Strength and fracture toughness of spray formed Al–Cu–Mg–Ag alloys

Abstract

Spray formed Al–4·5Cu–Mg–Ag alloys with small additions of titanium, zirconium, and manganese show improved mechanical properties compared with conventionally produced alloys of the same class. In particular, the combination of strength, fracture toughness, and microstructural stability at elevated temperature is clearly superior. At room temperature, typical yield strength values of over 420 MPa, elongations to fracture of 13%, and fracture toughness values of 75–85 MPa m1/2 in the peak aged condition have been measured. Good thermal stability up to 453 K (180°C) can be achieved by limiting the magnesium content to values below 0·4 wt-%. Compared to the commercial heat resistant alloy 2618-T61, spray formed Al–Cu–Mg–Ag alloys offer higher strength after 1000 h exposure to temperatures up to 423 K (150°C). In addition, they clearly exceed 2618-T61 in terms of fracture toughness. The high yield strength is mainly attributed to fine and densely distributed precipitates of Ω and Θ′ phases, and the fine unrecrystallised grain structure. This structure is stabilised by a fine distribution of zirconium containing dispersoids. An additional contribution to strength can be given by cold work before artificial aging. The fracture toughness can be improved by limiting the content of coarse copper and zirconium containing constituents. This is achieved by control of chemical composition and processing.