This study demonstrates the ability to fabricate lightweight, ductile but mechanically strong magnesium alloy (AZ91D) composites by introducing a small number of high crystalline multi-walled carbon nanotubes. It is demonstrated that 1 % of relatively short and straight carbon nanotubes distributed homogeneously on the outer surface of magnesium powders act as an effective reinforcing filler to prevent deformation, thereby contributing to the enhanced tensile strength of magnesium alloy composites (e.g., from 315 to 388 MPa).Keywords: Carbon nanotubes; Magnesium alloy; Powder processing; Mechanical property There has been strong recent interest in developing lightweight and high-strength materials to improve the energy-efficiency through the weight reduction of automobiles and aircrafts. For these purposes, magnesium alloys have attracted a lot of attention [1-3], as they have low density in its purest form, and in addition, they have been proved to have good mechanical properties through the incorporation of structural filler (e.g., silicon carbide whisker, aluminum and graphite particles, and carbon fibers) [4][5][6][7]. Within this context, the dimensionally nano-sized, mechanically strong, electrically and thermally conductive carbon nanotubes [8][9][10][11], considered to be the ideal reinforcing filler in various composite systems [12][13][14][15], have been incorporated into magnesium matrix [16][17][18][19]. Recently, Goh et al. [19] reported a simple way of preparing nanotube-reinforced magnesium composite by powder-powder mixing and subsequent hot extrusion processes. However, low enhancement (only 5 %), or even a decrease in, tensile strengths in nanotube-reinforced magnesium composites (see Table 3 in ref. 19) could be explained by the presence of aggregated carbon nanotubes within a magnesium matrix. To exploit carbon nanotubes fully as a mechanical reinforcing filler in a magnesium matrix, optimized fabrication processes including homogeneous dispersion of carbon nanotubes must be 1

This paper presents the mechanical properties and microstructure of Sn-Ag-Bi Pb-free solder. We evaluated the effects of Bi content on the mechanical properties of Sn-Ag-Bi solder such as tensile strength, elongation and deformation behavior at cross-head speeds of 0.1 mm/min and 500 mm/min. The experimental results show that at low cross-head speeds, the addition of Bi to Sn-Ag solder initially increases the tensile strength and decreases elongation due to solid-solution hardening of Sn-phase. As the Bi content is increased to 10 mass% and more, however, elongation increases to a maximum at Sn-Ag-Bi solder containing 57 mass%Bi. Deformation of Sn-Ag solder is governed by slip within the Sn phase, and for high-Bi solders (about 57 mass%Bi) deformation occurs due to slip at Sn-Bi grain boundaries. Intermediate-Bi solders, on the other hand, do not slip in either the Sn phase or at Sn-Bi grain boundaries. At high cross-head speeds, the elongation of both intermediate-Bi solders and high-Bi solders was low and almost constant, indicating slip at Sn-Bi grain boundaries becomes difficult. The impact resistance of these solders was investigated through charpy impact tests, and it is found that Bi has a marked effect on impact resistance. The impact absorption energy of Sn-Ag solder decreases rapidly with the addition of Bi.

This paper presents low-temperature Pb-free soldering technology using Sn-57Bi-1Ag (mass%). Here, the effects of hightemperature annealing on the mechanical properties of the solder such as tensile strength and elongation are investigated. The experimental results show that during annealing, the sizes of both of Sn and Bi phases coarsen, however the mechanical properties do not deteriorate. The deformation behavior of Sn-57Bi-1Ag is found to be dependent on sliding at grain boundaries between Sn and Bi phases, and this behavior remains consistent even after coarsening. The creep strength of solder joint at high temperature is also studied, and it is found that Sn-57Bi-1Ag exhibits superior creep strength at temperature below approximately 100°C compared to the Sn-37Pb (mass%) solder.The thermal cycling test of Sn-57Bi-1Ag solder joint is also conducted under the condition between 0°C and 90°C. The result shows that the length of crack is shorter than Sn-37Pb in the same conditions, which means Sn-57Bi-1Ag is an effective material for low temperature soldering.

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