Friction stir welded joints of magnesium alloys AXM410 and AZX912, both similar and dissimilar, were exposed outdoors for three years to evaluate the effects of joint type and environment on corrosion. Unsheltered exposure caused general corrosion, whereas sheltered exposure promoted localized attack. Similar joints (AXM410/AXM410, AZX912/AZX912) showed a slight but preferential attack on the SZ/TMAZ region. In contrast, dissimilar joints (AXM410/AZX912) developed corrosion grooves up to 0.3 mm at the SZ region under unsheltered exposure, though only minor attack occurred under sheltered conditions. Electrochemical tests indicated AZX912 had a more noble corrosion potential than AXM410 in 1% NaCl, with potential difference and galvanic current increasing from untested to sheltered to unsheltered specimens. GD-OES depth profiling showed a two-layered product: an outer carbonate-rich film and inner Mg-Al LDH under unsheltered exposure, while sheltered exposure produced different carbonate films with higher NaCl content. For dissimilar joints, differences in Al concentration of base materials appear to drive macrogalvanic corrosion under unsheltered conditions, but in sheltered conditions the effect is reduced due to localized attack of the base metal.

In the casting of aluminum alloys, fine grains are required to suppress the cracking and quality deterioration. Al-Ti-B alloy is commonly utilized as grain refiner. It is well-known that TiB₂ particles are serving as grain refiner. However, the effects of addition amounts of grain refiner and solidification conditions on the solidification structure have not been fully clarified with application of grain refiner. In this study, unidirectional solidification experiments of A1070 alloy have been performed to investigate the effects of additional amounts of grain refiner and solidification conditions on the columnar-to-equiaxed transition (CET). At the same time, the nucleation undercooling in the solidification of A1070 alloy with and without grain refiner, have been also measured. Moreover, Hunt model has been utilized with consideration of the measured results of undercooling to examine the obtained results by unidirectional solidification experiments.

In the present study, an Al-0.5%Mg₂Si alloy was fabricated, and the precipitation sequence was examined through a comparison between a wrought material subjected to solution treatment and aging after processing and a cast material aged directly after casting. Since the Al-7%Si-0.3%Mg alloy contains as much as 7% Si, the excess Si is expected to exert a significant influence on the precipitation sequence. In this study, the Al-0.5%Mg₂Si alloy was used as the base composition, and the effect of increasing Si content on precipitation behavior was examined. Age-hardening curves indicated that the hardness increased with aging time and decreased after peak aging. In the Al-0.5%Mg₂Si alloy, all precipitates were identified as the β′ phase, whereas β″ phase precipitation occurred with increasing Si content. In Si-added alloys, precipitates formed on dislocations exhibited a characteristic bright-spot arrangement similar to that observed in deformed Al-Mg-Si alloys. The growth of these dislocation-related precipitates was suppressed, and at the peak-aged condition, they were obscured by β″ phases formed in the matrix. The presence of Si particles was found to be associated with the observation of coarser β″ phases in the proximity of the particles, as compared to their distribution within the matrix.

The effects of anodizing and conversion treatment following laser irradiation on the adhesion of AZ91D magnesium alloy were investigated. Laser irradiation produced surface irregularities of approximately 10-50 μm, which increased as the scanning speed decreased. These irregularities remained after subsequent anodizing and conversion treatment, resulting in a surface morphology that was markedly different from that of the non-irradiated specimen. Adhesion tests revealed that the adhesion strength increased with decreasing laser scanning speed, indicating that the anchoring effect associated with increased surface roughness was a key factor in improving adhesion. Moreover, the conversion treatment exhibited superior adhesion to polyamide-based adhesives compared with anodizing.

AA2618 aluminum alloy is well-known as an age-hardenable aluminum alloy with higher strength at elevated temperatures. In this study, the effect of dynamic precipitation on creep properties of AA2618 forged aluminum alloy was investigated by creep test, tensile test, transmission electron microscopy and differential scanning calorimetry. The differently aged three samples with varied yield stress: i.e. short-, middle- and long-aged samples, were prepared and then crept at 180°C under applied stress of 160-250 MPa. Although yield stress of short-aged sample was the lowest at room temperature and 180°C, the creep rupture time was the longest, and the minimum creep rate was the lowest among the three samples. Such a discrepancy between tensile and creep strength was attributed to dynamic precipitation in short-aged sample, in which newly formed precipitates during creep test compensate the softening induced by the growth and coarsening of existing GPB zones and S′/S phases. Therefore, it was clarified from this study that less stable precipitate microstructure with higher solute concentrations in the α-Al matrix of short-aged sample is good for creep resistance of this alloy system, although the tensile strength is lower than those of middle- and long-aged samples.

Magnetic pulse welding of aluminum and copper was performed by changing of type of aluminum alloy used as a flyer plate. Welding experiments showed that weldable charging energy-gap condition differed depending on the aluminum alloy type. Finite element method analysis of collision of aluminum flyer plate and copper parent plate indicated that when a relatively low-strength aluminum alloy was used for the flyer plate, the tip of the flyer plate was rounded and deformed by electromagnetic force. When the high-strength aluminum alloy was used for the flyer plate, the tip of the flyer plate collided with the copper parent plate while remaining flat. The collision velocity and collision angle depended on electrical resistance and tensile strength, respectively. Smooth particle hydrodynamic analysis revealed that the pressure on the order of GPa above Hugoniot elastic limit was generated at the welding interface. Regardless of the aluminum alloy used for the flyer plate, the pressure at welding interface exceeded the Hugoniot elastic limit, and a region above the melting point at high pressure was observed within a few μm from the welding interface at weldable condition.