| Summary: | 碩士 === 國立臺灣海洋大學 === 機械與機電工程學系 === 99 === One of the materials of green environment, fly ash - aluminum matrix composites (ALFA), is not only to improve the mechanical properties, but also to effectively reduce the cost of raw aluminum. In general, there are no any compatibility and wettability between fly ash particles and aluminum-base melt. This is the main reason why they are difficult to be bond for. Hence, it is necessary to improve the interface characteristics of two-phase materials before casting.
In this study, a series of pre-treatments of fly ash particles was required to be implemented as well, such as particles sieving, pickling, coating, etc. Meanwhile, the activated magnesium alloying element was added to the aluminum-base melt to reduce its surface tension, and also to promote the wettability between fly ash particles and aluminum-base melt. Subsequently, a mechanical stirring way was applied to produce vortex in the aluminum-base melt and to force fly ash particles mixing into the aluminum-base melt as well as possible. Adding fly ash particles into the aluminum-base melt should be in constant feeding rate for the purpose of obtaining a good mixing effect on uniform distribution of particles. Upon completion of the mechanical stirring on the aluminum-base melt as particles distribution uniformity as well, a casting was produced by pouring the aluminum-base melt into the prepared mold. Sampling cut from casting was carried out for further steps of microstructure observation and mechanical property testing.
As a result of study, it was revealed that the main impact factors for the wettability and bonding capability of fly ash-aluminum matrix composites were pickling and coating of fly ash. In the other aspect, increasing the activated magnesium alloying element in fly ash-aluminum matrix composites could enhance the interface wettability for bonding to both materials, and further keep more fly ash mixing into the aluminum-base melt. As regard to distribution uniformity of fly ash in aluminum-base material, it was found that the clustering phenomenon on fly ash was significantly improved while increasing the wettability of bonding and time for mechanical stirring on the aluminum-base melt. In addition, the density of ALFA casting with well pretreatment of fly ash was higher than that of other castings which were not under well pretreatment. Therefore, it was concluded that the bonding effect of ALFA castings with well pretreatment could be better as compared to those castings without well pretreatment.
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