新型Mg-Bi-Al-Zn变形镁合金的微观组织与力学性能

Microstructure and mechanical properties of new Mg-Bi-Al-Zn wrought magnesium alloy

基于开发低成本非稀土型变形镁合金的目的,利用XRD、SEM、EDS、TEM和EBSD等检测手段对新型Mg-7Bi-1Al-1Zn(质量分数,%,BAZ711)合金的微观组织进行相关表征,同时采用万能试验机测试了其铸态及挤压态试样的力学性能。结果表明:铸态BAZ711合金中粗大的Mg_3Bi_2相呈连续网状分布于α-Mg枝晶晶界处,其平均二次枝晶臂间距约为50μm;挤压态BAZ711合金发生完全再结晶,平均晶粒尺寸减小为3μm,微米级Mg_3Bi_2相沿挤压方向呈条带状断续分布,同时,基体中弥散分布有大量50~200 nm的近球状或短杆状Mg_3Bi_2相;挤压后合金表现出典型挤压织构特征。由于组织细化和微/纳双尺度第二相的综合强化作用,挤压态合金力学性能较铸态显著提高,其拉伸屈服强度、抗拉强度和伸长率分别达到244 MPa、305 MPa和14%。

In order to develop cost-effective Mg alloy without rare earth(RE) addition, the microstructural evolution of newly developed Mg-7Bi-1Al-1Zn(mass fraction, %, BAZ711) alloy was investigated by XRD, SEM, EDS, TEM and EBSD. The tensile test was also carried out to study corresponding mechanical properties. The results show that the as-cast BAZ711 alloy is consisted of α-Mg matrix with an average second dendrite arm space(SDAS) of about 50 μm and coarse Mg_3Bi_2 phases distributing in the grain boundaries. However, the average grain size is reduced to about 3 μm after extrusion. The extruded BAZ711 alloy with fully dynamic recrystallized(DRXed) grains contains strip-like fragmented Mg_3Bi_2 particles along the extrusion direction(ED), demonstrating a typical basal texture. In addition, a large amount of Mg_3Bi_2 precipitates with sizes ranging from 50 nm to 200 nm were observed. The as-extruded BAZ711 alloy gives superior mechanical properties, a tensile yield strength of 244 MPa, an ultimate tensile strength of 305 MPa and an elongation of 14%, which is mainly due to grain refinement, and presence of micro/nano-size Mg_3Bi_2 particles.