Effects of Si on the aging behaviour and formability of aluminium alloys based on AA6016

The heat treatable 6xxx series (Al–Mg–Si–(Cu)) aluminium alloys are finding increasing use in automotive skin panel applications where relatively high formability and in-service strength for dent resistance are major requirements. In Europe, the alloy of choice for such applications is currently the low Cu-containing alloy AA6016, which typically contains approximately 0.4 wt.% Mg and 1.0 wt.% Si, and which derives its strength from the precipitation hardening phase, Mg2Si. The volume fraction of Mg2Si is, in turn, affected primarily through the level of Mg within the alloy, although the Si content is also important. The level of Si within the alloy influences the solution heat treated (T4) strength and the subsequent aging response of the 6xxx series alloys, again predominantly through its effect on the volume fraction of Mg2Si. In this paper, the effects of Si content on the aging behaviour and mechanical properties (formability) of alloys based on the AA6016 composition are described.