| Summary: | 碩士 === 國立東華大學 === 材料科學與工程學系 === 97 === This research tries to utilize plastic deformation of cold rolling process, and the variation microstructures and mechanical properties was investigated after different rolling reduction ratio. The materials were rolled at 10%、30% and 60% rolling reduction respectively, purpose refinement the coarse primary silicon particles, combination dispersion strengthening of primary silicon particles and work hardening of aluminum matrix, can improve the mechanical properties of hypereutectic Al-Si alloy , such as the tensile strength of room temperature and high temperature, and wear resistance. Use the electrical resistivity of material change to probe the intensity of the work hardening.
The experimental results show, primary silicon particles of as-extruded were coarse, and average silicon particle size were 17.9 μm. After 10% rolled, plastic deformation lend to coarse primary silicon particles crack. After 30% rolled, refinement silicon particles by increase plastic deformation, and the average silicon particle size were 14.5 μm. The microstructure after 60% rolled show, not only aluminum matrix were contraction but also between silicon particles to linkage. After 60% rolled, the average silicon particle size was 15.1 μm.
Improve the mechanical properties due to work hardening and dispersion strength, ultimate tensile stress from 275 MPa to 340 MPa. High temperature tensile test below 250℃, the material of 30% rolled were better than 60% rolled, due to dislocation pile-ups in deformation bands, dynamic recovery, climbing and cross-slip to promote local dislocation annihilation. When temperature to reach 350℃, tensile strength were decrease of each materials due to the material softening, but elongation were increase greatly.
At the wear test, increase hardness and effective to refinement primary silicon particles, can improve the wear resistance of material.
|
|---|
