Influence of preliminary heat treatment on structure and strength of high-strength aluminum alloy subjected to high pressure torsion with various strains

摘要

Samples with diam. 20?mm and thickness 1.5?mm from a high-strength commercial aluminum alloy?1965 with uni- and bimodal size distributions of nanoscale precipitates of aluminides of transition metals, as well as the main strengthening phase, obtained under preliminary heat treatment, were subjected to high-pressure torsion (HPT) under pressure 6?GPa at room temperature. Number of revolutions was varied in the range from 0.5?to?10. Methods of transmission electron microscopy and X-ray diffraction analyses were used to certify initial structure-phase states of the alloy and also to investigate the kinetics and mechanisms of deformation structuring of its matrix. On the basis of the data on evolution of structure and hardness of the HPT processed samples, the nature and features of the alloy deformation hardening, depending on heterogeneity of initial structure and strain, were studied. Parameters of the alloy static strength under tension at room temperature were estimated. It was shown that the strain-induced formation of the well-developed nanocellular structure in the alloy matrix may be most effective in terms of its enhanced structural strength: at a rather high level of the alloy hardening obtained, its ductility remained also quite high. Activation of fragmentation and continuous dynamic recrystallization with formation of extremely dispersed nanofragmented and?/?or nanograined structures, resulted in increased brittleness of failure amid even more enhanced alloy strengthening, as well as to sharp decrease in its ductility, and, hence, in loss of its durability. The role of the dispersed phases and strain in formation of the phase-structural state, ensuring the best balance of the alloy mechanical properties, is discussed.