RELATIONSHIPS BETWEEN MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF ALUMINUM-ALLOYS - 3 STUDIES PERFORMED AT ONERA

To illustrate ONERA's work in the field of Aluminium Alloys for aerona utical applications, the results of three different studies are presen ted. As regards rapidly solidified alloys, it is shown that an intrins ic phenomenon related to the composition of the alloys, is responsible for the ductility trough at intermediate temperatures. The strong ani sotropy in ductility and toughness of thick products depends on specia l microstructural features that are not observed in thin sheets. The s econd study is devoted to the detrimental effect of a post-ageing ther mal exposure at 70 degrees C on the fracture toughness of the 2091 Alu minium-Lithium alloy. The most striking result is that a low temperatu re ageing procedure reduces this effect. This conclusion may be applie d to other Al-Li alloys where the delta' phase contribution to hardeni ng is high. In the third study, belonging to the research programme fo r the future supersonic civil transport aircraft, the creep behaviours of three different 2048 rolled products are compared: in the high str ess range, the stress dependence of the minimum strain rate is roughly identical for these products. Deviation from this behaviour occurs at low stresses and is more pronounced when the grain size is small. Thu s this deviation is thought to be caused by grain boundary sliding.