Experiment Study And Theoretical Analysis On Hot Workability Of 7075 Aluminum Alloy

The experiment of 7075 aluminum alloy during hot compression deformation was carried on Gleeble-1500 hot simulator by using isothermal compression of cylindrical specimens at strain rates of 0.01, 0.1, 1, 10s-1, at temperatures of 300, 350, 400, 450℃and height direction reduction of 60%. We got the true stress-strain curve and microstructure at different conditions by experiment, thermal deformation behavior, damage sensitive rate, maximum damage value, critical damage factor and processing maps have been studied with the aid of regression analysis and finite element analysis. The main research contents and conclusions are as follows:1. Influence law of temperature and strain rate on flow stress and microstructure are analysed. The Arrhenius model, Fields-Backofen model and model containing softening ratio item of 7075 aluminum alloy are found, and compare respectively between predicted values and experiment. The results show that the Arrhenius model predicts well agrees with experimental results, and the maximum error between the predicted and experimental results is 20.95% and smaller than experimental results usually. Fields-Backofen model cannot describe stress-strain relation during the whole process of deformation. The model containing a softening ratio item predicts badly agrees with experimental results under temperature 300℃and strain rate 10s-1, the maximum error is 47%, and well agrees with experimental results under other conditions.2. The experiment of 7075 aluminum alloy during hot compression deformation is simulated by finite element simulation software DEFORM-2D. The change law of critical damage value with temperature and strain rate is analysed, critical damage factor of 7075 aluminum alloy is confirmed when crack appeared, and distributing regular diagram of critical damage factor is drawn at different temperatures and strain rates. The results show that the maximum damage value and damage sensitive rate are not an obvious regularity as changing of temperature and strain rate, the maximum damage value gradually increases as the strain adds, the damage sensitive rate gradually decreases as the strain adds, and trends to stabilization in the end. The critical damage factor of 7075 aluminum alloy is not a constant but a change with a range 0.255~0.453, it increases at first and then decreases with increase of strain rate at constant temperature and strain rate. 3. Based on the principles of dynamic materials model, processing maps are drawn and analysed with microstructure when strain is 0.2, 0.4 and 0.6. The dynamic recrystallization is gotten under different strain rates and temperatures, and the full dynamic recrystallization can be got under the deformation temperature range from 350 to 450℃and strain rate 0.01s-1,it is the best domain of hot working.In this paper, it provided the effective mathematical model for finite element simulation of 7075 aluminum alloy and the theoretical foundation for determining hot working process parameters, improving hot process performance, controlling microstructure and preventing defect.