Papers by Keyword: Al-Mg-Si

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Authors: Ai Serizawa, Shoichi Hirosawa, Tatsuo Sato
Abstract: The formation of nano-scale clusters (nanoclusters) prior to the precipitation of the strengthening β" phase significantly influences the two-step aging behavior of Al-Mg-Si alloys. In this work, two types of nanoclusters are found to be formed at different temperatures. The characterization of these two nanoclusters has been performed from the viewpoints of composition and thermal stability using a three-dimensional atom probe (3DAP) and differential scanning calorimetry (DSC). Mg-Si co-clusters formed at room temperature (RT), Cluster(1), play a deleterious role in the subsequent formation of the β" phase because of the high thermal stability even at the bake-hardening (BH) temperature of 443K. In contrast, the nanoclusters formed by pre-aging at 373K, Cluster(2), are effective in the formation of the refined β", suggesting that Cluster(2) transforms more easily into the β" phase than Cluster(1). The quantitative estimation of the chemical compositions of the two nanoclusters suggests that the Mg/Si ratio is one of the key factors in addition to the internal structures consisting of Si, Mg and probably vacancies. The detailed two-step aging mechanism in Al-Mg-Si alloys is proposed based on the characteristics of the two types of nanoclusters.
Authors: Ji Yong Yao, D.A. Graham, Malcolm J. Couper
Authors: Abdelali Hayoune, Nacereddine Titouche
Abstract: The effects of cold deformation and low temperature aging on the microstructural stability of a peak aged (PA) Al 6061 alloy were investigated by means of DSC and microhardness measurements. During aging at a relatively low temperature (100 °C) of the PA material, a small increasing of the mechanical properties was detected, which was explained by the formation of atomic clusters, GP zones and β phase. The response to the aging treatment of the cold deformed materials depends on both the level of the cold deformation and the aging temperature. During aging at relatively low temperature (100 °C), in contrast to the 75 % deformed material that shows a small variation in their mechanical properties, the mechanical properties, of the 30 % deformed material, are almost constant. This was attributed to the higher driving force of the recovery reaction in the heavily deformed material. In the other hand, aging at relatively higher temperature (140 °C) of the heavily deformed material, leads to a fast softening due to an increasing of the recovery kinetics.
Authors: Meng Liu, Jakub Čížek, Cynthia S.T. Chang, John Banhart
Abstract: Early stages of clustering in quenched Al-Mg-Si alloys during natural ageing were studied by positron annihilation lifetime spectroscopy utilizing its unique sensitivity to electron density differences in various atomic defects. Two different positron trapping sites could be identified, one related to a vacancy-type defect, the other to solute clusters. The first trap is deep, i.e. irreversibly traps positrons, the second shallow, from which positrons can escape, which creates the signature of a temperature-dependent positron lifetime. During the first 80 min of NA, the vacancy-related contribution decreases, while the solute clusters increasingly trap positrons, thus reflecting their continuous growth and power to trap positrons. Coincident Doppler broadening spectroscopy of the annihilation radiation shows that the annihilation sites are Si-rich after quenching but contain more Mg after 70 min.
Authors: Bradley Diak, Rathna Lanerolle
Abstract: The age hardening response of a quasi-binary Al-Mg2Si alloy was studied using activation distance analysis of precise strain rate sensitivity experiments at 78 and 300K. The alloy of Al-0.7Mg-0.33Si-0.024Fe-0.006Ti(at.%) has a stochiometrically balanced composition of Mg2Si. The alloy was solutionized at 550°C and ice water quenched before ageing in one of two ways: single-step or multi-step ageing. For single-step ageing: specimens were naturally aged for 70 days at room temperature (RT); pre-aged for 16 hours at 70°C; or artificially aged for 30 min or 10 hours at 175°C. For multi-step ageing: specimens were pre-aged at 70°C for 16 hours after natural ageing for 70 days at RT; artificially aged for 30 min or 10 hours at 175°C after pre-aging at 70°C for 16 hours; or artificially aged for 10 hours at 175°C after natural aging for 70 days at RT. The activation analysis reveals rate controlling obstacle dimensions ranging from 0.3 to 10 nm depending upon the ageing condition. A comparison is made to a prior three dimensional atom probe ageing study of the same alloy [Murayama and Hono, Acta Mater., 47 (1999) 1537-1578.].
Authors: Azusa Furihata, Kenji Matsuda, Junya Nakamura, Susumu Ikeno, Yasuhiro Uetani
Abstract: In this work, the age-hardening of Al- 1.0 mass% Mg2Si- 0.4 mass% Mg – 0.5 mass% Ag (ex.Mg-Ag alloy) alloy has been investigated. It showed increase of hardness and age-hardening response. Precipitates in this alloy aged at 523 K have been observed by high resolution transmission electron microscopy (HRTEM) and classified into five types based on characteristics in their HRTEM images.
Authors: Z. Horita
Abstract: The process of severe plastic deformation (SPD) makes it possible to reduce the grain size to the submicrometer or nanometer range in many metallic materials. When the SPD process is applied to age hardenable alloys, it may also be possible to control aging behavior. In this study, a technique of equal-channel angular pressing (ECAP) is used as an SPD process and aging behavior is examined on the three selected Al alloy systems such as Al-Ag, Al-Mg-Si and Al-Si-Ge. The microstructures are observed using transmission electron microscopy and the mechanical properties including hardness are measured. It is shown that the SPD process introduces unusual phenomena in the precipitation process and there should be a potential for enhancement of strength over the conventional age-hardening process or for improvement of ductility while keeping the high strength.
Authors: Masaya Nishikubo, Kenji Matsuda, Yoshihisa Oe, Jyunya Nakamura, Susumu Ikeno
Abstract: In this study, the aging behaviour of several Al-Mg-Si alloys (Al-Mg-Si-Cu , Al-Mg-Si-Ag and Al-Mg-Si-Cu-Ag) has been investigated by hardness tests and TEM observations. Comparing the age-hardening rate in the early period of these alloys, the alloys with Cu or/and Ag addition are faster than that of the base alloy, and the aging time to reach the maximum hardness of the alloys with Cu or/and Ag addition is shorter than that of the base alloy.Therefore the aging behaviour of that alloys has been investigated by TEM observations to understand the effect of Cu, Ag and Cu+Ag additions on aging precipitation.
Authors: Gonasagren Govender, Heinrich Möller, Ulyate Andries Curle
Abstract: Semi-solid metal forming is more than 40 years old but its full potential to near net shape form high strength aluminium alloys has been realised only to a limited degree. Alloys developed for traditional manufacturing processes were initially used but it became apparent that alloys specific to SSM forming needed to be developed. The main alloy development criteria revolved around SSM processing temperature, solid fraction (fs) versus temperature sensitivity and age hardening potential. This methodology while sound does not fully address the unique processing behaviour of SSM forming. By its very nature SSM requires the controlled solidification of a part of the melt before forming. From basic solidification fundamentals this results in the enrichment of the remaining liquid with alloying elements. During the forming process segregation of liquid phase essentially produces a component with very different compositions in the regions where the liquid solidifies last. From recent work completed on a wide range of standard alloy systems it has become apparent that this segregation effect has a significant impact on aging behaviour and strength. Low melting point structures formed in the these regions result in localised melting in the grain boundary region and along areas of gross liquid segregation during solution heat treatment, contributing to the poor mechanical properties. Although this behaviour can be addressed using modified heat treatment, this cannot be applied to all current alloy systems. Alloy design for SSM forming must take these phenomena into account in order to develop and or specify aluminium alloys with acceptable mechanical properties.
Authors: Jürgen Hirsch
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