the average grain size is about 15μm,and most of the dynamic recrystallization grains in the alloy are large angle grain boundaries.The strength and plasticity of EW75 magnesium alloy sheet after forging treatment are obviously higher than those of solid solution.With the decreasing of forging temperature,both the tensile strength and the specified plastic extension strength of EW75 magnesium alloy sheet show a gradual upward trend,while the elongation after fracture shows first increasing and then decreasing trend.When forging at470℃,the EW75 magnesium alloy sheet has the best plasticity,which is mainly related to the compatible plastic deformation of complete recrystallization and the fact that the larger orientation difference between grains contributes to the grain plane slip.