Inert Gas Atomised Al–Cr–Zr Alloy Powders Consolidated by Extrusion: Effect of Powder Variables and Extrusion Parameters on Extrusion Pressure

Abstract

The effect on extrusion pressure P of ram speed V (0·5–4 mm s⁻¹), extrusion ratio R (14:1−28:1), extrusion temperature T (300−450°C), median powder particle diameter (11−141 μm), and melt superheat during atomisation (150−300 K) has been studied for extrusion of argon atomised Al–5Cr–2Zr (wt-%) alloy powder. Mean powder particle size and T had the major influence on P; R and V had less influence and melt superheat during atomisation had no influence. The absence of a breakthrough pressure, attributed to the low values of V used, allowed extrusion at values of T as low as 300°C, retaining the integrity of the rapidly solidified microstructure. The relative importance of work of consolidation compared to that of homogeneous deformation, as demonstrated by a value of 4·6 for the ratio a/b in the equation P = a + b ln R at 350°C, was larger than reported for 7090 and 7091 alloys but smaller than for Al–2·4Fe (wt-%) at a comparable T. The magnitude of the temperature dependence of P was similar to that reported for other high strength aluminium alloy powders, the corresponding dependence for consolidation pressure being significantly lower. PM/0683