الفهرس 
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Abstract
The present thesis is devoted to study the microhardness
measurements, H, were obtained as sheets of Al-3wt.% Mg alloy and its
tertiary alloys containing Sn from 0 to 2.5 wt.% in the temperature range
443-503 K, applied loads 10-300 gm and dwell times 10-40 sec. The agehardening
curves showed a leveling off and pronounced oscillations
indicating instability reflecting a competition between the effect of dynamic
recovery or sub-structures coarsening and the effect of solute drag and
precipitation hardening. The indentation size effect index (ISE), m, was
calculated as 2 for the binary alloy indicating that, H, is independent on
indentation size, l, while the value of, m=0.5 for the tertiary alloys show the
presence of strong ISE for H. Sn addition which did not change the
behaviour of the obtained curves of the binary alloy, increasing temperature,
T, load, L, and dwell time, t, all caused a decrease in, H, and yield stress, σy,
due to the decrease of the amount of free Mg available for further
precipitation hardening during the aging process. The observed softening
makes the Al-Mg-Sn system similar to non –Newtonian fluid containing
rigid particles, Sn.