Temperature and strain rate dependence of the dynamic strain aging effect in an Al–Zn–Mg alloy

Hörnqvist, Magnus; Karlsson, Birger

doi:10.1179/174328406x74284

Cited by 10 publications

(5 citation statements)

References 29 publications

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“…It has been shown that, assuming proportionality between ∆g and the solute concentration at the dislocation line, the strain rate dependence of ∆g will be negative [9], indicating that S can take both positive and negative values depending on the relative magnitudes of k B T and ∂∆g/∂ln ε& .…”

Section: Discussionmentioning

confidence: 99%

Temperature and Strain Rate Effects on the Dynamic Strain Ageing of Aluminium Alloy AA7030

Hörnqvist

Karlsson

2006

MSF

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The effects of temperature and strain rate on the mechanical properties of aluminium alloy AA7030 (Al-5.4Zn-1.2Mg) in naturally aged and peak aged condition are investigated, with emphasis on the relation to dynamic strain ageing. It is found that the naturally aged material shows more severe signs of dynamic strain ageing, including inverse strain rate and temperature dependence of flow stress, inverse temperature dependence of the ductility and serrated yielding. The peak aged material also shows signs of dynamic strain ageing, but to a lesser extent, most pronounced through serrated yielding. The observed effects can be qualitatively explained in terms of a thermal activation based model for dislocation glide. Furthermore, inhomogeneous deformation is observed on several size scales ranging from localized glide bands to surface deformation effects (orange peel surface) and macroscopic flow localization in shear bands.

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Section: Discussionmentioning

confidence: 99%

Temperature and Strain Rate Effects on the Dynamic Strain Ageing of Aluminium Alloy AA7030

Hörnqvist

Karlsson

2006

MSF

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“…The NA samples were deformed with a total strain amplitude of 0.6% and the PA with 0.8%, this to yield plastic strain amplitudes of 0.2% at half-life, at temperatures of -20, 20 and 60ºC. Inspired by the results on the influence of temperature on the monotonic properties of AA7030 [1][2][3]13], it was decided to perform tests at both lower and higher temperatures than ambient, namely 20 C, 20 C and 60 C. …”

Section: Methodsmentioning

confidence: 99%

“…The alloy AA7030 has been shown earlier to exhibit strong DSA effects in naturally aged [1][2][3] and solution treated [4][5][6][7][8] conditions, while weak effects were found in the peak-aged material [1][2][3]8].…”

Section: Introductionmentioning

confidence: 99%

Dynamic strain ageing and dynamic precipitation in AA7030 during cyclic deformation

Hörnqvist

Karlsson

2010

Procedia Engineering

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The effects of dynamic strain ageing (DSA) and dynamic precipitation (DP) on the stress strain response during low-cycle fatigue of naturally aged (NA) and peak-aged (PA) AA7030 alloy at different temperatures was investigated. The results show that the PA temper is largely unaffected by DSA/DP, and the cyclic deformation behavior is controlled by the accumulation of dislocations and strain localization due to repeated shearing of precipitates. In the NA temper, on the other hand, the effect of temperature on DSA and DP is the main mechanism controlling the stress strain response. At temperature above room temperature, DP in the intense slip bands inhibits cyclic softening and the samples harden until the on-set of crack growth. At lower temperatures, the rate of DP is too slow to compensate for the softening in the slip bands and the stress amplitude saturates or decreases. The stress amplitude development is shown to primarily be a result of the evolution of the effective stress associated with dislocation precipitate interactions.

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“…Under plastic flow, dislocations are gliding until they come across an obstacle where they are stationary until the obstacles are surmounted. When the dislocations are stationary, solute atoms can diffuse towards the dislocations which result in an increase in the activation energy for further slip and consequently also an increase in the stress needed for overcoming the obstacle [92][93][94][95][96][97]. Thus, DSA is directly influenced by the deformation rate that affects the mobility of the dislocations and the temperature that influences the diffusion rate of solute atoms.…”

Section: Dynamic Strain Ageingmentioning

confidence: 99%

On High-Temperature Behaviours of Heat Resistant Austenitic Alloys

Calmunger¹

2015

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Advanced heat resistant materials are important to achieve the transition to long term sustainable power generation. The global increase in energy consumption and the global warming from greenhouse gas emissions create the need for more sustainable power generation processes. Biomass-fired power plants with higher efficiency could generate more power but also reduce the emission of greenhouse gases, e.g. CO 2 . Biomass is the largest global contributor to renewable energy and offers no net contribution of CO 2 to the atmosphere. To obtain greater efficiency of power plants, one option is to increase the temperature and the pressure in the boiler section of the power plant. Raised temperature and pressure increase the demands of the operating materials of the future high-efficient biomass-fired power plants. This requires improved properties, such as higher yield strength, creep strength and high-temperature corrosion resistance, as well as structural integrity and safety. Also, the number of start-and-stop cycles will increase, leading to demands on increased material performance under cyclic loading, both from thermal and mechanical loads.Heat resistant austenitic alloys, such as austenitic stainless steels and nickelbased alloys, possess excellent mechanical and chemical properties at the elevated temperatures and cyclic loading conditions of today's biomass-fired power plants. Today, some austenitic stainless steels are design to withstand temperatures up to 650• C in tough environments. Nickel-based alloys are designed to withstand even higher temperatures. Austenitic stainless steels are more cost effective than nickel-based alloys due to a lower amount of expensive alloying elements. However, the performance of austenitic stainless steels at the elevated temperatures of future operation conditions in biomassfired power plants is not yet fully understood.This thesis presents research on the influence of long term high-temperature ageing on mechanical properties, the influence of very slow deformation rates at high-temperature on deformation, damage and fracture, and the influence iii of high-temperature environment and cyclic operation conditions on the material behaviour. The research has been conducted on several commercial heat resistant austenitic alloys. Mechanical testing, such as impact toughness tests, uniaxial tensile tests at elevated temperatures using various strain rates and creep-fatigue interaction tests, has been performed. Also, thermal testing such as long term ageing and thermal cycling in a water vapour environment has been performed. The mechanical and thermal testing have been followed by subsequent studies of the microstructure, using scanning electron microscopy, to investigate the deformation, damage and fracture mechanisms as well as the precipitation and corrosion behaviours.Results shows that long term ageing (up to 10 000 hours) at high temperatures (up to 700• C) leads to the precipitation of intermetallic phases. These intermetallic phases are brittle at room temperatu...

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Temperature and strain rate dependence of the dynamic strain aging effect in an Al–Zn–Mg alloy

Cited by 10 publications

References 29 publications

Temperature and Strain Rate Effects on the Dynamic Strain Ageing of Aluminium Alloy AA7030

Temperature and Strain Rate Effects on the Dynamic Strain Ageing of Aluminium Alloy AA7030

Dynamic strain ageing and dynamic precipitation in AA7030 during cyclic deformation

On High-Temperature Behaviours of Heat Resistant Austenitic Alloys

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