Abstract
The Mg and Si contents and homogenization treatment in 6xxx alloys can affect the precipitation of nano-sized Al3Zr dispersoids and the subsequent mechanical properties. In this study, two Zr-containing 6xxx alloys with different Mg and Si levels were homogenized at two temperatures (400 °C and 550 °C) and hot extruded into a flat profile. The evolution of Zr-bearing dispersoids was studied after homogenization and extrusion using optical, scanning and transmission electron microscopy. In addition, the mechanical tensile properties were evaluated in the T4 and T5 tempers. Results showed that a finer size and higher number density of Al3Zr dispersoids was formed during low-temperature homogenization (400 °C) compared to a high temperature (550 °C). The number density of dispersoids was significantly higher in the high Mg and Si alloy. Both alloys exhibited higher mechanical properties after homogenization at 400 °C compared to 550 °C. However, this effect was weaker in the high Mg and Si alloy due to the rapid coarsening of dispersoids during extrusion at 500 °C.