Scandium in aluminium alloys

Abstract

A considerable part of the available literature on scandium in aluminium alloys is reviewed. Experimental data and assessments of the binary Al-Sc phase diagram, a wide range of ternary Al-Sc-X phase diagrams and a few higher order phase diagrams are accounted for, with emphasis on the aluminium rich part of the diagrams. The phase which is in equilibrium with Al, Al 3 Sc, can form by several different mechanisms, all of which are described. The precipitation kinetics of Al 3 Sc in binary Al-Sc alloys are discussed, and an overview of the reported influences of ternary alloying elements on the precipitation of Al 3 Sc is given. The Al 3 Sc phase particles can serve as a grain refiner in the Al melt, a dispersoid for controlling the grain structure of the alloy and a strengthening precipitate. Several examples of these three effects are mentioned, both in binary Al-Sc alloys, and in more complex alloys. The reported effects of Sc on the precipitation behaviour in Al-Cu, Al-Mg-Si, Al-Zn-Mg and Al-Li alloys are also revised. A brief account of the effects of Sc additions on the corrosion behaviour of Al and Al-alloys is given. Finally, some views on the current and future use of Sc-containing Al alloys are given.

Ultrafine-Grained Al-Mg-Sc Alloy via Friction-Stir Processing

“…This will cause retention of Sc in Al matrix as solid solution. [26] Subsequent heat treatment may cause it to precipitate. Hence, during aging or FSP, secondary Al 3 (Sc, Zr) dispersoids will precipitate out.…”

“…[26] Hence, during casting of this alloy, solidification of primary Al 3 (Sc, Zr) dispersoids should be expected. Primary Al 3 (Sc, Zr) dispersoids size distribution was carried out using SEM, Fig.…”

Friction-stir welding of an Al–Mg–Sc–Zr alloy in as-fabricated and work-hardened conditions

“…This temperature is well below the dissolution temperature of the β'-phase; thus, the Al 3 (Sc,Zr) particles are expected to be retained in the welds. However, severe plastic deformation of Al-Mg-Sc alloys at intermediate temperatures can lead to extensive coagulation of the β'-dispersoids and correspondingly degrade their coherency [14,6,[25][26][27][28]. This behavior can fundamentally degrade the ability of dispersoids to pin dislocations and grain boundaries.…”

“…Micro-alloying additions of Sc and Zr can effectively suppress or hinder recrystallization processes in heavily deformed Al-Mg alloys [14][15][16]. This stabilization of the microstructure can be attributed to the formation of coherent Al 3 (Sc,Zr) precipitates (i. e., a β'-phase with the L1 2 structure) ranging from 7 to 20 nm in size.…”

“…These dispersoids may also significantly enhance the work hardening effect [17]. Dispersoids generally increase the YS and the ultimate tensile strength (UTS) by more than 50% [14,[17][18][19][20][21]. However, conventional fusion welding of Al-Mg-Sc-Zr alloys leads to the dissolution of these unique precipitates and a corresponding degradation in the material strength [11,22,23].…”