American Journal of Materials Science 2015, 5(3C): 74-76 DOI: 10.5923/c.materials.201502.15 Post-ECAP Ageing Treatment of Aluminum 6063 Alloy T. S. Shanon 1 , N. Ahmed 1 , M. Bharath 1 , J. Valder 2,* , M. Rijesh 3 1 Department of Metallurgical and Materials Engineering, National Institute of Technology Surathkal, Karnataka 2 Department of Mechanical Engineering, St. Joseph Engineering College, Mangalore, Karnataka 3 Department of Metallurgy, Amal Jyothi College of Engineering, Koovapally, Kanjirapally, Kerala Abstract Equal Channel Angular Pressing (ECAP) has attracted much attention from the material community, because of its ability to produce ultrafine grained microstructures. The advantage in ECAP is that a large amount of strain can be imposed on the material without a significant change in geometric shape or cross section. In the present work, the effect of ECAP on the ageing of aluminum 6063 alloy was studied. The samples were first solutionized, followed by ECAP and were then aged at a temperature of 175°C. Multipass pressings were conducted on the billets for different processing routes such as routes- A, B A , B C and C. The pressings were performed at room temperature using a die having a channel angle of 150°. Post ECAP ageing was found to reduce the ageing time considerably till three passes. Keywords ECAP, Hardness, Route, Ageing, Strain 1. Introduction The effective post ECAP strengthening through low temperature ageing was linked to higher dislocation accumulation rate in the solutionized matrix, avoidance of fragmentation of precipitates in the pre ECAP peak aged alloy after few passes of ECAP, suppression of recovery by precipitation on the sub structure after ECAP and reduction of ageing temperature and accelerated ageing kinetics at low temperatures induced by a high dislocation density [1]. Ageing of 6082 alloy after severe plastic deformation revealed that a proper combination of grain-refinement strengthening and age-hardening can be fully exploited in solution annealed ultra fine grained (UFG) alloys only when isothermal ageing is performed at temperatures significantly lower than conventional values and for shorter periods. Ageing conditions have found to be tailored to specific amount of strain imparted during severe plastic deformation (SPD) and to alloy composition [2]. Micro-hardness evaluation as a function of ageing time can be used to study the effect of ECAP passes on the kinetics of isothermal ageing. It was found that even a single ECAP pass significantly accelerates the ageing kinetics of 6082 alloy. Ageing revealed to be more effective at 130°C rather than at 160°C and 180°C by virtue of the comparatively slower kinetics and of the limited over-ageing effects. The improvement in hardness achieved after optimised post-ECAP ageing was significant for the samples subjected to a limited amount of plastic strain but became * Corresponding author: jamesvalder@gmail.com (J. Valder) Published online at http://journal.sapub.org/materials Copyright © 2015 Scientific & Academic Publishing. All Rights Reserved negligible after a relatively large number of ECAP passes [3]. So the present study is carried out to know the effect of post ageing on 6063 aluminium alloy processed by ECAP by various routes at 175°C. 2. Experimental Details The material used in this work was 6063 aluminium alloy with the composition given in Table 1. The experiments were carried out using samples machined to size of 20 mm radius and 60 mm height which was solutionized at 525°C for 1.5h. The die angles of ø: 150° and ѱ: 30° were chosen for ECAP. The schematic diagram of ECAP process is shown in Figure 1 [4]. The pressings were carried out by route A, B A , B C and C up to three numbers of passes at room temperature. The four different processing routes are summarized schematically in Figure 2 [5]. After each pass the samples were cut into 8 equal sections for ageing and hardness studies. The ageing treatment was carried out at 175°C for different times. The hardness was measured before and after respective ageing treatments. 3. Results and Discussion The hardness testing conducted on the samples (before ECAP) aged for durations between 1 and 8 hours, gave a peak hardness value of 96 BHN between 6 and 8 hours. The hardness profile of the samples processed by first pass showed that the peak hardness was obtained between 1 and 3 hours of ageing, clearly indicating that ECAP reduced the ageing time. Peak hardness of 82 BHN was obtained, following which there was a constant drop in the hardness indicating over ageing, as shown in figure 3. The phenomena