KEIKINZOKU is a Japanese monthly journal published by The Japan Institute of Light Metals, JILM. Since 1951, this journal has original regular articles, reviews and technical reports, etc on current technology of light metals.
The present study investigated the influence of additional Mg on the intergranular corrosion (IGC) susceptibility of brazed Al-Mn-Si-Cu alloys. IGC did not occur in the water quenched samples, whereas samples treated with slow cooling rate showed high IGC susceptibility. As a result of anodic polarization measurement, non IGC susceptibility samples showed a single pitting potential, but high IGC susceptibility samples showed double pitting potentials. On slowly cooled Al-Mn-Si-Cu-Mg alloys, the precipitation of Al15 (Mn, Fe)3Si2 were observed in the grain interiors and on the boundaries, but Q-phase on the grain boundaries. Precipitated Q-phase induced forming Si/Cu/Mg-depleted zone near the grain boundaries. This zone, of which pitting potential is less noble than the grain, dissolved preferentially, hence IGC susceptibility increased. Furthermore, we clarified additional Ti improved the IGC susceptibility of Al-Mn-Si-Cu-Mg alloys. It was considered that potential gap due to Ti layered distribution prevented intergranular corrosion progress.
An increase in the volume fraction of pores in aluminum alloys causes a decrease in the elongation and the strength of alloys. To improve the mechanical properties of aluminum alloys, it is important to understand the growth and shrinkage behavior of pores. In this study, we analyzed the relationship between hydrogen desorption behavior and the growth/shrinking behavior of pores in A6061 alloys and pure aluminum using thermal desorption analysis and synchrotron radiation X-ray tomography. In pure aluminum, the fine pores began to annihilate at temperatures above 500°C and the relatively large pores coarsened. In contrast, the pores shrank with increasing temperature in A6061 alloy. The influence of second-phase particles has been discussed as a possible explanation for the difference in the nature of pores at elevated temperatures in pure aluminum and A6061 alloys. As in the A6061 alloy, much of the hydrogen desorbed from the pores due to heating is released externally from the second-phase particles on the aluminum surface, resulting in pore shrinkage due to the internal pressure drop of pores.
This study investigated the effect of Sn addition on clustering behavior of natural aging (NA) in Al-0.95mass%Si-0.56mass%Mg-0.04mass%Sn alloys by XAFS measurements, first-principles calculation and Vickers hardness measurements. XAFS measurements at the Sn-K edges were carried out at the BL14B2 beamline, at the Si-K and Mg-K edges were carried out at the BL27SU beamline at SPring-8. It was found that Sn addition brought about the retardation of cluster formations. This retardation was ascribed to the suppression of formations of Mg-vacancy (Va) pairs. By Sn addition, the ratio of Sn-Va pairs was increased from as-quench (AQ) to NA for 36 ks, however Sn atoms were not remarkably included in the clusters. The formation energy of the Sn-Va pair is the smallest in Al matrix, and Sn atoms preferentially bind to vacancies. Since the formation energy of Mg-Va pair is higher than that of the Si-Va pair, the formation of Mg-Va pairs is preferentially delayed. Based on the result of Vickers hardness measurements, negative effect of two-step aging was caused by the participation of Mg atoms in the clusters, not that of Si atoms. It was clarified that Mg atoms have a greater influence on negative effect in two-step aging than Si atoms have.
A softening behavior of 3104-H19 aluminum can body materials during the paint baking process in can productions is an impactful factor on can body strength. However, detailed investigations on the mechanism are limited due to simultaneous occurrence of multiple fine precipitations and recovery, as well as difficulty of observing fine precipitates under high-density dislocations. In this research, effects of solid solution of the additional or impurity elements on paint baking softening behavior were investigated by observing microstructural changes with the high resolution FE-SEM, TEM, and synchrotron radiations. Based on this study, the solute atoms are thought to react with lattice defects (dislocations, dislocation cells, subgrain boundaries) to suppress their movement and recovery during the baking process. Then, precipitations and coagulations of the solute atoms occurred as the baking time passed. It could end up with mitigation of the pinning effect and progress of the recovery. The bake softening behavior could be explained with these multiple stages of the precipitations and coagulations of the solute atoms and the recovery progression. On the base of observed microstructural changes during the baking, the softening curve was analyzed using the newly proposed kinetics equation. The results of this analysis support the mechanism mentioned above.