Effect of particle size on aging in alumina particle dispersed composite materials has been investigated by transmission electron microscopy. Age-hardening curves of composite materials containing larger alumina particles ranging from 8 to 15μm, were quite similar to those of mother alloy. In these composites, aging processes started with the formation of GPB zones and were followed by the precipitation of S' intermediate phases. While in the composite materials containing smaller alumina particles ranging from 1 to 3μm, the hardness under peak aging condition was lower than that of mother alloy. The electrical resistivity just after solid solution treatment had also lower values than that of mother alloy. Their aging processes started with the formation of GP zones and were followed by the precipitation of θ' intermediate phases. The dissimilarity of these aging processes depending on size of alumina particles caused by the decrease of magnesium content in the matrix due to the formation of spinels on alumina particles.

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The mechanical properties of friction welded joints of AZ31 magnesium alloy to 1050 aluminum, which were made by a brake type friction welding machine, were examined by mechanical tests and optical micrograph. The burr on the welds occurres from 1050 aluminum, and its enveloped in AZ31 alloy at the weld zone regardless of the welding conditions. It is recognized that the original fibrous structures disappeared at near the weld interface. Both compound layer and mechanical mixing layer were observed on the weld zone. Hardness of the weld interface has a higher value than those of the base metal. The tensile strength of welded joints are improved with increasing the friction time. In case of the friction pressure 70MPa, the tensile strength of welded joints are slightly higher than that of the 1050 aluminum, but friction welded joints under the friction pressure of 50MPa and 60MPa are inferior to the 1050 aluminum. The elongation of all the welded joints are inferior to that of the AZ31 alloy. All the tensile specimens are fractured at the weld interface. The impact specimens in which notch is put into the weld interface show impact strength lower than that of the AZ31 alloy.

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Mechanical properties and microstructures of Al-1-5mass%Li-2mass%Cu-1mass%Mg-0.15mass%Zr alloy castings, including 8091 alloy, were investigated. Many cracks at grain boundaries are observed in the as-cast castings containing 4 and 5mass%Li, and the elongation is extremely low in the under-aged castings containing 3mass%Li. The low ductilities may be due to δ (AlLi) formed during solidification. The mechanical properties of the above alloys can be greatly improved by reducing the Li content below 2.5mass% to be completely solid solution. The ultimate tensile strength of Al-2.5mass%Li-2mass%Cu-1mass%Mg-0.15mass%Zr alloy (8091 alloy) castings poured into permanent mold is 387MPa in T4 condition and 416MPa in T6, while these elongation are 13.8% and 2.2%, respectively. Those properties of sand mold castings are lowered by 78% than those of the permanent mold castings. The δ', T₁ and S' phases precipitate at 473K aging.

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AZ91D magnesium alloys and ADC12 aluminum alloys die cast panels with paint finishing were exposed for three years. The pretreatment films for painting on AZ91D magnesium alloys were formed from various chemical conversion and anodizing baths, and the films on ADC12 aluminum alloys were formed from chromating. The environmental factors, temperature, precipitation, wetness time, solar and UV radiant, concentration of chloride and sulfur oxide, which are generally believed to be associated with corrosion mechanisms were measured. The chromate and anodic oxide films were superior as pretreatment films for painting on AZ91D magnesium alloys judging from the adhesion of painting and corrosion resistance. And these showed same degree compared with paint coated ADC12 aluminum alloys.

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The corrosion rate and the residual stress of 5083 aluminum alloy sheets cold rolled after annealing or sensitizing were measured as a function of room temperature aging time after rolling. An age-softening-like secular change appeares for the annealed specimens, but not for the sensitized ones. The residual stress induced by rolling decreases with aging time, and reaches an almost constant value regardless of the rolling reduction ratio, after aging for 10 days and above. The corrosion rate also decreases with aging time, and reaches a constant value after long time aging in the case of sensitized specimens. But in the annealed specimens the rate with the total reduction ratio changes into a monotonously increasing type. This is probably because of the precipitation during aging. Taking such effect of precipitation into account the residual stress and the corrosion rate show the good correspondence.

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The solubility of hydrogen in molten aluminum has been determined for temperature from 973 to 1073K, employing the rapid quenching method. The results closely agree with Van't Hoff isobar and represented by the equation for the solubility under hydrogen atmosphere of 101.3kPa: logS = 3.256-2392/T, where S is a solubility in the unit of cm³•kg^-1, which means that the volume of hydrogen (at 273K, 101.3kPa) dissolved in the melt of 1kg, and T is the temperature of the melt in K. The results of present study show the considerably lower solubility compared with those from previous determinations adopted Sieverts' method.

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