Abstract:

The aircraft engineering in continuous development must take into consideration the requirements concerning the costs, performances or weight in selecting the materials that are to be used. Thus, in the case of ultrasonic aviation, in order to solve the problem of the heating of strength structure, there are chosen special alloys which resist at high temperatures or composite materials with resistance properties for a given weight, all of them being very interesting ones.
Concerning the aeronautical constructions, the essential element that has to be optimized, in the decreasing sense, is weight, which has, in this case, a cascade effect. Thus, a greater weight needs a lift surplus, which determines, at the same time, a greater head resistance, that is a greater fuel consumption, thus a greater weight, so that the cycle is repeated. Under these conditions, the weight is required to constitute a minimum. Other requirements and certain cheaper materials or a cheaper technology will have, as a consequence, a secondary character, so that some better solutions, even if they are more expensive, are preferred. The introduction of aluminium alloys in the aeronautical constructions has represented such a step at that particular moment when aluminium was a semi-precious metal, it could be obtained hard and it had not very good resistance properties. Throughout time, the alloys metallurgy has developed as well as the elaboration of alloys with satisfactory resistance properties so that the aluminium alloys are preferred to other materials.
The paper aims at practically applying the research activity concerning the use of aluminium alloys and improving their mechanical properties. The experimental tests carried out aim at modifying the hardness values of the aluminium alloys following some non-conventional heat treatments. The focus has also been laid on the influence of the alloying elements concentration upon the hardness while applying different heat treatments.

Keywords:

aluminum alloys, heat treatment, hardness, aircraft, education.