New Al-Mg-Li-C dispersion strengthened alloy Part 2 - Optimisation of material for forging applications

This paper describes work aimed at optimising the forging process and mechanical properties of a new powder route Al-Mg-Li-C dispersion strengthened alloy, specifically for forging applications. The alloy, of the AA 5091 type, has a nominal composition of Al-1.2Li-5Mg-0.35C (wt-%), and is non-heat treatable. Materials were supplied by AMC Ltd, and evaluated in laboratory based forging trials to determine the influence of forging parameters on mechanical properties, including an investigation of using extruded bar as forging stock. The process was scaled up to produce an industrial forging, using an EH101 helicopter part, which was cut up for detailed mechanical property assessment. It was found that adequate hot working of the material is needed for good toughness, and that the balance of strength to toughness can be controlled by the forging temperature. The new alloy, in the as forged condition, meets the minimum tensile and fracture toughness levels set in the draft AECMA Specification for AA 5091 forgings.