Multi Directional Forging of 2024 Al Alloy After Different Heat Treatments: Microstructural and Mechanical Behavior

Abstract

Improvement of mechanical properties and microstructure of 2024 aluminum alloy by performing a severe plastic deformation method, called multidirectional forging (MDF), and heat treatment was the aim of this research. In this work, the effects of different heat treatments such as annealing, solid solution, peak ageing and over ageing before MDF on mechanical properties and microstructure of the alloy were studied. Microstructure evolution during severe plastic deformation was considerably affected by the precipitates and non-shearable particles. On the other hand, the severe plastic deformation had different effects on precipitates in the microstructure. Fragmentation, scattering and dissolution of precipitates were the examples of these effects. The study of X-ray diffraction patterns of 8 passes MDFed annealed samples showed that the cell size was decreased to 310 nm while this value was 270 nm for 8 passes MDFed overaged samples. Also, SEM images showed that fragmentation and scattering of precipitates occurred in widespread. The results of hardness and shear punch tests illustrated that the hardness and shear strength of samples were heavily increased by MDF. The increased values were 55 % for 8 passes MDFed annealed samples and 40 % for 8 passes MDFed overaged samples. Applying 2 passes of MDF on super saturated samples resulted in dynamic precipitation and consequently shear strength was increased up to 70 %.