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Fabrication Of Sip/ZA27 In-situ Composites And Their Thixoforming

Posted on:2008-06-24Degree:MasterType:Thesis
Country:ChinaCandidate:C R YuanFull Text:PDF
GTID:2121360212490265Subject:Material processing
Abstract/Summary:PDF Full Text Request
In this thesis, in-situ silicon particle (Sip) reinforced ZA27 composites (Sip/ZA27) were fabricated by traditional casting technique, and the tensile properties and wear properties of the resulting composites were studied. The microstructure evolution of the 10 vol. %Si/ZA27 composite during partial remelting, and subsequent thixoforming process and tensile properties of the thixoformed composites were also investigated. The results are shown as followings:(1) The Sip/ZA27 in-situ composites could be successfully produced by traditional casting technique with phosphor modification. The size of Sip increased with the decrease of pouring temperature at certain silicon content or with the increase in silicon content at a certain pouring temperature. A Sip/ZA27 composite with regular shape, fine size and uniform distribution of Sip was obtained at the pouring temperature of 750 °C and a silicon content 10vol%.(2) The addition of silicon gave rise to the formation of a large numbers of porosities, which lead to a significant decrease in mechanical properties. The phosphor had an obvious modification effect on the Sip, and thus could enhance the mechanical properties.(3) The wear-resistant performance of all materials but Sip/ZA27 containing silicon 13vol% decreased with the increasing of testing temperature. The wear resistance of the composites increased initially with silicon content and then decreased, which followed by increasing again. Finally, the wear resistance tended to an constant.The dominant wear mechanism was adhesion and smearing in this situation. The formation of transfer layer gave rise to an increase of wear resistance. From above analyses, the formation of large number of porosities was the main reason why the mechanical properties decreased. So,decreasing porosities as far as possible was the best way to improve performance of the materials.(4) The efficiency of modification of Zr (K2ZrF6 (CP) ),B (KBF4 (AR) ) and Ti (K2TiF6 (AR) ) were investigated, and found that the Zr had the best modification effect.After being modified by Zr, the primary a became fine, and an ideal semisolid material was obtained after partal remelting.(5) The composites modified by Zr had good thixotropic properties and thixoforming could significantly increase tensile properties. The processing parameters had obvious effect on the integrity of the thixoforming product and the appropriate processing parameters were: hearting time of 90min, reheating temperature of 475 °C and die temperature of 300°C.
Keywords/Search Tags:in-situ, Sip/ZA27 composite, mechanical properties, wear, partial remelting, thixoforming
PDF Full Text Request
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