Experimental investigation of the dynamic impact responses of as-cast and homogenized A535 aluminum alloy

Abstract

Aluminum A535 alloy plates were received in the as-cast condition. Some specimens cut from the cast plates were homogenized at 400 °C for 5 h and then quenched in water to room temperature. SEM, EDS, and EBSD analyses of ground and polished specimens show that in addition to a change in crystallographic texture of the A535 alloy, significant reduction in pores and removal of microsegregation occurred during homogenization heat-treatment of the as-cast specimens. Homogenizing heat treatment also decreased the average grain size of the alloy by discontinuous static recrystallization mechanism. The dynamic impact responses of as-cast and homogenized aluminum A535 alloy were experimentally determined using the split Hopkinson pressure bar system. At a true strain rate between 4 × 103 and 14.2 × 103 s-1, the homogenized specimens exhibited better dynamic mechanical strength and ductility than the as-cast specimens. Higher strength in the homogenized specimen is attributed to higher grain boundary area and stronger evolution of CD||[110] grains than in the as-cast specimens. On the other hand, severe mechanical damage such as loss of roundness of cylindrical specimen, severe micro-cracks and formation of adiabatic shear bands occurred more in homogenized specimens than in as-cast specimens. Using the electron back-scattered diffraction technique, activation of multiple dynamic recrystallization (DRX) mechanisms and the role of crystallographic texture were observed in the investigated alloy. While continuous DRX occurred at the center of the deformed specimens, discontinuous DRX occurred homogenously on the entire polished surface of the specimen at particle sites. Microsegregation and texture-related conditions enhanced DRX more readily in as-cast specimens than in the homogenized specimens. The mode of dynamic failure and fracture in the investigated alloy deviates from those reported in the literature for wrought alloys.