低挤压比条件下挤压工艺对AZ31B镁合金组织和力学性能的影响

Influence of Extrusion Process on Microstructure and Mechanical Properties of AZ31B Magnesium Alloy at Low Extrusion Ratio

研究了低挤压比(挤压比8)下挤压温度和挤压速度对AZ31B镁合金微观组织和力学性能的影响。采用光学显微镜观察了显微组织,采用材料拉伸试验测试了力学性能,并用扫描电镜观察了拉伸试样的断口形貌。结果表明:低挤压比时棒材的组织为典型的混晶组织——由发生再结晶的细小晶粒包裹未发生再结晶的粗大晶粒;300~400℃时,随挤压温度的提高,材料的伸长率升高,抗拉强度下降;在300℃挤压时,随挤压速度的提高,材料的伸长率升高,抗拉强度下降,挤压棒的拉伸断口由混合断裂转变为明显韧性断裂;250℃时综合力学性能最好,抗拉强度340 MPa,屈服强度280 MPa,伸长率23%。

The influences of extrusion temperature and extrusion velocity on the microstructure and mechanical properties of AZ31B magnesium alloy were studied at low extrusion ratio （8）. The microstructure was observed by optical microscopy （OM）, the mechanical properties were examined by tensile test, and the tensile fracture morphologies were observed by scanning electron microscopy （SEM）. The results show that, the microstructure of bar at low extrusion ratio is typical mixed crystal structure, which is composed of many tiny recrystallized grains and a few bulky unrecrystallized grains. With the increase of extrusion temperature, the elongation of extrusion bar decreases and the tensile strength increases during the extrusion at 300-400 ℃. With the increase of extrusion velocity, the elongation of extrusion bar decreases and the tensile strength increases at 300 ℃. The tensile fracture of the extruded rod is changed from mixed fracture to obvious ductile fracture. The comprehensive mechanical performance of extrusion bar is best at 250 ℃. The tensile strength, the yield strength and the elongation are 340 MPa, 280 MPa and 23%, respectively.