The microstructure of both 5000 and 6000 series alloy sheet can be con
trolled to provide the properties required for particular automotive a
pplications. The work-hardening 5000 series alloys, with between 3 and
6% Mg as the major alloying addition, are supplied to the automotive
companies in the annealed temper and are characterized by a recrystall
ized grain structure which is influenced by the insoluble Fe-based int
ermetallics, dispersoids, and the work-hardening rate. The annealed st
rength and formability is strongly dependent upon grain size, Mg conte
nt, and, to a lesser extent, on crystallographic texture. The 6000 ser
ies alloys containing Cu, Mg, and Si are somewhat more complicated to
control, because of precipitation of the age-hardening phases during f
abrication. It is necessary to control the processes of dispersoid and
precipitate formation so as to obtain the desired strength, grain siz
e, and crystallographic texture in the final sheet. These alloys also
offer a low solution-treated strength for high formability, combined w
ith rapid age hardening to a relatively high strength in the formed co
mponent during the paint bake cycle.