A systematic through-process rolling and extrusion study of four experimental high-strength Al-Mg-Si alloys

Abstract

Al-Mg-Si alloys are an important class of Al wrought alloys. Further increasing their strength has significant economic potential. Previous approaches were focusing on increasing the amount of the main hardening elements Mg and Si, adding Cu and Zn for additional hardening potential, and adding dispersoid-forming elements such as Cr and Zr. In terms of processing, multi-step heat treatments and interrupted quenching have been pursued. Despite recent advances in the field, data points from the literature are difficult to compare due to widely varying alloy compositions and processing conditions. Here we present a comprehensive through-process rolling and extrusion study on four experimental high-strength Al-Mg-Si alloys (named A1–A4) with a particular focus on comparability of the results between our alloys and with the literature. Mechanical testing after artificial aging and in-depth microstructural investigations at various steps of the processing chain were employed, including scanning and transmission electron microscopy. We found that Cr addition leads to a strong increase in dispersoids and thus has a strong influence on hot workability, whereas the effect of increasing Mg and Si levels was negligible within the studied composition range. Al3Zr dispersoids were found to coexist with Al(Fe,Mn,Cr)Si dispersoids. Overall, the strength of the rolled sheets was slightly higher than that of the profiles. After 8 h of artificial aging at 180 °C, 2 mm thick sheet made of alloy A4, falling within the specification of AA6086, showed a notable yield strength of 393 MPa, due to nanoscale hardening phases that were smaller and appeared more numerous than in a commercial alloy (AA6082-T6).

Keywords

• 6xxx series
• Light metals
• Dispersoids
• Precipitation hardening
• Homogenization