Papers by Keyword: Al-Sc Alloy

Abstract: In this paper, precipitation of ScAl₃ phase during solutionizing and ageing and its impact to mechanical properties of hypoeutectic Al-Sc alloy and effect of Sc addition amount were investigated by TEM and SEM microstructure observation and mechanical property testing. During solutionizing at 640^oC for 24h, for Al-0.2wt.%Sc and Al-0.4wt.%Sc alloy, ScAl₃ particles formed in the course of solidification become smaller, indicating, as a whole, Sc is partially dissolved into Al solution. Simultaneously, precipitation of two types of ScAl₃ particles are observed by TEM. One has a size of 200~300nm, and the other is much small, 5~20nm in size. Though re-dissolution of Sc solute into Al solution and precipitation of large and fine ScAl₃ particles occur in the solutionizing course, but the strength and hardness are decreased. The key reason for it is thought to be the softening effect of high level of vacancies in matrix lattice from the high solutionizing temperature. After further aging at 300^oC for 3h, a great number of fine ScAl₃ particles are precipitated in the Al matrix, which leads to a considerable precipitation hardening effect, thus the strength and hardness are increased obviously. Increasing the Sc content in the alloy results in a considerable rise in as-cast and as-aged strength and hardness, due to the solution strengthening and precipitation hardening respectively.

Abstract: This study investigates the precipitation behavior of two similar cast Al-Mg-Sc-Zr alloys with different solidification and cooling rates. Microstructural analyses and hardness testing were performed after casting and ageing. In addition, the precipitation and hardness evolution after rapid quenching using electron beam re-solidification were studied. It was shown that the amount of Al₃(Sc,Zr) phases present after casting or re-solidification increases with decreasing solidification and cooling rate. Consequently, the degree of supersaturation in Sc and Zr at room temperature and thus the hardening potential in a subsequent ageing process increases with the solidification and cooling rate. Therefore, the electron beam re-solidified samples revealed the most pronounced hardening.

Abstract: This study investigates the hot deformation behavior of a new Al-Mg-Sc-Zr alloy under plane strain conditions. Flow curves corrected for deformation heating were calculated for strain rates between 0.01 and 10s^-1 in a temperature range of 200 to 400°C. To evaluate the deformation behavior, strain rate sensitivity as well as flow localization parameter maps were calculated for strains of 0.2, 0.4, and 0.6. In addition, microstructural investigations and hardness measurements were performed for selected samples. It was shown that the flow stress decreased with deacreasing strain rate and increasing temperature. The best formability was observed for high strain rates and low temperatures as well as for low strain rates and high temperatures. In these cases no flow instabilities were observed.

Abstract: The electrical conductivity of the molten salts of Na3AlF6-LiF-Sc2O3 system with different compositions was measured at different temperatures by the continuously varying cell constant technique. The main influence factors on electrical conductivity were analyzed. Experiment results showed that the technique of the electrical conductivity measurement is accurate and reliable and the result’s relative error is just 0.67% in comparison with those in relevant literature. With temperature rising, electrolyte conductivity increases at a rate of about 0.03S/cm for 1°C. And we also found that the conductivity increases slightly with the addition of lithium fluoride and adding scandium oxide makes the conductivity decrease slightly and more addition doesn’t cause significant effect. It was proved that the technique can measure accurately the electrical conductivity of aluminium electrolyte and other high-temperature molten salts.

Abstract: The paper studied the preparation of Al-Sc alloy by molten salt electrolysis. LiF-ScF3-ScCl3 as the electrolyte, Sc2O3 as raw material, liquid Al as cathode and graphite as anode. The process condition of preparating Al-Sc alloy includes the influence of current density, electrolysis time, temperature of electrolysis, Back EMF, content of Sc in alloy and current efficiency.The content of Sc in alloy prepared by this method has reached to the maximum of 3.437%. The components of alloys showed by SEM were uniform, it is applicable for commercial purposes. Preparation of Al-Sc alloys with scandium oxide as raw materials, it not only reduce environment pollution, but also decease the cost of production. It is reported in many documents, preparing aluminum base alloy by the method of molten salt electrolysis[1-3], people could make many alloys such as Al-Ce、Al-La、Al-RE、Al-Ti、Al-Si-Ti in the aluminum cell, also the method to prepare some rare earth alloys such as Al-Sr、Nd-Fe、La-Ni was reported[4,5]. Use the method of electrolysis to produce some aluminum base alloy with high-melting-point , difficult to restore , high-priced element is a good method because it is technological process is brief, economy is rational, the technology is feasible, this viewpoint is broadly approved in the world[6]. It isn’t necessary to use high-priced Sc as raw material in preparing Al-Sc alloy with molten salt electrolysis, it could control the Sc amounts in the alloy through the different current efficiency and electrolysis time, production in this method could be continuous or semi-continuous, so it is easy to be automatic controlled. A new molten salt system is used in this paper, we use molten salt electrolysis to produce Al-Sc alloy, take scandium oxide as raw material, through the study of the effect of the current intensity，electrolysis time and the electrolysis temperature , Back EMF and cell voltage, the final production Al-Sc alloy contains Sc 2~6%.

Abstract: The effect of fine, non-shearable, dispersoids on the grain refinement of aluminium alloys, severely deformed by ECAE, has been studied using a model Al-0.2%Sc alloy, during deformation by Routes A and BC (+90degrees rotation) using a 120°, or 90°, die. The microstructure in the dispersoid-containing alloy was compared to a single-phase alloy using high resolution EBSD analysis. With Route A the presence of fine dispersoids was found to significantly retard the development of new high-angle grain boundaries and the formation of a fine grain structure, by homogenising slip and inhibiting microshear bands. This difference was greatly enhanced, using Route BC. Similar results were obtained with the two die angles, but with Route A refinement tended to be slightly less effective when using the 90° die.

Abstract: It has been reported that scandium addition improved various properties of aluminum alloys. However, present authors can not find any reports about the addition of Sc to 6000 series alloys. In this study, Sc was added to 6061 alloy and various effects of the Sc addition on aging behavior were examined, comparing with Al-Sc binary alloy. In the STQ state, resistivity at 77K, ρD77, of 0.2%Sc added alloy (6061+Sc) was about 2.0n-m higher than the alloy of no addition (6061). The ρD77 increased in initial stage of isothermal aging up to 473K, then decreased. Though ρD77 of binary Al-0.176%Sc alloy began to decrease from 1.8Ms at 448K and 18ks at 523K, excess decrease in ρD77 of 6061+Sc corresponding to precipitation of Sc compounds was not clear. Peak value of the HV0.1 was decreased and peak aging time delayed by the Sc addition in aging up to 498K. However, softening by overaging was retarded by the Sc addition. These effects of the Sc addition are considered to come from vacancy trap by solute Sc atoms or interface between particles of Sc compound and matrix acting as vacancy sinks.