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a相的形貌和尺寸均达到最佳,其平均等积圆直径为88.85μm,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a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a相比未搅拌过的更细小、圆整,即经过电磁搅拌的初生a相形貌更佳,如当La含量为0.4%时,其平均等积圆直径由88.85μm降至84.14μm,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.
In order to obtain the fine,round and uniform distribution primary a phase in semisolid A356 alloy,the different amount of La was added into the alloy melt,and the melt was poured at 650 ℃ and slightlyelectromagnetically stirred under the condition of 30 Hz and 15 s,then,it was isothermally held at 590 ℃ for10 min.The microstructure of the samples was observed by OM and SEM.The influences of La and electromagnetic stirring on morphology of primary a phase in semisolid A356 alloy were studied,and the symbolization of the characteristics of morphology of primary a phase by the fractal dimension was discussed in this work.The results showed that the morphology of primary a 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 a phase showed better at first and then worse as the amounts of La increases,and the morphology and grain size of primary a 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 a phase in semisolid A356-La alloy by electromagnetic stirring was smaller and more rounded than that without stirring,that is,the morphology of primary a 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 a phase in semisolid aluminum alloy by the principle of fractal geometry.The morphology of primary a phase in semisolid A356 alloy by the different process parameters had different fractal dimension.The fractal dim
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2016年第6期698-706,共9页
Acta Metallurgica Sinica
基金
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
江西省教育厅科技项目GJJ14407资助~~
关键词
A356铝合金
LA
电磁搅拌
初生相形貌
分形
A356 aluminum alloy
La
electromagnetic stirring
morphology of primary phase
fractal
