Mechanical behavior and deformation mechanism of 7075 aluminum alloy under solution induced dynamic strain aging

Abstract

In this study the mechanical behavior and deformation mechanism of 7075 aluminum alloy sheets under dynamic strain aging induced by solution treatment were investigated. The uniaxial tensile tests were carried out at various strain rates (8.33 × 10−5 s−1, 1.67 × 10−3 s−1, 3.33 × 10−2 s−1 and 1.33 × 10−1 s−1) for samples treated by different solution processes (solution for 30 min at temperatures of 573 K, 623 K, 673 K and 748 K, and then quenching). The Portevin-Le Chatelier (PLC) effect (i.e., serration types of stress-strain curves, strain rate sensitivity (SRS) and critical strain) were analyzed, causing changes in tensile strength, work hardening rate and elongation. The morphology, sizes and quantities of precipitates under different solution-quenching conditions were observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the dissolution of secondary phase occurs during heat treatment, accompanied by coarsening behavior at lower temperatures, which leads to the transition characteristics of mechanical properties of the aluminum alloy in solid solution state. There exists a critical point of solution temperature (623K), namely, when the solution temperature is lower than this critical point, the microstructure after quenching is mainly composed of the matrix and secondary phase; otherwise it is mainly composed of solid solution. Therefore, the samples heated at different solution temperatures have different types of PLC effects. It is worth noting that the strong effect of dynamic strain aging induced at high solution temperature and low strain rate could simultaneously enhance the strength and toughness.