Microstructure Effects on Mechanical Properties of Al-Cu-Mn Alloy in Heat Treatment Process

Precipitate phase Al₂Cu is considered as one of dominant factors that produce good hardness and yield stress of Al-Cu-Mn alloy. The morphology and distributions of Al₂Cu can be obtained from mature hardening models that are applied in quenching and aging processes. Meanwhile, unexpected distortion caused by heat treatment is highly dependent on microstructure evolution. In this paper, some unordinary phenomena, such as negative strain rate strengthening and brittleness at elevated temperature for as-quenched samples, are observed by experimental tests, which cannot be explained only based on the effect of prime precipitate phases. Some precipitate phase like Al₂₀Cu₂Mn₃ and non-phase transformation phases like Al₃Ti also have contributed to plasticity and hardness. With the help of electron microscopes, the morphology and distribution of these phases are characterized and their effects on mechanical properties are discussed. The existing hardening models and constitutive models will be modified upon the phase analysis in heat treatment processes.