The wettability and applicability of the aluminum alloys for micro-soldering have been investigated using a wetting balance tester by using Sn-9Zn solder and triethanolamine-ammonium fluoroborate flux. Wettability was evaluated by wetting time, wetting force and contact angle between aluminum specimen and solder. Commercial alloys containning lots of impurity elements showed poor wettability whereas the alloys with small amount of elements possessed good wettability with short wetting time, large wetting force and small contact angle. The influence of each elements on wettability was estimated from the data on commercial alloys, and was investigated by using high purity binary alloys. Elements of Ti and Cu drastically lowered the wettability, Cr, Mn and Mg also lowered wettability. Especially, the alloys for microsoldering should have Ti less than 0.04 mass%. The cause of poor wettability depends on the additional elements, both the formation of stable intermetallic compounds and solution of elements were responsible to poor wettability. Pure aluminum, A1080 and some high purity binary alloys were considered to be suitable for micro-soldering under consideration of wetting time and contact angle.

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The influence of niobium on the L1₂ structure phase and thus on the thermal stability of the alloys was investigated for four melt-spun Al-Cr-Zr-Nb alloys; three alloys contain about 4vol% of L1₂-Al₃ (Zr_xNb_1-x) precipitate with different Zr/Nb ratios and one alloy contains about 8vol% of L1₂ precipitate. The microstructures of as-spun ribbons were characterized using an optical microscope and scanning transmission electron microscope. DSC and microhardness tests indicated that the alloys aged at 723 and 773K showed excellent thermal stability after annealing at 648 and 673K for up to 1000h. The Al-3.14Cr-4.03Zr-1.95Nb alloy, for example, attains microhardness of 204kgf/mm₂ in agehardened condition and retains 93% of that value, i. e. 190kgf/mm₂, after annealing at 648K for 1000h. Microstructural changes during annealing were identified and correlated with the microhardness data. The coarsening rate of the L1₂ structure precipitate is very slow at the test temperatures. The coarsening kinetics of the L1₂ structure Al₃(Zr_2/3 Nb_1/3) precipitate in the Al-3.14Cr-4.03Zr-1.95Nb alloy were studied at 648, 673 and 723K. Antiphase boundary evolved inside the L1₂ particles during annealing at 723K.

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Alumina short fiber/magnesium alloy matrix composites were fabricated by using a squeeze casting method. In this study, Mg-4%Zn alloy was selected as a matrix alloy because it has high thermal conductivity. Rare-earth elements were added to the Mg-4%Zn alloy as a third alloying element which is useful for improvement of high temperature strength. The effects of additions of 1%Nd and 1%Ce on structures and mechanical properties of the composites were investigated. RE elements in the liquid react with SiO₂ additives of alumina short fiber, and form needle shaped compounds consisted of Si and RE on the surface of fiber. Tensile strength of the composites at room temperature increases by both an addition of RE element and heat treatment. Nd has the highest contribution for an increase in strength among light rare earth elements. Tensile strength of the composites at 250°C depends only on fiber volume fraction and neither on the addition of RE elements and nor on heat treatment.

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ZE41 magnesium alloy matrix composites reinforced with alumina short fibe were fabricated by using a squeeze casting method. In the previous studies, it has been cleared that tensile strength of the Mg-Zn alloy matrix composites at room temperature increases by both adding rare earth elements and a heat treatment, but not at 250°C. In the present studies, a fiber volume fraction was increased to improve high temperature strength. The effects of fiber volume fraction on structures and mechanical properties of the composites were investigated. The experimental values were also compared with the estimated ones based on the rule of mixture. As a reeult, an MgO layer with 0.2-0.3μm in thickness is crystallized at the interface between the fiber and the matrix of the composites, and results in strong bonding. The composites with fiber volume fraction of 24% exhibit tensile strength of 160MPa at 250°C and more than 70GPa of elastic modulus. The values of tensile strength and elastic modulus of the composites at room temperature are in good agreement with those calculated values based on the rule of mixture, for the composites with fiber volume fraction of 14%. Whereas the experimental values are superior to calculated ones for the composites with fiber volume fraction over 14% due to change from a completely random orientation to two dimensional one.

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Stir-cast AZ91D magnesium alloy chips were reheated at semi-solid state and press-formed by employing a squeezecasting machine at semi-solid temperature. The structures and tensile properties of the formed specimen were investigated. Stir-cast chips show good fluidity and have little defects because of fine and spherical magnesium solid solution with a large amount of liquid phase. Tensile properties of the semi-solid press-formed specimen are, therefore, improved by the T6 heat treatment. The eutectic microstructure becomes finely by the rapid cooling, resulting in the increased 0.2% proof strength which exceeds the JIS-specified value. But tensile strength and elongation are less than the JIS-specified values. This is caused by oxide layer formed on the slurry surface during stirring.

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The effect of solution-treatment on the corrosion resistance of sand-cast EZ33A-T5 magnesium alloy has been investigated by salt spraying test (SST). The corrosion resistance of the treated alloys were up to seven times rather than that non-treated ones. However, the resistance was not changed with the treating time. This behavior seemed to depend on the dissolution property of the phase (2nd phase) consisting of precipitates network before treatment. Before treatment, corrosion rate was higher because of selective dissolution of 2nd phase surrounding primary phase, but was lower after the treatment because of uniform corrosion with no selective dissolution as a result of 2nd phase contraction. This corrosion behavior was discussed in terms of electrochemical phenomena.

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