Optimization Of The Plasticity And The Flow Stress Stability Of The Nanostructure Al-1%si Alloy

With improving the strength of the nanostructured aluminum and aluminum alloys, the poor plasticity and flow instability remain unsolved. Therefore how to improve the mechanical properties of nanostructured materials is one of the main challenges in the material science.In this paper, the Al-1%Si alloy with second phase particles has been chosen, and the nanostructured Al-1%Si alloy was prepared by cold rolling to a reduction of 98%. Controlling the rolling process to refine the structure, second phase particles and applying additional deformation to the nanostructured alloy were used as two approaches to optimize the ductility and flow stability. Scanning Electron Microscopy(SEM), Transmission Electron Microscopy(TEM) and Electron Backscatter Diffraction(EBSD) were employed to characterize the microstructure. The strain rate sensitivity and strain hardening rate of the samples were analyzed to explore the mechanisms responsible for the improved ductility and flow stability of the alloy. The main results are as follows:① Through ordinary cold rolling(with strain 98%), nanostructured Al-1.0%Si alloys with lamellar microstructure are produced. The lamellar boundary spacing is 520 nm and the average second phase Si particle size is about 41 nm. The yield strength of the nanostructured Al-1%Si alloy is 152 MPa and tensile elongation is 7%.② Through well controlled the cold rolling process, nanostructured Al-1.0%Si alloys with lamellar microstructure are produced, the lamellar boundary is 230 nm and the average second phase Si particle size is about 21 nm. The yield strength of the nanostructured Al-1%Si alloy is 253 MPa and tensile elongation is 16.5%.③ Low temperature annealing and additional deformation are applied to the two cold-rolled nanostructured Al-1.0%Si alloys. It is found that the additional deformation can improve the ductility of the nanostructured Al-1%Si alloy with coarser second phase particles, but it has little effect on the ductility of the nanostructured Al-1%Si alloy with finer second phase particles.④ The strain rate sensitivity and strain hardening rate of nanostructured Al-1%Si alloys are analyzed. The results show that the ductility and flow stability are improved because of the increase in the strain rate sensitivity and work hardening rate.