半固态过共晶铝硅合金的电磁搅拌工艺与性能研究

【作者】 彭著刚；

【导师】 樊刚；

【作者基本信息】 昆明理工大学 ， 材料学， 2005， 硕士

【摘要】 过共晶铝硅合金具有低密度、良好的热稳定性和高耐磨性,是一种理想的耐磨耐热材料。过共晶铝硅合金在耐磨性能和物理性能上的优势性随着硅含量的增加而更加明显,但同时其力学性能低、切削性能差的缺点也变得非常突出,使大过共晶铝硅合金的应用受到限制。半固态金属成形技术作为一项新兴的金属成形技术,是一种具有巨大发展潜力的加工技术。本文利用实验室自行研制的电磁搅拌装置,对过共晶铝硅合金进行了等温电磁搅拌实验和连续冷却电磁搅拌实验,考察了温度、搅拌时间、冷却速度、搅拌功率等工艺参数对合金微观组织的影响规律。 研究结果表明:电磁搅拌取得了较好的效果,搅拌20 min～30 min时,初生硅的尺寸明显变小,分布更加均匀,初生硅的边角更加钝化,细化后的初生硅粒子均匀分布到周围的基体上。 等温电磁搅拌时,等温温度在580℃时,熔体的过冷度较600℃时大,熔体的固相率高,有利于初生硅相互碰撞和摩擦,使初生硅更加细小均匀。但低温也有其负面影响,在搅拌时间过长时,初生硅容易团聚长大。连续冷却电磁搅拌时,在搅拌时间超过30 min后,初生硅会团聚长大。随着冷却速度的增大,合金熔体的过冷度也增大,会析出更多的晶核,使初生硅的尺寸变小,因此在相同搅拌时间条件下,冷却速率越大,搅拌破碎后的初生硅越细小。但如果冷却速度过大会使搅拌时间受到限制,因此不能使冷却速度过大。在其它搅拌条件相同的情况下,搅拌功率提高后,电磁搅拌产生的剪切作用力增强,对初生硅的作用力更大;而且搅拌功率提高后,合金熔体的旋转速度增加,初生硅粒子碰撞的几率增加,使初生硅组织越细小。过共晶铝硅合金经半固态电磁搅拌处理后,由于初生硅的细化和边角钝化及球状α相的产生,合金的力学性能得到显著提高。更多还原

【Abstract】 Hypereutectic Al-Si alloy with the quality of low density, good heat stability and high wear-resistance, is an ideal wear-resistant and heat-resistant material. Its wear-resistance and physical property increase with the increase of silicon content. However, the ductility and mechanical property of the alloy will be deteriorated for the increase of silicon content so that the use of high silicon content Al-Si alloy is restricted. Semi-solid metal forming technology is a new metal forming technology and it is a forming technology with enormous developmental potentiality. Using self-made electromagnetic stirring device of the laboratory, two groups of experiments, isothermal electromagnetic stirring and continuously cooling electromagnetic stirring were carried out to investigate microstructure of semi-solid hyper-eutectic Al-Si alloy influenced by these parameters i.e. isothermal temperature, stirring time, cooling rate and stirred power.The experiments results show that primary silicon crystal fragmentation occurs in the course of stirring and the size of primary silicon phase tends to constant after 20-30 minutes and homogenized distribution.In the condition of isothermal electromagnetic stirring, the solid phase proportion of 580℃ is more than that of 600℃, and high solid phase proportion is propitious to collision and friction of primary silicon phase, so the size of primary silicon is small. But low temperature has negative effect that the primary silicon will reunite easily if the stirring time is too long. In the condition of continuously cooling electromagnetic stirring, primary silicon will reunite and grow if the stirring time is more than 30 minutes. The size of the primary silicon will be smaller for the increase of cooling rates. So the cooling rates is higher, the primary silicon is smaller in the condition that other parameters are same. If the cooling rate is too high, the stirring time will shut down, so the cooling rate can not be too high. In the condition that other parameters are same, the cut force of the electromagnetic stirring and collision probability of primary silicon will rise by the increase of stirring power, so the size of primary silicon is smaller than lower stirring power. For hypereutectic Al-Si alloy, the mechanical property of semi-solid metal(SSM) sample is higher than that of metal mold sample because primary silicon turns to be smaller and α -phase evolves toward sphericity.更多还原