挤压态WE43镁合金低温断裂研究

Study on low temperature fracture of as-extruded WE43 magnesium alloy

为了研究挤压态WE43镁合金低温断裂原因及断裂机理,利用Gleeble-3800热模拟试验机在变形温度150℃、应变速率0.001~1 s^-1下进行WE43镁合金压缩试验直至试样断裂。通过光学显微镜和扫描电子显微镜观察了断裂试样裂纹附近区域微观组织及断口形貌。结果表明:低温下挤压态WE43镁合金塑性变形软化现象不明显,合金达到强度极限即断裂,并且流变应力对应变速率不敏感。低温压裂后WE43镁合金组织仍为等轴晶,但分布不均匀。沿着裂纹扩展方向及裂纹附近区域发现的孪晶、第二相粒子是挤压态WE43镁合金低温断裂的主要原因,能谱分析结果表明第二相为富Y的颗粒状沉淀以及富Nd的条状沉淀。挤压态WE43镁合金低温断口形貌为一系列解理面和少量由第二相粒子导致的韧窝,断裂机制为以穿晶解理为主的韧-脆混合型断裂。

To study the low temperature fracture causes and fracture mechanisms of as-extruded WE43 magnesium alloy,the compression tests of WE43 magnesium alloy specimens were carried out on Gleeble-3800 thermal mechanical stimulator until fracture at 150℃and strain rates of 0.001-1 s^-1.The microstructure and fracture morphology near the crack were observed by optical microscope(OM)and scanning electron microscope(SEM).The results show that the plastic deformation softening phenomenon of as-extruded WE43 magnesium alloy at low temperature is not obvious,the alloy breaks when it reaches the ultimate strength,and the flow stress is not sensitive to the strain rate.After fracture at low temperature,the microstructure of WE43 magnesium alloy is equiaxed but is not distributed evenly.Twinning and the second phase found along the crack extension direction and near the crack region are the main reasons for low temperature fracture of as-extruded WE43 magnesium alloy,and the energy diffraction scanning(EDS)results show that the second phase is Y-rich granular precipitation and Nd-rich strip shaped precipitation.The fracture morphology of as-extruded WE43 magnesium alloy at low temperature is a series of cleavage surfaces and a small amount of dimples caused by the second phase particles.The fracture mechanism is the ductile-brittle hybrid fracture dominated by transgranular cleavage.