| Abstrakt: |
The effect of the milling time and ageing on the hardness, density, and wear characteristics of Al 7150 alloy specimens made via powder metallurgy was studied. The different constituents of Al 7150 alloy were processed in a planetary ball milling set up with a BPR of 10:1 for 5, 10, and 20 hrs. At 400°C, the milled powders were subsequently hot compacted in a punch die setup. The hot -pressed specimens were solutionized initially, then aged artificially at 115°C for 3, 6, 12, 24, 30, 45, 60, and 96 hrs. The relative density was inversely proportional to the milling time. Microhardness tests showed a maximum VHN of 255 for the 24 h aged T6 specimens produced from 20 h milled powders whereas the non -aged specimens, made from unmilled 7150 alloy powders showed a VHN of 40. However the samples showed a decline in microhardness beyond 24 h of ageing. Under various conditions of sliding distance and loading conditions, the samples subjected to T6 aging showed a reduced volumetric wear rate indicating the beneficial effect of artificial aging up to 24 hrs. The volumetric wear rate gradually declined for the samples aged beyond 24 hrs of aging. The HRTEM studies revealed a high density of uniformly scattered (MgZn 2) precipitates in the base matrix, as well as (MgZn 2) phases precipitating along grain boundaries. The presence of such second phase precipitates in the matrix improved the wear characteristics of the alloy matrix. The results showed that with the optimization of process parameters such as milling time, ageing as well as reducing the particle size of the base powders, the hardness and wear behavior of Al 7150 alloy may be improved. [ABSTRACT FROM AUTHOR] |
