چكيده به لاتين
Abstract:
In this research, the equal channel angular pressing (ECAP) process was used to produce ultra fine grained (UFG) Al matrix composite reinforced with Al65Cu20Ti15 metallic glass particles. The research includes two phases. In the first phase, effects of the amount of glass particles and consolidation temperature on the consolidation process and also, the structural evolution and mechanical properties of the consolidated composites have been investigated. Therefore, the composite with 7, 13 and 20 wt% of reinforcements and also, pure Al were consolidated at different temperatures. After determining the optimum condition for consolidating, the second phase (increasing the ECAP pass numbers) started. After different passes, microstructural evolution and mechanical properties were examined.
The results of the first phase revealed the glass particles remained unchanged to consolidation temperature up to 250 ºC but, by increasing the consolidation temperature to 300 ºC some intermetallic compounds include Al5CuTi2, Al3Ti and Al4Cu9 precipitated from metallic glass particles. Consolidation temperature did not affect the matrix grains size of the composite while the grains size decreased by increasing the amount of glass particles. A transition region of ordered atomic structure of the matrix to disordered structure of reinforcing particles created at the matrix/reinforcements interface as a result of the restricted mutual diffusion of elements. The Al/13Am composite consolidated at 250 ºC, exhibited the best combination of yield strength and ductility of 184 MPa and 0.48, respectively. Increasing the ECAP pass number (the second phase) was performed on this composite and pure Al. The amorphous structure of reinforcements was preserved in higher passes. Based on the TEM observations, after 4th pass, the grains size of composite and pure Al reached to 0.49 and 0.57 µm, respectively. Also, the fraction of high angle grain boundaries increased gradually by raising the pass number. The mechanisms of grain refining process were discussed according to the results. The compressive yield strength and ductility of composite enhanced in higher pass numbers and finally reached to 242 MPa and 0.52, respectively after 4th pass. The strengthening mechanism of low angle grain boundaries possessed the highest contribution (about 50 %) in the strength of composite.
Keywords: ECAP process, Ultra fine grained bulk composite, Al65Cu20Ti15 metallic glass particles, Matrix/reinforcements interface, Strengthening mechanisms
