Effect of precipitate size distribution on hardness of aluminium 6063 alloy

In this study, the effects of precipitate size and size distribution on the hardness of Aluminium 6063 alloy were examined. Al 6063 samples were subjected to a solution treatment at 530^oC for 4 hours and quenched in water followed by storing in freezer (-18^oC) to prevent natural aging. Aging treatment was done at 190⁰C for 135, 180, 225, 270 and 315 minutes. Precipitates distributed in the matrix were identified as Fe-Si-rich and Fe-Si-Mg-rich precipitates by performing Scanning Electron Microscope (SEM)/ Energy Dispersive Spectroscopy (EDS) analysis. Number of precipitates, average size and area covered by precipitates were calculated by image J software based on the precipitates observed in SEM images. For all heating profiles, precipitate size was less than 3.2 µm. The maximum hardness of 143.90 HV was achieved for 270 minutes aging time. A significant decrease in hardness was evident when the particles are coarsening above 1.5 µm, possibly due to overaging, for aging time beyond 270 min.