Improvement of Thermal Stability and Evaluation of Fatigue Behavior of an Ultra fine-Grained Al-Mg-Sc Alloy Using ECAE
Grant-in-Aid for Scientific Research (C)
|Allocation Type||Single-year Grants|
Physical properties of metals
|Research Institution||Kanazawa University|
MONZEN Ryoichi Kanazawa University, Engineering, Professor, 工学部, 教授 (20166466)
KITA Kazuhisa Kanazawa University, Natural Science & Technology, Research Associate, 自然科学研究科, 助手 (10195240)
WATANABE Chihiro Kanazawa University, Natural Science & Technology, Research Associate, 自然科学研究科, 助手 (60345600)
|Project Period (FY)
2002 – 2003
Completed(Fiscal Year 2003)
|Budget Amount *help
¥2,700,000 (Direct Cost : ¥2,700,000)
Fiscal Year 2003 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 2002 : ¥2,200,000 (Direct Cost : ¥2,200,000)
|Keywords||Al-Mg-Sc alloy / ECAE / thermal stability / ultra fine grain / fatigue behavior / dislocation structure / coherent Al_3Sc precipitate particle|
The microstructure evolution of an ultrafine grained Al-3wt%Mg-0.2wt% Sc alloy produced by equal channel angular pressing during annealing at 573 K or 623 K has been examined. Annealing at 623 K for a short time caused complete recrystallization of the ultrafine grains. The structure development at 573K can be divided into three stages as follows :
(1)Initial stage (〜30min). The hardness decreases rapidly with annealing time and the grain size increases from 300 to 600 nm. The dislocation, density becomes lower by recovery, The grain growth and the reduction in dislocation density bring about the decrease in hardness.
(2)Intermediate stage (30min〜11h). The hardness increases and the grain size remains almost unchanged. Fine precipitated Al_3Sc particles are formed in grain interiors. These particles cause primarily the increase of the hardness. The small Al_3Sc particles on grain boundaries pin grain boundaries and restrict their migration.
(3)Later stage (11h〜). At this stage, again the
grain growth occurs and the hardness decreases. This is because the pining force and the particle strengthening gradually decrease with increasing the Al_3Sc particle size. From the linear relationship between the grain size and Al_3Sc particle radius, it is concluded that the grain growth is controlled by the rate of coarsening of the Al3Sc particles.
Plastic-strain-controlled low-cycle fatigue tests of an Al-Mg-Sc alloy containing Al_3Sc particles with average diameters 4 nm and 11nm were carried out. The results and conclusions are summarized as follows :
(1)Specimens with Al_3Sc particles of 4nm in diameter show cyclic softening at higher plastic-strain amplitudes (ε_<pl>【greater than or equal】1×10^<-3>). All other specimens show cyclic hardening to saturation.
(2)Dislocations were very uniformly distributed in specimens with Al_3Sc particle of 11nm in diameter. At higher strain amplitudes, the slip bands were observed in specimens with Al_3Sc particles of 4nm in diameter.
(3)The fatigue softening of specimens with 4 nm Al_3Sc particles is unambiguously related to the dissolution of the Al_3Sc particles within the slip bands. Less
Research Products (13results)