Clustering during Natural Aging and its Effect on Precipitation Hardening in Al-Mg-Si Alloys
The effect of clustering during natural aging of three different Al-Mg-Si
alloys with equal Mg/Si-ratios, but different Mg+Si contents have been
studied through hardness measurements and transmission electron mi-
croscopy (TEM). Hardness measurements were performed both during
natural aging (NA) and after various NA times followed by subsequent
artificial aging for all alloys, while TEM-investigations were performed
on selected samples. The results from the experiments were compared
and the existence of three different clustering processes were discovered.
The first process was established to be Si-Si clustering causing a slight
hardness increase during natural aging and a strong hardness increase
after subsequent artificial aging. The second process was found to be
Mg-Mg clustering causing a significant hardness increase during natural
aging, and a clear decrease in hardness after subsequent artificial aging.
The third process was found to be Mg-Si clustering and simultaneous
transformation of mono-clusters into co-clusters. This combined process
causes a hardness increase both during natural aging and after subse-
quent artificial aging. The hardness increase is caused by a refinement
of alloy microstructure including a higher number of smaller needles.
This precipitate type was observed for all alloys and conditions. The
negative effect of Mg-Mg clusters on precipitation hardness is suggested
to be related to the repulsion of Si from these clusters. This hinders the
co-clustering of Mg and Si in the areas surrounding these clusters.
Place, publisher, year, edition, pages
Institutt for fysikk , 2011. , 130 p.
ntnudaim:6481, MTFYMA fysikk og matematikk, Teknisk fysikk
IdentifiersURN: urn:nbn:no:ntnu:diva-13636Local ID: ntnudaim:6481OAI: oai:DiVA.org:ntnu-13636DiVA: diva2:441335
Holmestad, Randi, Professor