【作者】 任振国；

【导师】 曹志强；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2005， 硕士

【摘要】 为了节约有限的能源和保护地球环境,人们开始提出汽车的轻量化和材料的再生利用等问题。电磁半固态铸造能有效地提高铝合金件的性能并在很大程度上减轻铸件的重量,因而得到了工业上的青睐。 为了给工业尘产提供理论指导,推动其在工业上进一步应用。本文根据需要研制了电磁搅拌器,对电磁搅拌下合金熔体的性质和A1-24%Si过共晶合金的组织进行了研究,并重点研究了各试验参数对A1-6.6%Si亚共晶合金凝固组织的影响。结果表明:A1-24%Si过共晶合金在电磁搅拌下出现了非搅拌凝固中所没有的α-A1相晶粒,且在降温速率为10℃/min时,初生硅呈簇状分布在基体上,当降温速率达到60℃/min时,初尘硅呈点状分布在基体上,并且α-A1相晶粒尺寸变小;A1-6.6%Si亚共晶合金在电磁搅拌作用下的凝固过程中首先析出枝晶状α-A1相,树枝晶在混合机制作用下发生断裂,混合断裂机制即合金液在电磁搅拌作用下凝固时,首先析出的枝晶因搅拌力的作用在枝晶根部发生弯曲,导致枝晶根部产生位错,位错聚集,位错的合并和塞积,形成根部颈缩,电磁力、位错和热起伏为根部提供足够的能量,导致了枝晶从根部迅速断裂;随着搅拌强度的增大和降温速率的降低,A1-6.6%Si亚共晶合金所得到的非枝晶α-A1相晶粒变得越来越细小;当A1-6.6%Si亚共晶合金熔体的温度降低到大约620℃后,合金液内的α-A1相晶粒迅速合并长大,单位体积内的α-A1晶粒个数大幅度降低。 最后通过对不同铸造条件下凝固的合金进行力学性能研究分析,结果表明无论是A1-24%Si过共晶合金还是A1-6.6%Si亚共晶合金在电磁搅拌作用下凝固时,其硬度、塑性和强度与非搅拌铸造相比,都有很大的提高。更多还原

【Abstract】 The problems of lightening motorcar and recycle of material were brought forward for sparing energy sources and protecting environment of the Earth. The electromagnetic semi-solid casting is appreciated in the field of motorcar since it is the effective way of improving performance of Al-alloy accessory and lightening casting weight.In this paper, the electromagnetic stirring device was manufactured according to the demands, and the characters of melt, the structure of AI-24%Si hypereutectic alloy and the effect of various parameters on the structure of Al-6.6%Si hypoeutectic were investigated for providing theory direction in the field of industry production and improving its application further. The results indicated: the particles of α -Al phase that were non-existent through non-stirring casting in AI-24%Si hypereutectic alloy appeared through electromagnetic agitation and the primary silicon with cluster distributed on the matrix of alloy when the cooling rate was 10℃/min and the primary silicon with dot distributed on the matrix of alloy and the particles of α -Al phase became small when the cooling rate was 60℃/min; the α -Al phase of dendritic structure appeared firstly during solidification of the Al-6.6%Si hypoeutectic alloy under the electromagnetic agitation, the rupture of dendritic taked place under the mix convection mechanism and the dendritic firstly appeared was incurvated at roots under stirring force, which led to the dislocations occurring at the roots of dendritic, the dislocations getting together, incorporating and stuffing up and necking at the roots; the electromagnetic force and dislocations and heating undulation provided the root with enough energy, which led to the dendritic rupturing rapidly at the roots; the particles of non-dendritic α-Al phase were little with increasing the stirring intensity and decreasing the cooling rate; the particles of α -Al phase were incorporated rapidly and the number of α -Al phase particles in the unit volume greatly decreased when the temperature of AI-6.6%Si hypoeutectic alloy melt reduced to about 620℃.At last, the mechanical properties of alloy under different conditions of casting were investigated. The results indicated: the hardness , plasticity and intensity of Al-24%Si hypereutectic alloy and Al-6.6%Si hypoeutectic alloy under electromagnetic stirring were both greatly improved comparing with non-stirring casting.更多还原