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Clustering during Natural Aging and its Effect on Precipitation Hardening in Al-Mg-Si Alloys
Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, Department of Physics.
2011 (English)MasteroppgaveStudent thesis
Abstract [en]

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.
Keyword [no]
ntnudaim:6481, MTFYMA fysikk og matematikk, Teknisk fysikk
URN: urn:nbn:no:ntnu:diva-13636Local ID: ntnudaim:6481OAI: diva2:441335
Available from: 2011-09-15 Created: 2011-09-15

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