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金属学报  2016, Vol. 52 Issue (6): 698-706    DOI: 10.11900/0412.1961.2015.00496
  论文 本期目录 | 过刊浏览 |
电磁场作用下半固态A356-La铝合金初生相形貌及分形维数的研究*
刘政1(),徐丽娜2,余昭福2,陈杨政2
1 江西理工大学机电工程学院, 赣州 341000
2 江西理工大学材料科学与工程学院, 赣州 341000
RESEARCH ON THE MORPHOLOGY AND FRACTALDIMENSION OF PRIMARY PHASE IN SEMISOLIDA356-La ALUMINUM ALLOY BY ELECTRO-MAGNETIC STIRRING
Zheng LIU1(),Lina XU2,Zhaofu YU2,Yangzheng CHEN2
1 School of Mechanical and Electrical Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China
2 School of Materials Science and Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China
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摘要: 

利用稀土La对液态A356铝合金进行了细化处理, 并在电磁搅拌技术下制备了半固态A356-La铝合金浆料, 研究了稀土La和电磁搅拌对半固态A356铝合金初生相形貌的影响, 并用分形维数对其初生相形貌进行了表征. 结果表明, 添加适量的稀土La可有效改善半固态A356铝合金初生相的形貌, 无论是否经过电磁搅拌, 随着稀土添加量的增加, A356 铝合金的初生相形貌均呈先变好后恶化的演变规律, 当稀土La的添加量为0.4% (质量分数)时, 其初生α相的形貌和尺寸均达到最佳, 其平均等积圆直径为88.85 μm, 平均形状因子为0.78; 当稀土La的添加量相同时, 经过电磁搅拌作用的A356-La 铝合金初生α相的平均等积圆直径均比未经过电磁搅拌的更小, 其形状因子则相反, 均比未经过电磁搅拌的更大, 说明经过电磁搅拌的半固态A356铝合金初生α相比未搅拌过的更细小、圆整, 即经过电磁搅拌的初生α相形貌更佳, 如当La含量为0.4%时, 其平均等积圆直径由88.85 μm 降至84.14 μm, 平均形状因子由0.78升至0.81. 此外, 实际的合金凝固组织具有分形特征, 应用分形几何的原理来描述和分析半固态铝合金中初生相的形貌变化规律甚至初生相形成机理是完全可能的. 且不同工艺参数下所获得的半固态铝合金初生相形貌具有不同的分形维数, 随着半固态初生相由树枝状向颗粒状或球状变化, 其分形维数逐渐变小.

关键词 A356铝合金La电磁搅拌初生相形貌分形    
Abstract

In order to obtain the fine, round and uniform distribution primary α phase in semisolid A356 alloy, the different amount of La was added into the alloy melt, and the melt was poured at 650 ℃ and slightly electromagnetically stirred under the condition of 30 Hz and 15 s, then, it was isothermally held at 590 ℃ for 10 min. The microstructure of the samples was observed by OM and SEM. The influences of La and electromagnetic stirring on morphology of primary α phase in semisolid A356 alloy were studied, and the symbolization of the characteristics of morphology of primary α phase by the fractal dimension was discussed in this work. The results showed that the morphology of primary α phase in semisolid A356 alloy was effectively improved by the suitable addition of La, no matter whether the semisolid slurry of A356-La alloy was prepared by electromagnetic stirring or not, the morphology of primary α phase showed better at first and then worse as the amounts of La increases, and the morphology and grain size of primary α phase reach the optimal state when the content of La was 0.4% (mass fraction). At the same time, the average equal-area circle diameter of the morphology of primary phase in semisolid A356-La alloy by electromagnetic stirring was finer than that without stirring, on the other hand, the shape factor was bigger than that without stirring. It implies that the primary α phase in semisolid A356-La alloy by electromagnetic stirring was smaller and more rounded than that without stirring, that is, the morphology of primary α phase in semisolid A356-La alloy by electromagnetic stirring was better than that without stirring. In addition, the real microstructure has fractal characteristics, and it was feasible to describe and analyze the change regularity and even the formation mechanism of the morphology of primary α phase in semisolid aluminum alloy by the principle of fractal geometry. The morphology of primary α phase in semisolid A356 alloy by the different process parameters had different fractal dimension. The fractal dimension of the semisolid primary α phase gradually became smaller with its morphology changed from dendritic-like to particle-like or globular-like.

Key wordsA356 aluminum alloy    La    electromagnetic stirring    morphology of primary phase    fractal
收稿日期: 2015-09-23      出版日期: 2016-04-01
基金资助:* 国家自然科学基金项目51144009和51361012, 江西省自然科学基金项目20114bab206014和江西省教育厅科技项目GJJ14407资助

引用本文:

刘政,徐丽娜,余昭福,陈杨政. 电磁场作用下半固态A356-La铝合金初生相形貌及分形维数的研究*[J]. 金属学报, 2016, 52(6): 698-706.
Zheng LIU,Lina XU,Zhaofu YU,Yangzheng CHEN. RESEARCH ON THE MORPHOLOGY AND FRACTALDIMENSION OF PRIMARY PHASE IN SEMISOLIDA356-La ALUMINUM ALLOY BY ELECTRO-MAGNETIC STIRRING. Acta Metall, 2016, 52(6): 698-706.

链接本文:

http://www.ams.org.cn/CN/10.11900/0412.1961.2015.00496      或      http://www.ams.org.cn/CN/Y2016/V52/I6/698

图1  未添加稀土的A356合金初生α相形貌的OM像
图2  添加不同含量稀土的A356合金初生α相形貌的OM像
图3  添加不同含量稀土并经电磁搅拌处理的A356合金初生α相形貌的OM像
图4  A356-La合金在有无电磁搅拌作用下初生α相的平均等积圆直径与形状因子
Mass fraction of La / % No stirring Stirring
0.2 1.4246 1.4079
0.4 1.4074 1.4015
0.6 1.4184 1.4075
0.8 1.4433 1.4260
表1  不同工艺条件下半固态A356合金初生相形貌的分形维数
图5  未经电磁搅拌处理的A356-0.2%La合金初生相形貌图像处理后的边界二值图和分形维数计算的双对数图
图6  未经电磁搅拌处理的A356-0.4%La合金初生相形貌图像处理后的边界二值图和分形维数计算的双对数图
图7  经过电磁搅拌处理的A356-0.4%La合金初生相形貌图像处理后的边界二值图和分形维数计算的双对数图
图8  A356-0.4% La合金的二次电子像和EDS分析
图9  A356-0.4%La合金的XRD谱
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