Effect Of Ultrasonic Treatment On Microstructure And Mechanical Properties Of Squeeze Cast Al-5.0Cu-xFe Alloys

Al-Cu alloy with high strength and excellent formability is widely used in transportation fields. However, as the common impurity, iron forms iron-rich intermetallics easily during solidfication that do great harm to the mechanical properties. To elimilate negative effects of Fe element, compound field with pressure field and ultrosonic field is adopted. In this paper,the effect of single pressure field, single ultrosonic field and compound field with different Fe content on the microstructures and mechanical properties have been studied. The results are as follows:The effect of applied pressure on the microstructures and mechanical properties of Al-Cu cast alloys with different Fe contents has been studied. The results show that the applied pressure decreases shrinkage, porosity and secondary dendrite arm space of the alloys,increases the nucleation rate. A large amount of iron-rich intermetallics becomes more dispersive, and, a part of needle-like β-Fe phases thansforms into Chinese script morphology.In addition, the applied pressure improves the ultimate tensile strength, yield strength and elongation of the cast alloys, However, the influence to that at T5 heat treatment condition is not obvious.The effect of Fe content on the microstructures and mechanical properties of Al-Cu cast alloys has been studied. When the Fe content increases from 0.1 wt% to 2.0 wt%, the volume fraction of iron-rich intermetallics increases gradually. And, the elongation of the as-cast and T5 heat-treated alloys decreases. There is a peak value of the ultimate tensile strength and the yield strength of the as-cast alloy with 0.5 wt% Fe, which is 216 MPa and 167 MPa,respectively. However, the ultimate tensile strength and yield strength of T5 heat-treated alloys descend.The effect of ultrosonic field on the microstructures of Al-5.0Cu-1.0Fe cast alloys has been studied. The ultrosonic field breaks the dendrites, promotes the free flow of the molten metal and decreases the casting defects. The solubility of Cu element in the α(Al) matrix increases.And some needle-like Al7Cu2 Fe intermetallics transform into Chinese scriptAl6(CuFe).The effect of compound field on microstructures and mechanical properties of the Al-5.0Cu-1.0Fe cast alloys has been studied. Compared with the single field, the compound field can reduce the secondary dendrite arm space of the alloy and lessen the casting defects.Under compound field, the volume fraction of Al2 Cu reduces more obviously and the alloy has a highest micro-hardness, which is not the summation of that in the single field.Meanwhile, large amounts of iron-rich phases transform from an acicular shape to Chinese script morphology and become thinner and more dispersive. And the acicular iron-rich phases disappear completely. The compound field can reduce the harmful effect of Fe, but when the Fe content is above 1.5 wt%, the modifying effect gets weak.The mechanism of compound field has also been preliminarily analyzed. The applied pressure raises the tempratures of solidification and undercooling to improve the nucleation.The cavitation effect and acoustic streaming are induced by ultrasonic field. The huge instant pressure strikes the second phases intensely, and the flow accelerates. The combined effect of the two fields transforms the metastable Al7Cu2 Fe to stable Al6(CuFe).