| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 102 === This study investigated the effect of different chemical etching times on surface morphologies and its influence on the sliding wear of a hypereutectic Al-30 wt.% Si alloy. The Al-30 wt.% Si samples were etched in acid aqueous for 5, 10, 15 and 20 min, and observed the changes in silicon particle height and interparticle spacing. Subsequently, the wear tests of etched samples were conducted using pin-on-disk wear machine under both dry and lubricated sliding conditions. A normal load of 45.5 N and a sliding speed of 1 m/s were used in all tests. It was shown that, at the short etching time, the silicon particle height increased with etching time, but interparticle spacing presented a slow increase. However, in the over-etching region, there were numbers of etched pits on the sample surface, due to the detachment of silicon particle from the aluminum matrix. These resulted in the large fluctuation of the silicon particle height and interparticle spacing. From the results of wear tests, the etched samples presented lower friction coefficient and wear rate compared to the unetched sample. Among the different etching time, after 10 min etching, the sample had lowest friction coefficient and wear rate during wear test. In addition, after 4000 m of lubricated sliding wear, silicon particle maintains a protruded height from the matrix. However, etching longer than 10 min, the obvious wear damages evidenced on the worn surface due to the over-etching occurred, which tended to weaken the wear resistance of alloy. Therefore, during etching treatment, etching time must be carefully controlled to protrude the silicon particles but avoid over-etching.
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