Influence of the creep ageing process on the fatigue properties of components from V95pchT2 (analog 7175T76) and V95ochT2 (analog 7475) aluminium alloys

Influence of conditions of technological process of forming thick panels of a given geometry on fatigue limit of flat specimens from the V95ochT2 and V95pchT2 (analogues 7475 and 7175T76) alloys (Al-Mg-Cu-Zn) has been analysed. The process has been simulated experimentally on flat samples for temperatures 20, 165 and 420 degrees C. The process includes: non-elastic strain in the range 10(-5) - 10(-2) s(-1) up to 2% of total strain, followed by heat treatment according to T2 mode (quenching and aging). Fatigue life tests were carried out both on solid samples and on samples with a hole. It has been shown that resistance to fatigue of the observed alloys after forming at the annealing temperature (420 degrees C) is comparable to the basic material resistance to fatigue. Meso-structure analysis showed absence of stress in grains. It is established that, on average, the shape of the grains is the same for a series of samples for different temperatures and loading rates. The results of testing samples with a hole showed that fatigue limit slightly decreases in samples which were previously deformed at (420 degrees C), with respect to the durability of samples from the material in basic state. With an increase in rate of pre-strain, the relative number of cycles before destruction occurs increased.