LAUSR

Presence of impurities in a mechanical system have a great effect on its mechanical properties, some impurities can defeat fatigue life, while others may exert a highly careful effect. The principal usage of Aluminum alloys is in the production of plane light structures, panels, and metallic frameworks. The second largest consumer is the industrial vessels; this shows clearly the fastest growth with aluminum alloys as an alternative solution instead of steel and cast iron in industry. Two aluminum alloys were used to study effect of adding alloying element such as Silicon (Si) on mechanical dynamical properties (fatigue life) of these two selected alloys, they are Al-5Si (4043) and Al-12Si (4047). Fatigue tests are carried out on these specimens under rotating bending conditions to get the S-N curves. The S-N curves show fracture at around over 10 8 cycles without certain endurance limit for both alloys where the two employed specimens are aluminum based alloys, hence, each one will not exhibit a specific value of endurance limit. The final results showed that, for the first alloy, cracks initiate in the medium of aluminum and then rapid progress towards the alloying element (Si), so this means crack initiation is the governing factor for fatigue life for this aluminum alloy. For the second alloy, cracks start from alloying element (Si) at first and then directed towered the aluminum matrix, also. Al-12Si (4047) shows best largely fatigue resistance than the other alloy, sure this depends on the so small volume occupied by alloying element comparing with aluminum matrix.