Effects Of Mg, Si And Cu On Ageing Response Of Dilute 6xxx Series Aluminium Alloys
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Date
2011-02
Authors
Jaafar, Che Nor Aiza
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
The effects of magnesium (Mg), silicon (Si) and copper (Cu) on ageing response of
heat treatable dilute 6xxx series aluminium alloys have been investigated. The alloys
contained between 0.22 to 0.79 wt% Si and 0.20 to 0.51 wt% Mg. In this study,
some alloys contained 0.1 wt% Cu and others contained 0.001 to 0.002 wt% Cu
which were considered as Cu-free alloys. In order to study the effect of composition
on the ageing response, the alloys samples were solution treated at 530 5 oC for 5
minutes and then water quenched into ice water at 0 oC before naturally aged at
room temperature and artificially aged at elevated temperature. The effects of
natural ageing and artificial ageing on the ageing response were investigated using
Vickers hardness test and tensile test, respectively. The microstructures of
artificially aged alloys were investigated by transmission electron microscopy
(TEM). The results showed a correlation between ageing response and composition,
hardness, strength and microstructure of the alloys. The higher solute contents of
Mg2Si and Silicon in excess (ExSi) in the alloys produced higher hardness and
tensile strength and consequently the strongest ageing response. Addition of small
Cu content (0.1 wt%) gave only a slight increase in hardness, strength and ageing
response during artificial ageing but not in the case of natural ageing. The TEM
results revealed that the precipitates formed during artificial ageing at 185 oC were
needles and at 300 oC were needles and rods with their major axes parallel to [100]
of the matrix direction. The number density of precipitates increased as their solute
content of Mg2Si and ExSi increased. Addition of 0.1 wt% Cu refined the
precipitates and increased slightly the number density of precipitates in the dilute
alloys. It was found that prolong ageing time for 1000 hours at 300 oC resulted in the
formation of coarse precipitates in the most of over-aged alloys. Analysis by TEMEDX
on coarse precipitates of over-aged alloy of alloy Al-0.50wt%Mg-0.76wt%Si
indicates that Mg2Si, AlFeSi, -AlMnSi and Si precipitates were coexist in this
alloy.
Description
Keywords
The effects of magnesium (Mg), silicon (Si) and copper (Cu) on ageing , response of heat treatable dilute 6xxx series aluminium alloys