Aluminium does not have good casting or mechanical
properties. These properties can be achieved by adding
magnesium and silicon to aluminium. The addition of these
alloying elements increases the aluminium response to heat
treatment due to formation of Mg2Si intermetallic compound,
which improves the casting, corrosion resistance
property as well as the strength of the alloy. This alloy is
named as the 6063 aluminium alloy. Al±Mg±Si alloy is also
known as architectural and decorative alloy; because of its
easy extrudability property, distinctly superior ®nishing
quality and strength. Almost half of all the aluminium
extrusions produced in UK are used in building as reported
by Helby [1].
Zajac at el. [2] in 1993 investigated the hot deformation
behavior of AA 6063 and AA 6005 aluminium alloy. It was
found that small amount of manganese signi®cantly helps in
homogenizing and transforming the plate like b-AlFeSi
phase to more rounded a-AlFeSi phase, which increases
the ductility of the material. The addition of manganese also
increases quench sensitivity of the alloy even when the
cooling rate is as low as 508C minÿ1
. This was con®rmed
by Musulin and Celliers [3]. They found that addition of
manganese accelerates the transformation of b-AlFeSi phase
to a favorable a-AlFeSi phase.
Okorafor [4] investigated the corrosion resistance property
of 6063 alloy in under-aged, peak-aged and over-aged
conditions. The results show that weight loss and rate of
weight loss were both function of exposure time and heat
treatment temperature.
Jiang et al. [5] found that fatigue crack propagation in
crystalline material is normally divided into two successive
stages. In stage I, crack develops along the active slip plane
and it is normal to the direction of applied stress. In stage II,
the propagation of the crack begins in under-aged 6063 Al±
Mg±Si alloy. The alloy exhibits heterogeneous deformation
and slip bands are formed only by one slip system. There is
strong tendency for single slip system activation, which can
be attributed to the high volume fraction and small size of
GP zone and low content of dispersoids.