The importance attached to the development of aluminum-lithium based alloys may be deduced from the fact that over the past seven years four major international conferences (1-4) have been devoted to these materials: The first was held at Stone Mountain, Georgia, in 1980 (1), and the most recent was in Paris in 1987 (4). This rapid sequence of conferences reflects intense research and devel­ opment activity within the laboratories of the aerospace companies, the aluminum companies, many universities, research institutes, and govern­ ment research establishments. One reason for this activity was the need for more fuel efficient aircraft because of escalating fuel prices during the 1970s: the addition of lithium to aluminum simultaneously reduces the density and increases the elastic modulus of the resultant alloy. A second and continuing impetus for the development of these materials comes from the requirements of military aircraft.

Aluminum-lithium alloys

Superplasticity at high strain rates in a SiC Whisker reinforced A1 alloy

Structural evolution and the Hall-Petch relationship in an Al-Mg-Li-Zr alloy with ultra-fine grain size

Slip behavior, fracture toughness, and fatigue thresholds of a high purity Al-Li-Cu alloy with Zr as a dispersoid forming element have been studied as a function of aging time. The fracture toughness variation with aging time has been related to the changes in slip planarity,i.e., slip band spacing and width. Although the current alloy exhibits planar slip for all aging conditions examined, the crack initiation toughness,Klc, compares favorably with those of 2XXX and 7XXX aluminum alloys. Near threshold fatigue crack growth results in air and vacuum suggest that irregularities in the crack profile and the fracture surfaces and slip reversibility are some of the major contributing factors to the crack growth resistance of this alloy.

Fatigue crack growth and fracture toughness behavior of an Al-Li-Cu alloy

The mechanical properties of Al-(Mg)-0.5Sc alloys have been investigated. Room-temperature tensile and toughness properties were found to reflect a superposition of the properties of Al-Mg and Al-0.5Sc alloys and are quite competitive with high-performance Al alloys. A combination of substructure refinement by Mg and stabilization by Al3Sc precipitates produces exceptional superplasticity as exemplified by superplastic forming (SPF) elongations in excess of 1000 pct at a strain rate of 0.01 s-1. Overall, these alloys demonstrate an extremely attractive combination of strength, toughness, density, and SPF fabricability.

Mechanical properties and microstructures of Al-Mg-Sc alloys

The topics covered in this volume include: methods of alloy preparation (including ingot casting, rapid solidification, and mechanical alloying); processing and alloying effects on microstructure and properties; superplastic deformation; and physical metallurgy fundamentals. Other topics discussed include: weldability; sodium and hydrogen effects on fracture; corrosion behavior (including general corrosion, stress corrosion, and high-temperature oxidation); and monotonic and cyclic properties at ambient and elevated temperatures. Attention is also given to the use of Al-Li alloys in aircraft structures.

E.A. Starke

Papers

Aluminum-lithium alloys II