Abstract
Age-hardening behavior in final aging of TMT, in which plastic deformation is applied after pre-aging but prior to final aging, has been studied. The hardening behavior in this type of TMT is in general correlation with that in two-step aging. The strength of TMT materials increases with rising pre-aging temperature. The amount of age-hardening is degreased by plastic deformation prior to final aging due to heterogeneous precipitation on dislocations. Pre-aging prior to plastic deformation is more effective in increasing the maximum hardness in final aging than in two-step aging. This is attributed to retardation of heterogeneous precipitation on dislocations. In commercial 6061 alloy, the strength can be increased by TMT as high as 10% in contrast to the high purity alloy of the same Mg2Si content. Such differences in two-step aging and TMT behaviors between high purity and commercial alloys are attributed to metallographic heterogeneity existing in the latter.
