Yu-Qiang Jiang

Hot compressive deformation behavior of 7075 Al alloy under elevated temperature

The hot compression tests were conducted with wide strain rates and forming temperature ranges to study the high-temperature deformation behavior of 7075 Al alloy. The material flow behavior and microstructural evolution during hot-forming process are discussed. Based on the measured stress–strain data, a new constitutive model is proposed, considering the coupled effects of strain, strain rate, and forming temperature on the material flow behavior of 7075 Al alloy. In the proposed model, the material constants are presented as functions of forming temperature. The proposed constitutive model gives good correlations with the experimental results, which confirms that the proposed model can give an accurate and precise estimate of flow stress for 7075 Al alloy.

A New Creep Constitutive Model for 7075 Aluminum Alloy Under Elevated Temperatures

Exposure of aluminum alloy to an elastic loading, during “creep-aging forming” or other manufacturing processes at relatively high temperature, may lead to the lasting creep deformation. The creep behaviors of 7075 aluminum alloy are investigated by uniaxial tensile creep experiments over wide ranges of temperature and external stress. The results show that the creep behaviors of the studied aluminum alloy strongly depend on the creep temperature, external stress, and creep time. With the increase of creep temperature and external stress, the creep strain increases quickly. In order to overcome the shortcomings of the Bailey-Norton law and θ projection method, a new constitutive model is proposed to describe the variations of creep strain with time for the studied aluminum alloy. In the proposed model, the dependences of creep strain on the creep temperature, external stress, and creep time are well taken into account. A good agreement between the predicted and measured creep strains shows that the established creep constitutive model can give an accurate description of the creep behaviors of 7075 aluminum alloy. Meanwhile, the obtained stress exponent indicates that the creep process is controlled by the dislocation glide, which is verified by the microstructural observations.

Creep and Creep-rupture Behavior of 2124-T851 Aluminum Alloy

Abstract High temperature creep and useful creep life behavior of Al-Cu-Mg (2124-T851 aluminum) alloy was investigated by conducting constant stress uniaxial tensile creep tests at different temperatures (473–563 K) and at stresses ranging from 80 to 200 MPa. It was found that the stress and temperature dependence of minimum creep rate could be successfully described by the power-law creep equation. The power-law stress exponent, n = 5.2 and the activation energy for secondary creep, Q = 164 kJ mol−1, which is close to that observed for self diffusion of aluminum (~140 kJ mol−1). The observed values of n and Q suggest that the secondary creep of 2124-T851 aluminum alloy is governed by the lattice diffusion controlled dislocation climb process. A Monkman-Grant type relationship between minimum creep rate and time for reaching 1.5% creep strain is proposed and could be employed for predicting the useful creep life of 2124-T851 aluminum alloy.