电磁物理场对Al-5wt%Cu合金凝固过程和凝固组织的影响

【作者】 杨效田；

【导师】 许广济；

【作者基本信息】 兰州理工大学 ， 材料加工， 2005， 硕士

【摘要】 本文以Al-Si合金和Al-5wt%Cu合金为研究对象。分别研究了:电流在一般凝固条件下和定向凝固条件下对合金的凝固行为的影响;旋转磁场作用下Al-5wt%Cu合金的凝固行为和交互场(旋转磁场+方波脉冲电场)对合金凝固的影响。并且从不同角度分别探讨了他们的作用机理。 以Al-5wt%Cu合金为研究重点。实验表明:在未加旋转磁场的空冷试样的凝固组织为大的发达的树枝晶组织。导入旋转磁场后,组织呈现有向等轴晶发展的趋势。 磁场强度的不同,所得到的凝固组织也不同。当磁场强度较小,组织相对于原样粗大,但已不再表现出树枝晶。而且显示出的短柱状晶相对原样粗而短。已表现出向等轴晶发展的趋势。当磁场强度增加到100V时,横向组织已显示为排列整齐的柱状晶和等轴晶。纵向的柱状晶已经破碎或接近破碎,而且变得明显细小。 旋转磁场的导入会在金属液体内部产生电磁力,进而在液体内部产生电磁搅拌,在搅拌过程中,由于温度起伏、成分起伏和曲率起伏,曲率大的枝晶侧臂根部产生较大的曲率过冷度,有可能导致枝晶的熔断。细化晶粒,改变晶粒形貌。 在非定向凝固条件下,脉冲电流的导入改变了合金的凝固组织和结晶温度,并且不同的电参数影响效果不同,基本的趋势是树枝晶消失或近似消失,变为梅花状晶、颗粒状的等轴晶、短柱状晶。但存在一个对组织影响最为明显的电参数。 在定向凝固的条件下,脉冲电流对Al-5wt%Cu合金凝固组织的影响不仅改变柱状晶的的大小,形貌和一次枝晶间距,还使柱状晶的取向发生改变。脉冲电流的频率对固/液界面形貌的影响呈现多样性,反映了固/液界面形貌与外界干扰的非线性机制,并且,在合适电参数时,组织和枝晶间距都非常细小,排列致密。实验还发现枝晶根部熔断现象非常明显。更多还原

【Abstract】 In this article, Al-Si alloy and Al-5wt%Cu alloy are served as investigated object imposed rotating electromagnetic field (REMF) and pulse current. Al-5wt5%Cu is been as studying keystone .The experimention indicates:Comparing to sample structure in single REMF and single pulse current, alloy structure is smaller in the compound field (REMF + pulse). Axis crystal grains take on evidently, and have arranged in order.The rotating magnetic field function produced electromagnetism force, and make alloy fluid flow round axis at column sample surface layer, and pulse electromagnetism reinforce the electromagnetism force, spurring system flow as three dimension. The first, this force strengthen scour force to solidification branch crystal, and make branch crystal break. The second, this effect make melting alloy temperature uniformity, which cause breaking off, dissociative crystal preserving at the volley. This is in favor of forming axis crystal.the pulse current can change alloy solidification structure and crystal temperature, and different pulse current parameter lending to different result. But the generic direction change from branch crystal to plum blossom crystal, axis crystal and puncheon crystal. At the same time, we find having better current parameter affect alloy solidification better.In the directional solidification condition, the current not only changed columnar crystal size, appearance, crystal space, but also changed columnar crystal tropism. The current also changed clearly branch crystal size, appearance, crystal space.In this article, we discussed the mechanism.In the processing of the directional solidification in pulse current operation, the introducing of energy and substance is a opening system. The processing of solidification keeps away from balance state. The introducing of energy and substance induce structural gurgitation, leading to self-structure dissipation. With different disturbing frequency, solid-liquid interface take on diversity, and behave non-linear. Because compelled once branch space is one of the foremost characters of the solidification structure. It is good for studying.These experiment results showed that imposed physics filed could have special effect to solidification processing and structure of alloys. It could become a new method for controlling solidification. This is worthy of continuing study.更多还原