| The Zn-9%Al-3%Cu (ZCA-9) alloy was subjected to Equal Channel Angular Extrusion (ECAE) process using two different processing techniques, routes A and BC at 65°C. For route A, the specimens are processed along the extrusion axis without any rotation whereas the specimens are rotated 90° counter-clockwise around its extrusion axis between successive passes for route BC. The influences of the ECAE passes and its routes, on the mechanical properties such as strength, hardness, ductility and damping and the tribological properties such as wear, friction were investigated. The specimens were tested in uniaxial tension, compression, creep, nanoindentation and frequency scan damping tests were conducted to determine the mechanical properties. Wear and nanoscratch tests were also conducted to determine the tribological properties of the as-cast and ECAE processed ZCA-9 alloy. The microstructural features such as grain size, texture and presence of different phases in the as-cast, as-ECAE and post-ECAE aged alloy at the temperature of 160°C and 250°C were correlated with the mechanical properties. An upper bound model was developed to predict the extrusion pressure required during the ECAE process and was compared with experimental results.;Microstructural observations revealed a greatly refined and equiaxed grain structure with the crystallite size between 0.2-0.8 microm in as-cast and the ECAE processed ZCA-9 alloy. After post-ECAE aging of this alloy processed by route BC for 300 hours, the grain sizes were found to be in range of 1.65--1.88 microm at temperature of 160°C and grain sizes between 2.10--3.37 microm at the temperature of 250°C. The grain sizes were found to have increased with increase in number of passes. In the specimens processed by route A, elongated grain structures were observed with agglomerates of Zn-rich and Alrich grains while in route B C specimens, the equiaxed grains were observed.;The ECAE process was found very effective in improving the mechanical properties of ZCA-9 alloy. The mechanical properties were found to vary significantly with the grain size, strain rate and temperature. The ultimate tensile strength (UTS), yield strength (YS), hardness and damping capacity were found to increase after one pass and then gradually decreases with further increase in number of passes, i.e., increase in grain sizes. Aging at temperature of 160°C of the as-cast and ECAE processed specimens showed a slight increase in the UTS, YS and hardness compared to the unaged specimens. However, the as-ECAE processed specimens showed exceptionally high ductility with increase in number of passes compared to the aged specimens. In compression, the YS and the work hardening rate were found to increase with increasing strain rates. The strain hardening exponent was seen to decrease with increase in number of passes. Tension-compression asymmetry in the YS was observed in the as-cast and one pass ECAE processed alloy with asymmetry more in the favor of compression (higher).;The ECAE processed specimens exhibited poor creep resistance and duration to failure compared to the as-cast specimen. This creep resistance of the ECAE processed specimens was seen to deteriorate at a higher testing temperature of 160°C. The wear results demonstrated that the wear resistance of the alloy can be improved with eight ECAE passes of route A. No significant change in the coefficient of friction was observed with change in sliding speeds. The damping capacity of the ZCA-9 alloy was found to decrease with increase in frequency.;The upper bound study shows that there is a good agreement between the theoretical and experimental pressure required to extrude the material through the equal channel angular die. |
