Understanding the effect of heat treatment on microstructure and mechanical properties of A205

Abstract

Advancements in aero-engine technology are constantly bringing down the operating temperatures of cold structures in engines. Aluminium alloys, having a low density and being significantly cheaper than Titanium alloys - which are currently being used for many cold structures, could potentially bring cost and weight savings. Aluminium A205 is one such recently developed castable Al-Cu-Mg-Ag(AMS4471) alloy containing in-situ formed TiB2 and Al3Ti particles, shown to have better mechanical properties at elevated temperatures(above 150oC) relative to other high strength aluminium alloys.

In this thesis, a general understanding of the theory behind A205 has been developed. The effect of T7-heat treatment with a special interest on aging parameters on microstructure and hardness was understood. The change in mechanical properties of the T7-heat treated A205 after prolonged thermal exposures at 150oC and 200oC were investigated. The tensile properties at room temperatures and elevated temperatures were investigated. The Low Cycle Fatigue(LCF) properties of T7 heat treated A205 were investigated with fractography and the predominant initiators were identified. Fractography and EDS analyses were performed on fractured LCF and tensile tested specimens to reason out the fracture mechanisms and role of microstructural features on crack propagation on LCF life and tensile properties.

Applicability of ThermoCalc-Prisma to predict the precipitate(CuAl2) growth and coarsening during aging and prolonged thermal exposures was explored. A simple and functional tool that uses Larson-Miller Parameter has been proposed to predict the yield strength of T7 treated A205 after prolonged thermal exposures at temperatures less than 200oC. Further to this, a mathematical tool to effectively optimize the aging temperature and time has been proposed and validated with experimental results.