Aging behavior of ultra-fine grained Al^|^ndash;0.5%Si^|^ndash;0.5%Ge alloy fabricated using ARB process

Abstract

Using Vickers hardness measurements and TEM observation, this study investigated the aging behavior of ultrafine-grained UFG Al-0.5%Si-0.5%Ge alloy fabricated using six-cycle ARB processing. The hardness of the starting specimen of ultrafine-grained Al-0.5%Si-0.5%Ge alloy is about 2.3 times higher than that of the coarsegrained specimen. The starting UFG specimen showed ultrafine grains with mean size of 156 nm. The hardness of a UFG specimen aged at 473 K decreased monotonously with increasing aging time. From TEM observations of the microstructure of UFG specimen aged after long-term aging at 473 K, results show that the mean size of ultrafine grains increased significantly with increasing aging time. Furthermore, few precipitates exist inside gains, although many coarse precipitates exist at grain boundaries. The hardness of UFG specimen aged at 373 K showed the maximum value. From TEM observations, results showed many elongated ultrafine grains, with many precipitates formed on the grain boundaries and inside grains of the specimens aged at 373 K. These results suggest that precipitation hardening strongly affected the hardness in this alloy because it has many elongated ultrafine grains. Many fine Si-Ge precipitates formed inside grains of the UFG specimen aged at 373 K in long-term aging.

Methods for Designing Concurrently Strengthened Severely Deformed Age-Hardenable Aluminum Alloys by Ultrafine-Grained and Precipitation Hardenings

“…Table I summarizes previously reported experimental results on concurrent strengthening by SPD and the age-hardenings technique for a number of age-hardenable aluminum alloys. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Although the specimens under no SPD condition (i.e., equivalent strain less than 4) possess relatively good agehardenability, most of the severely deformed and then artificially aged specimens exhibit either suppressed age hardenings or age softening as denoted by smaller D or large .. The following are the main features extracted from Table I, where attained values of hardness/ strength, the degree of age hardenings/softening, and the corresponding microstructures are reviewed according to the alloy system, equivalent strain, and aging temperature.…”

“…Reported Experimental Results on Concurrent Strengthening of Age-Hardenable Aluminum Alloys by Severe Plastic Deformation (SPD) and Age-Hardenings Technique[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] …”