Phase transformations in commercial alloys 1424, V-1469, and 1441 during long-term low-temperature exposures

Abstract

The problem of changes in properties, which are caused by long-term low-temperature exposures, is typical of all Al-Li alloys. In this study, electron transmission microscopy and X-ray diffraction were used to investigate the structure of aged sheets of commercial Al-Mg-Li alloys 1424, 1441, and V-1469, which were subjected to additional long-term low-temperature exposures (LLTEs) at 85°C for up to 7500 h, at 85 and 130°C for up to 2000 h, and at 125 and 150°C for up to 2000 h, respectively. For structural studies, a JEM-200CX electron microscope and a D/MAX 2500 X-ray diffractometer were used. The X-ray diffraction studies included the phase analysis and special measurements of reflection intensities in a 2θ angular range from 1° to 25°, which allowed us to investigate an additional decomposition at 85°C (which yields disperse particles) using small-angle X-ray scattering effects. In the 1424 and 1441 alloys, the structural changes during LLTEs are determined by the specific features of the δ′ phase, whereas the structural changes in the V-1469 alloy after artificial aging and subsequent LLTEs are due to the precipitation of the Ω′ phase.