Al–Mg–Si alloys have recently been used for both automotive body sheet panel in order for weight saving. However, this is partially caused by poor press formability in these alloys, though both specific stiffness and strength are sufficiently high. In this paper, the high temperature characteristics of two kinds of 6XXX aluminum alloy rolled sheets in T4 condition have been investigated with special reference to the applicability to superplastic forming. Constant cross head speed tensile tests were conducted at temperature and initial strain rate ranging from 623 K to 803 K and from 1×10−5s−1 to 1×10−1s−1, respectively. The total elongation vs. strain rate diagram has a minimum of 150% near the strain rate 1×10−3s−1 both at 773 K and at 803 K. It is to be noted that the dominant deformation mechanism changes from grain boundary sliding in lower strain rate range to transgranular deformation in higher strain rate range. Total elongation increases rapidly with decrease in strain rate resulting in superplastic elongation more than 300%. The deformation mechanism is discussed on the basis of rate controlling processes. The anisotropy in ductility is also examined.
