Microstructure and properties of twinned dendrites in directionally solidified A356 alloy
Microstructure and properties of twinned dendrites in directionally solidified A356 alloy
复制标题
定向凝固A356合金孪生枝晶的显微组织与性能
DOI：
10.1016/j.msea.2018.07.079
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发表时间：
2018-09-12
期刊：
影响因子：
6.4
通讯作者：
Zhong, Hong
中科院分区：
文献类型：
--
作者：
Li, Yang;Li, Shuangming;Zhong, Hong
采用Bridgman凝固法在A356合金中分别产生了孪晶和规则枝晶。电子< 110 >背散射衍射（EBSD）结果表明，孪晶树枝晶的初生主干沿沿着方向生长，并被共格的（111）孪晶面分裂，这与< 100 >规则树枝晶不同。孪晶枝晶的生长被发现有一个共同的方向周围的旋转关系< 110 >。与规则枝晶试样相比，孪晶试样的平均抗拉强度、伸长率和韧性分别从230 MPa提高到239 MPa、16.69%~ 18.99%、34.45 J/m3提高到40.88 J/m3。同时，孪晶枝晶试样的热膨胀系数（CTE）在473 K时单调增加，最高可达2.28 × 10 ~（-5）K ~（-1）。在323 K以上温度下，该材料的热膨胀系数比规则枝晶材料的热膨胀系数降低，在473 K时达到最大值，降低幅度为4.2%。两种试样的断口均起源于韧窝形成的富硅区。此外，通过透射电镜（TEM）和高分辨透射电镜（HRTEM）对孪晶共格孪晶界（CTB）的详细分析表明，孪晶和位错-CTB相互作用机制可以提高孪晶枝晶A356合金的强度和塑性。
Twinned dendrites and regular dendrites have been respectively produced in A356 alloy by Bridgman solidification. The primary trunks of twinned dendrites grew along < 110 > direction and were split by a coherent (111) twin plane were characterized by electron backscattered diffraction (EBSD), which is different from the < 100 > regular dendrites. The growth of twinned dendrites was found to have a rotation relationship around a common < 110 > direction. With respect to the specimens with regular dendrites, the mean tensile strength, elongation and toughness of the specimens with twinned dendrites were increased from 230 MPa to 239 MPa, 16.69-18.99%, 34.45 J/m(3) to 40.88 J/m(3), respectively. Meanwhile, the coefficient of thermal expansion (CTE) of the specimen with twinned dendrites increase monotonically up to 2.28 x 10(-5)K(-1) at temperature of 473 K. This CTE was successfully lowered than that of specimen with regular dendrites at the temperature above 323 K, and reaches the maximum decrease around 4.2% at 473 K. The fractures of two types of specimens were both originated from the Si-rich regions where dimples formed. In addition, detailed analyses on coherent twin boundary (CTB) of twinned dendrites by transmission electron microscope (TEM) and high resolution TEM (HRTEM) indicate that the mechanisms of twin and dislocation-CTB interactions can enhance the strength and ductility of the A356 alloy with twinned dendrites.