Mechanical Properties and Constitutive Behavior of as-Cast High Strength AA7xxx Alloys below Solidus Temperature

Abstract

High strength AA7xxx alloys have been extensively used in aerospace industry. However, experience in cast house demonstrates that such alloys are particularly prone to cold cracking and ingot distortion during direct chill (DC) casting, which leads to big amount of scraping or even total rejection of ingot. Those stress induced defects are greatly affected by casting process, and fine tuning of casting parameters is critical to improve the quality and productivity. Recently, numerical modeling has been widely utilized in direct-chill casting for the purpose of thermal mechanical analysis and cracking evaluation. Parameter optimization has become convenient. The model needs the input of constitutive properties of the AA7xxx alloys, of which the microstructure should resemble those formed during DC casting. Unfortunately, these constitutive data are not yet available in literatures. In this study, the mechanical properties of two high strength AA7xxx alloys were measured at temperature range from solidus down to room temperature through on-cooling compressive tests and the effect of strain rate on stress-strain behavior was also studied. The results were fitted to extended Ludwik equation which has been proved to be able to properly describe the stress-strain response of aluminum alloys. The results of the current work shed some light on the evolution of mechanical behavior of high strength AA7xxx alloys during cooling from high temperature.