In-situ fabrication of functionally graded Al/Mg 2 Si by electromagnetic separation Li Jianguo School of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai , China 2 nd Sino-Germany Workshop on Electromagnetic Processing of Materials

Outline: 1. Motivation 2. Principle of the process 3. Experiments and results 4. Summary

Motivation The in-situ Al-Mg 2 Si composites have great potential applications in the automotive and aerospace industries due to their excellent properties. 1.Problems:Hard and fragile primary phases (eg. Mg 2 Si in Al-Mg-Si) may harmful to mechanical properties 2.Solution:Gradient distributed from the surface to the center—Functionally graded materials(FGMs).

The process of FGMs by EMS The process of in-situ FGMs by electromagnetic separation (EMS) method is recently proposed by our laboratory. It produces the in-situ FGMs using usual casting under electromagnetic field by one-step. So it lower the production cost. And it can produce the thermodynamically stable systems by in-situ nucleation and growth of the reinforcing particles from the parent melt.

Principle of the process Principle of the process of in-situ FGMs by Electromagnetic Separation method Movement direction B I Primary particles Melt Casting mould

Movement analysis of particle Electromagnetic Archimedes force acting on a spherical primary particle can be written: The buoyant force due to gravity imposed on the primary particle is stated as: (1) (2)

The terminal migration velocity of primary particle as: The motion drag force of the primary particles in the molten metal is expressed as: (3) (4) When these forces are in the balance: (5)

where v is the velocity of the primary particle and the viscosity of the melt. And when the mode of the movement is transition flow, ( 6 ) C D is the drag coefficient, which is related to the Reynolds number. with laminar flow, ( 7 )

Experiments and results Equipments of experiment Effects of Element Ti Effects of process parameters

Equipment Electromagnet Molten metal Casting mould DC Power N S CathodeAnode Upper mould Lower mould Casting gate (a) (b) Schematic of equipments used in the process of FGMs by EMS method: ( a ) Top view of the equipments, ( b ) Front view of the equipments.

Effects of element Ti on Microstructures of particle packed region (b) 0.5mm (c) 0.5mm (c) Process parameters: Pouring temperature: 850 o C Mould temperature: 400 o C Electromagnetic force: 5×10 4 N/m 3 Composition: Al-15Mg 2 Si –5Si Composition: Al-15Mg 2 Si –5Si-4Ti

α β δ 50μm (a) 50μm (b) β β is Al 3 Ti δ is a kind of Al-Si-Ti ternary intermetallic compounds, and composition is 65.12at.%Al-13.47at.%Si-21.41at.%Ti Microstructures at higher magnification of Al-15Mg 2 Si –5Si-4Ti samples

Process parameters: Pouring temperature: 850 o C Mould temperature of : 400 o C Electromagnetic force: 5×10 4 N/m 3 Composition: Al-15Mg 2 Si –5Si-4Ti 0.5mm (a) (b) 0.5mm (c) 30mm 20mm A D B C E 0.2mm (d) 0.2mm (e) Microstructures of in-situ Al/MgSi FGMs by EMS Method B I

0.5mm (b) Microstructures of upper side in the samples 0.5mm (a) 0.5mm (c) 5×10 4 N/m 3 3×10 4 N/m 3 1×10 4 N/m 3 Effects of the electromagnetic force on particle distributions

Movement time of particles for unit distance (1mm) vs the electromagnetic force

0.5mm (a) 0.5mm (b) 0.5mm (c) Microstructures of upper side in the samples 600 o C 400 o C 200 o C Effects of mould temperature on particle distribution

0.5mm (b) 0.5mm (c) 0.5mm (a) Microstructures of upper side in the samples 850 o C 800 o C 750 o C Effects of pouring temperature on the particle distributions

Cooling curves of melt Effects of mould temperature Effects of Pouring temperature

Al-15Mg 2 Si-5Si-4Ti 0.5mm (b) 0.5mm (c) 0.5mm (a) Microstructures of upper side in the samples Al-20Mg 2 Si-5Si-3.75Ti Effects of the composition on particle distributions Al-25Mg 2 Si-5Si-3.5Ti

Summary 1. In-situ Al/Mg 2 Si FGMs was successfully prepared by EMS method. 2. Additional element Ti can prevent primary Mg 2 Si particles from forming the particle clusters. 3. There exists a critical value of electromagnetic force, and the In-situ Al/Mg 2 Si FGMs can be prepared by EMS method only when the electromagnetic force is beyond it. 4. Increasing of the electromagnetic force and the content of Mg 2 Si and decreasing of the solidification rate can make the particle volume fraction of the particle packed region and the gradient of particle distributions increase.

Acknowledgements: The work is supported by the National Natural Science Foundation of China. We express our sincere thanks for their financial support.

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