Mg–17~21 mass%Li–7.2~12.4 mass%Al ternary alloys were melted in order to improve the specific strength, and their heat treatment characteristics and tensile properties were investigated. Specific gravity of investigated alloys is in the range between 1.20 and 1.34, which is lower than that of the conventional Mg–Li alloys. The investigated alloys exhibit a marked decrease in lattice parameter and consequently are hardened by the isothermal holding at the temperature higher than 200°C, but their elongation decreases remarkably. Alloying elements are solutionized to some extent and the growth of recrystallized grains are restricted by shortening the holding time at 300°C or 350°C. Consequently, high strength and reasonable elongation can be obtained by such a heat treatment. The tensile strength of both as-rolled and as-quenched specimens increases with a decrease in lithium content and an increase in aluminum content. Additionally, age hardening at room temperature and 50°C occurs in the specimens quenched after isothermal holding at 350°C for 1 h. The appearance of side-bands in the results of X-ray diffraction patterns suggests that the hardening may be attributed to spinodal decomposition.

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In this study, 0.5 mass%Ca, Si, Zr or 1 mass%Y as a fourth alloying element was added to Mg–20 mass%Li–10 mass%Al alloy in order to restrict recrystallization and growth of recrystallized grains. Effects of the alloying elements on heat treatment characteristics and tensile properties of the warm-rolled specimens were investigated. Quenching of the specimens after isothermal holding at the temperature more than 200°C for 1 h results in increasing hardness and strength and in decreasing elongation, because aluminum is resolved into the β phase. Recrystallized grains of the quaternary alloy containing 0.5 mass%Si become fine, but resulting in no increase of elongation. An addition of 0.5 mass%Ca makes strength high, whereas no sign of the improvement of elongation is recognized. Zr does not show any large difference in the microstructure and tensile strength of the ternary alloys. As a result, there is no significant increase of ductility for the examined alloys although the recrystallized grain size is reduced as compared with the ternary alloys.

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The influence of the variation of the silicon content in the matrix on mechanical properties was investigated for aluminum-borate whisker reinforced aluminum alloys. An age-hardenable Al–4.5%Cu–Si alloys were selected as the matrix, in which silicon content was varied from 0% to 12%. Young's modulus and 0.2% proof stress of the composites increased with the silicon content in the matrix, however, tensile strength of the composites decreased. The silicon content in the matrix had little influence on age-hardening behavior and interfacial reaction of the composites. Crystallization of silicon particles around the whiskers was frequently observed. And fracture of whiskers with silicon particles on the fracture plane was often observed after tensile fracture. The whiskers surrounded by silicon crystals increased with the silicon content in the matrix, and the fracture of the whisker was caused by the brittle fracture of the silicons around the whiskers. Increase in tensile strength was not found for the aluminum-borate whisker reinforced Al–4.5%Cu–12%Si alloy, being consistent with the results of the observation.

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The influence of the variation of magnesium content on mechanical properties was investigated on aluminum-borate whisker reinforced Al–Cu–Mg alloys, which were fabricated by a squeeze casting process. Tensile strength of the composites decreased with the increased magnesium content in the matrix. However, with the magnesium content above 2%, tensile strength increased and showed a maximum at 3%. In case of the magnesium content below 2%, the whiskers were degraded by the polygonal reaction products which formed on the whisker surfaces by the reaction with magnesium in the matrix. Moreover, the age-hardening of the composites was small due to the consumption of solute magnesium in the matrix. While, in the case of the magnesium content above 2%, a part of magnesium in the matrix contributed to the precipitation, and the larger age-hardening took place in the composites. In addition, the whisker surfaces were covered with the reaction layer. Therefore, irregularity of the whisker surfaces became smaller than that for the magnesium content below 2%, and the decrease of the tensile strength by the whisker degradation also decreased.

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According to recent research the inferiority of electrical discharge machining performance of Ti–6Al–4V alloy was obvious. In this paper an efficient machining process, which combines electrical discharge machining and multiple ultrasonic vibration, is proposed for improving the material removal rate. The experimental results show that the materials removal rate of both SKD11 and Ti–6Al–4V alloy is remarkably improved with the proposed machining process, especially for Ti–6Al–4V alloy at small pulse duration. The improvement mechanism is assumed to be a fact that multiple ultrasonic vibration accelerates the ejection of debris out of the small gap between the facing materials, i.e., the electrode and workpiece. It is also shown that lower relative electrode wear is obtained, and the most significant effect is observed when machining with lower pulse duration or higher discharge current. Experimental result indicate that comparing with conventional electrical discharge machining, the proposed machining process produces a thinner recasting layer, although it is with slight deterioration in the finished surface.

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This paper deals with the possibility of distilled water as a dielectric fluid for electrical discharge machining of Ti–6Al–4V alloy, and the comparison of electrical discharge machining characteristics using both distilled water and kerosene is also investigated. The experimental results indicate that when machining Ti–6Al–4V alloy in distilled water, the material removal rate is larger than that of using kerosene. This indicates obviously that distilled water is the more effective dielectric fluid for electrical discharge machining of Ti–6Al–4V alloy. It is also found that the material removal rate is remarkably enlarged with increasing discharge current and pulse duration. Since the distilled water has higher thermal conductivity, the rapidly solidificated debris has a certain thickness of fine grains around the debris, while columnar grains around the debris produced using kerosene is observed. It is also found that there is only a thin recasting layer on the surface when machining in distilled water, while a thicker recasting and hardened layer produced in kerosene is observed. Although machining Ti–6Al–4V alloy using distilled water has a significant effect on the electrical discharge machining characteristics, particularly in the material removal rate, but a higher roughness of surface than using kerosene is also obvious.

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Vacuum brazability of aluminum alloys containing magnesium more than 1 mass% has been reported to be very poor. This study was aimed to examine brazability of those alloys in a high vacuum atmosphere of the order of 10⁻⁵ Pa. A6061, A5052 and A5083 alloy sheets with BAS211P brazing sheets were high vacuum brazed into invers T-type specimens. All of these alloys exhibited fairly good fillets. Spread of the brazing alloy on the surfaces of the brazed alloys and erosion of the brazing alloy into the brazed alloys were both limited in the high vacuum brazing. The behavior of magnesium during brazing is discussed, based on the results of EPMA analysis.

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