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采用“多向锻造(MDF)+挤压+在线冷却”技术制备的AZ40(直径为160 mm)镁合金棒材具有混晶组织和力学性能各向异性,通过光学显微镜(OM)、扫描电镜(SEM)、X射线衍射织构测量和室温拉伸试验对上述特征进行表征和分析。结果表明:混晶组织来源于半连续铸锭中Al的微观偏析。均匀化处理((380°C,8 h)+(410°C,12 h))不能完全消除这种微观偏析。在后续MDF和挤压过程中,Al含量为3%~4%(质量分数)的枝晶心部转变成细晶区,而Al含量约为6%的枝晶边缘转变成粗晶区。表层、R/2和心部的XRD宏观织构都呈现典型的纤维织构特征,且表层的[0001]//Ra D取向强度(11.245)约为R/2处(6.026)和心部(6.979)的两倍。挤压态AZ40镁合金棒材沿挤压方向和半径方向具有优异的伸长率(A)和中等抗拉强度(Rm):A为19%~25%,Rm为256~264 MPa;然而,屈服强度(Rp0.2)呈现出各向异性和内外不均匀性,即Ra D为103 MPa,ED-C(心部)为137 MPa,ED-O(边部)为161 MPa,这主要是织构造成的。(155°C,7 h)+(170°C,24 h)时效处理对AZ40镁合金棒材的强度和伸长率几乎没有影响。
AZ40 (160 mm in diameter) magnesium alloy bars fabricated using “Multi-forging (MDF) + extrusion + online cooling” technology have mixed-grain structure and mechanical anisotropy and are characterized by optical microscopy (OM) Electron microscopy (SEM), X-ray diffraction texture measurement and room temperature tensile test were used to characterize and analyze the above characteristics. The results show that the mixed crystal structure is derived from the microsegregation of Al in the semi-continuous ingot. Homogenization (380 ° C, 8 h) + (410 ° C, 12 h) does not completely eliminate this microsegregation. In the subsequent MDF and extrusion, the dendritic core with Al content of 3% -4% (mass fraction) transforms into fine grain region, while the dendrite edge with Al content of about 6% transforms into coarse grain region. The XRD macro-texture of the surface layer, R / 2 and the core showed the typical fiber texture and the [0001] // Ra D orientation intensity (11.245) of the surface layer was about R / 2 (6.026) 6.979). Extruded AZ40 magnesium alloy bars have excellent elongation (A) and moderate tensile strength (Rm) along the extrusion direction and radius: 19% to 25% for A and 256 to 264 MPa for Rm; however, The yield strength (Rp0.2) shows anisotropy and internal and external inhomogeneities, ie Ra D is 103 MPa, ED-C (core) is 137 MPa and ED-O (edge) is 161 MPa, which is mainly Textured (155 ° C, 7 h) + (170 ° C, 24 h) Aging treatments have almost no effect on the strength and elongation of AZ40 magnesium alloy bars.