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Precipitation behavior of Mg_(17)Al_(12) in SiC particulate reinforced Mg-9Al-1Zn composite has been studied in the present study. Two types of Mg_(17)Al_(12) precipitate form in α-Mg matrix with aging treatment. The continuous Mg_(17)Al_(12) precipitate has a plate-type morphology and has a same orientation relationship with the α-Mg matrix as in monolithic Mg-Al-Zn. The kinetics of the discontinuous Mg_(17)Al_(12) precipitation can be successfully described by Johnson-Mehl-Avrami`s model, which indicates that a reaction front of the discontinuous precipitation stop when it meets an immobile grain boundary. The hardness of SiC particulate reinforced Mg-9Al-1Zn composite reaches a maximum value after aging for 30hours. The overaging phenomena observed after aging over 30hours is due to the increased fraction of continuous and discontinuous Mg_(17)Al_(12) precipitates and interlamellar spacing of discontinuous Mg_(17)Al_(12) precipitates.

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This study was focused to investigate the effect of die casting on the microstructure and mechanical properties of SiC_p(10 and 20vol.%)/Al alloy composites. Die casting was performed using the preheated mold at the pouring temperature of 650∼700℃ under the pressure of 916 ㎏f/㎠. The speeds of slow and high speed injection were 0.3∼0.4 and 1.4 m/s, respectively. It was found that the SiC particles were homogeneously distributed in refined Al matrix. This results from the rapid mixing of molten Al and SiC particles during injection and the improvement of segregation due to rapid solidification. Therefore, the tensile strength of SiC_p/Al alloy composites die cast at 700℃ appeared to be superior to that of the composites die cast at 650℃ with 10 and 20 volume fractions.

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PREP(plasma rotating electrode process) powders of 316 stainless steel were loosely sintered to fabricate porous filters. Porosity, size and structure of pores, permeability and mechanical strength of the filters were investigated with the variation of powder sizes and sintering conditions, and were discussed in conjunction with mathematical analysis. Porosity was nearly constant about 32∼34%, but mean pore size, permeability, pore structure and mechanical strength were changed markedly with sintering conditions.

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Taguchi matrix experiments with orthogonal arrays were conducted to evaluate the effects of PTA (Plasma Transferred Arc) process variables on the characteristics of weld-overlayers. The materials investigated were Ni-based Metco 16C and Co-based Stellite 6 powders. The characteristics of PTA weld-overlayers were assessed in terms of surface hardness, dilution, and maximum deposition thickness. Main results are that dilution is decreased as the main arc current is decreased and/or powder feeding rate is increased; surface hardness is increased as the main arc current is decreased; deposition thickness is increased as the powder feeding rate is increased and/or travel speed is decreased. Confirmation runs from the results of Taguchi matrix experiments showed good quality weld-overlayers, but did not exhibit the best quality weld-overlayers.

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The aim of the present study was to investigate age hardening properties of the AZ91 Mg alloy. Rockwell hardness test, energy dispersive X-ray spectroscopy, optical microscopy and scanning electron microscopy were performed to identify the age hardening behaviors. The degree of age hardening of AZ91 alloys was changed with the time and temperature of the artificial aging treatment. Higher aging temperature shortened initial aging time and time for reaching the peak hardness, while too high temperature reduced the amount of age hardening. So it is necessary to choose suitable aging temperature and time. It was found that precipitated Mg-Al compound was the age strengthing phase in AZ91 Mg alloy. And hardness increased abruptly at the beginning of intragranular precipitation after intergranular precipitation was nearly saturated.

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The distributions of the radial and vertical components of magnetic flux and induced current densities as well as the rotational component of electromagnetic force generated by rotating electromagnetic field have been calculated using 3 dimensional FEM with a finite length cylinder system. The effects of frequency and geometrical factors of the melt container and the inductor have also been analysed. It has been found that the stirring effect can be maximized by choosing the frequency such that the magnetic Reynolds number becomes about 4.5.

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