5083铝合金中θ-Al_(45)(Mn,Cr)_7相的孪晶现象

Twinning of θ-Al_(45)(Mn,Cr)_7 phase in 5083 aluminum alloy

应用高分辨透射电镜观察了5083铝合金轧制退火组织中弥散相的形态和微观结构。结果表明:呈球状或不规则形状、尺寸约200～300 nm的弥散相为θ-Al_(45)(Mn,Cr)_7相,属单斜结构,晶胞大小a=2.5196 nm,b=0.7574nm,c=1.0949 nm,β=128.72°。另外,还发现该相颗粒内部易产生孪晶、孪晶畴和复合孪晶,伴有二次孪晶(或微孪晶)和反相畴界等晶体缺陷,孪晶面分别为(111)或(111),共轭面为(110)或(110)。同时从晶体学角度解释了该相孪晶和复合孪晶等缺陷的生成机制。

The morphology and microstructure of dispersoids in 5083 alloy with H116 temper condition were investigated using JEOL 2100F transmission electron microscope equipped with EDS and STEM. The results show that the discrete spherical-like or irregular-shaped θ-Al45(Mn,Cr)7 phase which has monoclinic structure with a unit cell of a=2.5196 nm, b=0.7574 nm, c=1.0949 nm,β=128.72° is observed in 5083 alloy. One type of twin is shown to be a (111) or (111) twin with the (111) or (111) plane serving as the twinning plane, and another type of orientation twin is seen to be a (110) domain with the (110) plane serving as the coherent plane. The boundaries of both (110) domain and (111) twin are found to be coincident with the twinning plane. In addition composite-twins are also observed in θ-Al45(Mn,Cr)7 particles. Possible formation mechanisms of the twins are discussed based on a crystallographic consideration.