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Authors: Shoichi Hirosawa, Tatsuo Sato
Abstract: The formation of nano-scale clusters (nanoclusters) prior to the precipitation of the strengthening b” phase significantly influences two-step aging behavior of Al-Mg-Si alloys. In this work, the existence of two kinds of nanoclusters has been verified in the early stage of phase decomposition by differential scanning calorimetry (DSC) and three-dimensional atom probe (3DAP). Pre-aging treatment at 373K before natural aging was also found to form preferentially one of the two nanoclusters, resulting in the remarkable restoration of age-hardenability at paint-bake temperatures. Such microstructural control by means of optimized heat-treatments; i.e. nanocluster assist processing (NCAP), possesses great potential for enabling Al-Mg-Si alloys to be used more widely as a body-sheet material of automobiles.
Authors: Kenji Matsuda, Susumu Ikeno
Abstract: The precipitation sequence of Al-Mg-Si alloys has been studied by high-resolution transmission electron microscopy (HRTEM). G.P. zone is a fine-plate having dimensions of a mono- layer in thickness, 2.5nm in width, and less than 30nm in length. Its elongated direction is parallel to the <100>m direction. Several types of metastable phases were observed in the excess Si alloy and they were classified with the b ’-phase in the balanced alloy. Especially, the b ”-phase was the typical phase in the excess Si alloy aged at low temperature or at the early stage during aging.
Authors: Koichiro Fukui, Mahoto Takeda, Takao Endo
Abstract: Precipitation behaviour in an Al-Mg-Si alloy aged at 403 K to 483 K was studied with respect to thermal stability and morphology of the metastable precipitates, using high resolution transmission electron microscopy (HRTEM), Vickers microhardness tests and differential scanning calorimetry (DSC) measurements. The quantitative analysis of the DSC measurements revealed that the change in the first exothermic peak (the peak P) of the metastable phase is proportional to the increases in the Vickers hardness. The HRTEM observations showed the four types of the precipitates in morphology during the isothermal ageing and the change in the peak P was mainly caused by the formation of the precipitates with irregular contrast and the ones with the network interior angle between 65°and 80°
Authors: Seong Taek Lim, Yong Yun Lee, Il Sang Eun
Abstract: An effort has been made to present optimum alloy designs of commercial 7175 and 7050 type alloys to be used in thick forgings with proper microstructures and properties. The effects of changing alloy constitutions, primarily [Zn+Mg+Cu] and Zn:Mg ratio, on the evolutions of the coarse equilibrium phases and age hardening response are investigated. As a result, equilibrium phases (M,T,S) are evolved depending on alloy constitutions and cooling rate following solutionizing. The formation of the T- and S-phases is effectively controlled in the novel alloys (dilute and with high Zn:Mg ratio). In the slow quench, the redesign promotes homogeneous precipitation of η-phases, leading to higher mechanical properties than conventional alloys. The novel alloys provide microstructural homogeneity and extended heating range, ensuring 7xxx thick forging applications.
Authors: Dong Woo Suh, Sung Man Sohn, Moon Yong Lee, Sang Yong Lee
Abstract: The deformation behaviors of fully annealed or T6-treated 6061 and 7075 aluminum tubes are investigated at elevated temperature using uniaxial tensile test. Fully annealed 6061 and 7075 tube, and T6-treated 7075 tube do not show sharp local necking with an elongation of 50% at tensile temperature of 300oC, accordingly, it is expected that warm hydroforming process can be applied. The increase of tensile temperature does not significantly affect the total elongation of T6-treated 6061 tube.
Authors: P.K. Seo, Byung Min Kim, Chung Gil Kang
Abstract: The parts manufactured by die casting process usually contain liquid segregation and porosities. To solve these problems, the semi-solid forming process has been applied. The process enables material in the semi-solid state to be completely filled, and parts with the complicated shape to be fabricated by applying relatively low pressure. This process is necessary in order to control the microstructure of the billet as well as to achieve the desired semi-solid billet state. In this study, a horizontal high-frequency induction heating device which can be fabricated by semi-solid forming irrespective of a billet's size was developed. A globular structure of the reheated billet and a billet's temperature distribution during the reheating process for A356 were investigated.
Authors: J.K. Kim, Dong-Seok Chung, H.S. Park, Manabu Enoki
Abstract: The effect of beryllium (Be) on the precipitation behaviors and mechanical properties of Al–Cu–Li–Mg–Zr–(Ag) alloys was investigated. The results show that adding 0.02%Be to Al–Cu–Li–Mg–Zr–(Ag) alloys, the elongation of the alloy increased without significant decrease in strength and the aging response was accelerated. In a Al–Cu–Li–Mg–Zr–(Ag) alloy, G.P. zone was formed at early aging time (2 h) and T1 and q′ phases were formed at peak-aging and over-aging times, while in Al–Cu–Li–Mg–Zr–(Ag)–Be alloys T1 and q′ phases were formed at early aging time (2 h) and the density of q′ phase was very low and fine T1 phases were homogeneously distributed at peak-aging and over-aging times.
Authors: C.-S. Chi, Y. Jeong, S.S. Kim, J.H. Lee, H.J. Oh
Abstract: The increase of capacitance on dielectric layer is associated with enlargement of etched surface area of electrodes for aluminum electrolytic capacitors. Etched tunnels extending along [100] directions are formed by crystallographic dissolution of aluminum in a chloride solution. This study has been focused primarily on the effects of addition of inhibitors to hydrochloric acid solution on the increase of the surface area by Electrochemical Impedance Spectroscopy (EIS). The addition of 3 % ethylene glycol was more effective for the enlargement of the surface area comparing with those of 1M sulfuric acid and no additive. And it was observed by TEM that the tunnels were grown straight and parallel to [100] directions.
Authors: Moo Young Huh, J.P. Lee, Jae Chul Lee, Jong Woo Park, Young Hoon Chung
Abstract: The evolution of annealing textures and microstructures in the aluminum alloy 3103, which was subjected to deformation by either cold rolling or equal channel angular rolling (ECAR), was investigated. Samples of AA 3103 sheets were repeatedly deformed by ECAR up to six passes. In addition, AA 3103 was cold rolled to the same hardness level of the ECARed samples. Upon annealing, the cold rolled sample was recrystallized by the discontinuous recrystallization which gave rise to the formation of the cube texture and large grains bigger than 30 µm. In contrast, the ECARed sample was recrystallized by extended recovery which led to the formation of ultra-fine grains having a size smaller than 3.5 µm.
Authors: Dong Suk Lee, Gyu-Sam Shim, Mok Soon Kim, Won Yong Kim, Hiroshi Yamagata
Abstract: Compressive deformation behavior of pre-sintered Al-10Si-5Fe-1Cu-0.5Mg-1Zr (wt%) alloy containing 15% of porosity was investigated in the temperature range from 753 K to 793 K and at strain rates from 10-4 to 100 s-1. From the microstructural observation, it was revealed that the occurrence of grain boundary sliding accomodated by dynamic recrystallization during the compressive deformation was closely associated with the considerable decrease in the porosity of the pre-sintered alloy. In the specimens deformed at 793 K with 10-4~100 s-1 and at 773 K with 10- 4~10-2 s-1, we have found an evidence of the occurrence of a liquid phase during compressive deformation in the microstructure. The liquid phase was considered to promote particle boundary sliding and hinder the reduction of the pore.

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