PHASE-TRANSFORMATIONS IN HEAT-TREATMENT OF AL-LI ALLOYS AND OPTIMIZATION OF OPERATIONAL PROPERTIES OF SEMIFINISHED PRODUCTS FROM THESE ALLOYS

In recent years Al - Li alloys have become very popular in the aircraf t industry. These alloys are characterized by a high specific strength and rigidity which increases substantially the load ratio and fuel ef ficiency of the parts. As a rule, Al - Li alloys are used in an undera ged state, which provides a high ductility over the height of the semi finished products. However, the threshold stress (a,) in corrosion cra cking in this state does not usually exceed 25 - 50 N/mm(2), and the y ield strength is not always satisfactory. The results of a study of th e mechanical properties and corrosion resistance of some AI-Li alloys are described and the ways for optimizing these properties are describ ed on the basis of the phase transformations in the alloys.