Papers by Author: S. Hamamda

Abstract: The effect of pre-aging and maturing at room temperature on the hardening response of an Al-Mg-Si alloy is investigated using differential scanning calorimetry (DSC), hardness measurements (Hv) and scanning electron microscopy (SEM).Two experimental conditions are examined. First, natural aging for different times (3 weeks and 1 month) followed by artificial aging at 180°C as a function of time. Second, pre-aging at temperatures in the range 75-100°C followed by artificial aging at 180°C after natural aging for the same periods. The present results indicate that the effect of the pre-aging just after the heating and quenching is used in order to correct the undesirable effect of aging at room temperature. However, during the artificial aging, the alloy hardening becomes faster. Aged samples which have already undergone pre-aging and maturing reveal the precipitation of ''phase. This later phase has the highest hardness value.

Abstract: This research is aimed at determining the thermal expansion coefficient, α(T), along three directions, X, Y, and Z, of a graphite sample pressed along the direction of weak interactions (Z), over the temperature range [25-500°C]. The experiment results showed that pressing completely alters the dilatometric behavior of the material, and the shape of the α(T) curve changes significantly from one direction to another. Comparing αX, αY, and αZ, a strong anisotropy in the thermal expansion coefficient is observed. This is in good agreement with results published by other researchers who have shown that the electrical conductivity and thermal conductibility of a similar material exhibits strong anisotropic behavior. Pressing has also led to anisotropy in the basal plane, i.e. between αX and αY which have opposite signs. [Pressing results in a significant decrease in α(T) along the Y axis, which is considerably lower than that reported in the literature. αZ is clearly higher that of non-pressed graphite. The wide divergence among the three coefficients is believed to be attributed to the intensification of the membrane effect.