Effect of homogenization cooling on the precipitation behavior of 6061 Al alloy

Abstract

In the present study, effect of homogenization cooling on the precipitation behavior of 6061 Al alloy has been investigated. Homogenization cooling is essential for any homogenization process to improve the extrudability because a fully solutionized 6061 Al alloy is difficult to extrude due to solid solution strengthening. Homogenized 6061 Al alloy (580°C for 8 h) samples were cooled to room temperature with four different cooling rates i.e. 500, 250, 150 and 30°C h-1. With decreasing cooling rates, the lengths of the Mg2Si precipitates were increased. Electrical conductivity and hardness showed an inverse relationship as the cooling rate decreases. Fine Mg2Si precipitates were observed at 500°C h-1 cooling rate. Further decreasing the cooling rates, (i.e. 250, 150 and 30°C h-1) the size of Mg2Si precipitates became large which are difficult to re-dissolve during the extrusion process and leads to surface defects. Hence the present study confirmed that 500°C h-1 is the optimum homogenization cooling rate for 6061 Al alloy which results in homogeneous structure with fine Mg2Si precipitates and sufficient hardness to improve the extrudability of 6061 Al alloy.